The Official AVS Antenna Topic! [Text View] - Page 11

chinatti

08-25-05, 10:25 PM

I just got a new D* HR10-250 installed, including the D* OTA antenna. Good thing I talked the D* CSR into giving me the OTA for free, because it didn't pick up a single OTA channel. It's a Winegard Sensar GS-2VRD, it says "amplified" on the box, and I can see some components inside, but there was no power unit of any kind installed, so I'm guessing there's something missing.

Anyway, Antennaweb reports that I will need a Large Directional w/ preamp (Violet) in my location, Westford, MA, about 25 miles from the Boston towers, all within a few degrees of each other, all UHF. The antenna is mounted on my roof (above 2nd floor), with high trees facing Boston.

So I went over to the local Radio Shack and picked up their $25 40" UHF Yagi (listed as for "Red" locations), fully expecting to take advantage of the 30 day money back guarantee, mainly using this to figure out where I stood, and what my plan of attack should be. So with this antenna, I now get the following stations:

ABC: no digital lock, signal strength bouncing around 0~20
CBS: digital lock, signal strength ~60
NBC: no digital lock, signal strength 0~15
FOX: no digital lock, signal strength 0~15

Also, I plugged in my Analog TV and looked at some UHF stations out of Boston, and I'm basically getting a pretty weak signal (lots of snow, but you can see the picture), but no noticable ghosting, so I'm thinking I have more of a signal strength issue as opposed to multipath.

I'm looking for recommendations as to what to try next. Here are the options I see:

1. Buy a good preamp w/ the RS ant, maybe a channelmaster 7775/7
2. Buy a better antenna (CM 4228, or maybe a CM 4221). I might prefer to mount the 4228 in the attic - I have a window facing Boston, basically at the same level the antenna was mounted on the roof.
3. Buy #1 and #2 together, return the RS antenna.

I guess I'm wondering how much of an improvement I'd get from adding a good preamp vs. getting a better antenna. And I'd prefer the 4221 (smaller, easier to mount, etc), but I wouldn't have a problem with the 4228 *if* I need it, and I'd hate to get the 4221 only to find I need the 4228 - most places won't let you return these things.

Anyone have any gems of wisdom?

Thanks in advance...

sregener

08-26-05, 08:47 AM

Are there any larger antennas than the 91XG that I should consider?

I have a chimney, but we burn wood all winter long, so I'm guessing the soot/heat wouldn't be good for the antenna and I should go with a mast somewhere else on the roof rather than a chimney mount. Am I on the right track?

What are some good ways to address the lightning issue without negating the benefits of a roof mount?

There are few antennas larger than the 91XG for UHF reception, and the jury is out as to whether the European imports are better or the same. For the price, you can't do better, and you could spend a lot more and do worse.

IIRC, there's no real harm in being over an active chimney. The heat isn't that great up there, and soot shouldn't impact reception. Figure you might lose a year or two of antenna life if you go with a chimney.

The way to address lightning is to properly ground your antenna (grounding block.) This makes it less attractive to lightning than other nearby objects. You can spend a lot more money, but it isn't going to make it a lot safer. My installer told me they've almost never seen a tower hit by lightning - wind is the only real problem they deal with.

sregener

08-26-05, 08:54 AM

I'm looking for recommendations as to what to try next. Here are the options I see:

1. Buy a good preamp w/ the RS ant, maybe a channelmaster 7775/7
2. Buy a better antenna (CM 4228, or maybe a CM 4221). I might prefer to mount the 4228 in the attic - I have a window facing Boston, basically at the same level the antenna was mounted on the roof.
3. Buy #1 and #2 together, return the RS antenna.

I guess I'm wondering how much of an improvement I'd get from adding a good preamp vs. getting a better antenna. And I'd prefer the 4221 (smaller, easier to mount, etc), but I wouldn't have a problem with the 4228 *if* I need it, and I'd hate to get the 4221 only to find I need the 4228 - most places won't let you return these things.

Anyone have any gems of wisdom?

You're fortunate in that one of the best antenna shops in the country is nearby - Stark Electronics (www.starkelectronic.com). They carry both of the Channel Master antennas you list, as well as the preamplifier.

If it was me, I'd return the Radio Shack antenna and buy the 4228 and 7777. You can try the 4228 in your attic both with and without the preamplifier, and if it works without the preamp, you can return the preamp. Otherwise, it's up on the roof you go. Note that the 4228 isn't good for use with a rotor, but you said the stations are all in the same direction, so probably not an issue for you.

Preamplifiers help some, but nothing substitutes for a good antenna at the get-go. The 4228 has a lot of gain compared to the Radio Shack antenna (somewhere in the neighborhood of 6db or 4x as much signal gathering ability.) The 4221 is a good antenna for people who don't have a lot of trees to deal with and are at your distance. I'd say it's probably about 3dB better than the Radio Shack, which doesn't give you nearly as much hope of success. Not to say it wouldn't work, but if you want a slam-dunk solution, the 4228 is the best choice.

kurtlingle

08-26-05, 10:31 AM

I just love these forums. Many thanks for everyone sharing their knowlegde!

I have an older style antenna on my roof that is 10+ years old. So the wire running from it to my TV is the dual antenna wire.

1. I would imagine it would be better to run RG-6 from the attenna to my TV, right? Instead of the current wire? It's probably < 50 ft.

2. What do I need to buy to connect the Attenna to the RG-6? I assume there is some gadget similar to take the 2 wires from the antenna and run the RG-6.

Thanks in advance!

colofan

08-26-05, 12:11 PM

Is there a web site where i can find all the Tv stations within 100 to 150 miles to where I live?

The FCC maintains a database where you put in your longitude and latitude and then the radius in kilometers from that location to show the stations in the area.

This is the link they also provide a lookup based off your address to get the long and lat.

http://www.fcc.gov/fcc-bin/audio2?x=tvq.html

sregener

08-26-05, 01:41 PM

1. I would imagine it would be better to run RG-6 from the attenna to my TV, right? Instead of the current wire? It's probably < 50 ft.

2. What do I need to buy to connect the Attenna to the RG-6? I assume there is some gadget similar to take the 2 wires from the antenna and run the RG-6.

1. RG-6 is less prone to interference than 300-Ohm wire. It also doesn't break down in the elements as quickly. You should replace your 10-year old wire, but which you use is up to you.

2. What you need is a balun (balananced/unbalanced) connector. Get one rated for outdoor use. Should cost you about $2.

Neil L

08-26-05, 01:54 PM

1. I would imagine it would be better to run RG-6 from the attenna to my TV, right? Instead of the current wire? It's probably < 50 ft.
The advice sregener gave is good. I would add that the trade off between 300 ohm twin lead and 75 ohm RG-6 is:

Twin lead = less signal loss, (due to the baluns mostly, and the cable design), but more noise pick-up.

RG-6 = fully shielded from noise and interference, with about 3db loss of signal compared to twin lead.

My setup has about 18" of twin lead from the antenna to the pre-amp, then of course, RG-6 from the pre-amp output into the house. I'm just overly cautious about loosing any signal, because I don't have much to begin with.

August West

08-26-05, 02:52 PM

Hello all,
I've read many posts in this forum and I'm trying to do my best to research this before I just start climbing up on the roof and trying different antennas :).

I live in 21704, Frederick, MD. I am 32-35 miles away from the TV towers in Washington DC. They are all within a 3 degree range so I don't think I'll need a rotor. Baltimore stations are 30 degrees or more away and there's more terrain between us so I'm writing them off for now.

What I am really interested in is getting the major networks from Wash in DTV. I checked antennaweb (neat site!) ... while it lists many/all DC and Baltimore stations for my street address, NONE of them have the DTV check next to them (save PBS in my town) ... :(

I suppose this comes down to my elevation and terrain between here and there. I'm at about 400 ft above MSL, I could GPS it if needed for more accuracy. Someone on the other side of town, another 5-10 miles away from DC but up on a mountain side gets 20 DTV stations and antennaweb agrees with what they're getting.

Is it possible to exceed the antennaweb estimates with the right hardware? Are there any antennas/pre-amps I can get that should have a good chance of pulling in DTV in this case? I'm not directly behind any hills but I'm not on the highest ground either.

I have a HOA and don't want to offend anyone TOO MUCH, on the other hand, I really want to make OTA DTV work, and I'm willing to put a mast on the roof (2 story home, I don't want to go too crazy with the mast height though).

Can anyone make suggestions about types/models of antennas I should try or am I just out of luck if antennaweb says I don't get DTV?

Thank you so much!!

You may want to look at the larger Channel Master UHF/VHF combo antennas - maybe the 3020 (one of the deep fringe rated ones).

Relative to doing better than Antennaweb says you should do, I have a CM 3016 that is about a size too small per Antennaweb and in my attic to boot. It is doing pretty well with only slight pixelation with channel 45. VHF is doing well. Given the realtively small dollar differential between a medium directional and a large directional, I would suggest getting the largest you can that the HOA will allow (downside of the 3020 - its something like 12' long)

sregener

08-26-05, 03:11 PM

I would suggest getting the largest you can that the HOA will allow....

HOAs cannot restrict terrestrial antenna size. But why get a VHF antenna at this point when it just adds size and bulk and doesn't get him *any* digital signals? Eventually he may want a hi-VHF for channels 7 and 9 when they revert at the analog shutoff, but that's a few years away and a hi-VHF-only antenna would still be much smaller than a VHF antenna that gets channels 2-6.

August West

08-26-05, 05:12 PM

HOAs cannot restrict terrestrial antenna size. But why get a VHF antenna at this point when it just adds size and bulk and doesn't get him *any* digital signals? Eventually he may want a hi-VHF for channels 7 and 9 when they revert at the analog shutoff, but that's a few years away and a hi-VHF-only antenna would still be much smaller than a VHF antenna that gets channels 2-6.

Maybe I read the original post too quickly. I see that he was not specifically looking to pick up signals (analog and digital) from DC and baltimore, only DTV from DC. I must have been reading into it as I live in the same general area as the original poster and had a desire to pick up analog channel 5 from DC (to get Redskins games not shown on the Baltimore FOX affiliate).

bmcent1

08-26-05, 05:52 PM

Thanks for all the feedback!!

I really appreciate your ideas and pointers and I am learning quite a bit just following the conversations in this thread. That is a good point about wanting analog for blacked out games, I hadn't even thought of it and I'll tuck that away in case I need it later. However, at this point my main goal is DTV reception (and HDTV programming) with analog being a very distant second.

Thanks again and I'll keep watching the thread for any replies and for the general information flowing here.
- - -

While I'm posting... can anyone recommend a web site or program that does the following:
- Input your location, lat and lon and possibly antenna height
- Input a TV tower location, lat and lon and height about ground (available from FCC public info)

Then the webapp/program shows you a cross section of the topography between those two points and shows whether or not there is clear line of site...

Has anyone seen anything like that? I actually did it with a program at work but the feature wasn't built in for antenna solutions so it's lacking in details (like line of sight and needs better scale) ... but as a proof of concept, it was pretty slick.

Seems like this could be done with free census maps and GRASS (an open source GIS program) thought it would probably be a lot of work and if something like this already exists, well that would make it easier :)

sregener

08-26-05, 07:09 PM

That is a good point about wanting analog for blacked out games, I hadn't even thought of it and I'll tuck that away in case I need it later. However, at this point my main goal is DTV reception (and HDTV programming) with analog being a very distant second.

While I'm posting... can anyone recommend a web site or program that does the following:
- Input your location, lat and lon and possibly antenna height
- Input a TV tower location, lat and lon and height about ground (available from FCC public info)

You wouldn't need analog to beat blackouts. The same game is shown on analog and digital. Thus, if you get WTTG-DT, you'll be seeing the same game as on WTTG-5. I suspect the other poster is trying to bust blackouts of Baltimore games by watching the game from D.C., but IIRC, the blackout radius of both cities extends enough that the other can't show the game if it's blacked out.

There are topographic programs that do what you describe, but the best prices I've seen on them are around $300. You could also do a Longley-Rice calculation using free tools as described here: http://www.tvtechnology.com/features/On-RF/F_Lung-02.02.05.shtml

bmcent1

08-27-05, 01:24 AM

There are topographic programs that do what you describe, but the best prices I've seen on them are around $300. You could also do a Longley-Rice calculation using free tools as described here: http://www.tvtechnology.com/features/On-RF/F_Lung-02.02.05.shtml

Thank you! Thank you! Thank you!!! The link you provided went to an article describing a program named SPLAT! which runs on Linux and uses Census and USGS data that is freely available... and it blew my mind! :)

The program does exactly what I wanted, shows terrain profile, line of sight and obstructions, and a beautiful path loss map.

Again, thank you for the reference, SPLAT is very cool.

rhwimmers

08-27-05, 10:58 AM

After I got my 4228 and 9/10 setup with the amplifier (its been so long since ive done anything with my anteanna setup, i forget what all I have!)..I set it and forgot it, I got fox in HD and thats pretty much all I wanted. now that football season is about to start I would like to start to find other channels that I can pull...Im in Muncie, IN and get all my HD from indianapolis, about 45 miles and fox is usually at 100%.
My question is whats the best way to scan to see what all channels I can get that are above 80% or so (if thats the number to use..) and also how to tell what channel it is you picked up.
THEN, I would like to write down all the angles for what channels in what cities
FINALLY - is there a program that you can enter in all the channels you can get to see what is on where. Im a packer fan (raisied as a cheesehead) so would like to be able to get as many Packer games as possible..
Thanks for the help
Ross

RockyF

08-27-05, 12:17 PM

Try www.antennaweb.org. Just put in your address, and it should give you all the info you want. Also, be sure and look for your local thread here in this section of the forum.

holl_ands

08-27-05, 04:51 PM

While I'm posting... can anyone recommend a web site or program that does the following:
- Input your location, lat and lon and possibly antenna height
- Input a TV tower location, lat and lon and height about ground (available from FCC public info)

Then the webapp/program shows you a cross section of the topography between those two points and shows whether or not there is clear line of site...

Has anyone seen anything like that? I actually did it with a program at work but the feature wasn't built in for antenna solutions so it's lacking in details (like line of sight and needs better scale) ... but as a proof of concept, it was pretty slick.

Seems like this could be done with free census maps and GRASS (an open source GIS program) thought it would probably be a lot of work and if something like this already exists, well that would make it easier :)

I've been using RADIO MOBILE to do not only topography, but also signal strength and fade margin calculations.
The mapping features include automatic download of hi-rez topography, road maps and satellite images.
The program is FREE, runs under Windows and has a very active Yahoo User Group for tricks and advice:
http://hdtv.forsandiego.com/messages/1/2846.html?1122107959

Note that I also posted an Excel spread sheet calculator, including detailed explanation, that takes the Longley-Rice
Diffraction Path Loss calculation and then melds in the "missing" parameters, such as broadcast tower antenna pattern,
clutter loss, attic/indoor loss, antenna gain vs frequency, sensitivity degradation due to VSWR mismatch,
cascaded System Noise Figure, Noise Figure vs Temperature, et. al.

See fol. for additional topography programs:
http://www.avsforum.com/avs-vb/showthread.php?t=546066

holl_ands

08-27-05, 05:05 PM

My question is whats the best way to scan to see what all channels I can get that are above 80% or so (if thats the number to use..) and also how to tell what channel it is you picked up.
THEN, I would like to write down all the angles for what channels in what cities
FINALLY - is there a program that you can enter in all the channels you can get to see what is on where. Im a packer fan (raisied as a cheesehead) so would like to be able to get as many Packer games as possible..
Thanks for the help
Ross

Antennaweb.org has been found to be extremely conservative in predicting which DTV stations people will receive.
So only the highest quality make the cut. It usually leaves out a large number of viewable stations.

The following won't tell you how good the stations will be received, but it will give you
an exhaustive list of all DTV and/or Analog stations within a selected range, sorted by distance,
with antenna pointing angle calculated for your convenience:
www.2150.com/broadcast

If you don't know your lat/long, the site includes a link you can use.
The fol link is easier to determine lat/long, only requiring your street address:
http://www.geocode.com/modules.php?name=TestDrive_Eagle

Oldfart

08-27-05, 05:21 PM

I just got my HD TiVo two days ago; it is replacing a Sony HD 200 and a Series 2 TiVo. My problem is that a number of OTA channels that I received perfectly on the HD 200 are not received at all on the HD TiVo. I get the message "Searching for signal on: Antenna In". When I check the signal strength on what used to be my best OTA channel, I get a signal in the 20s on tuner 1 and no signal on tuner 2. The only thing that the installer did was to disconnect the antenna line from the Series 2 TiVo setup (and lay it aside) and disconnect the antenna line from the HD 200 and connect it to the HD TiVo. Are the tuners in the HD TiVo known to be less sensitive than that in the HD 200? Should a signal amplifier work, or should I get a new antenna? My attic access is not large enough to accommodate a CM 4228.

Ratso Gonzales

08-27-05, 06:17 PM

I need a digital TV antenna for a small bungalow in San Diego. Antenna Web lists two stations in the red with the rest in yellow or dark green (3035 Olive Street, San Diego, 92101). The site recommends a medium directional. Unfortunately, the primary stations here come from 3 different directions, in an almost perfect wishbone shape from my house. The red stations being in the opposite direction of the other two. My questions:

1) If I get a medium directional and point it in towards the red stations, will it pick up the yellow and green stations behind it pretty well too?

2) for the usual reasons I would like to stick this in our "attic." (about 4' high...) Is this viable? If it is remotely viable, I will at least try it.

3) Make & model would you recommed for the attic installation vs a roof install?

Thanks so much!

Steve

greywolf

08-27-05, 06:31 PM

Oldfart,

The usual problem is the the HR10-250 is more sensitive. An attenuator is sometimes needed to reduce the effect of multipath interference.

Ratso Gonzales

08-27-05, 10:03 PM

I am surrounded by the 3 DTV broadcast towers in my area (3035 Olive Street, San Diego, CA 92104). Two of the towers are in the yellow & dark green with the third in the red (and perhaps even blue...) areas. Fortunately all VHF stations are at the easy towers. Here is my plan:

1) Get omnidirectional antenna to recieve from the first two towers (Channelmaster CM 3000 or Winegard MS1000/2000)

2) Get directional UHV antenna for final tower (Channelmaster CM 4221/4228 or Winegard PR4400/8800)

3) Stick all in my attic, join the coax cables, and be done with it.

Will this work? If so, do you think I need an amplified omnidirectional? Will the small bowties be enough? (Channelmaster claims theirs theirs to be a Large Directional while Winegard claims theirs, with comparable specs, to be only a small directional.)

Thanks!

Steve

Jeremy Tebo

08-28-05, 01:07 AM

I'm in dire need of some help here. I live in Denver, CO, and our local CBS channel broadcasts from a skyscraper that is about 1 mile away from me, yet I can't pick it up. It appears the problem is that I live on the second floor of a big five story building, and on the opposite side of the tower. That means there are dozens of thick concrete walls in between.

I've got a USDigital receiver. Originally I just tried a cheap $7 RCA antenna, but that wouldn't pick it up. So then I bought a $30 Philips amplified one, and that got a signal, but it just bounced up and down. Today I went to buy a Silver Sensor, but all they carried was Terk, so I got a HDTVi. It works slightly better, but it still won't lock on to add the channel.

Any suggestions? I played around with it for an hour or two trying to find a signal, but had no luck. The signal will go up to almost totally full, but then drops back down to zero. An outdoor antenna isn't really an option for me. Thanks!

sregener

08-28-05, 08:54 AM

3) Stick all in my attic, join the coax cables, and be done with it.

Will this work?

Joining multiple antennas pointed in different directions without some serious filtering almost never works. You'd be better off with a rotor and one good antenna.

sregener

08-28-05, 08:55 AM

I'm in dire need of some help here. I live in Denver, CO, and our local CBS channel broadcasts from a skyscraper that is about 1 mile away from me, yet I can't pick it up.

Try your local thread, but your best option is probably cable until the tower situation in Denver is worked out or a good receiver with the Linx chipset is available.

Jeremy Tebo

08-28-05, 01:45 PM

I've been pestering the locals for a while, someone there just showed me the link to the "Deuling Silver Sensors" page - http://www.hdtvprimer.com/ANTENNAS/silver.html. Might have to give it a try.

No cable for me, my loft building is prewired for D* only, and it's not HD capable. Long, sad, angry story. I used to have HD cable, and loved it.

Kathy

08-28-05, 03:27 PM

Oldfart,

The usual problem is the the HR10-250 is more sensitive. An attenuator is sometimes needed to reduce the effect of multipath interference.

Greywolf,
I have the exact same problem as Oldfart, I replaced the exact same equipment, now I cannot receive the OTA channels I used to receive, and I have a lot more pixelation on those I do receive, making viewing unbearable. I have a Channel Master 4228 (pretty sure that's the model) in my attic. What is an attenuator, where would I purchase one, and where is in installed?

jjwjr

08-28-05, 03:33 PM

I live on the Framingham/Sudbury line in MA (outside of Boston) and currently use a CM3018 with a CM SPARTAN 3 preamp with a Humax STB. The antenna is aimed at about 116-118 (direction of all stations) which are about 11-12 mi away.

Most channels come in beautifully with few drop-outs. However 2-2 (a PBS) and 5-1 (ABC), 5-2 will go through periods of heavy drop-outs (enough to make me occasionally switch to my good old analog tuner , hey I have to watch football somehow! :) ). When the signals are coming in they read 90% or above on the Humax strength meter, dropping to 0% when the drop-outs occur. My house sits in a forested area with full grown pines in line of site of the towers. The trees are quite dense (no horizon is visible at all from that side of the house). Non-HD OTA reception does exhibit ghosting so I believe multipath may be causing my problem.

I am wondering if moving to a more directional (and UHF only) antenna is the right way to go. I have been considering something like a CM 4221/3021 or CM 4228. I am not sure, but it seems that the trees are either anttenuating the signal, or causing the multipath issues and I am hoping a new antenna could solve one or both of these problems.

Any help would be much appreciated!

-JJW

holl_ands

08-28-05, 04:42 PM

RF Variable Attenuator is available for about $10 from Radio Shack (15-678).

If you are close to the transmitter towers, too much signal may be causing some channels to have problems.
"Too close" usually means within about 5 miles, but could be 10 miles if a high gain antenna (such as the CM4228) is used.
Dial in just enough attenuation to clear up the problem.

Presuming you wouldn't use a preamp within 20 miles of the closest transmitter tower,
the attenuator would be inserted on the coax going into your On-Air Receiver.

Jeremy Tebo

08-28-05, 05:44 PM

Would an RF Variable Attenuator help me? I'm one mile from the tower, which sits atop a 714 ft skyscraper. It has to go straight though my building though, which is over one city block long.

Nitewatchman

08-28-05, 06:12 PM

Kathy in Cincinnati,

If I recall your reports on Cincinnati thread from quite some time ago, I think you had said your analog OTA reception of the Hi-power Cincinnati analog stations(Including hi power UHF analogs) off your attic antenna was very poor and "snowy", and perhaps "ghosty" as well.

Since the digital stations broadcast off the same towers, and "snow" on analog stations suggests weak signals(Ghosting=Multipath), In your particular case, I don't think it is likely an attenuator is likely to improve your reception. It is interesting however that the Sony performed better for you and Oldfart than your new receiver does -- although perhaps for alltogether different reasons.

I do think you are on the right track concerning your post today in Cincinnati thread concerning finding a knowledable, professional OTA antenna installer to install an antenna outdoors for you.

hope this helps,

theroys88

08-28-05, 08:53 PM

Hey guys,
Looking for some advice. This weekend I put two very large ufh/vhf antennas up on a chimney mount. One toward Norfolk Va and the other toward the Richmond stations. Norfolk stations are 76 miles away from my house and Richmond stations 7 miles. Tried the
Richmond antenna without a preamp and signal strength was too weak for a good lock on my Voom box. Added a preamp and had 96-98 on the box. My lot is heavily wooded with hills. My property is on a hill with the next 3 houses graduating up. Inside antennas have been impossibe for the Richmond stations. I was able to get a great analog picture with some ghosting and locks on the digital stations with occasional dropouts but when the wind picks up and the trees move I get lots of dropouts. Norfolks stations were a bust but I am not sure that a better antenna with higher gain might pull in those stations. My antennas that I bought were antennacraft d9000 with 92 elements. These boys are beasts! I was looking at the antennacaft xg91 with a 16db gain or the 4228. Does anyone have any thoughts and does anyone know someone in Central Virginia that installs antennas. I think need a pro to be able to tame this multipath issue. Is anyone in Central Virginia interested in the other antenna I took down. Thanks Joseph

kurtlingle

08-28-05, 09:54 PM

1. RG-6 is less prone to interference than 300-Ohm wire. It also doesn't break down in the elements as quickly. You should replace your 10-year old wire, but which you use is up to you.

2. What you need is a balun (balananced/unbalanced) connector. Get one rated for outdoor use. Should cost you about $2.

Thanks for your input! Well, I have not used my attenna for 2 years and now it looks like UHF does not come in anymore.

Currently I need to pick up analog from Philly, PA. I'm 7-8 miles from most of the signals and in the yellow /green zones (via antennaweb) so I picked up the CM 3016 from Lowes. I'm trying it out tomorrow.

Though I'm only needing analog now, I plan to get the new Sony 42 LCD for X-mas (for the family, of course! :) So if the CM 3016 works for the analog signals in UHF, will it also be fine for the Digital? Lowes also carries the 3018 also. Any input would be great.

Thanks.

holl_ands

08-29-05, 02:24 AM

Would an RF Variable Attenuator help me? I'm one mile from the tower, which sits atop a 714 ft skyscraper. It has to go straight though my building though, which is over one city block long.

It will cost you all of $10 to find out one way or the other...
But being only a mile away you can't help but be saturated with signal strength.

The signal will bounce off of numerous buildings, even if they are several miles away, arriving from many different angles.
These multipath signals can cause very severe null regions when the multiple signals are out of phase with each other.
That's why it is important to also search around for the best antenna location for each station.

sregener

08-29-05, 09:32 AM

This weekend I put two very large ufh/vhf antennas up on a chimney mount. One toward Norfolk Va and the other toward the Richmond stations. ...I was looking at the antennacaft xg91 with a 16db gain or the 4228.

You don't say if you joined the two antennas together. I'm going to assume you ran two lengths of coax to your tuner box.

If, at 7 miles, you don't get much but snow from Richmond, your odds of getting Norfolk are pretty low.

The 4228 is not recommended for a rotor, and is generally outperformed by yagi designs when installed outdoors. The 91XG is a fine antenna, and has way more gain than your D9000s do on UHF, so it may help things a lot. Still, if the signal isn't there, no antenna is going to make it appear.

I'm still loving my 91xg, after a year of living with it. (www.geocities.com/figbert/antennasdirect91xg.html)

bmcent1

08-29-05, 10:48 AM

I've been using RADIO MOBILE [...] runs under Windows...[/url]

You say that like it's a good thing! ;-) ... Just kidding!!

Thank you for that reference, I may try that program out too. I am very happy with SPLAT! so far but it never hurts to get a second opinion / run a second model.

Note that I also posted an Excel spread sheet calculator, including detailed explanation, that takes the Longley-Rice
Diffraction Path Loss calculation and then melds in the "missing" parameters, such as broadcast tower antenna pattern,
clutter loss, attic/indoor loss, antenna gain vs frequency, sensitivity degradation due to VSWR [...]
Thank you for that thread reference as well, I read it and it's obvious you have given this a lot of thought and effort!

Holl_ands and Sregener, a question about antennas to both of you:

The XG91 looks very promising, but it also appears I have the option of the DB8 since I will be going with a roof mount or chimney mount no more than 10' above by roof line. We get winds here sometimes but I think I could get a pretty sturdy install at that height.

I am about 34-38 miles from transmitter towers in both DC and Baltimore. I am also somewhat down a hill so I don't get line of sight in either direction, I will be counting on scatter or... something else? I originally thought DC stations would come in better, and they do (3dB according to L-R calcs) but I thought the difference would be more pronounced.

If I get the XG91, I have to point it to the best direction as DC and Balt are 50 degrees apart from my location.

Would the DB8 be a better antenna for trying to pull in those two different directions? Though terrain isn't great for my sight, those towers put out huge power (1000 kW typically), they are pretty high, and I am hoping my distance <40 miles to them will help pull in those signals.

Any thoughts about making the choice between those two antennas?

Jeremy Tebo

08-29-05, 10:53 AM

It will cost you all of $10 to find out one way or the other...

Good point, might have to give it a whirl.

Unrelated whining, but anyone else get the feeling that you've gone back 20 years to the days when you had to screw around with antennas to watch TV? Seems ironic that I'm doing all this to watch HD, a new technology. Get out the tin foil...

bmcent1

08-29-05, 12:09 PM

Jeremy -
Yes, in some ways I agree, it does seem "retro" to be thinking about antennas; kinda reminds me of my younger years, those "weird" UHF stations and messing with the rotor to tune in different channels.

On the other hand, if antenna quality has improved and I can apply more science to it than what we had back then (just accepting was was installed when we moved in)... and if that means I can pick up, CLEAR, UNCOMPRESSED, HDTV broadcasts, OTA... *for FREE* ... well, I'll raise an antenna to that :)

Ultimately, this does seem anacronistic and I think the obvious future will include TV delivered over that fiber optic cable we are all waiting for be hooked up to our residences. Then HDTV will not have to be compressed to fit inside the cable operators' bandwidth. Then again, I am still waiting for my flying car and, should that fiber optic future come to be, we won't be discussing it in the "official Antenna Topic" and I would miss out on the great contributions :-)

Oldfart

08-29-05, 01:28 PM

sregener

08-29-05, 03:40 PM

If I get the XG91, I have to point it to the best direction as DC and Balt are 50 degrees apart from my location.

Would the DB8 be a better antenna for trying to pull in those two different directions?

Marginally better. But probably not good enough to get both. Why not a 91XG with a rotor? That way, you can point the antenna to whichever city you want to watch. (Note:bowtie antennas are murder on residential-grade rotors.)

FWIW, I don't have line-of-sight to a single transmitter, and get great reception from the stations 30 miles away with the 91XG. I also get good/fair reception of stations some 75+ miles away.

If your analogs look like the ones on this page (http://www.geocities.com/figbert/8vsb.html) then you definitely want a preamplifier if you don't already have one. Most recommend the CM7777.

bobchase

08-29-05, 06:43 PM

Kathy in Cincinnatti seems to have the same problem as I do; our new HD TiVos are not as sensitive as our discarded Sony HD 200s, and we thus do not now receive digital OTA channels that we previously did. My problem can't be that I need an attenuator since I am more than 35 miles from the Miami antenna farm; thus I'm looking for a better antenna. My attic access is too tight to get a CM 4228 up there, so I'm considering using two CM 4221s. Can someone tell me if this is a good idea, and if so, how I should hook them together for the best results? I don't have the room to stack them one above the other.
Two 4221s put side-by-side are the same size as a 4228. If you do try to combine the 4221s, the only thing you can easily do is use a combiner (a splitter hooked up backwards). You will have more loss doing this than with a 4228 but if your attic opening can only get a 4221 thru, then may the force be with you.

You may need to try a CM7777 pre-amplifier with whatever antenna you put in the attic (even the one you have now). The pre-amp makes up for the loss of the signal penetrating the roof. The net gain is about 6 dB (amp gain - attic attenuation), so you could end up about where you were with the Sony.

You might want to consider a Winegard SS1000 outside. It's a bit far for that antenna to perform properly but almost any antenna outside is better than most antennas inside an attic. It look nice and has a high WAF (Wife Aceptance Factor).

Bob Chase
KHWB-TV

cpcat

08-29-05, 06:57 PM

If I get the XG91, I have to point it to the best direction as DC and Balt are 50 degrees apart from my location.

Would the DB8 be a better antenna for trying to pull in those two different directions? Though terrain isn't great for my sight, those towers put out huge power (1000 kW typically), they are pretty high, and I am hoping my distance <40 miles to them will help pull in those signals.

Any thoughts about making the choice between those two antennas?

The DB8's beamwidth probably doesn't differ that much from the XG91. The AD website gives you the impression it's omnidirectional, but it most certainly isn't. I wish they would fix that already.

If you really want consistent reception at 40 miles with a 50 degree spread you'll need a rotator or two separate downleads (and antennas) into an A/B switch.
The rotator is your best option IMO and will give you the ability to fine-tune aim as well as play around with other markets/directions as well. The yagi/corner reflector (XG91) is definitely easier on the rotator and the installation. That's probably the biggest difference between the two.

bmcent1

08-29-05, 09:03 PM

The DB8's beamwidth probably doesn't differ that much from the XG91. The AD website gives you the impression it's omnidirectional, but it most certainly isn't. I wish they would fix that already.

If you really want consistent reception at 40 miles with a 50 degree spread you'll need a rotator or two separate downleads (and antennas) into an A/B switch.

Okay, I'm definately zero'ing in on the right antenna. I am going to drop the 50 degree spread idea and just try to pick up DC (or Baltimore if DC doesn't work out.) The only reason I thought about splitting the difference was if that was reasonable with the DB8. From comments here and reading articles, it appears that wider spread = less gain, kinda obvious in hindsight ;-)

The reason I don't want to a rotor is that my goal is to feed a MythTV DVR setup. Changing the rotor before recording is out of the question. On that front, if I hit the lotto and felt like getting really fancy (bad idea ;-) I might run two separate antennas into two separate tuner cards so that they wouldn't interfere with each other.

Famous last words, but I think this is my final question before purchase: Are there significant performance differences between 8-bay antennas and the corner yagi when terrain and upper 30-miles distance to towers are the primary factors? It appears the CM 4228 and DB8 8-bay antennas have slightly higher gain than the XG91. What caught my attention is that the gain graphs suggest the 8-bay antennas have better gain over the whole UHF channel spectrum while the corner yagi is biased toward the upper channels. The Wash channels I was shooting for were 34,36,39,48, and 51.

Ratso Gonzales

08-29-05, 11:01 PM

Joining multiple antennas pointed in different directions without some serious filtering almost never works. You'd be better off with a rotor and one good antenna.
Thanks for your advice, and I wish that were an option...Unfortunately, I am stuck with attic install and a good antenna with a rotor simply won't fit. Also the antennas are for a dual-tuner media center so I would like to be able to use the tuners for recording and also simultaneously tuning two stations at once (football season arrives Saturday1)

Do I stand any chance?

Thanks!

Steve

cpcat

08-30-05, 08:12 AM

Okay, I'm definately zero'ing in on the right antenna. I am going to drop the 50 degree spread idea and just try to pick up DC (or Baltimore if DC doesn't work out.) The only reason I thought about splitting the difference was if that was reasonable with the DB8. From comments here and reading articles, it appears that wider spread = less gain, kinda obvious in hindsight ;-)

The reason I don't want to a rotor is that my goal is to feed a MythTV DVR setup. Changing the rotor before recording is out of the question. On that front, if I hit the lotto and felt like getting really fancy (bad idea ;-) I might run two separate antennas into two separate tuner cards so that they wouldn't interfere with each other.

Famous last words, but I think this is my final question before purchase: Are there significant performance differences between 8-bay antennas and the corner yagi when terrain and upper 30-miles distance to towers are the primary factors? It appears the CM 4228 and DB8 8-bay antennas have slightly higher gain than the XG91. What caught my attention is that the gain graphs suggest the 8-bay antennas have better gain over the whole UHF channel spectrum while the corner yagi is biased toward the upper channels. The Wash channels I was shooting for were 34,36,39,48, and 51.

In theory that is true but in practice there's just not much of a difference. Some have even said that the XG91 is better on the lower channels. The xg91's PCB balun might add a small advantage.

sregener

08-30-05, 08:54 AM

Thanks for your advice, and I wish that were an option...Unfortunately, I am stuck with attic install and a good antenna with a rotor simply won't fit. Also the antennas are for a dual-tuner media center so I would like to be able to use the tuners for recording and also simultaneously tuning two stations at once (football season arrives Saturday1)

Do I stand any chance?

A 4228 or 4221 should rotate just fine in most attics - they only need 4' or 2' respectively of clearance to rotate. And both are fine, quality antennas.

Do you stand a chance if you do things wrong? I won't lie. Yes. You stand a chance. But don't go into it expecting success if you want to give it a try.

sregener

08-30-05, 09:15 AM

Famous last words, but I think this is my final question before purchase: Are there significant performance differences between 8-bay antennas and the corner yagi when terrain and upper 30-miles distance to towers are the primary factors? It appears the CM 4228 and DB8 8-bay antennas have slightly higher gain than the XG91.

There are performance differences between the bowtie and corner-reflector/yagi antennas, but they probably won't be significant inside of 40 miles. Don't put too much faith in those gain charts. The 91XG is a top performer, and the 4228 is, too. Generally speaking, though, the yagis work better outdoors while the bowties work better indoors, so I'd go with the 91XG. Believe me when I tell you that mine works very, very, very well all the way down to channel 20, and quite probably below that, too, though it's harder to test and verify below that point.

Nitewatchman

08-30-05, 10:46 AM

The xg91's PCB balun might add a small advantage.

When did they start putting those on XG91's? My XG91(purchased last December) did not come with a PCB balun. It has a plastic "balun box"(should help with waterproofing), but inside is a standard looking balun("sort of" cigar shaped labeled "matching transformer"), with short piece of "twinlead"(It's actually 2 wires that appear to be heavier guage than most) that hooks to 300 ohm terminals on the driven element.

In my case, I removed its balun(and 1/2 of it's "balun box" which easily "comes apart") as I'm using a short piece of twinlead hooked to a mast-mount preamp(Winegard AC-4990) with 300 ohm input. I am not using the balun from it for anything right now, but I have used it for various things and it seems to work as good(or better but can't really say) as any ferrite-core balun I've used.

wdmoody

08-30-05, 11:47 AM

My local CBS station recently upgraded their power from 400kw to 1,000kw. Since the upgrade I experience frequent dropouts that appear to be multipath interference. Before the upgrade my reception was fine. The signal bounces off of a repeater that is within 25 miles of my house. I can see the lights on the tower at night, so I have a clear path to the signal. I have a 100" Channel Master antenna that I bought when all of the local HD signals were lower power (some still are low power). Is my antenna too big? What can I try to straighten this problem? I'd rather not have to move the antenna if I can avoid it. Thanks.

Walt

sregener

08-30-05, 01:32 PM

My local CBS station recently upgraded their power from 400kw to 1,000kw. Since the upgrade I experience frequent dropouts that appear to be multipath interference.

Try a variable attenuator from Radio Shack.

cpcat

08-30-05, 03:26 PM

When did they start putting those on XG91's? My XG91(purchased last December) did not come with a PCB balun. .

I'm not sure, but they're there now unless they are advertised incorrectly.
http://www.antennasdirect.com/91XG_HDTV_antenna.html
I always thought it was a re-branded Euro antenna anyway (?Funke), but maybe not if they used to have the ferrite balun.

Jeremy Tebo

08-30-05, 03:34 PM

FWIW, I bought a variable attenuator ($10 version) and it did not help. The signal still bounces up and down and will not lock on. Multipath has officially pissed on my parade and ruined an entire HD football season. :(

Nitewatchman

08-30-05, 03:44 PM

I always thought it was a re-branded Euro antenna anyway.

I did a little research on this a while back. Looks like it's actually made(and was designed) in China by a company called "CEDA", with several different brand names used throughout the world.

I also think different Driven elements(and perhaps different baluns) are used by various antenna "companies"/distributors selling these things in different countries/etc -- with the Funke's, I think different driven element is used depending upon application/model #.

Here's a link with picture of it from the Chinese company(CEDA) that designed the antenna and actually manufacture them :

http://ceda-antenna.en.alibaba.com/product/50054703/50249080/Outdoor_Antennas/UHF_Outdoor_Antenna.html

Here's some info on CEDA's company profile -- I Gotta take my hat off to Those of their 10 R&D who worked on the "XG91's" design! - They have several other antenna designs which I find interesting as well -- Including some I've seen "elsewhere", and some I haven't :

http://ceda-antenna.en.alibaba.com/profile.html

Here is the antenna in Australia, as a Jaycar LT3182:

http://www1.jaycar.com.au/productView.asp?ID=LT3182&CATID=31&keywords=&SPECIAL=&form=CAT&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=478

Couple of different versions of it on this Funke page(again - the difference being different driven elements for different frequency coverage , I beleive) :

http://www.funke.nl/aerials/00352003.htm

Here it is in Poland, as a Dipol A3710 :

http://www.dipol.com.pl/esklep/a3710.htm

kosar1985

08-30-05, 04:19 PM

Nitewatchman

08-30-05, 04:25 PM

I'm not sure, but they're there now unless they are advertised incorrectly ...... but maybe not if they used to have the ferrite balun.

I didn't break the balun apart to see what is in there ... I don't know if it's possible for a PCB balun to be in there or not, I could be wrong but I wouldn't think so.

Attached is a pic of the Balun that was inside the "black box" on (Dec 2004) XG91. As you can see, it's about 2.25" long(including the female F-connector) and it's about 3/4" wide. I did remove clips on its 300 ohm terminals in order to use it for "other purposes"(specifically on the back of a FM receiver that has those "push in" 300 ohm antenna terminals.

Nitewatchman

08-30-05, 04:44 PM

does anyone have any info on the vu-75xr. I live in Medina, OH and i get channels 5.1,8.1,43.1 in at about 93% with a silver sensor indoor antenna. I can get channel 19.1 at about 63-69%, channel 3 doesnt come in at all. Do you guys think this antenna will work

Given the results you're getting off the indoor antenna(even pulling in one VHF-HI station with a UHF antenna), especially If you mount the VU-75XR outside and aim it North I'd say you've got a decent shot at it. No guarentees, however. Getting good Lo-VHF(Ch 2-6 - 54~88MHZ) digital reception has seemingly proved difficult for many folks, perhaps especially so when indoor antennas are used. "Impulse noise" and other RFI is likely one reason for this. You'll probably find more info+advice concerning WKYC-DT reception on the Cleveland thread.

Looks like Medina is about 25 miles from the lake ... I didn't look up exactly where the Cleveland transmitters are, and you should check antenna web to see what the headings to transmitters are, but I do seem to recall looking at where WOIO-DT was once, and that it was near the lake, pretty much North of you.

Keep in mind, the channel numbers you are referencing are the PSIP remapped virtual channel numbers, not the actual channels the digital stations transmit on. If you go to www.antennaweb.org and punch in your address, it will show the actual channels the stations transmit on in your area the far right column, labeled "frequency assignment". Among other things, PSIP is info the station sends which tells your receiver to "show" it as being on the remapped channel number, even though that is not where it's actually transmitting.

WKYC-DT(DT callsign designation means it's a digital station) actually transmits on VHF channel 2(the analog station transmits on channel 3, the digital remaps to 3.x), WOIO-DT actually transmits on VHF channel 10 and remaps to 19.1, WOIO analog transmits on UHF channel 19.

Good luck,

cpcat

08-30-05, 08:44 PM

I didn't break the balun apart to see what is in there ... I don't know if it's possible for a PCB balun to be in there or not, I could be wrong but I wouldn't think so.

Attached is a pic of the Balun that was inside the "black box" on (Dec 2004) XG91. As you can see, it's about 2.25" long(including the female F-connector) and it's about 3/4" wide. I did remove clips on its 300 ohm terminals in order to use it for "other purposes"(specifically on the back of a FM receiver that has those "push in" 300 ohm antenna terminals.

That looks like a common ferrite core balun to me. Either they've changed it since you bought your xg91 or they are advertising incorrectly. Here's a pic of the PCB balun on one of my Funke psp 1922's. My Triax Band A's have one that looks very similar.

Nitewatchman

08-30-05, 10:40 PM

Cpcat,

From what I can tell, the size of the housing in your pic looks similiar(if not the same) as the housing("balun box") on the XG91. So, even if the housing didn't change but balun did, it certianly seems like it could easily accomodate a similar sized board. Perhaps someone interested who purchases xg91 soon, or has purchased one recently can check theirs before installation, or if it's an indoor install and easily accesable.

Unfortunetly, I can't take a good pic of it, or examine it closely as it's up 40ft on the tower/mast.

If I recall correctly however, I think one side of the housing is riveted-* to the boom, with holes(there were "waterproofing" boots there as well) on the side of the top 1/2 of the housing so the bottom side of the folded dipole (driven element) where the terminals are goes into the top 1/2 of the housing(plastic). The female F-connector on the included balun then fits snugly in a "Hole"(1/2 of which is on top 1/2 of housing, 1/2 of that hole on bottom 1/2 of housing), and protrudes out of that hole so you can hook up the coax.

* - In addition to the rivet(s) (If one is there, I'm particurarly hazy on that), there may have instead been a remvoable fastener(bolt with a wing nut perhaps).

I don't think it will tell us anything more, but I think I should have the bottom 1/2 of the housing out in garage in one "antenna stuff I might need someday" box, as If I recall correctly I had to leave the bottom 1/2 of the balun housing off in order to run 300 Ohm twinlead from the terminals on the driven element to mast-mount preamp - which was what I wanted to do, given the preamp I am using.

---------------------

I was also thinking, another possibility could be that have it so it can support either PCB board or ferrite core balun(or no balun as in my case) per customer preference. I ordered it off antennadirect website, and don't seem to recall specifing anything like that, but I suppose my memory could be hazy .... I do recall calling them to ask about expected shipping date and ended up having a nice "antenna" and TV/DTV Dx'ing conversation with the fellow I was talking to .. I seem to also recall telling him I'd be using 300 ohm input on preamp+a short piece of twinlead and he said it would "work" ...

Probably more than anyone wanted to know, though ... LOL ....

clangro

08-31-05, 10:07 AM

I'm looking to buy an antenna now, but I have no idea what to get.

According to antennaweb.org, I'm 20-24 miles away from most of the towers. They recommend a small, multidirectional antenna. Almost all of the signals are UHF, so UHF quality matters the most. Compass orientation is 205 and 207 on almost all of the stations, which is good that they are so close.

Here's the deal. I live on the 2nd story of a 3 story apartment complex. I need a small, indoor antenna I can purchase locally so I can return it easily if I have any problems. Any help on what to get, where, and how much?

It's funny, because I'm buying this antenna almost exclusively for 1 TV show, Veronica Mars on UPN, which Comcast cable doesn't offer in HD. :(

poster

08-31-05, 06:41 PM

Hi everyone,
I just pulled the trigger on a Panny 50" 50U and it is getting delivered tommorrow. I do not have HD set up from D* yet, and have heard I can get a cheap antenna for locals. I tried searching and couldn't find any old threads. Can anyone suggest a cheap indoor antenna for local signals? Would this be neccessary to have after D* hooks up my dish and box? Thanks in advance for the help!

theroys88

08-31-05, 10:41 PM

Anyone have any sure fire way to tame dynamic multipath other then bombing the entire area with agent orange? Live in a are with lots of trees and multipath issues anyway. Ghosting on all analog channels. Have a very large directional uhf/vhf antenna on the roof and when the wind kicks up I get lots of dropouts. On the analog side uhf channels seem to also suffer from this. Signal fluctuates on uhf analog. Have a Voom box which I think is a 4th generation tuner. Any advice would be helpful.

Ratso Gonzales

09-01-05, 02:25 AM

I would love to use a rotor, but I have a dual-tuner HTPC and would like to run PIP to watch football as well as record TV via a PVR. I might sacrafice the PIP and the ability to watch one station while I record another, but can the rotor automatically point to whatever tower the PVR is trying to tune? My old-school memory of rotors are of things you have to actuate manually. If I can't record with my PVR I think it is a deal-breaker.

Thanks!

Steve

manufanatic

09-01-05, 08:22 AM

Hello, I have brighthouse Digital cable but I want to use my Directv HD receiver to get the local HD channels OTA.

Any recommendations on an Indoor HDTV antenna that can pick up the signal say about 20-25 miles away?

Thanks

sregener

09-01-05, 08:25 AM

Anyone have any sure fire way to tame dynamic multipath other then bombing the entire area with agent orange? Live in a are with lots of trees and multipath issues anyway.

Sadly, this type of problem is very, very hard to solve. The problem actually isn't multipath, it's varying signal strength (the real kind, not the kind most on-screen meters show.) Essentially, your tuner has what's called an automatic gain control, which figures out how strong the signal is and adjusts itself accordingly to receive the signal. If the signal is weak, it turns up the juice and listens to the weak signal. If the signal is strong, it ratchets things down. Either way, the incoming signal after the AGC is at the same level, so the tuner can optimally handle it. When the trees sway, the AGC control can't keep up, so the signal is rapidly changing from strong to weak, confusing the tuner.

Other than getting above the trees, there's very little you can do to defeat this. You might do better with a stacked bowtie-style antenna like the 4228.

sregener

09-01-05, 08:25 AM

...but can the rotor automatically point to whatever tower the PVR is trying to tune?

Newer rotors can be controlled using remote-controls, so if you could program an IR blaster, you should be able to do this...

Joe_M

09-01-05, 08:31 AM

There should be some good info here:
http://www.avsforum.com/avs-vb/showthread.php?t=381623

Oldfart

09-01-05, 08:40 AM

I just got my HD TiVo last week; it is replacing a Sony HD 200 and a Series 2 TiVo. My problem is that a number of OTA channels that I received perfectly on the HD 200 are not received at all on the HD TiVo. I get the message "Searching for signal on: Antenna In". When I check the signal strength on what used to be my best OTA channel, I get a signal in the 20s on tuner 1 and no signal on tuner 2. The only thing that the installer did was to disconnect the antenna line from the Series 2 TiVo setup (and lay it aside) and disconnect the antenna line from the HD 200 and connect it to the HD TiVo.

My current antenna is a Terk 35 in the attic. Should a signal amplifier work, or should I get a new antenna? My attic access is not large enough to accommodate a CM 4228, but I understand that it is possible to drill out some rivets and then fold the antenna, later replacing the rivets with nuts and bolts. Does anyone have any experience in this regard? Alternatively I can get two CM 4221s and hook them together side by side. What would be the best way to do this? I understand that the intact reflector screen of the 4228 is what provides the high band VHS performance of the 4228, and I do not want to lose that.

Neil L

09-01-05, 05:05 PM

I understand that it is possible to drill out some rivets and then fold the antenna, later replacing the rivets with nuts and bolts. Does anyone have any experience in this regard?Rather easy to do. Much easier to get good results this way than trying to join two 4221. A 4228 is really just two 4221's with all the necessary hardware to mount them together, already in place.

holl_ands

09-01-05, 07:27 PM

It isn't so much the bigger reflector on the CM4228 that extends performance into the upper VHF band,
as it is the center feed structure: http://www.solidsignal.com/prod_display.asp?PROD=ANC4228&xzoom=zoom#xview
Look at the individual view angles to see the detailed connection.

For UHF frequencies the "quarter-wavelength" feed structure combines the signals from eight individual
bowtie elements, with impedance matching as best as can be expected for a wideband antenna system.

However, for VHF frequencies the feed structure is only a small fraction of a wavelength,
so the entire antenna structure acts more like one very wide (and fat) center fed dipole
(with a reflector screen that is closer than optimum spacing).

If you simply use an RF Combiner (even a low loss Lindsay Stripline Combiner) to combine two CM4221's,
the VHF performance will be considerably worse than a CM4228.

holl_ands

09-01-05, 08:45 PM

Holl_ands and Sregener, a question about antennas to both of you:

The XG91 looks very promising, but it also appears I have the option of the DB8 since I will be going with a roof mount or chimney mount no more than 10' above by roof line. We get winds here sometimes but I think I could get a pretty sturdy install at that height.

I am about 34-38 miles from transmitter towers in both DC and Baltimore. I am also somewhat down a hill so I don't get line of sight in either direction, I will be counting on scatter or... something else? I originally thought DC stations would come in better, and they do (3dB according to L-R calcs) but I thought the difference would be more pronounced.

If I get the XG91, I have to point it to the best direction as DC and Balt are 50 degrees apart from my location.

Would the DB8 be a better antenna for trying to pull in those two different directions? Though terrain isn't great for my sight, those towers put out huge power (1000 kW typically), they are pretty high, and I am hoping my distance <40 miles to them will help pull in those signals.

Any thoughts about making the choice between those two antennas?

Have you ever seen an XG91 up close and personal?
It's a huge weather vane, with lots of surface area in the individual elements.
And that's before you get winter ice buildup!!!
Better have a very heavy duty mount to prevent twisting.....and a heavy duty rotator:
http://www.geocities.com/Figbert/antennasdirect91xg.html

On the other hand, the PR8800 is just a few sticks with very low wind resistance.

Although the CM4228 8-Bay has higher wind resistance (rear screen) than the PR8800,
it has the advantage of providing considerable gain for the upper VHF channels 7-13,
which will be important when DTV stations revert back to their final assignments.

Funke, like many European manufacturers, provide very detailed specs.
Unlike most manufacturers, their specs conveniently also include windloading:
156 N (Newtons) for the monster 91XG.
84 N (Newtons) for their 4-Bay w Reflector (TG-4500-21/69, similiar to DB-4).
So if you double it, an 8-Bay is about the same windloading as 91XG,
but in a more compact structure to reduce the torque load.

=========================================================
The DB8 and the XG91 are high gain, narrow beamwidth antennas that usually need a rotator.
I haven't seen data on the DB8, but the Funke DC.4591-21/69 data sheet (see above)
says the -3 dB beamwidth is 36-22 degrees (that's +/- 18 to +/- 11 degrees).
Pointed mid-way between DC and Balt, the gain at +/- 25 degrees is going to be down quite a few more dB.
And you are going to have a very hard time keeping it precisely pointed mid-way.
Just a few degrees of pointing error is going to cause a considerable drop in signal for one direction.

Although neither the XG91 or DB-8 are included in the fol. antenna comparison,
click on the Winegard PR8800 8-Bay antenna to see a "similiar" antenna pattern:
http://www.hdtvprimer.com/ANTENNAS/comparing.html

At +/- 25 degrees, the NEC simulation results for PR8800 shows a very strong null.
So the gain towards DC and Balt may be 15-20 dB lower than the gain towards the mid-way direction.
Of course these are simulations, and real world results may be better or worse for any given channel.

If you click on the other high gain antennas (CM4228, CM4248, DAT-75),
you'll see that they all exhibit this sort of performance.
The DB8 and XG91 can be expected to do the same sort of thing,
since antenna gain is obtained by narrowing the beamwidth.

On the other hand, the antenna pattern for the somewhat lower gain 4-Bay antenna
provides a very wide beamwidth (see CM-4221 and PR4400).
The gain is down by about 4 dB from the maximum at +/- 25 degrees.
The similar Antenna Direct 4-Bay antenna would be the DB4.

========================================================
Punch some numbers into SPLAT to compare a mid-way pointed 4-Bay to a high gain antenna on a rotator.
But whether or not a 4-Bay antenna pointed mid-way provides enough gain can only be determined by trying it.

Using my spread sheet calculator, I'm still collecting data on how much fade margin is enough
to ensure an "acceptable" frequency of signal dropouts.
Unfortunately, it is difficult to pin down some of those assumptions, such as loss through trees,
clutter loss, sensitivity loss due to VSWR, et. al.
Right now, I think it is in the ballpark of 20-30 dB, give or take 10 dB.

poster

09-01-05, 10:44 PM

theroys88

09-02-05, 04:14 AM

Just read that the senate is getting close to a consensus for a true hard date for digital
transition date of 2009. That seems realistic to me. That gives the digital tuner manufacturers time to beat multipath.

holl_ands

09-02-05, 05:33 AM

Guys please help a noob. I have D* and just got my TV. I was under the impression that an indoor HD antenna would boost my local signal. I live in a suburb of Milwaukee and my locals come in just fine. I take it that you need an indoor antenna only if you can't get locals due to location. For example if you live deep in the county. I bought one today but see no way to hook it up because my satelite is in the way. Bring it back right? Thanks again for helping a noob out. :)

I'm a little confused by your question, even after reading your other posts on this forum, so let's see how far we get.
First let's start with D* manual download page:
http://www.directv.com/DTVAPP/learn/Manuals.dsp

Most of the new D* HD Receivers have an input specifically designed for an On-Air DTV Antenna, typically called "OFF AIR IN".
This is where you would connect the usual TV antenna.
If your D* Receiver does not have this capability, then you would connect to your Panny's On-Air Antenna connector.

The D* Receiver would be more convenient than using your Panny's internal ATSC On-Air Tuner,
since you would only need to deal with a single integrated program guide and your Panny would always be set for watching the D* input.

D* should provide all ANALOG local channels and a few HD channels.
But most areas do not yet have ALL of the local DTV channels (some are HD and some are still low-rez).

You should set up a free account at www.titantv.com to see which D* channels and On-Air channels you get in your area.
You can also use one of the pull-down selectors to see ONLY HD program listings.

You should also start by entering your address/zipcode into www.antennaweb.org and see whether all of the stations you want
can be received with a simple indoor antenna (yellow, sometimes green).
Usually, an indoor antenna is limited to perhaps 10-15 miles distance.
You can also see if any of the on-air stations require an antenna that covers both the VHF and UHF bands.
[Most DTV stations are in UHF band today, but many will move to the VHF band in the near future.]

Typical unamplified indoor antennas commonly discussed in this forum include the Terk HDTVi (LPDA with VHF rabbit ears),
the Philips/Zenith/Sears Silver Sensor (LPDA without VHF rabbit ears) and the Radio Shack 15-624 (two-bay bowtie).

If you are more than about 10 miles from the closest transmitter, you should be able to use an amplified indoor antenna,
such as the Radio Shack 15-872 (LPDA without rabbit ears) or one of the many (and less desirable) amplified loop plus rabbit ears (for VHF).

poster

09-02-05, 08:14 AM

I'm a little confused by your question, even after reading your other posts on this forum, so let's see how far we get.
First let's start with D* manual download page:
http://www.directv.com/DTVAPP/learn/Manuals.dsp

Most of the new D* Receivers have an input specifically designed for an On-Air DTV Antenna, typically called "OFF AIR IN".
This is where you would connect the usual TV antenna.
If your D* Receiver does not have this capability, then you would connect to your Panny's On-Air Antenna connector.

The D* Receiver would be more convenient than using your Panny's internal ATSC On-Air Tuner,
since you would only need to deal with a single integrated program guide and your Panny would always be set for watching the D* input.

D* should provide all ANALOG local channels and a few HD channels.
But most areas do not yet have ALL of the local DTV channels (some are HD and some are still low-rez).

You should set up a free account at www.titantv.com to see which D* channels and On-Air channels you get in your area.
You can also use one of the pull-down selectors to see ONLY HD program listings.

You should also start by entering your address/zipcode into www.antennaweb.org and see whether all of the stations you want
can be received with a simple indoor antenna (yellow, sometimes green).
Usually, an indoor antenna is limited to perhaps 10-15 miles distance.
You can also see if any of the on-air stations require an antenna that covers both the VHF and UHF bands.
[Most DTV stations are in UHF band today, but many will move to the VHF band in the near future.]

Typical unamplified indoor antennas commonly discussed in this forum include the Terk HDTVi (LPDA with VHF rabbit ears),
the Philips/Zenith/Sears Silver Sensor (LPDA without VHF rabbit ears) and the Radio Shack 15-624 (two-bay bowtie).

If you are more than about 10 miles from the closest transmitter, you should be able to use an amplified indoor antenna,
such as the Radio Shack 15-872 (LPDA without rabbit ears) or one of the many (and less desirable) amplified loop plus rabbit ears (for VHF).

I really appreciate the help. I am sure a newbie like me can confuse alot of people with knowledge on the subject. Thanks for bearing with me. I still have my standard D* box. HD cant be installed until the 17th :(. After looking at it, I see the Antenna In outlet. I will plug it into there and check it out after work. I am within 10-15 miles of all of the towers so I should be OK there. They all come in, just wondered if this antenna woul dmake it a little bit better. I bought an RCA amplified antenna from Best Buy for a cheap price. This should help boost my local signal and give me a better picture right? Thanks! :)

greywolf

09-02-05, 10:23 AM

You are taking information about HD receivers and applying them to your situation. It does not work that way. Non HD receivers do not have antenna inputs because they do not have tuners for anything but satellite. You cannot put an antenna on your receiver.

HD receivers do have antenna inputs because they have OTA, over the air, tuners as well as satellite tuners. These do not improve the satellite picture. They allow the receiver to tune local digital channels, including some which carry HD programming some of the time. Local channels through the dish are compressed standard definition and don't look as good. The improvement comes from tuning in a different source, OTA as opposed to satellite. It's just that an antenna is needed to get the signals to the OTA tuner.

poster

09-02-05, 10:55 AM

colofan

09-02-05, 11:01 AM

milehighmike

09-02-05, 11:27 AM

Greywolf,

I beg to differ with you regarding antenna inputs on non-HD satellite receivers. I have two E* 311's. They have OTA antenna inputs that I am, in fact, using for my analog locals.

chinatti

09-02-05, 11:47 AM

I have a CM4228 and CM777 preamp on order, and I'll be trying them in the attic (at least initially) to go with my new HR10-250. I know that you want to place the preamp unit as close to the antenna as possible, but I was wondering if the placement of the power supply makes any difference. I could place the power supply up in the attic near the preamp, but I'd have to run an extension cord. I have a more convenient spot where the RG6 goes by a power outlet (at my "distribution" area where all my RG6 converges). If there is no difference, I'll place the power supply there, but if it's advantageous, I'll run the cord and put it in the attic (or alternatively, place it at the other end at the receiver).

Thanks in advance.

Nitewatchman

09-02-05, 11:58 AM

Using my spread sheet calculator, I'm still collecting data on how much fade margin is enough to ensure an "acceptable" frequency of signal dropouts.

Unfortunately, it is difficult to pin down some of those assumptions, such as loss through trees, clutter loss, sensitivity loss due to VSWR, et. al.
Right now, I think it is in the ballpark of 20-30 dB, give or take 10 dB.

Are you estimating 20-30db "necessary" fade margin for your own reception conditions, or as a overall "expected" figure, or as a "worse case" thing? That seems AWFULLY high to me, at least from my DTV reception experience. 5db (or even a bit less) fade margin seems to be enough here for perfect, dropout free reception, but I like to have an extra 10db for "extra insurance" where possible.

While I don't have time right now for a completely "detailed" report(as if the below isn't long enough ...) :

#1.) I can tell you I have experienced(that I've noticed) a total of 5 or 6 reception related dropouts at my location with local DTV reception since November 2001 (all of those occuring before 2004) and fortunetly I was able to detirmine what caused all of those. In two cases, involving a local DTV station on RF 10, it was due to noise spikes from VERY nearby lightning strikes, both occuring in Spring 2002. The other 3 or 4 dropouts were due to STRONG co-channel interference via "tropo" signal propagation.

#2). With my current antenna system, I have to pad signals(by adding extra attenuation in feedline) from Local DTV stations(There are 14 of them I receive "perfectly" located 12~39 miles distant) by anywhere between -20db to -60 db to get down to near threshold levels. Only 2 stations are down "near threshold" if I pad them by about -23db. The rest need at least -30db extra attentuation or more. Most require around, at or above -50db to get down to near threshold levels.

Note : when padding these signals the figures above are based on how much extra attenuation it took to get "down" to the minium level required to still achieve perfect, dropout free reception(for the period I was observing while padding the signals). As, It proved too difficult, given my means of "measurement"(don't have a spectrum analyzer/etc) to try to get somewhat accurate measurements concerning how much extra attenuation added to feedline was required for the signal to drop below a signal lock or in between that and "perfect reception", although the difference between "PSIP" lock and perfect reception was generally only around 3~4db or so. I have noted that it seems to take a little less(perhaps around two db or so) to acheive a PSIP lock than it does to achieve a "full" signal lock with at least some degree of video/audio decoding occuring.

#3). With the use of other antennas/padding the signal/etc, I have experienced no reception related dropouts - over long periods of time with as little as 6db (or less) "margin" available. In fact, concerning local DTV signals and my previous "main" antenna system(given the attenuation in feedline from splitters/etc I was using at the time, which is more than I'm using now) In use for DTV reception between Nov. 2001 and Dec 2004 -- Without adding any "add'l" attenuation in feedline, My weakest receivable local signal(DT on 24) only required about 6db "extra" padding to LOSE a lock, and the only 2 dropouts I experienced from that station which occured during that time period due to a co-channel analog(nearly off back side of antenna) 150 miles away really "blasting" in via "tropo", as reported farther above ... While I do see this co-channel station fairly often via tropo given proper antenna aiming, it has only been that one time that I've noticed that the signal has been strong enough to raise "noise floor" enough to cause a dropout(2 in this case over the hour or so when the co-channel station was exceptionally strong) to local station. Since the "new" antenna setup here should have a better F/B ratio than the old antenna, I expect it is/will even be more rare to see dropouts due to this co-channel situation.

Antenna setup Note : The "old" main antenna was a large VHF/UHF combo antenna(Radio shack VU210 specically), which I installed in 1992 mounted at 35FT AGL, 838FT ASL. Preamp was a early 80's vintage Blonder-tongue mast mount preamp(I think the specs were about 15db gain on UHF/10db gain VHF, 4.5db NF). The Coax run was new in early 80's as well. Along with new coax runs, New UHF antenna is XG91 at same height(35 FT AGL, 838 ft ASL), Winegard AC-4990 mast mount preamp(2.9db NF, 29db gain) for UHF, VHF antenna is Winegard PR-5030 with CM7778 preamp(VHF specs 15db gain, 3db NF).

"other antennas" involved with #3) above are mainly simple indoor antennas(used indoors with a cheap RS distribution amp, or no amp). "Rabbit ears", UHF loop or bowtie(folded dipole -- no reflector - "wire" in the shape of a bowtie, specifically).

location information - Terrain and trees : My location is in a small, steep, very forested valley. With the tower "base"(and the foundatation of my house) at 803 FT ASL, and the UHF antenna at 838FT ASL, there is terrain 50FT higher than antenna in most directions within 1/4 mile, and in some directions, terrain 50FT higher than antenna as close as 300Feet away from it, with terrian rising as much as 300Feet higher than antenna in some directions within a few miles. However, most of the terrain in my immediate vicinity(within a mile or so) If fairly flat, and ranges between 850FT and 900FT ASL.

However, Luckily, it's somewhat "open" in the directions of the local stations' towers, however, not to the extent that there is completely unobstructed RF "line of sight", according to somewhat seat of pants caluclations using Delorme's Topo USA software and elevation profile plots to the towers+antenna height info from stations licensed facilities/etc. on FCC site.

I was also able to have detailed longely-rice studies done for my location for a couple of local stations by a broadcast engineer friend using the comsoft package. In one case, involving my weakest, receivable local DTV signal as discussed above(DT on 24 at 54 KW ERP, 39 miles at 1099FT ASL on a 300ft stick), (given my antenna height) the longely-rice study predicted :

43dbu field strength
131.8dB Base loss

attenuation by terrain :

Diffraction : 26.9db
Fresnel : 11.5db

-------------------------------------------------------------

While I would not want to draw any conclusions from this for other locations, or overall in any sort of general way -- nevertheless, from MY location anyway -- I've found Excellent, dropout free(more or less) reception has been achieivable with as little or 6db or even less "fade margin", including with Early receivers(such as RCA DTC-100, which I believe is 1.5 or 2nd generation), and over long periods of time over which there have been plenty of oppurtunities for changes in Dynamic Multipath conditions(high winds as high as 70mph gust moving tree limbs around, places flying over/etc) Certianly, I have more than that with the antenna system I'm currently using, and it doesn't hurt to have a little "insurance" I'd say ... but, in my case at least, I would say 10db fade margin is certianly more than enough "extra insurance".

--------------------------------------------------------------

That being said -- I can however report that I *do* have a 15th local DTV station(DT 39) that is a problem. Although I have no way of knowing, While I expect 10db fade margin for it would probably be "enough"(or close to it) for this particular station+reception difficulties involved, I suspect it might require a bit more margin than that - I'd guess 15~20db would be a good bet for some "extra" insurance.

Even though this station is only 12 miles distant from my location - I'm quite sure that insufficent signal strength is the MAIN issue involved, and There are significant issues involving :

Their STA, relatively low antenna height and directional antenna pattern that doesn't favor my direction(they send about 2KW ERP in my direction according to the relative field strength shown on FCC sitefor their current facilities for their current operating permit), terrain issues(this one is in a significantly different location from the others, in a direction where terrain is a particularly difficult issue), as well as a direction which is perhaps more significantly impacted by atteunation by trees/leaves.(the heavy tree cover(trees 30~100FT tall) starts only 15 feet from my antenna in that directon).

When the leaves are off trees, Mid-fall through early spring at my location -- I am often able to receive at, or near threshold signals from this station, often enough to achieve "perfect", or near perfect reception with perhaps a dropout occuring every now and then if a slight breeze moves the tree limbs around/etc. If it is quite windy however(with leaves off trees), I might get a decodable frame every now and then, but that is about it. When the leaves are ON trees however, signal is quite a bit below threshold, It seems at least 4~5db less. While this is a bit more attenuation than I would expect on due to "leaf cover" alone, I suspect the combination of combination of issues mentioned above are a culprit. In this case, I suspect IF I could raise my antenna "higher"(or move it to a "hot spot"), I could fairly easily improve reception of this station. I have no need to do that however, as this is a TBN affiliate, and even if I were a frequent TBN viewer, I expect it won't be much of a problem once they raise their antenna height/etc and go to "full power", if their analog station which booms in here from a higher transmitting antenna on the same tower).

I would also note that, especially during the time this station is not receivable during spring/summer/fall months, I DO occasionally see good signals via tropo from co-channel stations such as DTV from Southern Michigan and NE Ohio, and Central KY, and the local, although it is only 12 miles away, does not seem to be raising the noise level "much" given stations being received from different directions ... Another "clue" that this signal is particularly weak.

greywolf

09-02-05, 12:00 PM

Greywolf,

I beg to differ with you regarding antenna inputs on non-HD satellite receivers. I have two E* 311's. They have OTA antenna inputs that I am, in fact, using for my analog locals.The question was re: a D*system and DTV, not E* and analog.

deconvolver

09-02-05, 12:10 PM

Sorry I posted before in the wrong section so any ideas?

So has anyone tried the blondertongue BTY series of antennas? I mean I have a CM4228 and it still isn't get the job done. I had a CM3023 before.

This antenna is for single channels and comes out at 75 ohm instead so no need for a balun. It appears that these are the antennas that cable and TV stations use to feed their front ends.

Not that I want to spend a fortune trying to get the networks but really 45 miles away from a 10 kilowatt station that is behind a 50 foot hill is becoming a challenge

Ideas comments please?

I doubt that a different antenna in the same place will make a huge improvement over a CM4228. Assuming you already have a good non-overloaded pre-amp like a CM 7777 and interfering channels are not the issue then unless you can re-locate the antenna to a better (higher) place it will be difficult to go from an unusable to a good signal. How close to watchable is the station now? If it is not almost fine with a few too many dropouts then don't expect miracles.

milehighmike

09-02-05, 02:02 PM

greywolf

09-02-05, 02:46 PM

Once again, the quote is out of context. It was part of an answer in response to a question about DirecTV receivers, not Dish Network receivers.

Nitewatchman

09-02-05, 03:19 PM

FWIW, I have 2 311 E* receivers as well.

It has a RF input(which could be used for an antenna), but 311 does not have even an internal NTSC tuner. All it does is pass signal from its RF input through to it's RF output, if you're using the 311's RF out jack. So, for example, you can hook up an OTA antenna to 311's RF input jack, then 311 from it's RF out jack to your TV's RF input and still use the signals off the antenna when you aren't using the RF modulator(on channel 3 or 4) on the 311.

"RF Input", Or "ant in" might not really be correct terminology, though, as there's nothing in the receiver to actually "input" signals from an antenna into. It just "passes it through when you aren't outputting signals from the sat receiver via 311's RF modulator(on channel 3 or 4).

holl_ands

09-02-05, 03:29 PM

poster

09-02-05, 05:57 PM

Thanks for the help greywolf. So just so I have this straight, I should wait until my D*HD is hooked up, then i can put the antenna on that box? Thanks for helping me out! :)

bump, sorry to do this but I am still unsure as to whether or not I should keep this antenna or bring it back to the store. Thanks!

Nitewatchman

09-02-05, 06:15 PM

poster,

Why not use, or at least try out the OTA portion of your D* HD receiver with your antenna before taking it back so you can receive(or see if you need a "better" antenna setup) local HD from the broadcast Nets? I must admit, I am confused concerning whether you already have the D* HD receiver, or are waiting for D* to bring it to you when they come to Install your HD setup.

I haven't follwed the D* HD LIL schedule, and I'm not that familiar with D*(as I don't use it)(and someone please correct me if I'm wrong), but I doubt Milwaulkee HD locals are carried LIL over the satellite, yet.

Meaning, you'll probably need to use OTA DTV/HD(over the air)+an antenna to receive HD from some, or all the broadcast nets(ABC, CBS, NBC, PBS, Fox, WB, UPN - you may not have affiliates for all 7 in your area providing HD however) from your local broadcasters. Otherwise, all you'll get is SD locals(usually originating from analog stations) via "the dish", if(and you said you are) you are subscribing to D* locals.

In some markets, stations that are Network O&O's for a couple of networks "allow" D* subs to use the D* DNS HD feeds, otherwise, you'll need OTA for non O&O affilaites, or nets that don't provide DNS feeds to D*.

sregener

09-02-05, 07:37 PM

Have you ever seen an XG91 up close and personal?
It's a huge weather vane, with lots of surface area in the individual elements.
And that's before you get winter ice buildup!!!
Better have a very heavy duty mount to prevent twisting.....and a heavy duty rotator.

Well... um... hmmmm....

I had a Winegard HD8200P on my tower before I replaced it with the 91XG. 16' long. 12' wide at the widest point. Used a standard-grade Channel Master rotor for it. That's what the professional installer recommended. Then I put up the 91XG. Need I tell you that it looks tiny in comparison? Those not "in the know" looked at it and were sure that performance would be much, much worse than the 8200P - how could something so small (half the length, and skinny as a rail) outperform something so big?

Those same installers say don't put up a Channel Master 4228 on a rotor or a tower - the wind load is a killer. I'm not an engineer, just a guy who listens to the installers tell their stories about towers that fall over and what people had up on them at the time.

And here in Minnesota, we get plenty of ice. The 91XG, perhaps because it can't operate as a "sail" the way the 4228 can, doesn't put the same load on a mount. And a conventional, $65 rotor is more than enough to hold it stable in even heavy winds.

sregener

09-02-05, 07:41 PM

I know that you want to place the preamp unit as close to the antenna as possible, but I was wondering if the placement of the power supply makes any difference.

You should place the power supply as close to the tuner (not the antenna) as possible. If you have a long cable run after the power supply, your amplified signal will suffer line loss (and potentially interference.)

Nitewatchman

09-02-05, 07:51 PM

I disagree Sregener.

All the power supply does is supply power to the amp via the coax. Shouldn't matter where it is placed(unless the power is being blocked by a splitter/etc. that won't pass the power - most preamps require DC power, but most Winegard amps/power supplies use AC), the preamp on the mast is what "effects" the OTA signals, not the power supply.

AntAltMike

09-02-05, 08:09 PM

When installing a rotor, you should cut the upper mast as short as possible. For conventional combo antennas, a foot is long enough. For UHF Yagis with corner reflectors, maybe 2 feet. I've installed a lot of the largest Chanel Master and Winegard combo antennas with residential grade rotors and with no auxilliary bearings, and have never had one fail.

cpcat

09-02-05, 09:04 PM

Sorry I posted before in the wrong section so any ideas?

So has anyone tried the blondertongue BTY series of antennas? I mean I have a CM4228 and it still isn't get the job done. I had a CM3023 before.

This antenna is for single channels and comes out at 75 ohm instead so no need for a balun. It appears that these are the antennas that cable and TV stations use to feed their front ends.

Not that I want to spend a fortune trying to get the networks but really 45 miles away from a 10 kilowatt station that is behind a 50 foot hill is becoming a challenge

Ideas comments please?
I'm assuming you're using a quality preamp already?

Either get the antenna up higher to clear the obstruction or if that's not feasible you could narrow the beamwidth further/increase gain by horizontal stacking. It works for me at 65-130 miles.

The problem with the unweildy 4228 is that it's nearly impossible to stack horizontally unless you're willing to put up two masts. You're much better off with a yagi/corner reflector. Right now if I was starting over I'd probably go for two XG91's. Do some research here on horizontal stacking and I'd be glad to help you as necessary if you want to try. Here's an example: The top two are wide band uhf and the bottom two are high band vhf (7-13).

poster

09-02-05, 09:13 PM

cpcat

09-02-05, 09:18 PM

Have you ever seen an XG91 up close and personal?
It's a huge weather vane, with lots of surface area in the individual elements.
And that's before you get winter ice buildup!!!
Better have a very heavy duty mount to prevent twisting.....and a heavy duty rotator:
http://www.geocities.com/Figbert/antennasdirect91xg.html

So if you double it, an 8-Bay is about the same windloading as 91XG,
but in a more compact structure to reduce the torque load.

=========================================================
.

You're way off here. The torsional load from the XG91 (and any other uhf yagi/corner reflector I can think of) is easily handled by the CM 9521 rotator. It's really not that long (7ft). The biggest load on the rotator is the length of the lever arm above it. Re-syncing a rotator after a storm is no big deal. Breaking the top off the rotator is.

The 4228 is murder on a rotator due to the added lever arm above the rotator necessitated by the design (and it's weight) not to mention it acts like a sail if pointed up or down wind.

I can't disagree with a sturdy mount, though (who can?).

Nitewatchman

09-02-05, 10:16 PM

I tried it, and it seemed like the picture was similar. It is ok, I get all of my locals clearly. I am 9-15 miles from all of the towers. I am sorry I was confusing. I just have normal D*. What I wonder is will this antenna help me get a better picture when I do get D*HD. Any thoughts. Thanks again, and sorry for the confusion.

You can't try OTA HD/DTV reception, or see what it looks like without a ATSC(Digital Television) receiver(and Antenna), such as what is in all D* HD receivers that also must be properly hooked up to your HD display via appripriate connections(Component HD, DVI/etc) in order for you to see the HD "difference".

I'm still confused concerning what Over the air receiver you are currently using with your antenna. If it isn't a ATSC receiver, it sounds like it must be analog only and you are receiving SD analog(in which case it's fairly likely you will see some "ghosts", or "snow" from some of the stations with an indoor antenna), OR you are still receiving the SD locals over the dish(and just don't realize it), which origniate from ANALOG stations and D* retransmits them in "digital" form over the dish, that's not the digital/HD stations.

It should give good instructions in the manual for your D* receiver, I'd think, but if not you can tell us the model # of the "normal" D* receiver, perhaps someone who is familiar with it could tell you more.

In any event, when you get your D* HD receiver installed, it should become clearer. Take the antenna back if you want before then, but you'll probably need to getting another one after you get your D* HD receiver in order to receive HD locals .....

Marcus Alzona

09-02-05, 11:05 PM

Greywolf,

My comment regarded the following quote from your post:

"Non HD receivers do not have antenna inputs because they do not have tuners for anything but satellite."

Perhaps I am still misunderstanding you, but I have a non-HD receiver (Dish 311) and it has antenna inputs.

Mike - You are correct about this. There are DirecTV non-HD receivers (including the one widely in stores now, the D10) that have antenna inputs. Just because you can get non-HD local channels via the satellites, it doesn't mean you have to get them that way.

Greywolf - You can check out the manuals for the DirecTV non-HD receivers if you'd like verification of this. Here are a couple of samples, both of which have analog OTA inputs:

http://www.directv.com/learn/pdf/System_Manuals/DIRECTV/DIRECTV_D10.pdf
http://www.directv.com/learn/pdf/System_Manuals/Hughes/HNS_SD_HBH.pdf

greywolf

09-03-05, 12:46 AM

poster

09-03-05, 01:32 AM

You can't try OTA HD/DTV reception, or see what it looks like without a ATSC(Digital Television) receiver(and Antenna), such as what is in all D* HD receivers that also must be properly hooked up to your HD display via appripriate connections(Component HD, DVI/etc) in order for you to see the HD "difference".

I'm still confused concerning what Over the air receiver you are currently using with your antenna. If it isn't a ATSC receiver, it sounds like it must be analog only and you are receiving SD analog(in which case it's fairly likely you will see some "ghosts", or "snow" from some of the stations with an indoor antenna), OR you are still receiving the SD locals over the dish(and just don't realize it), which origniate from ANALOG stations and D* retransmits them in "digital" form over the dish, that's not the digital/HD stations.

It should give good instructions in the manual for your D* receiver, I'd think, but if not you can tell us the model # of the "normal" D* receiver, perhaps someone who is familiar with it could tell you more.

In any event, when you get your D* HD receiver installed, it should become clearer. Take the antenna back if you want before then, but you'll probably need to getting another one after you get your D* HD receiver in order to receive HD locals .....

Thanks for the reply. I think I am seeing analog channels. My Panny says it is in 480i. I have the original box that came with my D* when i got it 3 years ago. It is the crappy one that is slow. I don't see a number on the front. I know its a Phillips though. I will keep the antenna, since it will come in handy in a couple of weeks when my HD box arrives. Thanks again for your input. Greatly appreciated by this noob! :D

Marcus Alzona

09-03-05, 04:05 AM

Now with that I am familiar. Those are antenna thoughputs. There are no OTA tuners in those boxes. It's just a way for people whose TV's only have one antenna connection and no other video inputs to be able to get programming OTA or with CATV with their TV tuner or via satellite with RF out without adding a switch.

Yeah - the DirecTV receivers don't have analog tuners. Just pointing out that, to be accurate, the receivers (the non-HD DirecTV ones in question) *do* have ports labeled "Antenna/Cable In". Which, of course, work exactly as you described (i.e. as a throughput). (I wonder if the DishNetwork receivers that others have mentioned also work this way.)

bmcent1

09-03-05, 09:50 AM

Hey all,
Sorry if this is long, but I really want to make sure I understand this stuff correctly, or if I don't, that many people here will kindly set me straight :) ... For anyone out there with experience using Longly-Rice or another signal propagation model, can you check my math / let me know if I am close to doing this calculation right?

I'm running the SPLAT open source Longley-Rice program. (As an aside, if I'm doing this right, and if it proves to be a reasonably good predictor of the channels I end up receiving, I will try to put some of this functionality up on a web site for others to use...)

An equation in the man page says:

"To determine the signal-to-noise (SNR) ratio at remote location where
random Johnson (thermal) noise is the primary limiting factor in recep-
tion:

SNR = T - NJ - L + G - NF"

T is the ERP of the transmitter in dBW
NJ is Johnson Noise in dBW, given as -136 dBW for a 6 MHz TV channel
L is the Longly-Rice path loss computed by the program
G is gain in dB over isotropic
NF is the receiver noise figure in dB

My first question is, can you just add and subtract when the units include dBW and dB or is there some conversion between those two units?

To convert from ERP in kW (found on FCC queries) to dBW, I have been using this equation:

T = 10 * Log (ERP in kW * 1000)

Here is an example, using a 1000kW transmitter, 170dB L-R computed path loss, an antenna with a 16dB gain, no preamp, and a 7dB noise figure for a receiver:

T = 10 * Log (1000*1000) = 60 dBW

SNR = 60 - (-136) - 170 + 16 - 7 = 35

SPLAT also recommends a Signal Margin calculation to compute how much more signal is available over the minimum to a achieve a specific signal to noise ratio. At least 15.5 dB above SNR is recommended for ATSC DTV reception. So, Signal Margin is computed as:

SM = SNR - 15.5 = 35 - 15.5
SM = 19.5

If I understand this correctly, this means there is an extra 19.5 dB signal available over the minimum necessary to receive that station with that antenna, assuming the L-R prediction for this tower and this receiving location (granted, those are big IFs.)

Several sources have recommended L-R offers widely variable results but that if you build in a margin of 10dB the preditions start to line up pretty well with real, measured results. I take that to mean if (SM - 10) is still a positive number, this is a good indicator that reception for these parameters should be achieved.

Am I correct, or on the right track? Or do I need to go back to the books?! Thanks!!

Nitewatchman

09-03-05, 10:46 AM

(I wonder if the DishNetwork receivers that others have mentioned also work this way.)

That's("throughput, no internal tuner) how I said Dish 311 receiver is on post in one of my posts previous page of this thread .... I can't comment on any other specific D* SD receivers. I've "tested it" to make sure.

You can't tune the locals from the box, as there is no OTA tuner. I don't subscribe to E* LIL, but I think I'd read somewhere that with the 311 anyway, the LIL locals via sat are on different channel numbers.

Nitewatchman

09-03-05, 11:42 AM

bmcent,

I haven't used splat but I think I can comment on a couple of things in your post.

I did read the Doug Lung article ( http://www.tvtechnology.com/features/On-RF/F_Lung-02.02.05.shtml ) on it, and looks like it would be fun to "play with". Looks like I'd have to install linux(or Sun Solaris for x86 - I have ver 8 around here somewhere+ was using it on a machine(keyword WAS) on a partition somewhere(it won't be the 1st time that's happened). Perhaps I might get around to doing that someday.

To convert from ERP in kW (found on FCC queries)

I'm sure you know this -- but just in case -- if the station in question is using a directional antenna pattern, make sure you calculate ERP properly for the "direction"(such as bearing from the tower to your antenna) or "directions" being used. Make sure not to miss the "pattern rotation" info as well, as, if there is a 30 degree pattern rotation for instance, the relative field strength listed for, say 0 degrees would actually be correct for 30 degrees.

This calulation is :

Relative field strength Squared x "max" watts ERP(the ERP listed on FCC site for the station) = Watts ERP being sent in that direction.

For example, if info on FCC site on a station's antenna pattern shows a pattern rotation of 0 degrees, and a relative field strength value of .550 for 130 degree true azimuth bearing from their tower, and the stations ERP for a relative field value of 1.000 is 250KW ERP (This will be the ERP listed in the operating permit - STA or licensed facility/etc)the ERP sent at 130 degrees should be :

(.550x.550) x 250,000 watts = 75,625 Watts ERP being sent towards 130 degrees in this case IF the actual antenna pattern matches the info on FCC site.

To convert from ERP in kW (found on FCC queries) to dBW, I have been using this equation:

T = 10 * Log (ERP in kW * 1000)

According to this (if you plug in 60dbW at following link), your calcuation here is correct :

http://www.vernonboyce.org/wattsconverter.htm

At least 15.5 dB above SNR is recommended for ATSC DTV reception. So, Signal Margin is computed as:

Yes, ATSC documents say 15.9 db SNR (Signal over noise ratio) is the theoretical minimum signal required for perfect DTV reception. "real world" results of course may differ.

If I understand this correctly, this means there is an extra 19.5 dB signal available over the minimum necessary to receive that station with that antenna, assuming the L-R prediction for this tower and this receiving location (granted, those are big IFs.)

Sounds right to me.

Several sources have recommended L-R offers widely variable results but that if you build in a margin of 10dB the preditions start to line up pretty well with real, measured results. I take that to mean if (SM - 10) is still a positive number, this is a good indicator that reception for these parameters should be achieved.

Seems reasonable, and 10db seems a good bit of insurance to me for most circumstances. Athough, in many cases(In a real sense, not a predicted sense) I don't think you are going to need as much as 10db "signal margin" over the ~16db SNR minimum required for reception.

You could do a study for your location, and then "test" it in the real world using a variable attenuator to pad down the signal until it gets down to threshold(just above or at a signal lock, where signal is just decoded), and hopefully, you'll be able to get an idea if the software's prediction for "L" is in the ballpark based on how much you need to pad the signal(which should hopefully be close to SM). Of course, some variables here could involve differences in various RF performance issues concerning front-end of any specific receiver model - But, it seems to me 16db SNR minimum threshold required is a good rule of thumb to use.

Am I correct, or on the right track?

Seems like it to me given the recommended formulas they suggest you use, but I'm certianly no expert ...

Update: Another variable to factor into this which you didn't mention that may be of some importance, may be the beam tilt of the transmitting antenna. The studies I'd received from a friend using comsoft seemed to indicate that beam tilt was a factor it could take into account. I don't see any specific mention about beam tilt+splat in the Doug Lung article.

holl_ands

09-03-05, 02:28 PM

I really want to make sure I understand this stuff correctly, or if I don't, that many people here will kindly set me straight :)
I'm running the SPLAT open source Longley-Rice program.

An equation in the man page says: SNR = T - NJ - L + G - NF"
My first question is, can you just add and subtract when the units include dBW and dB or is there some conversion between those two units?

To convert from ERP in kW (found on FCC queries) to dBW, I have been using this equation: T = 10 * Log (ERP in kW * 1000)

SPLAT also recommends a Signal Margin calculation to compute how much more signal is available over the minimum to a achieve a specific signal to noise ratio. At least 15.5 dB above SNR is recommended for ATSC DTV reception. So, Signal Margin is computed as:

SM = SNR - 15.5 = 35 - 15.5
SM = 19.5

If I understand this correctly, this means there is an extra 19.5 dB signal available over the minimum necessary to receive that station with that antenna, assuming the L-R prediction for this tower and this receiving location (granted, those are big IFs.)

Several sources have recommended L-R offers widely variable results but that if you build in a margin of 10dB the preditions start to line up pretty well with real, measured results. I take that to mean if (SM - 10) is still a positive number, this is a good indicator that reception for these parameters should be achieved.

Am I correct, or on the right track? Or do I need to go back to the books?! Thanks!!

1. In the Basic Gain/Loss Equation you first take the Transmitter ERP and convert it to dBm:
dBkW = 10 log (ERP in kW), dBm = dBkW + 60 dB (that's 30 dB for every factor of 1000).
You then add the Gain (dBi, not dBd) for each antenna and subtrace the several different dB Loss values.
That yields the received signal strength, Rin in dBm.
SNR (dB) = Rin (dBm) - Nin (dBm),
where the Thermal noise is calculated using Boltzman's constant.

2. The Signal Margin (aka Fade Margin) is the amount of signal in excess of the absolute minimum
required SNR for ATSC under perfect, non-fading conditions.

ATSC typically is said to require 15.5 dB SNR, although it varies from chip to chip.
For example, the much hailed Zenith/LG 5th Gen Prototype was tested and found to meet the 15.5 dB SNR value for moderate signal strength, but it required 15.9 dB SNR
under weak signal strength conditions. The Linx/Micronas Prototype was 15.1 dB SNR under moderate and weak signal strength conditions.

3. As you said, the Individual Location Longley-Rice (ILLR or simply L-R) simulation results have been found to underestimate the path loss in on-the-air test studies,
which is a known shortcoming of the original model since it did not have a sub-module to calculate the effect of local Clutter Loss.

FCC-00-185, "Establishment of an Improved Model for Predicting the Broadcast Television Field Strength Received at Individual Locations", May 2000, recognizes
that the ILLR model results need to have a Clutter Loss calculation and provides recommendations for various environments (I think I'm in the 7 dB category).

A Clutter Loss calculation module is one of the major selling points for the various commercially available VHF/UHF Propagation Prediction Programs.
They are usually carefully tailored to a particular urban environment, based on either ground-based or space-based radar measurements.

RADIO MOBILE includes a simplified Clutter Loss calculation module that is perhaps better suited for short inter-urban microwave and wireless systems
than for long distance DTV paths. So I don't use it. I don't know what is in SPLAT.

4. The amount of Fade Margin that you "need" is probably the most difficult to determine.

a. First of all, it is supposed to be the amount of additional signal strength needed to overcome all but a very small fraction of the multipath signal dropouts.
Under most tested multipath conditions, it was under 10 dB, if it worked at all.
See my 8/16 and subsequent posts in the fol thread re LG and LINX test reports:
http://www.avsforum.com/avs-vb/showthread.php?t=519678&page=11&pp=30

b. Second, it includes a guestimate for how much signal is lost due to antenna placement for the worst case channel frequency.
This signal "banding effect" would be different for each channel frequency, as discussed in fol. thread:
http://www.hdtvprimer.com/ANTENNAS/siting.html

c. Third, it includes all of the "unknown" fudge factors, such as various underestimation errors.
In the thread sited below, I'll post some actual measurements for Preamp Noise Figures that are nowhere close to the manufacturer's spec values, with a couple of notable exceptions.
In So. Calif. (and other parts of the country), we get nasty temperature inversions that can cause a big signal loss when the signal gets scattered away, or big signal increases when it gets scattered in your direction.
I also will add some additional references re how much Sensitivity is lost (3-10+ dB) due to VSWR mismatch between the Antenna and the DTV Tuner (or Preamp).
I'm still struggling with how much to assume for tree, attic and indoor loss since these values have been found to have a very wide range.

5. I have been collecting data for several months now, using my DTV FADE MARGIN CALCULATOR spread sheet
to compare actual reception results for different locations to ANTENNAWEB.ORG and RADIO MOBILE path loss calculations.
The DTV FM CALC spread sheet also includes detailed explanations and cites
references for the various loss assumptions.
In the not too distant future, I'll also post the comparison results in the fol thread:
http://hdtv.forsandiego.com/messages/1/2846.html?1122107959

amirm

09-03-05, 02:40 PM

Trip in VA

09-03-05, 02:45 PM

Antennaweb is very conservative and often seems to underestimate what can be received.

For example, last time I used them they told me I should only be able to get ONE digital station. Without moving my antenna I get 7 (plus another that's not on the air yet).

- Trip

Nitewatchman

09-03-05, 06:50 PM

Holl_ands,

Just got a chance to look at some of your fine work you've been doing with your DTV signal fade margin spreadsheet, and DTV signal overload spreadsheet ...

I'm wondering about something, though :

If I change ft (relative field polar plot - B21) in your Fade margin calulator spreadsheet from 1.000 to .207 (as shown on FCC site for KFMB-DT's biggest Null at 270 degree bearing from their stick) -- the calulation for "lta"(B59) only shows -5.7db antenna pattern loss, even though I beleive it is actually about a ~14~15db or so null(that's via quick "in my head" calulation using -3db for each 2x decrease in power).

AS I posted in my last post, A correct formula(according to broadcast engineers I have talked to) to calulate ERP from the relative field value for an antenna pattern given a particular azimuth heading is as follows :

Relative field value(V/m) SQAURED x WATTS ERP(that equal 1.000 relative field value) = ERP in watts sent in that direction.

In this case, for 270 degrees from KFMB-DT :

(.207x.207) x 703,000 watts = 30.1 KW ERP, or approx 14~15db or so less than if you were getting 1.000 relative field value or 703KW ERP.

This doesn't seem quite the same as what is occuring from the 10*Log(B21) "calulation" in B59(or B60 for "preamp" column). ... Am I missing something?

-------------------------

In the thread sited below, I'll post some actual measurements for Preamp Noise Figures that are nowhere close to the manufacturer's spec values, with a couple of notable exceptions.

FYI, One URL you posted in your most recent post on that thread in San Diego forum thread is currently broken(you left the "s" off at the end) This is the URL you're looking for :

http://www.hdtvprimer.com/ANTENNAS/basics.html

In So. Calif. (and other parts of the country), we get nasty temperature inversions that can cause a big signal loss when the signal gets scattered away, or big signal increases when it gets scattered in your direction.

While I would imagine this could be more of an issue when significant terrain obstructions are a significant issue for local reception(or perhaps with the sticks(broadcast towers) are on mountains with the population at much lower elevations ....

Nevertheless -- Generally speaking, from most of the "info" I've seen, including my own experience with local "RF line of sight" reception, and "DX" reception via Tropo scatter/ducting: I did not think it common enhanced Troposperic scatter signal propagation brought about by temperature inversions are generally likely to cause significant signal increases/losses for signals received via "normal" "RF line of sight" propagation.

I would be interested in finding out more on this. Any comments from the broadcast engineers who post here, or, Could you provide any additional info or links(such as to field test data) concerning Troposperic scatter signal propagation brought about by temperature inversions causing significant signal increases/loss of local, "RF line of sight" signals ?

Certianly, Co-channel interference issues occuring due to enhanced signal propagation via tropo scatter/ducting can be a significant issue for many areas of the country(The Gulf coast states probably particuarly so due to the flat terrain, lots of water and common occurance of temp inversions), especially for viewers using antennas with minmal directivity, or if the interferening, distant co-channel station is in the same direction as the desired local co-channel signal.

Doug Lung has a couple of excellent articles concerning enhanced signal propagation, which are available here :

http://www.tvtechnology.com/features/On-RF/f-DL-signals.shtml

http://www.tvtechnology.com/features/On-RF/f_DG_Enhanced_propagation.shtml

There is also excellent explanation of various "modes" of VHF/UHF signal propagation signal propagation at following site :

http://www.dxfm.com

And, here's some of BBC's excellent info on Temp inversions+reception :

http://www.ravfm.com/bbc_interferance.pdf

I also will add some additional references re how much Sensitivity is lost (3-10+ dB) due to VSWR mismatch between the Antenna and the DTV Tuner (or Preamp).

I'm looking forward to seeing your post on this. There was at least one good discussion about VSWR earlier in this, or another thread here I believe(I think you'll find it in this thread with a search for either VSWR or SWR), and there are references to this issue concerning DTV in the following articles :

http://www.tvtechnology.com/features/On-RF/antennas.shtml

http://www.tvtechnology.com/features/On-RF/f-DL-receive.shtml

Note : There was also an article in TVtechnology at one point which gave expected VSWR for a few popular receive antennas, but I can't seem to find it.

Although there is no practical, legal way I know of for "viewers" to measure VSWR of their receive antenna system, and it's likely to vary quite a bit for many reasons -- Nevertheless, It would be nice if manufacturers would specify expected VSWR for the TV bands/frequencies their antennas "cover" ....

I'm still struggling with how much to assume for tree, attic and indoor loss since these values have been found to have a very wide range.

Yes, it would seem to me those factors would seem difficult to "pin" down to any sort of meaninfgul, narrow range - It would be nice if an average caluclated from many field tests would be useful, but I'm not so sure that is the case.

holl_ands

09-03-05, 09:14 PM

Holl_ands,

Just got a chance to look at some of your fine work you've been doing with your DTV signal fade margin spreadsheet, and DTV signal overload spreadsheet ...

AS I posted in my last post, A correct formula(according to broadcast engineers I have talked to) to calulate ERP from the relative field value for an antenna pattern given a particular azimuth heading is as follows :

Relative field value SQAURED x WATTS ERP(that equal 1.000 relative field value)

This doesn't seem quite the same as what is occuring from the 10*Log(B21) "calulation" in B59(or B60 for "preamp" column). ... Am I missing something?

-------------------------
Yes, it would seem to me those factors would seem difficult to "pin" down to any sort of meaninfgul, narrow range - It would be nice if an average caluclated from many field tests would be useful, but I'm not so sure that is the case.

1. My mistake, it should be 20 log (field strength value) vice 10 log ().
By definition, "Field Strength" is measured in volts per meter and not power.
http://www.its.bldrdoc.gov/fs-1037/dir-015/_2219.htm
I'll post a corrected spread sheet in the near future after I add some more references re VSWR. Thanks for taking the time to check it over.
[I remember telling myself that it's volts and not power, but somehow it didn't make it into the Fade Margin spread sheets. The others are not affected.]

2. I fixed the URL. Thanks again.

3. Tropospheric propagation is usually due to propagation physics involving scattering off of inhomogenities (dust, rain, turbulence) in the atmosphere.
See fol report that addresses various propagation modes for signals in San Diego interfering with Goldstone radio telescope facilities way North of us in the Mohave Desert:
http://ipnpr.jpl.nasa.gov/tmo/progress_report/42-148/148D.pdf
Unless you are using 15+ foot dishes, it's probably not a viable DX mode.

4. Thermal Inversions are a different phemenoma which affect TV signals by bending or "refracting" the signal.
We usually call it "ducting" when a high flying signal that would normally not reach us is bent back towards the earth.

The Longley-Rice model will accept Relative Permittivity, Ground Conductivity and Surface Refractivity values for your "local" area.
Most references would have you believe that these are the same throughout the entire So. Calif. region, from the coast to the mountains to the desert.
Refractivity actually changes dramatically throughout the day and throughout the region (see fig 9):
http://anquetil.colorado.edu/~arlowry/Papers/Refract_RS.pdf
http://home.cogeco.ca/~dxinfo/tropo_wam.html

Most propagation models do not have the benefit of near-real-time data from GPS Occultations and/or thermal profiles from Weather Balloons.

5. I've seen those refs. They are all excellent. In fact I've cited most of them in the past.

6. The best articles re degradation of DTV sensitivity due to VSWR are by O. Bendov in IEEE journals.
They seem to say that the interconnection distance makes no difference.
(But isn't it small delay, zero dB echos causing the degradation?)
And very poor VSWR (typ 2:1 to 3:1) in most broadband antennas is apparently only slightly less
than the poor VSWR in the ATSC Tuner (maybe 2:1)....aaaccckkkk.
And I haven't seen any data re VSWR for Preamps, although I would hope that the broadband nature
of the device would keep VSWR under control better than the tuned front end in an ATSC Tuner.
Theoretically, a carefully designed antenna/preamp or antenna/tuner combination could minimize this degradation.

7. See my 6/8/05 post #2080 in this thread re Kerry Cozad's live antenna range measurements of various indoor and outdoor antennas.
Also see my 3/28/05 post #1743 re Degradation of DTV Sensitivy due to antenna VSWR. (with more to come in the near future).

8. Longley-Rice is a probabilistic model derived from mountains of signal path loss measurements that for the most part ignores all of the site unique "assumptions" found in my spread sheet. The same can be said for Clutter Loss, Attic/Indoor Loss, VSWR Sensitivity degradation across the frequency band, et. al. Of course these predictions are only going to yield ballpark guestimates. My goal is to try to reduce these uncertainties, or at least provide insight as to the magnitude of the various assumtions (unlike the one-size-fits-all approach in antennaweb.org.)

Nitewatchman

09-03-05, 11:05 PM

By definition, "Field Strength" is measured in volts per meter and not power.

Yes. However, FCC operating permits specify ERP in watts and I think it's an easier "concept" to understand for many folks who, I think in some cases it may help if a null in their direction is expressed in watts(and perhaps the associated db reduction compared to main lobe) ...

3. Tropospheric propagation is usually due to propagation physics involving scattering off of inhomogenities (dust, rain, turbulence) in the atmosphere.

While I would agree dust/rain/turbulance is involved with "everyday" Troposcatter propagation, My understanding is It usually has more to do with the refractive capabilites of the "air" in lower levels of atmosphere, involving small changes in temperature, dew point/humidity and barometric pressure. Beyond RF line of sight, signals via tropo scatter are typically weak+fluttery(but can be quite strong and steady given the right conditions, that do not necessarily involve ducting), and generally have a maximum receiveable distance from about 300~500 miles --- on an everyday basis, with typical weak, tropo signals you need VERY sensitive receive equipment for the beyond 300 mile variety ... It's the same "basic" reason why "RF line of sight" is different that "actual line of sight". It's ALLWAYS present to at least some degree.

There is an excellent explanation of Tropo scatter(not ducting) which can be found here in the signal propagation section at www.dxfm.com site I also referred in my last post, and I would encourage you to read that full section on tropo scatter and tropo ducting if you want to learn more. Follows is just the first paragraph of the info on that page concerning "everyday" troposcatter propagation :

quote:

"Tropo-scatter is always present to some degree just about everywhere. Tropospheric scatter at FM and TV frequencies is caused when the paths of radio signals are altered by slight changes in the refractive index in the lower atmosphere caused by air turbulence, and small changes in temperature, humidity and barometric pressure. The signal is scattered in random fashion. The tiny portion of the transmitted signal that is scattered forward and downward from what is called the "common scattering volume" is responsible for signal paths longer than the normal line-of-sight horizon.

:end quote

And, on that same page, the first paragraph of an excellent section explaining Tropo ducting and a bit of how it works(again, see the full info in signal propation section on Dxfm.com site for an excellent, detailed explanation) :

:quote

"Tropospheric Ducting - This is where things start getting interesting for the FM and TV DXer. Strong temperature inversions with very well defined boundaries sometimes form from as high as several thousand feet above the surface of the Earth. If the inversion is strong enough, a signal crossing the boundary into the inversion will be bent sufficiently to return it to Earth. The inversion boundary layer and the surface of the Earth form the upper and lower walls of a "duct" that acts much like an open-ended wave guide. Signals "trapped" in the duct follow the curvature of the Earth, sometimes for hundreds or even thousands of miles. In the tropics and over large bodies of water, strong inversions that cover large geographic areas are quite common, and stable ducts can remain in tact for days on end. This form of ducting is responsible for fairly reliable propagation between California and Hawaii at VHF and higher frequencies.

: end quote

4. Thermal Inversions are a different phemenoma which affect TV signals by bending or "refracting" the signal. We usually call it "ducting" when a high flying signal that would normally not reach us is bent back towards the earth.

That is somewhat correct in that ducting is very "different" than troposcatter. However, refraction is involved with both, and temp inversions can be involved with tropo enhanced signal propagation without true ducting occuring.

7. See my 6/8/05 post #2080 in this thread re Kerry Cozad's live antenna range measurements of various indoor and outdoor antennas. Also see my 3/28/05 post #1743 re Degradation of DTV Sensitivy due to antenna VSWR. (with more to come in the near future).

Thanks, and thanks for your add'l(and future) VSWR info.

[Update 9/4 - 04:00 Z ) ah hah! I had searched a couple of times for more info from Cozrad's studies mentioned in one of the Doug Lung articles and looks like I finally found it via one of the URL's you provided elsewhere - server has timed out a couple of times while I've tried to download the powerpoint file, but hopefully I'll get to check it out soon :

https://secure.connect.pbs.org/conferences/technology/2005/Sessions/TC05_43.htm

8. Longley-Rice is a probabilistic model derived from mountains of signal path loss measurements that for the most part ignores all of the site unique "assumptions" found in my spread sheet. The same can be said for Clutter Loss, Attic/Indoor Loss, VSWR Sensitivity degradation across the frequency band, et. al.

At least it's better than FCC's contour prediction methodology(IMO and in most circumstances, anyway), which I don't think even tries to take terrain into account other than involving TX ANT HAAT, which seems to me to have very limited usefulness in many situations ... Unless the terrain in the entire service area is ALL "average" -- meaning Flat ...

[end update]

My goal is to try to reduce these uncertainties, or at least provide insight as to the magnitude of the various assumtions

Good luck! The amount of work+time and effort you have put into these issues+digging up info is much appreciated -- I'm sure there are quite a few folks out here like myself who enjoy reading many of your fine posts and the info/references/etc. you've posted -- BUT in my case anyway, I do not allways have the extra time to respond in an "adequete" manner ..

holl_ands

09-04-05, 11:50 AM

Clarification re "Field Strength" correction:

The FCC data base lists the transmitter ERP (Effective Radiated Power) in kW,
but this is the value attained only in those directions where the antenna Field Strength plot is 1.0.
The ERP is actually the product of the power delivered to the antenna times the maximum gain of the antenna system.
(If you search APPLICATION LIST, you might find the actual transmitter power.)

The FCC data base also contains the transmit antenna polar plot, expressed in Field Strength (volts/m)
rather than the more commonly encountered Power Gain (dB) plot.
Note that the plot is normalized to 1.0 at the point of maximum gain.
Hence loss in any other direction is found by calculating 20 log (Field Strength).
This method was probably chosen because it emphasizes the usually small variations.

==========================================================
re BEAM TILT:

Unfortunately, it isn't easy to find Antenna Beam Tilt info on the FCC Query page,
other than listing the broadcast antenna model number, which is usually so old
it is no longer found on the manufacturer's websites and even if it was, the
beam tilt may be tailored to individual locations.

If you search the APPLICATION LIST, you may eventually find that particular application
that just happens to contain an exhibit containing this non-mandatory information.
However, it will probably only be valid for certain selected (maximum gain) azimuths and
doesn't describe the elevation antenna pattern throughout all azimuths.
This problem was discussed in the fol. formal comment to the FCC:
http://www.h-e.com/pdfs/mb03-15pet.pdf

Since the antenna gain pattern is three dimensional, what is needed is a geographical map
that depicts the ACTUAL GAIN throughout the coverage area.

See Bob Chase's earlier post #2440 on 7/31/05 re being too close to the tower,
including some transmit beam tilt curves (he's broadcast engineer in Houston).

and a few more refs:
http://www.tvtechnology.com/features/On-RF/F_Lung.shtml
http://www.tvtechnology.com/features/digital_tv/F_CharlesRhodes.shtml
http://www.dielectric.com/broadcast/slotted.asp
http://www.tcibr.com/PDFs/881webp.pdf

At a healthy distance from the tower, the transmit beam tilt should have been designed to maximize gain
where it is needed most and presumably causes minimal beam tilt loss when predicting signal levels.

I don't think RADIO MOBILE (or SPLAT?) include beam tilt loss at shorter distances,
since there does not appear to be an easy way to enter data for a specific broadcast antenna.
Of course this would be more of a concern for Los Angeles with the towers located 5000 feet above the city.

Nitewatchman

09-04-05, 01:54 PM

Clarification re "Field Strength" correction:

The FCC data base lists the transmitter ERP (Effective Radiated Power) in kW,
but this is the value attained only in those directions where the antenna Field Strength plot is 1.0. The FCC data base also contains the transmit antenna polar plot, expressed in Field Strength (volts/m)
rather than the more commonly encountered Power Gain (dB) plot.
Note that the plot is normalized to 1.0 at the point of maximum gain.

Yes. Good clarification. See the formula in my posts above to caluclate ERP(if desired) for relative field strength values other than 1.000.

Hence loss in any other direction is found by calculating 20 log (Field Strength).

Absolutely, that is ONE way of doing it.

Another way is to calculate ERP for the relative field strength value other than 1.000, and then calculate -3db loss for every "1/2'ing of power".

This method was probably chosen because it emphasizes the usually small variations.

Especially in this day of TX antennas side mounted to towers, and increased co-channel conflicts with both the analogs+digitals on the air, It is not uncommon to find directional antenna patterns(and DTV STA's especially) with significant variations. It's also more common with LP analog stations and translators, and possibly somewhat not unusual in situations when the population desired to be served by a stations coverage area are in certian directions from the tower(especially when the transmitters are located away from the market), or due to "geographic" reasons. For instance, there might not be much reason for a chicago station transmitting from sears tower to squirt much signal towards Lake Michigan.

For instance, I'd call KFMB-DT's -13.7 db null to the west (.207 v/m relative field strenth shown for their pattern at 270 degrees) significant, and it is not uncommon to find patterns with relative field strength values lower than .1, which is a very "significant" variation.

The ERP is actually the product of the power delivered to the antenna times the maximum gain of the antenna system
(neither of which is readily found in the data base).

It's usually there(except for STA's) if you do a little digging.

The transmitter power output,, max. gain of transmitting antenna and transmission line loss, among other details can be found in CDBS/FCC info In the applications send FCC for license to cover(their CP), or CP apps. If you use TV query, and chose the "detailed info+CDBS links" option, for each "entry" that results there is a "application list" link. IF you click on that link, a list of all the stations applications appears. At far right, is often a blue "application" link. If you click on this, you'll be taken to the application itself, and for instance, if it's an application for "license to cover", their will be a form, and in the "tech box" portion of the form, the details you are looking for are available.

For instance, here is KFMB-DT's latest "license to cover" app, File # BLCDT-20000302AKK, granted by FCC on 3/22/2000 :

http://svartifoss2.fcc.gov/cgi-bin/ws.exe/prod/cdbs/forms/prod/prefill_and_display.pl?Application_id=492582&Service=DT&Form_id=2&Facility_id=42122

As you can see, in the sec. III "Engineering" of the form, it shows KFMB-DT using :

Transmitter output power : 12.64 dBk 18.37 kW
Transmission line loss : 0.54 dB
Antenna input power : 12.1 dBk (note: this is TPO - Transmission line loss)
Maximum Antenna power gain : 16.37 dB
Maximum effective radiated power : 28.5 dBk 703 kW

Unfortunately, the FCC data base does not contain info re Antenna Beam Tilt,

Probably best to go to the station's engineer's for info on beam tilt, but, You CAN sometimes find info on beam tilt in exhibits(some are available from downloading PDF from "within" the applications") attached to the station's applications sent to FCC - which are often accessable as I described above. The exhibits attached to the applications are sometimes available for download, but oftentimes they are not. Other interesting technical details can also sometimes be found in such attached exhibits, which are sometimes have such titles as "Comprehensive techical exhibit", or "antenna elevation/gain exhibit"/etc/etc/etc. ]

For instance, here's a link to an application to modify a construction permit for WDKY-DT 4 in Central KY. (Note: the station has since filed a license to cover the facilities described in this application+attached exhibits, the license was recently granted by FCC).

http://svartifoss2.fcc.gov/cgi-bin/ws.exe/prod/cdbs/forms/prod/cdbsmenu.hts?context=25&appn=100702393&formid=301&fac_num=64017

Near bottom of the form, you will see a list of exhibits including such details as antenna elevation pattern, directional azimuth pattern/etc, and links to two 2 PDF files which contain those exhibits :

WDKY-DT antenna pattern data :
http://svartifoss2.fcc.gov/prod/cdbs/forms/prod/getattachment_exh.cgi?exhibit_id=188903

WDKY comprehensive technical exhibit dated nov 2003) - Note - IF I recall correctly this is a somewhat large file) :

http://svartifoss2.fcc.gov/prod/cdbs/forms/prod/getattachment_exh.cgi?exhibit_id=188904

deconvolver

09-04-05, 06:42 PM

I thought I start a thread and see how people have managed to exceed the level of reception predicted by antennaweb.com. Let me start with my situation and reason for asking for this information.

At our regular house on a hill overlooking Seattle, I can pick up many digital stations with just a piece of wire. So life is great here. However, we have a vacation home about 40 miles northwest of here on Whidbey Island. The house faces the Puget Sound but the direction facing Seattle digital stations has a row of very tall pine trees in front of it about half a mile away from the roofline.

Antennaweb predicted that I would only be able to pick up two stations to the north (opposite of Seattle) and indeed, I could easily get these with a standard attic antenna the home owner left us. Hoping to do better, I went out and bought a Channel Master 4228, DB-8 style antenna and paired it with a 7777 pre-amp. The antenna is outside on a mast on top of a two-story house. We then aligned the antenna toward Seattle and was jumping with joy when the receiver claimed to have found 7 stations. But my hopes were dashed when I saw that half were shopping channels, another one was a religious channel! The only was somewhat useful to us was PAX. All of these stations are in Bellevue it seems which is both closer to the house and has a more clear view of the antenna.

I was really hoping to get PBS or one of the major networks but no amount of fine tuning of the antenna seems to get us there. And hence this thread.

So have people achieved better results in general? If so, what equipment did you use? Are there more sensitive receivers? I use the LG DVD+ATSC tuner and the tuner card in my Media Center PC btw.

Has anyone modified the 4228 to have two baluns and a combiner rather than the cheap feed lines they use? And if so, how much more gain do you get out of it? I noticed that DB-8 from anteannasdirect comes with these. Does it work better than 4228 as a result?

Amir
To know what signals you should receive you need a prediction like Antennaweb used to make, unfortunately the current predictions are so pessimistic that you can't see what might be borderline stations even by inputting a nearby address at the top of a hill with a multi-story house. If you can figure out how to run the radiomobile program then you can see the field strength predicted at your house for each station. You can then use the old fcc grade B contour levels of 36 microvolts/meter VHF and 41 microvolts per meter UHF as rough threshhold levels to see what stations you might get. Even better would be to check the spreadsheets that holl_ands has posted to get a more accurate idea of the threshhold to use. If you have any fairly close stations an important possibility is overload in the pre-amp or TV; holl_ands has posted info on that as well. If you don't have something significant wrong like overload then the possibility of major improvements over the 4228 plus 7777 in the same antenna location for UHF stations are not very good. If you are missing out on VHF stations then you can definitely improve on the 4228- especially for channels 7&8 or in the unlikely possiblity you have a digital channel in the 2-6 range.

deconvolver

09-04-05, 07:03 PM

(Edit) As pointed out by holl_ands I read the fcc document too quickly; the first fcc document below gives level for NTSC *not* ATSC so that's not the reason for antennaweb's pessimism. Oh well...

I think I know why Antennaweb has switched to such a pessimistic threshhold value. For SHVIA viewer eligibility to receive distant networks the fcc has established threshhold levels to use with Longley-Rice predictions that are about 20dB more pessimistic than the original levels used to estimate coverage contours. See this document for the new levels that were set to include fade margins:
http://a257.g.akamaitech.net/7/257/2422/12feb20041500/edocket.access.gpo.gov/cfr_2004/octqtr/pdf/47cfr73.683.pdf
More recently the fcc has added a clutter loss for the UHF band of about an additional 6dB depending on land use category, see here:
http://www.fcc.gov/Bureaus/Engineering_Technology/Orders/2000/fcc00185.doc
Put together this seems to create fairly pessimistic predictions. A quick check of these levels with the output from radiomobile for predictions to my house seemed about as pessimistic as antennaweb now is. This will be good news for those that want to receive distant networks from satellites because they can't get their local network OTA, but the predictions don't seem very relevant to those with good antenna installations. One reason the predictions may be so pessimistic is that although the fcc set the levels so the predictions had about the same number of overpredictions as underpredictions they ignored all sources of reception difficulties other than signal level like multipath or interfering channels when making the study.

holl_ands

09-04-05, 07:12 PM

Nitewatchman: I tweaked the wording above re how "easy" it is to access antenna infomation in the FCC TVQ database.
....but I find it requires a lot of poking around, inspect each application in the list, wait for the database search engine, etc.

I didn't get anywhere trying to use CDBS SEARCH PAGE, even after trying various search selections....

Maybe you have some database search tricks???

holl_ands

09-04-05, 07:40 PM

I think I know why Antennaweb has switched to such a pessimistic threshhold value. For SHVIA viewer eligibility to receive distant networks the fcc has established threshhold levels to use with Longley-Rice predictions that are about 20dB more pessimistic than the original levels used to estimate coverage contours. See this document for the new levels that were set to include fade margins:
http://a257.g.akamaitech.net/7/257/2422/12feb20041500/edocket.access.gpo.gov/cfr_2004/octqtr/pdf/47cfr73.683.pdf
More recently the fcc has added a clutter loss for the UHF band of about an additional 6dB depending on land use category, see here:
http://www.fcc.gov/Bureaus/Engineering_Technology/Orders/2000/fcc00185.doc
Put together this seems to create fairly pessimistic predictions. A quick check of these levels with the output from radiomobile for predictions to my house seemed about as pessimistic as antennaweb now is. This will be good news for those that want to receive distant networks from satellites because they can't get their local network OTA, but the predictions don't seem very relevant to those with good antenna installations. One reason the predictions may be so pessimistic is that although the fcc set the levels so the predictions had about the same number of overpredictions as underpredictions they ignored all sources of reception difficulties other than signal level like multipath or interfering channels when making the study.

The first reference (sec 73.683) lists the Grade A and Grade B contours for analog NTSC.
They are the same as have been used for many years (decades?) now.
Where's the 20 dB difference?
DTV Contours are 28 dBu (CH2-6), 36 dBu (CH7-13) and 41-20*log(615/Fc) dBu (CH14-69).
But you have to know that NTSC power is always measured with a peak reading meter, whereas DTV power is measured with an average reading meter.
That means that NTSC peak power must be 8+ dB higher than DTV average power to provide the same average receive signal.
DTV also requires a much lower SNR than NTSC.
The seemingly lower DTV Contour levels were postulated to provide the same number of households with "acceptable" performance as a Class B NTSC contour.
And in many tests people have found that DTV actually does provide equal or better reception under these constraints.

=======================================================
The second reference, while very valuable, isn't all that new, it's May 2000, which I cited above.

========================================================
The FCC uses the ILLR prediction program to prevent/minimize interference between stations when broadcasters submit an application.
For that reason, ILLR (and RADIO MOBILE) include a calculation of interference between co-channel stations.
But, quite frankly, the FCC doesn't really want to know how many viewers within the NTSC Grade B or DTV contours actually receive a reliable signal.
And oh by the way, they assume we all use moderate gain outdoor antennas 30 feet in the air.....

The FCC has NOT endorsed using the ILLR prediction program to determine whether you can theoretically receive on-air signals,
and if not, use those results to justify a Satellite waiver.

Hiring someone to make actual signal measurements has been endorsed,
give or take some lawyerly mumble jumble that I guess so far has succeeded
in putting Satellite waivers into a semi-permanent holding pattern.

amirm

09-04-05, 08:19 PM

deconvolver

09-04-05, 08:25 PM

The first reference (sec 73.683) lists the Grade A and Grade B contours for analog NTSC.
They are the same as have been used for many years (decades?) now.
Where's the 20 dB difference?
DTV Contours are 28 dBu (CH2-6), 36 dBu (CH7-13) and 41-20*log(615/Fc) dBu (CH14-69).
But you have to know that NTSC power is always measured with a peak reading meter, whereas DTV power is measured with an average reading meter.
That means that NTSC peak power must be 8+ dB higher than DTV average power to provide the same average receive signal.
DTV also requires a much lower SNR than NTSC.
The seemingly lower DTV Contour levels were postulated to provide the same number of households with "acceptable" performance as a Class B NTSC contour.
And in many tests people have found that DTV actually does provide equal or better reception under these constraints.
...
The FCC has NOT endorsed using the ILLR prediction program to determine whether you can theoretically receive on-air signals,
and if not, use those results to justify a Satellite waiver.

Hiring someone to make actual signal measurements has been endorsed,
give or take some lawyerly mumble jumble that I guess so far has succeeded
in putting Satellite waivers into a semi-permanent holding pattern.
Well, it looks like an oops on my part for the signal strength numbers. I may have been confused when I read quickly because all around that table it is talking about ATSC. That rule also states the following:
" (d) For purposes of determining the
eligibility of individual households for
satellite retransmission of distant network
signals under the copyright law
provisions of 17 U.S.C. 119(d)(10)(A),
field strength shall be determined by
the Individual Location Longley-Rice
(ILLR) propagation prediction model.
Guidance for use of the ILLR model for
these purposes is provided in OET Bulletin
No. 72. This document is available
through the Internet on the FCC Home
Page at http://www.fcc.gov. "
Which does sound like the fcc endorses ILLR for determining distant network eligibility. I think I was confused by looking for the levels for the SHVIA eligibilty and those still seem to be based on Analog reception which is why when I looked up the levels I got the Analog numbers. I should have known it was referring to analog reception because I knew they were currently basing eligibility on NTSC not ATSC reception. My Bad. So, I guess the reason for the overly pessimistic antennaweb numbers remains a mystery.

Nitewatchman

09-04-05, 08:42 PM

Maybe you have some database search tricks???

Unfortunetly nothing too helpful that I've been able to find -- It certianly does take quite a bit of "nosing" around. I have found where your local stations are concerned, just being familiar with their current+past filings can save time later on. Otherwise , Sometimes, it can even be difficult to figure out with 100% certianity what operting permit(or Program Test Authority) the station is actually currently operating with.

I think Using the CDBS search page is especially "clumsy" for this application, although for other applications(such as looking for which stations filed First round conflict resolution forums) it can work quite well. But, Sometimes just figuring out which selections(including muliple ones) in CDBS searh page you have to make for the query to get the info you want in the drop down boxes is frustrating.

Over the past 4 years, I have been fairly regularly using "Search by radius" query function of TV query ( http://www.fcc.gov/mb/video/tvq.html ) for my location to the distance required(65km in my case) so all my locals stations pop up, while using the "detailed info+CDBS links) option and then checking the "application list" for new applications/info to look at which I'm interested in ... so, just being familiar with the past filings from the stations you are interested in saves time when looking at anything new ...

Also, certian things do stand out, which can speed things up a bit when you're trying to find what you are looking for ... For instance, A date of 6/23/05, and a status of either "approved" or disapproved" is currently indicated for the first round election form for every station I've seen. A file number designation with a "STA" in it is for a STA (unfortuently, as mentioned above they have not made any STA applications available). Also, the file number(in any case, for any application/filing submitted to FCC) itself will contain the date the filing was submitted to FCC. And of course, under "service", "DT" stands for applications related to the digital station, "DS" is STA DTV designation -- However(and this seems a bit odd) Although you will find all CP Apps, CP MOD apps, CP extension requests and "license to cover" apps, and DTV STA applications/extensions for DTV stations listed under either "DT" or "DS" for service ... Some other info pertaining to DTV stations, such as first round Elections are shown under "TV" service, which "normally" applies currently to the analog station ... go figure ..

------------------------------

By the way, predicted contour maps(for field strengths holl_ands mentioned above -- 41dbu for UHF, 36dbu for hi-VHF, 28dbu for lo-VHF) for DTV stations using FCC's contour methodology are also available via TV query+with use of the TV query and "Detailed info+CDBS links" option.

For instance, If I use TV query by callsign and choose detailed info+cdbs links option, I get these results for my query of "KFMB" :

http://www.fcc.gov/fcc-bin/tvq?state=&call=KFMB&arn=&city=&chan=&cha2=69&serv=&type=0&facid=&list=0&dist=&dlat2=&mlat2=&slat2=&dlon2=&mlon2=&slon2=&size=9

As you notice, first, a detailed section of info for their analog station on 8 shows up, followed by info on KFMB-DT's licensed facilities, and for some reason, a construction permit filed in 2000, and granted in 2001(if you look at the application list and match up the file numbers). So, since there is no new "license to cover" the CP at bottom of list, I must assume they are operting with the parameters shown for the info concerning their "licensed" facilities.

So, In the list of links right under the info on their antenna pattern/etc, at bottom line of links, it says : Area : Then a link that says "Service Contour Map(41dbu). Click on "service Contour Map(41)dbu, and you'll see a map of the area(I've included URL to this below), including the predicted 41dbu contour for KFMB-DT's currently licensed facilities :

http://www.fcc.gov/fcc-bin/FMTV-service-area?x=DT492582.html

Doesn't look like anyone but the fish will be impacted by their -13.7db null to the west :)

bobchase

09-04-05, 08:48 PM

The FCC has tightened up the DTV minimum field strength rules for city of license -

Channels 2 through 6 were 28 dBu now 35 dBu
Channels 7 through 13 were 36 dBu now 43 dBu
Channels 14 through 69 were 41 dBu now 48 dBu

The 7 dB change was to account for their overly optimistic tuner noise contribution and their abnormally high antenna gain, among other things. (This is assumed because they never gave reason for the change.)

This is for the city of licence only. The Grade A and Grade B contours do no have a corollary contour in DTV.

Just a clarification....

Bob Chase
KHWB-TV

Nitewatchman

09-04-05, 09:06 PM

AntAltMike

09-04-05, 09:08 PM

I see that my stored link to bsexton.com is no longer operational. Has that site moved, or is it gone? The last time I visited it, they had only analog signal strength info available, but it was still useful to the extent that one might use analog Grade B levels to roughly predict the location of the cut-off perimeter of similarly situated, full powered DTV transmitters.

To the extent that the participants in this thread desire to actually discern whether the ambient signal levels where they are located can be developed to a level at which reliable viewing can be sustained, I consider all of this to be an exercise in futility.

We rely on the antenna manufacturers for antenna gain information, but they are in the business of selling antennas, and thus will present whatever info they have on gain in the manner that justifies publishing the biggest possible gain numbers.

Gain is expressed relative to dipole or isotropic radiator, but, as I understand it, that just gives a measure of "no-load voltage" measured at the terminals of the active element. But when we try to determine the sufficient power level needed to assure reliable operation of our tuners, the sufficiency values we are given are expressed in referenced decibel millivolts, which is not so much a measure of voltage as it is a measure of wattage actually delivered thought the connected, referenced load.

When you place a load across an antenna active element in an RF field, the voltage drops somewhat. It is my understanding that the maximum power transfer will occur when the load impedance matches the source impedance, so a 300 ohm dipole will develop its maximum power in dBmV or dBm when impressed upon a 300 ohm load, but I don't know if the calculations contained in this thread incorporate the voltage drop that occurs when the active element is loaded.

Even if they do, or even if there is an accepted value for the voltage drop that occurs when a 300 ohm dipole drives an optimal load (I'll guess 3dB, because half the voltage drop occurs across the load and the other half occurs across the source), the signal maximizers here often try to reduce the "balun loss" by using zero loss coax baluns, but such a balun may have the adverse consequence of reducing the efficiency of the reception loop, since a 75 ohm load will suck down the voltage level of a 300 ohm source more than a 300 ohm load will. With 60 cycle transformers, this effect is significant. Maybe at RF frequencies it is, for some reason, insignificant, but I don't know that to be the case. It may well be that the reduction measured in dBmV or dBm caused by the impedance mismatch of loading a 300 ohm dipole with a 75 ohm load is greater than the saving of that no-loss, tuned coax balun versus the much vilified, "ferrite" balun.

I also believe that the frequency response of tuners is likely to vary by several dB over the input spectrum range. I place no more stock in a manufacturer's claim that its tuners have noise figures of 9 or 10 dB (when they even bother to publish them) than I do in the published loss figures that Channel Master and Winegard give for their baluns, as anyone who has tested them knows that they vary by several dB over the broadcast spectrum.

I also am skeptical of one being able to rely on an S/N ratio to be able to reliably predict uninterrupted decoding. Any analysis of S/N ratios that suggests that 15.9dB is the threshold level that will get us the performance reliabilty we desire is really making assumptions regarding the nature of the variation in noise as it occurs in nature. Sure, we can degrade a signal with our flat, white noise generator until it fails to be decoded, and we might establish, from that, a consistent S/N minimum value that can withstand the effect of flat white noise degradation, but real noise occurs in bursts that have multiple dimensions of frequency, amplitude and duration, and it is the unique collective effect of each noise invasion that determines whether the frame being processed is corrupted beyond repair.

FWIW, someone once posted in these forums that the critical data within the 8VSB signal has been arranged such that it would tend to be relatively immune to the degrading effects of the co-channel analog picture carrier at +1.25Mz, and in fact, he said that the 8VSB signal can supposedly withstand an NTSC peak that is within 2dB of the RMS value of the 8VBS plateau. Maybe someone here with more time on his hands than I have could experiment with that and gradually increase the value of his own, modulator-generated NTSC co-channel to see how robust the 8VSB is when subjected to that kind of interference which does occur naturally, but which is not best analyzed by just measuring the 6Mz bandwidth RMS value of the NTSC signal.

Nitewatchman has mentioned that he has experienced disruptions on channel 10 from lightning strikes, and another forum member from Northampton, Massachusetts reported similar lightning disruptions on channel 11. It could be that lightning noise is the achilles heel for VHF highband, just as some kind of terrestrial impulse noise seems to wreak havoc on VHF lowband channels 2 and 3. Or it could be that our sample of two unhappy campers is statistically insignificant.

deconvolver

09-04-05, 09:14 PM

Thanks for the comments on why antennaweb may be using pessimistic modeling. Even as an eletrical engineer with some RF experience, I am too lazy to try to dig into the reception modelling described here :).

So question. Has anyone tried the low-noise amps from Research Communications? I have gone to their web site but it is hard to figure out how to buy one of these. I have an email into them. When testing, I got a marginal signal on King-DT but not enough to get a lock on it. I am hoping that the 1.6db gain over the 7777 pre-amp may do it for me. What you all think? ANd doesn't anyone in US make a very low-noise amp so I don't have to import this darn thing?

Amir
Of course I have had to edit my post because my guess about antennaweb was wrong. In the HD hardware forum ctdish has posted that he will be trying out a low noise amp soon. His antenna array is on a tower so it may take him awhile to try it. The posts below about pre-amps not meeting noise specs makes me suspicious of manufacturer's specs. I have seen some posts in the Hartford thread about people who bought the research communications pre-amp not getting better results so they wanted to sell the amp. I would think a more effective way to get more signal is to move the antenna. If it isn't blocked by anything close that would probably mean going higher.

deconvolver

09-04-05, 09:24 PM

deconvolver

09-04-05, 09:44 PM

Thanks Bob -- Here is also a link with the info you mentioned straight from the "rulebook"(this seems to be well updated), part 73.625 :

http://www.hallikainen.com/FccRules/2005/73/625/

I also recall reading about that, I think in one of the more recent DTV transistion related R&O's, but can't recall which one ...
This rule does indicate that the height above average terrain is used to compute the service area contours doesn't it? I have always thought that that is how the coverage maps from the TV query site are generated. If true then of course they are not very useful as compared to the ILLR model for predicting reception for a given location. I wonder then if those field levels have any applicability to ILLR? I guess a good technique for an individual to determine the required field strength with ILLR is to use holl_and's spreadsheet with the details for their installation.

Nitewatchman

09-04-05, 09:51 PM

I see that my stored link to bsexton.com is no longer operational. Has that site moved, or is it gone?

What you are talking about from the old bsexton URL was available via a "free coverage maps" link from this site for a time, but I believe it is now gone "completely" :

http://www.ardman.net/

Nitewatchman has mentioned that he has experienced lightning disruptions on channel 10 from lightning strikes<snip>, ..... Or it could be that our sample of two unhappy campers is statistically insignificant.

It's insignificant in my case. I am certianly not"uphappy camper" becuase of TWO dropouts due to TWO VERY NEARBY(to the receive antenna) lightning strikes Over FOUR YEARS of viewing this station.

It's statistically insignificant even concerning my DTV reception over the past four years during thunderstorms occuring at MY location, and if my reception was the only "sample" available ...

To further clarify .... I have viewed the local VHF DT station on 10 through numerous storms(or storms in the signal path) and it wasn't a problem, at all.

Now, also, when I said very nearby lightning strikes, I mean I could hear the sound of the air being disturbed at the exact moment of the strike, and the flash was VERY bright(inside a room with blinds and shades that let in very little light with my eyes focued on the TV which is nowhere near any windows) ..... and I have no doubt I would have seen quite a bit of "static" IF I had been watching a UHF analog station at the time ....

Add in the other FOUR reception dropouts(to the DT on 10, and a DT on 24 NONE on my other 12 local DTS) I've seen due to "extreme" co-channel interference during abnormal signal propagation OVER 4 YEARS TIME, adding up to a total of about 6~8 seconds of "disrupted viewing" on 14 local DTV stations(I was OTA only viewer until adding E* service a year ago, so this wasn't just a few hours of watching local DTV stations a week), and I am certinaly in NO shape or form a "unhappy camper" when it comes to DTV ....

Update:

That being said, we have had a number of posters on our local thread which have seemingly ran into difficulties with reception of this station not only involving lightning, but man-made impulse noise and other RFI which we tend to think of being much more of a problem on Lo-VHF. I say seemingly, however as it is often difficult to detirmine with any sort of certianity via posts on this forum what "difficulties" are causing reception problems in any specific case.

To the extent that the participants in this thread desire to actually discern whether the ambient signal levels where they are located can be developed to a level at which reliable viewing can be sustained, I consider all of this to be an exercise in futility.

While I tend to agree somewhat with this assesment in a general way : Nevertheless I think some of the details which have been provided here can be useful to some for various reasons. Also, certianly a Longely-rice study even without "extra precise information" on such factors as receive antenna gain can be beneifical for those in terrain obstructed receiving locations who want to get at least a bit of an idea of whether or not they may have a chance at reception of a given station.

deconvolver

09-04-05, 10:04 PM

...

To the extent that the participants in this thread desire to actually discern whether the ambient signal levels where they are located can be developed to a level at which reliable viewing can be sustained, I consider all of this to be an exercise in futility.

...
I think you are being overly pessimistic. Programs like radiomobile are readily available on the web to predict the transmission loss of radio waves between the transmit and receive antennas and statistical modelling of various disruptions has always been a part of reception studies like were done in creating Longley-Rice. You can also download free or cheap antenna modelling software like 4nec2 or eznec or multinec plus antenna models from the hdtvprimer web site to get good estimates of real antenna power gains. Or, just look at the plots at hdtvprimer. There are also balun loss and pre-amp noise measurements available. So if you are using a balun and pre-amp with independently measured performance then predictions should be possible. The final piece to the puzzle of the needed fade margin for a reasonable time reliability can be determined by comparing prediction results to experience the way holl_ands appears to be doing.

AntAltMike

09-05-05, 11:28 AM

But the relatively new mission is, we are now trying to estimate the performance margin necessary to assure glitch-free decoding of digital images that persist for as long as one second at a time and intervals of audio disruption that may endure for even longer, rather than to minimize the slight visible degradation of analog pictures that persist for only 1/30th of a second.

We can calculate what it takes to develop a TASO Grade 1 analog picture, and, in most situations, our input data are accurate within a few dB, and even if it isn't, most of us can't discern the difference between a picture with, say, a 43dB S/N ratio rather than a 46dB ratio. If a plane files overhead and causes a reflection that lasts one frame on an analog picture, we probably won't notice it, any more than people noticed the "subliminal" advertising that may or may not have been shown in movie theaters (and in a great Colombo episode) back in the 1970s, and we may or may not even notice one frame of impulse noise speckles on an analog program if the background was solid and still versus complex and moving.

While we engineered performance margins that gave us Grade 1 or 2 analog pictures, when those systems failed to meet that margin we usually didn't notice, and when we did notice, we usually didn't care, and so we really have no idea how often those reception links failed to attain our calculated threshold signal quality levels, but when the reception link fails to develop sufficient signal quality for a minuscule but critiical interval in the reception of the data stream, we notice.

I will not, under any circumstance, install a residential off-air reception antenna as a subcontractor because, if the customer ever has a one second freeze-up on his $6,000 plasma display which is part of his $20,000 home theater, he will be strongly inclined to call his contractor to complain, who, in turn, would be inclined to call me to make sure that I didn't do something wrong. I can take on that kind of responsibility from my own customers because most of them are commercial, and as far as the few residential installations I did are concerned, I made them acknowledge that I had told them that every once in a while a glitch could occur and that it didn't mean that their system needed on-site service, in-warranty or otherwise, but because I couldn't similarly browbeat them as a subcontractor, I simply decided not to take them on as customers.

I've installed master antenna systems with multiple antenna arrays in about a dozen high-rise buildings and I wish I could say that I am certain that my installations have been glitch free, but the fact it, I so thoroughly conditioned the customer, meaning the management, to screen out complaints that I really can't say for sure that all of my systems have been as reliable as they appear to be. I think they have been, because I have a lot of S/N margin to work with in my market, but I understand that by having effectively preempted potential complaints, I just might have buried a few of them.

chwilson0607

09-05-05, 05:28 PM

holl_ands

09-05-05, 05:40 PM

My TV has a read-out of the AGC value for a channel. I am thinking that if I tune to an empty channel I might be able to use this to compare pre-amps. Since the pre-amp gain would also affect the AGC value I need a relative measure of pre-amp noise. With satellite dishes you can measure the noise increase between pointing the dish at the empty sky and the sun to get a figure of merit for the antenna plus pre-amp. I wonder if a similar method might work with a good antenna. Normally a TV antenna's temperature is set by the ground temperature (I think) but what if you pointed it straight up and measured an empty channel's signal level and then pointed it straight down and repeated the measurement? I would think that if a pre-amp had a very low noise factor like 0.5 then you should see a bigger difference. Of course this would require an antenna with a good front to worst-case rear spec and a truly empty channel to work. Or is there some reason the antenna temperature wouldn't tend to track the sky vs sun or ground temperature like it does with a satellite dish?

I would be careful about making any conclusions based on the AGC value in your TV Tuner.

I would hope that most modern designs apply AGC to the RF front end, but some may not.
The best RF AGC would be developed based on signal overload within the RF bandwidth,
which would include strong RF signals several channels away, rather than the heavily filtered
IF bandwidth that may only include adjacent channel signal levels.
But most modern designs develop AGC in the IF bandwidth and then apply that same signal to both RF and IF.

Several of the few detailed designs that I've seen disclosed employ either "stepped" AGC schemes
that apply 10, 20, 30 or 40 dB attenuation or employ linear AGC control range up to about 40 or 50 dB.
Below a (sometimes variable) signal threshhold, the AGC attenuation is set for minimum,
depending on the dynamic range of the RF amplifier for the first several decades of signal strength.
Above the maximum attenuation setting, the amplifier responds to increasing signal levels with more intermods.

This latter effect will mean that the displayed AGC value will be at minimum attenuation
for a fairly wide range of low level input signals.

======================================================
Radio Telescope systems regularly check to make sure that the sky noise temperature is close
to their specified minimum and then can scan around to find the direction of unwanted interference.

So can you do the same with a Preamped TV antenna? Probably not.
A TV antenna has a fairly wide beamwidth and significant sidelobes that let in multipath reflections
from all sorts of unexpected directions.
Unless you are in the Australian Outback, the Preamp will almost always be presented
with moderate to strong signals that will generate intermod products that are above the noise floor.

holl_ands

09-05-05, 05:52 PM

I am relatively new to HDTV programming through my satellite service. However I think I am just about ready to roll. My question is on getting broadcast HD channels. I have been hearing I need to set up an antenna and connect it to the HD receiver. As a test, I tried hooking an indoor antenna to the HDTV itself located in my basement however it was quite fuzzy.

In the stores, I see large antennas for mounting on the roof or on the side of the house and I also see smaller ones for indoors. What is the recommendation for receiving HD broadcast channels? According to the first post I saw, bigger antenna, higher up (roof mount). Any thoughts? Thanks.

Carl

FUZZY??? You must have been watching an old analog TV station.

DTV signals display in either decimal (e.g. 5.1) or dashed (e.g. 5-1) format.
They are either extremely sharp or they suffer from blocks of pixels being scrambled
or when it's really bad, signal dropouts that can last for seconds to minutes at a time.

You need to get the antenna out of the basement and as high as possible.

deconvolver

09-05-05, 07:39 PM

I am relatively new to HDTV programming through my satellite service. However I think I am just about ready to roll. My question is on getting broadcast HD channels. I have been hearing I need to set up an antenna and connect it to the HD receiver. As a test, I tried hooking an indoor antenna to the HDTV itself located in my basement however it was quite fuzzy.

In the stores, I see large antennas for mounting on the roof or on the side of the house and I also see smaller ones for indoors. What is the recommendation for receiving HD broadcast channels? According to the first post I saw, bigger antenna, higher up (roof mount). Any thoughts? Thanks.

Carl
You can go to antennaweb.com and type in your address to get an idea of the digital channels that should be fairly easy to receive. The antennaweb prediction is pessimistic though so with a good antenna system (and antenna pre-amp for rural locations) you may be able to get more stations than antennaweb says. Some receivers can get both the old-fashioned fuzzy analog stations and the new digital ones, it is the digital ones that will be clear (and sharp when they broadcast HD like most major network affiliates mostly do during prime time).

deconvolver

09-05-05, 08:19 PM

I would be careful about making any conclusions based on the AGC value in your TV Tuner.
...
======================================================
Radio Telescope systems regularly check to make sure that the sky noise temperature is close
to their specified minimum and then can scan around to find the direction of unwanted interference.

So can you do the same with a Preamped TV antenna? Probably not.
A TV antenna has a fairly wide beamwidth and significant sidelobes that let in multipath reflections
from all sorts of unexpected directions.
Unless you are in the Australian Outback, the Preamp will almost always be presented
with moderate to strong signals that will generate intermod products that are above the noise floor.
Thanks for the info holl_ands. The AGC value seems different for each channel and is much higher for empty/very weak channels. Given how you say most AGC's work I suspect that my TV's AGC readout would not work well enough as a signal level meter. My house is in a bit of a hole so I don't have a direct path to any station. For instance the radiomobile prediction for my strongest digital UHF station is +23 dB above a threshhold of 39 microvolts/meter. I had hoped that intermod products would be negligible so the noise floor for some weak stations would be the antenna thermal noise+cascaded noise factor. This might be true for a few select regions of the UHF band which seem to be very empty for my location. I still expect that you are right that since I don't have an under-illuminated dish for an antenna I will see lots of noise level variation depending on leakage of energy through minor lobes and wouldn't be able to sort out when the noise level is mostly determined by pre-amp noise even with a good signal level meter.

bmcent1

09-05-05, 11:16 PM

FUZZY??? You must have been watching an old analog TV station.

DTV signals display in either decimal (e.g. 5.1) or dashed (e.g. 5-1) format.
They are either extremely sharp or they suffer from blocks of pixels being scrambled
or when it's really bad, signal dropouts that can last for seconds to minutes at a time.

Second that! Over this long weekend, I built a VERY makeshift dipole and hooked it up to my new ATSC PC tuner card. The antenna is U-G-L-Y, masking taped to a wall, aligator clips connecting it to the inner wire on a run of coax strewn across the floor to plug into the card...

I checked a few UHF NTSC channels first on a regular TV, to see if my antenna worked at all, it did, but the picture was less than perfect. Good, antenna works. Now connected the antenna to the ATSC tuner card... WOW!! Crystal clear SDTV on 62.1 and when I tuned to 62.2, an HD channel, even clearer HDTV. My wife thought I was a little crazy the way the "lab" looks right now, but even she was quite excited about the picture quality and couldn't believe it was coming in over that little makeshift antenna.

On a side note, I have really enjoyed all the conversation about the SNR equations. Some of it even made sense :) ... I will definately factor in the antenna pattern. Luckily, many transmitters in my area are non-directional. Holl_ands and Nitewatchman in particular, thank you! I'm not going into this expecting absolutely correct results, but it will be nice if I can get somewhat more accurate results from modeling than what antenna web provides. And if both my modeling and antenna web say my location is a no-go, then I know not to bother buying an antenna at all. My personal feeling on drop-outs is that a tiny drop out here or there will be okay by me, much better than watching BLURRY analog NTSC ALL THE TIME on a 42" plasma. Just sayin' ;-)

Nitewatchman

09-06-05, 12:08 AM

but even she was quite excited about the picture quality and couldn't believe it was coming in over that little makeshift antenna.

That's the kind of stuff I like to hear about ! :)

-------------------------------------------

I was thinking how much easier this might be for many folks if stations would post predicted coverage map on their website of their service area based on Longely-rice studies, perhaps with simply labled shaded areas such as "fringe signal area", "strong signal area", "big honkin' single channel antenna array area"(or "good luck" area)/ etc .....

rogo

09-06-05, 03:33 PM

Hey, guys, I bought a CM4228 and get signal strength mostly in the 70s (some 80s) per the HD Tivo. But I'm still concerned about dropouts. We saw one yesterday (could be a transmission glitch, duno). I have to go topside to remove an old antenna anyway, so I'm wondering a preamp might not help me.

I'm about 25 miles from the main tower and 20 from the secondary tower which is on a similar line. There is one VHF station on the secondary tower (soon) and the rest are UHF.

Would a 7777 help? Is a 7778 the better choice as lower gain seems all that might be needed? Is either overkill? Pleas help!

greywolf

09-06-05, 06:24 PM

It sounds like you're doing fine already. With those numbers, occasional glitches are not a strength problem. You're just about at the inside limit for a preamp and the HR10-250 is an easy receiver to overload. If you want to try something, a 15 db preamp rather than a mid 20s might be okay. If I were you, I'd leave well enough alone. I'm 11mi away with 90-94 for numbers and I get more glitches than you do.

holl_ands

09-06-05, 08:07 PM

We rely on the antenna manufacturers for antenna gain information, but they are in the business of selling antennas, and thus will present whatever info they have on gain in the manner that justifies publishing the biggest possible gain numbers.

Gain is expressed relative to dipole or isotropic radiator, but, as I understand it, that just gives a measure of "no-load voltage" measured at the terminals of the active element.

When you place a load across an antenna active element in an RF field, the voltage drops somewhat. It is my understanding that the maximum power transfer will occur when the load impedance matches the source impedance, so a 300 ohm dipole will develop its maximum power in dBmV or dBm when impressed upon a 300 ohm load, but I don't know if the calculations contained in this thread incorporate the voltage drop that occurs when the active element is loaded.

The biggest problem is that most manufacturers don't publish gain vs freq.
And then there is the trick of citing the maximum (vice average) gain value.
And/or using dBi rather than the usual dBd number for another 2.15 dB inflation.
I usually assume they've done both (like DAT-75) if they don't specify otherwise.

I've posted a comparison chart between actual measured antenna gain
vs manufacturer spec sheet data vs NEC Simulation results for both the
Channel Master CM4228 and the Winegard PR8800 8-Bay Antennas in
the fol. thread:
http://hdtv.forsandiego.com/messages/1/2846.html?1126050076
The spread sheet summarizes spec sheet info for many different, mostly UHF, antennas.

Unfortunately, these are only two antennas tested by Kerry Cozad that also
have detailed frequency response specs released by the manufacturers.
Hopefully you will note that for both antennas, the actual measurements
were about 2 dB HIGHER than the spec sheet claims.

Also note for several antennas, the NEC Simulations underestimated gain below CH30.

Dielectric recently posted a white paper to accompany the vu-graph presentation:
http://www.dielectric.com/broadcast/pdf/Measured%20Performance%20Parameters%20for%20Receive%20Antenn as%20.pdf
Note measurements were conducted per IEEE-STD 149-1979 cited below.

===================================================
Antennas are measured with either a 75-ohm or 300-ohm resistive load.
Of course real Preamps and TV Tuners will exhibit a VSWR of their own,
but the antenna manufactures have no control over that aspect.

The applicable spec is ANSI/IEEE-STD 149-1979, "Standard Procedures for Antennas"
which you can buy on-line for not quite a "C" note or find a well equipped library.

Since that is usually not very convenient, here are some alternative links:
How to measure 50-ohm base station antennas, based on IEEE-STD 149-1979:
http://www.guerrilla.net/reference/antennas/TIA329-b-sept-1999.pdf
The Mexican government's adaptation of IEEE STD 149-1979:
http://www.justnet.org/pdffiles/N20402.pdf

Exercise for the (Norwegian) Student:
http://www.tele.ntnu.no/radio/fag/TTT4165/AntenneLab/AntPatternMeas.pdf
using HP-9720C Vector Network Analyzer:
ftp://ftp.testequity.com/pdf/8719-22c.pdf
which has a VARIABLE input impedance from 0.001 to 1000 ohms, so there
is no need to use a balun or 75/50-ohm minimum loss pads.

theroys88

09-06-05, 09:57 PM

hey guys,
Hope you guys can give me some advice. Live in Richmond and have two antennas. One toward the Richmond stations and one towards Norfolk. My son loves the WB and they are on channel 33. The antenna I have toward Norfolk is a antennacraft d9000 with 92 elements. It is manufactured by the same folks that make the radio shack antennas. I do know that it has a adverage gain of 9db but not what each channel gain is. I am able to pick up 33 fairly well at night and early morning but it gets unwatchable during the day with no audio. Norfolk is around 70 miles from my location. My question is that the antennasdirect xg91 gain on channel 33 is 15.7 and the 4228 is around 11. I am leaning toward the XG91 but may try both out and see which one does best with a uhf preamp. With these antennas and the higher gain do you guys think that I could get a watchable picture during the day? I figure having twice the elements for uhf and so much more gain that I should get a decent picture. Also I am confused. Antennaweb told me that the Norfolk stations are 136 and 137 degrees from my location but when I pointed my antenna to that degree mark I couldn't get a picture but when I pointed to 180-190 degrees I got the best picture. Also why does the picture detiorate during the day. All the literature I have read states it shouldn't. Any advice would be appreciated. Thanks Joseph

colofan

09-07-05, 12:00 PM

I doubt that a different antenna in the same place will make a huge improvement over a CM4228. Assuming you already have a good non-overloaded pre-amp like a CM 7777 and interfering channels are not the issue then unless you can re-locate the antenna to a better (higher) place it will be difficult to go from an unusable to a good signal. How close to watchable is the station now? If it is not almost fine with a few too many dropouts then don't expect miracles.

Well I have a 7775 since all I am trying to receive is UHF. I was wondering the reading I have seen mentioned local hot spots as well as dips in signal. How far apart is channel 35? I believe it is around 500 Mhz so is this a single wavelength distance or what?

holl_ands

09-07-05, 03:08 PM

My question is that the antennasdirect xg91 gain on channel 33 is 15.7 and the 4228 is around 11. I am leaning toward the XG91 but may try both out and see which one does best with a uhf preamp.

Kerry Cozad's actual measurement for CM4228 on CH32 was 14.7 dBd,
which is about 3 dB higher than the spec sheet info.

I don't know where you found the 15.7 dB from, but I suspect that it may be dBi (relative to isotropic)
rather than dBd (relative to dipole gain), such as is used by Channel Master and Winegard.
To obtain dbd from dBi, subtract 2.15 dB.

None of the XG91 websites cited in Nitewatchman's post #2599 on 8/31/05 indicated whether their antenna gain numbers were in dBi or dBd.
By looking at other simple antennas on the Funke website, such as the FM 2-element Yagi and VHF 4-element Yagi, it is clear that Funke uses dBd.

Their gain plot shows a gain of about 14 dBd on CH33 for the XG91 type antenna.

So they are within about a dB of each other on that channel and both have about the same shape to the curve and hence appear to be fairly close across the UHF band.

sregener

09-07-05, 09:59 PM

So they are within about a dB of each other on that channel and both have about the same shape to the curve and hence appear to be fairly close across the UHF band.

I've been told by those with the expertise to know that the 91XG is a fraction better than the other common antennas (including the 4228.) I do know that for those with a rotor, there really is no reason to chance the 4228's sail-potential.

PExeter

09-07-05, 09:59 PM

Please help me, Im so lost!! Ok, i've never had experience with OTA programming or any antennas for that matter. I took the forums advice and today UPS brought me a CM 4228 8-Bay Bowtie UHF Antenna and a CM 7777 Amp. I am trying to receive channels that are all 33 miles away at 360 degrees. Thats not the problem, as soon as I dumped out the box, I felt LOST. I can use anything as a mast? I figured it might come with one...dont ask why please. I was figuring on just strapping that sucker on to the roof and run a cable to my HR10-250 direct tv tivo and that was it. But now its looking pretty diffucult and a task I might not be able to handle. Im sure I have the correct diameter pipe lying around to mount this to, but according to the directions everything else looks complicated, they are very vauge. Can anyone point me in the right direction? A step by step website? Personal experience with the same antenna? You coming over to my house and installing it for me? Im only going to be able to get NBC and FOX and im starting to think its not worth it. Please help me@!

amirm

09-07-05, 10:58 PM

Sorry, but are you talking about mechanical part of this or electrical? If it is mechanical, you need to have a mast attached to your house somehow. Then the antenna just clips onto it with the U-bolts.

Once you have it mounted, the rest is really trivial. There is a "balun" that you need to connect. This is a black cylinder that on one side has two wires, on the other, a single "coax" connector. The two wires go on the antenna posts in the center and lock up using two wing nuts. The other side should just be connected to an RG-6 coax wire. One side of the coax hooks up to the balun, the other to the "combo VHF+UHF" input of the 7777. Don't use the connector next to it for now. Now, run a wire from the connector on the other side of the box far away from these two (sorry, don't remember th label) and hook this up to the power supply box. This box has two coax connections: one that feed power to the remote amplifier, and at the same time recieves the signal from it to amply. The other connector is what you hook up to your TV.

So the signal stream is from the center post of the antenna, through the balun (to convert it from 300 ohm parallel wires to 75 ohm round coax wire), to the pre-amp, then power supply and then your TV. It is really simple.

Once you have all of that, then you need to align the antenna. 360 means that the elements need to point north and the screen behind it. Also note that at 33 miles, you may not even need the amp. So just hook up the antenna first directly with the balun and see if that works. If it doesn't, then insert the amp per above.

And yes, I just did all of this and while I am an electrical engineer, all of it was really trivial.

Good luck and ask again if you have any questions.

Amir

PExeter

09-07-05, 11:07 PM

Thank you very much. I didnt realize the place where I picked up my antenna sells all the mounting equipment I would need. Thanks again, that really helped me out.

greywolf

09-07-05, 11:46 PM

Important reading for DIY installers may be found at http://www.hdtvprimer.com/ANTENNAS/basics.html

Pay special attention to grounding procedures.

holl_ands

09-08-05, 02:26 AM

Please help me, Im so lost!! Ok, i've never had experience with OTA programming or any antennas for that matter. As soon as I dumped out the box, I felt LOST. Can anyone point me in the right direction? A step by step website?

Suggest you start by reading Channel Masters Antenna Installation Guidebook:
http://www.channelmaster.com/pdf/AntInstallGuide.pdf

chinatti

09-08-05, 10:38 AM

I just received a CM4228 antenna that I ordered from an online vendor. A couple of the edges were slightly bent (looks like typical UPS shipping "white glove" treatment - the box edges were crushed a little. Also, the screen isn't sitting completely flush. Is this something I should be worried about? How critical is the alignment of the various parts of the antenna? Should I just try and bend things back a little with pliers? The amount of bending isn't really that bad, and it seems to an uneducated person like myself that the screen would be moving around a bit in the wind anyway, so I can' t believe that this is that critical.... I could probably get it 90% back to the original shape if I attempt to bend it back.

Thanks in advance.

PExeter

09-08-05, 11:40 AM

I just receieved mine too, and it was a little off, but I dont think it will affect it much...

Neil L

09-08-05, 05:35 PM

When my 4228 arrived, it was a little bent up as well. I don't think it will affect performance much, but I straightened mine out anyway. I'm just a perfectionist, I guess.

bmcent1

09-08-05, 08:03 PM

Okay, I'm going to purchase the XG91, I'm sold and lots of signs point to a good chance of getting good reception here.

A couple questions:
Should I buy the AD "extended length J mount" or is there a better mounting option?

Is the J mount all that's needed or do I still need to buy a 1.5" mast from somewhere?

Last... I *doubt* that an attic mount it going to work in my location, but I still want to try that first. If an attic mount actually works out, do I still need to ground the antenna?

Thanks!!

greywolf

09-08-05, 09:00 PM

If an attic mount actually works out, do I still need to ground the antenna?No wind, no static buildup. It's not necessary.

sregener

09-09-05, 12:38 PM

Should I buy the AD "extended length J mount" or is there a better mounting option?

Is the J mount all that's needed or do I still need to buy a 1.5" mast from somewhere?

Last... I *doubt* that an attic mount it going to work in my location, but I still want to try that first. If an attic mount actually works out, do I still need to ground the antenna?

You can use the J mount, but you don't need to. Any mast connecting solution would work. It does appear as though you could attach an antenna directly to the J mount, but I'd be sure to make the post strictly vertical. You want to point your antenna at the horizon, not up in the air!

As our resident expert here said about grounding, you do not need to ground an indoor antenna.

deno

09-09-05, 03:24 PM

I was wondering, if I install a CM7775 preamp about a foot below my outside antenna, cut the coax and run thru the wall and attach to a wall plate, attach a seperate coax to the outside of the wall plate which would then go to the power supply, and then from the power supply to my satellite receiver, would the power from the power supply be able to reach the preamp ok, or would the wall plate degrade it's effectivness. Thanks in advance.

Deno

sregener

09-09-05, 03:25 PM

...would the power from the power supply be able to reach the preamp ok, or would the wall plate degrade it's effectivness.

While each cut in your coax reduces your signal by a fraction of a dB, as long as the line is a straight-through line (i.e. no splitters,) there's no problems with using a wall plate with a preamplifier.

f300v10

09-09-05, 04:30 PM

Well, shoot! Why didn't I think of this sooner?

Get a second identical antenna and combine the two like MAX HD says. If the antennas are identical and the feedlines to the splitter are exactly the same length, you've got yourself a vertical stack and it should work just fine. (Point the antennas in precisely the same direction, too.)

If it doesn't, you could still buy a Jointenna.

But I'm betting that a vertical stack hooked up like this would work great - and it might even improve reception on other stations you're not getting.

Way back in March I posted about my reception issues. To re-cap, I live in a very wooded area, and use an XG42 Yagi. I keep having to adjust the antenna vertically as the leaves on the trees change with the seasons. Well I am back to wanting to try the vertical stack idea folks here suggested.

My question is what vertical separation to use with 2 XG42 Yagi from antennas direct. I emailed antennas direct, and they told me to ask the question here. Most of the stations I need are in the low 20's, and the highest is 39.

Thanks for any help on this.

sregener

09-09-05, 08:19 PM

My question is what vertical separation to use with 2 XG42 Yagi from antennas direct. I emailed antennas direct, and they told me to ask the question here. Most of the stations I need are in the low 20's, and the highest is 39.

While others will be able to tell you the specific height of a wave at 626 Mhz, I would suggest a little experimentation. 36" is a good starting point, and you can work out or in from there as your results suggest. The measurement is from the active-element to active-element, not from the tip of the reflector screens. When I tried a vertical stack of Channel Master 3023s, I couldn't space them closer than 36" because of the reflectors.

f300v10

09-09-05, 11:29 PM

Thanks sregener, I will let y'all know how it works out.

deconvolver

09-10-05, 09:32 AM

cpcat

09-10-05, 01:05 PM

Way back in March I posted about my reception issues. To re-cap, I live in a very wooded area, and use an XG42 Yagi. I keep having to adjust the antenna vertically as the leaves on the trees change with the seasons. Well I am back to wanting to try the vertical stack idea folks here suggested.

My question is what vertical separation to use with 2 XG42 Yagi from antennas direct. I emailed antennas direct, and they told me to ask the question here. Most of the stations I need are in the low 20's, and the highest is 39.

Thanks for any help on this.

36 inches would be reasonable. You may have to experiment a little as well. The calculation which seems to work best in practice for me is S=51/bw where bw is the beamwidth in the plane of stacking and S is the center-center spacing in wavelengths at the lowest channel you want to receive. It follows from this that narrower beamwidth antennas require more spacing. You may need to email antennasdirect for the vertical beamwidth (-3db) on the xg42. See http://www.astronwireless.com/stacking.html

I guess you have already decided against upgrading to the xg91 for some reason? That might be the simplest first step.

AntAltMike

09-10-05, 03:18 PM

I doubt that there is any discernible benefit in selecting a vertical stacking distance for UHF antennas any greater than one wavelength. I once experienced a significant improvement in front-to-back ratio by spacing two VHF high band antennas at exactly one half a wavelength apart. The whole experience was a fluke, actually. I was taking down and discarding abandoned antennas on a highrise, and when I took off an old, abandoned, unconnected channel 9 antenna, which, through luck, was exactly half a wavelength below the channel 7 antenna, all of a sudden the ghost from a rear reflection became much stronger. I then bolted the channel 9 antenna back on the mast exactly where it had been and the ghost image practically went away. Apaparently, some kind of resonance was taking place between the elements on these antennas. When I moved the disconnected channel 9 antenna up about a foot and down about a foot, the ghost image got stronger. I then bough another channel 7 antenna exactly like the one already in use and spaced them at one half wavelength and the ghost became nearly invisible (isn't that what ghosts are supposed to be?).

If you know that just one channel is your problem channel, you might as well start by putting them 3 feet apart and then move one up and down incrementally until the performance of the problem channel peaks, but you will probably enjoy better performance by following deconvolver's advice and just finding two "sweert spots" for different channels and using an A/B switch as appropriate.

Carl_Ballard

09-10-05, 05:42 PM

I'm going to try an outdoor antenna next weekend and have a question. How long do I need to hold a direction with the antenna. Does the HD tuner take a while to lock on, or does it see the signal immediately. That is, can I sweep the antenna, or do I have to try a poistion and wait some period before trying another?

jucojames

09-10-05, 08:27 PM

I am using an indoor old school antenna that gets UHF and VHF, but two of my locals send HD over VHF. Is there something I can do to determine/insure that I a receiving the HD signal and not the analog? thanks

POWERFUL

09-10-05, 11:59 PM

yeah it should be on a digital sub the number would be for ex. 11-1 or 11.1

RBMD

09-11-05, 03:32 PM

deconvolver

09-11-05, 06:14 PM

Quarter or half wave transmission line stubs are sometimes recommended as traps to eliminate unwanted strong channels. Another choice for notching out channels is the Join-Tenna from Channelmaster. Channelmaster states that the VHF Join-Tenna affects channels adjacent to the one being notched and that the UHF Join-Tenna affects up to five channels on either side of the notched channel. I was curious how a stub affects other channels so I used the 4nec2 program to model an antenna with a stubbed transmission line. I started with the double bowtie model from the hdtvprimer website that can be downloaded from http://hometown.aol.com/kq6qv/SIMS/ thanks to the creator of the original models. I chose the double bowtie because it has a low SWR (typically less than 2:1) when unmodified. I then added a half meter transmission line to an eighth meter (1/4 wave for 600Mhz) open stub to notch channel 35 followed by another half meter transmission line. The result showed that the SWR was still sixty to one at 8 channels away from the stubbed channel and that over the range from channel 15 to 65 the SWR was above ten to one. Next I replaced the open stub with a quarter meter (1/2 wave at 600 Mhz) shorted stub. As long as you aren't trying to pass VHF then a shorted stub is a possibility for UHF (shorted stubs also notch the doubled frequency so the SWR from a channel 14 notch would also rise again near the top of the UHF band). The result was better than the open stub- at eight channels from the notch the SWR was about fourteen to one and the typical SWR for the UHF band was about seven to one. See the enclosed plots of the SWR for the three cases modelled over the range of channel 15 to 65. Overall the results suggest that the insertion loss for the quarter wave stub means other notch solutions are preferred and that the Join-Tenna is probably a better choice than either stub.

deconvolver

09-11-05, 06:17 PM

Here are the plots.

deconvolver

09-11-05, 06:24 PM

Here are the plots.
I needed to make the image less than 800 pixels wide so I cropped off channel 65. Note that the SWR is computed only for the odd numbered channels.

bobchase

09-11-05, 11:05 PM

Advice appreciated. I live 54 miles from my HD uhf towers. I have a huge Wineguard HD8200p uhf/vhf antenna going to a winegard preamp ( 29 db uhf/vhf) at the base of my antenna which is 35 ft off the ground then split to 2 tv's with the cable runs bout 75 Ft to each tv. My tuner meters uhf usually show signals about 70-90 in good wheather. My antenna unfortunately points to fir trees which I cannot avoid which are about 30 ft taller than the antenna located about 100ft from the antenna. Last night a big storm rolled in with black clouds and thunder and very heavy rain, during which I lost all signals except analog receiption remained excellent. Are my signals just too weak during times like this or actually are the signals too strong with multipath problems. Anything to try? Just accept? It rains all the time in Oregon, and having installed this set up in the summer with dry weather may have been misleading. Appreciate help.
Rich
Rich,

If the analog channels were truly excellent, then you may have been overloading the STB or digital tuner at the input due to high signal levels out of your preamp. On the other hand, if there were diagonal lines (bars) moving through the analog picture, then your pre-amplifier was being overloaded. Also, if there was a buzzing sound in the audio when the screen tended to get bright (a white background in a commercial) then the preamp was overloading. To solve that, then you need to reduce the effective gain of the pre-amp with a fixed pad or use a pre-amp with less gain.

However, if the analog pictures were crystal clear, you may be able to solve this problem by putting a 6 dB pad on the input to the digital tuner (or STB) after the pre-amp. Some folks like to use the Radio Shack variable attenuator instead for this kind of problem.

Bob Chase
KHWB-TV

PS The fir trees aren't the problem either if the analog pictures are excellent.

RBMD

09-12-05, 05:10 AM

Thanks Bob,
I put a RS 6db attenuator before the tuner and 2 of my lower signal stations evened out and went up on the meter from 58 to 65. Can't tell if I lost a couple of signals as it's 2:00 am and they may be off the air. I also have to wait for rain. Thanks for the help.
Rich

jucojames

09-12-05, 12:02 PM

sregener

09-12-05, 02:01 PM

If I am using OTA (older rabit ears), how can I tell if it is receiving a 21 analog versus a 21.1 digital signal? The indoor antenna I have has a clock-style nob that can be switched that affects the signal but I don't have a manual that explains what this does. That is the only "setting" I see that I can imagine could make a difference. Sorry about such an ignorant question......

Your antenna is receiving all the frequencies simultaneously. What determines whether you are tuning to the analog or digital signal from the broadcaster is your TV or set-top-box (STB.) The TV or STB must be able to receive and decode ATSC 8VSB signals. Your antenna has nothing to do with which signal you're watching, just as your antenna has nothing to do with whether you're watching ABC or CBS.

There are two types of switches I've seen on antennas. One is an "on/off" switch that controls an amplifier. Generally speaking, you'll want an amplifier turned off for an indoor antenna when receiving digital signals. The other is a "directional" switch that has multiple points you can turn to in a 360-degree radius. That type of switch is supposed to bias the antenna in different directions, but rotating the antenna itself is probably a better choice.

jucojames

09-12-05, 02:56 PM

I appreciate your patience - you are like a kindergarden teacher! I knew the answer was probably very simple.

luvu2hrs

09-12-05, 10:05 PM

atye

09-13-05, 01:57 AM

deconvolver

09-13-05, 09:08 AM

Newb here, really need some of your expert advice. Thanks in advance for your knowledge. Here goes. Bought the Shack HD recieverand hdtv indoor antenna on sale. I live in a multistory building in Brooklyn NY and reside on the seventh floor. My HD transmitters are within 4 miles of my place. Right now the meter reads a steady 49 and about 17 dbs. I get no picture right now, and I know i need a reading of about 75 to get picture (I tried the same setup at my girlfriends house and she gets channel 5,7,9 and she live about 15 miles away from the HD transmitters). Antennaweb website reccomends i should get a red coded outdoor multidirectional antenna. I do have a terrace, but i would like to try and figure this problem out with a indoor antenna and amplifier if possible. If it isn't possible, what do you guys and gals recommed i setup on my terrace without my neigbors complaing. Thanks for your advice in advance.
First of all, when trying to get a reading for an individual channel that was missed in the scan you need to tune to the digital channel number not the analog one. Once the receiver locks the signal it will re-map the digital number back to the old analog number with something like "-1" added to it. So for instance for WABC you put in 45 then check the meter reading; once the channel comes in it will display as channel 7-1. I expect that an amplifier may cause more problems than it solves because an overloaded amplifier or receiver has terrible performance. A directional antenna like the zenith silver sensor usually works better than an omni antenna as long as re-aiming the antenna is not an issue. That is because in a city a mis-mash of reflected signals that interfere with each other often exists; a directional antenna helps in selecting only the best signal. You should be able to get more specific advice in the NY,NY OTA thread:
http://www.avsforum.com/avs-vb/showthread.php?p=6166989

sregener

09-13-05, 10:37 AM

A SolidSignal rep suggested a Winegard PR8800 for me. I'm almost exactly 60 miles from the towers in the Twin Cities, Minnesota. I was looking at the ChannelMaster 8 bay rig, but this guy said he always suggests the Winegard for the Cities towers. Any opinions about this?

The Winegard is lighter, and has a slightly different performance curve, but in real-world use, the difference between the two is probably minimal. Either should work well for you, and if they don't, switching to the other wouldn't make a difference.

Will Collier

09-13-05, 01:09 PM

My house still has an ancient (1970's) era TV antenna attached to the chimmney; I still use it for SD PIP occasionally. It picks up the stronger VHF (analog) channels pretty clearly, and several of the UHF channels with varying amounts of fuzz and/or static. It doesn't have a rotation motor, but according to the HD maps, I need a "Red" antenna for all the stations in my metro area (Atlanta), which are fortunately clustered in a fairly small wedge southeast of my house.

N00b time: any chance this old clunker would work with an HD tuner, perhaps along with an added preamp? Sure would be nice, particularly from a cost/hassle perspective...

suncom3

09-13-05, 03:53 PM

please help me figure this out, I have a channel master 3018 and a hd tivo, I get fox and wavy in the 90% range,but cbs and ch 13 wvec,keep going from 60 % to back to 0 % constantly over and over,Its odd that at night time it seems to level out,Ive tried moving the ant from 263 deg to 259,it doesnt help. this ant is about the same range as the 4228.

I was going to try and just get a 4228 from domes but they want 100 bucks for it and it retails for 59 bucks,whats the deal with that?

deconvolver

09-14-05, 12:45 AM

amirm

09-14-05, 01:04 AM

I bought a house that has a mast with two stacked Yagi antennas (with no reflectors) designed to pick up a signle VHF channel (9). One antenna is 4-5 feet above the other.

I have no use for the above antenna and instead mounted a CM 4228 between them to pick up the digital UHF channels. Since the gap between the two Yagis was more than the hight of CM 4228, I now have one about a foot higher than the CM 4228 and the other a few inches below. Would either one of these elements (which are not hooked up to anything) have any effect on the performance of the CM 4228? My RF knowledge is failing me here :).

Thanks,
Amir

sregener

09-14-05, 12:14 PM

I now have one about a foot higher than the CM 4228 and the other a few inches below. Would either one of these elements (which are not hooked up to anything) have any effect on the performance of the CM 4228? My RF knowledge is failing me here :).

Yes, and probably negative.

quarque

09-14-05, 10:26 PM

amirm

09-14-05, 11:42 PM

I know DB-8 and 4228 work differently because in one case the screens are connected together and in the other not. I have not looked at DB-4 but the same might be true there.

Amir

cpcat

09-15-05, 01:06 AM

anyone care to comment on this statement from our local OTA forum:

"...a Multidirectional antenna might give you problems, like the DB4, but the 4221 is really more one direction, but with a wide reception angle, and far more gain."

Aren't these two identical in design and performance?

They are very similar really and should give similar results with the main difference being the DB4 costs more. The DB4 is certainly not a multidirectional antenna.

I would agree with "..a multidirectional antenna might give you problems", though.

The screening difference between the DB8 and the 4228 mainly effects the high band vhf performance, improving it on the 4228 over the DB8.

atye

09-15-05, 02:59 AM

The Winegard is lighter, and has a slightly different performance curve, but in real-world use, the difference between the two is probably minimal. Either should work well for you, and if they don't, switching to the other wouldn't make a difference.
Is it likely that the 91XG from Antennas Direct would offer better performance than a bowtie type?

sa69

09-15-05, 08:26 AM

Thank you for information

sregener

09-15-05, 09:11 AM

Is it likely that the 91XG from Antennas Direct would offer better performance than a bowtie type?

Different antennas work better in different situations. Outdoors, the yagis (like the 91XG) seem to have a leg up. In an attic, the bowties seem to be a little better. You also have to consider which frequencies you're after. If you need something above channel 51, the 91XG is probably the better choice. Which is better in your particular situation? Hard to tell. But if a yagi isn't working, trying a bowtie is better than trying another yagi, and vice-versa.

atye

09-15-05, 01:08 PM

Thanks! Are the Yagi's more directional than the combination UHF/VHF I have now, or about the same? I have a CM 3678.

sregener

09-15-05, 02:30 PM

Thanks! Are the Yagi's more directional than the combination UHF/VHF I have now, or about the same? I have a CM 3678.

You have a Yagi right now. (Technically, it's a yagi-corner reflector hybrid, but most commercial UHF antennas are.) But the bulk of your antenna is a log-periodic setup for VHF, with the UHF section just pasted on the front.

What makes an antenna more directional is the number of elements it has (or the arrangement thereof, but that's moot for the current question.) Ignore the VHF elements for a minute - they aren't doing anything for your UHF reception. There's probably between 20-30 UHF elements on your CM3678. There's 91 on the 91XG. It is going to be far more directional when the yagi half of the hybrid is being used. (On lower channels, the corner reflector becomes the primary means of gathering the signal, and these are not, by rule, very directional.) When the corner reflector portion comes into play, the 91XG has a better corner reflector than the CM3678, but most of that is going to be gain, not directionality.

It is a fact that a UHF-only antenna will outperform a similar UHF/VHF combo antenna with similar-sized UHF sections. The UHF/VHF combo is a compromise, one that works well for many, but still a compromise.

colofan

09-15-05, 02:34 PM

Is there a DIY for antennas to build your own UHF antenna?

I have seen web pages for HAM stuff but I haven't located a resource for a kit or make your own.

sregener

09-15-05, 07:14 PM

Is there a DIY for antennas to build your own UHF antenna?

I have seen web pages for HAM stuff but I haven't located a resource for a kit or make your own.

http://www.wfu.edu/~matthews/misc/dipole.html

http://www.clarc.org/Articles/uhf.htm

holl_ands

09-16-05, 05:59 AM

colofan

09-16-05, 01:06 PM

What would be your eventual goal in a DIY project? I don't think "kits" exist.

Which channels do you want (a few or entire band) and which need the most gain?
Do you want to build a really big super high gain antenna (but smaller than Aricebo)?
Or are you simply looking for a moderate gain antenna on the cheap?

Would it help if you only knew the detailed measurements for commercial antennas,
such as are used for input to NEC simulation runs?

Would you want to use an NEC simulation program to try out your design and tweak various parameters?

The HAM stuff you mention has lots of guidance on building very narrowband high gain Yagi type antennas (one or two channels)
as well as very wideband, moderate gain LPDAs (Log Periodic Dipole Array).

What's your preference?

Well actually both. I have one channel (35) I would like to build for and then see if I can improve upon the commercial grade antennas. i have built a lot of stuff both electronic and not so the above references are a good start.

When you say narrow band are you talking only a single channel with good rejection from the adjacent channels?

I saw that channel master made a parabolic dish at one time but you can't buy that unit anymore and besides it is the higher UHF band I would like to receive better. Ideas?

dr1394

09-16-05, 05:38 PM

Another DIY webpage:

http://www.mtmscientific.com/yagi.HTM

Ron

holl_ands

09-16-05, 10:06 PM

Of course you want it all....don't we all.
Narrow band would not have good rejection for any of the near adjacent channels.
For that you would need an input filter.

Various versions of NEC Sim can determine how well a design will work (gain, VSWR, etc.)
You might find the hdtvprimer NEC files of interest. Start with readme and xls files.

Suggest you look in the fol. section on "Practical Antennas: VHF/UHF"
http://www.cebik.com/
Especially note that he presents lots of NEC simulation run results and tips.

There are several narrow band Yagi and wideband LPDA designs for the
UHF band (up to 40 elements!!!).

=======================================================
Some comments re the so-called Yagi. The original Yagi-Uda design uses
a dipole as the only fed element (and usually a folded dipole for wider
bandwidth and better impedance) .
A slightly longer simple rod is used as the reflector element and any number
of decreasing length directors may be used.
The resultant designs are fairly simple to calculate using a spread sheet.

An array of rods (W-G PR4400 and PR8800 use a Triad Reflector) or a complete
Reflector Screen may be used to supplement the reflector element
(Corner Reflector) to increase the gain and F/B ratio.
Some antennas, such as the XG-91 type, use wider bandwidth bow-tie elements.

Beyond that, modern Yagi design becomes more black magic.....
A classic Yagi-Uda would have very narrow bandwidth (only a few UHF channels),
as you'll see in the various NEC Sim runs.
In order to expand the bandwidth to cover nearly the entire UHF band, the element spacing
and lengths are moved around to "de-tune" the antenna.
With a computer, thousands of possible detunings can be analyzed.
Some have said that a monkey randomly picking alignments can do about
as well as a trained antenna engineer.

And the DAT-75 type is an entirely different animal, using three stacked Yagis
pointed towards the reflector screen.

========================================================
You might find the fol. LPDA spread sheet calculator of interest.
I punched in the max sized LPDA that the spread sheet would permit:
result was a fairly big 15 element array, with 10 dBi = 7.85 dBd gain.

An LPDA is fairly difficult to fabricate, esp one built to withstand the elements.
But once you understand the spacing rules, it shouldn't be too difficult to model and
build either a Log Periodic Toothed Array (such as the overly small Silver Sensor)
or even a simpler Zig-Zag Log Periodic Array, like the ones I described in the fol:
http://hdtv.forsandiego.com/messages/1/2944.html
I have an old roll of RG-58 out in the garage that would be ideal to simply string up
on a frame in the garage whenever they fire up DTV in the VHF band.

I also found the Corner Reflectors fed by a simple Dipole element to be interesting.
But these are SUPER-SIZED reflectors with a lot more gain.
I just wonder what happens when a super sized reflector is used with a big Yagi...

Unfortunately both the Yagi and the LPDA are fairly large, require significant rigidity
to survive outdoors and need to be truly monsterous to out perform the CM-4228.

=======================================================
The CM2251 parabolic may not be available, but Wade/Taco and Lindsay in Canada still are:
http://www.wade-antenna.com/upa.htm
http://www.lindsayelec.com/antenna/commercial.catv/6-pbu-uhf.html

Note that the Lindsay has a short LPDA pointed towards the reflector.
Hard to see, looks like maybe a 4-element LPDA (too keep it close to the focus point).
I can't make out what the Wade/Taco uses as a feed antenna.
If you blow up the below jpg, you'll see the CM4251 7-foot Parabolic is fed by a
2-Bay Bow-Tie with Reflector Screen. A Balun module attaches to the screen.

You could do a DIY project, either constructing your own reflector or an old "BUD"
(Big Ugly Dish for C-Band SAT).
A 3-D parabolic would be best, but a 2-D parabolic is also possible by simply folding over some wire mesh.
Or use a Super-Sized 2-D or 3-D Corner Reflector.

Once you have a reflector, you'll need some sort of small UHF antenna to feed it.
You might want to try a 2-Bay Reflector (like the DB-2) or a 2 or 3-element YAGI or a Silver Shadow LPDA.
Or one of the short broadband zig-zag structures like the radio telescope feeds shown in the zig-zag link above.

Let us know what looks good in NEC and of course, what works.

atye

09-18-05, 12:09 AM

You have a Yagi right now. (Technically, it's a yagi-corner reflector hybrid, but most commercial UHF antennas are.) But the bulk of your antenna is a log-periodic setup for VHF, with the UHF section just pasted on the front.

What makes an antenna more directional is the number of elements it has (or the arrangement thereof, but that's moot for the current question.) Ignore the VHF elements for a minute - they aren't doing anything for your UHF reception. There's probably between 20-30 UHF elements on your CM3678. There's 91 on the 91XG. It is going to be far more directional when the yagi half of the hybrid is being used. (On lower channels, the corner reflector becomes the primary means of gathering the signal, and these are not, by rule, very directional.) When the corner reflector portion comes into play, the 91XG has a better corner reflector than the CM3678, but most of that is going to be gain, not directionality.

It is a fact that a UHF-only antenna will outperform a similar UHF/VHF combo antenna with similar-sized UHF sections. The UHF/VHF combo is a compromise, one that works well for many, but still a compromise.Thanks so much for all your input, sregener! What I need is an antenna that will have much higher gain for the Twin Cities towers, and I'd like to pick up the Eau Claire channels on the back side. (I'd like to stay away from a rotor) I need the following channels: 15-26-32-35-39-50(and someday 49). Nothing is above 50. Given all my desires, which type would you try first?
I'm actually wondering if I NEED the biggest of the big because the dB specs quoted for the 43XG and the DB4 are both significantly greater than the unit I currently have, and I usually get servicable reception for all but 26 (FOX9) and 50 (ABC5).

holl_ands

09-18-05, 07:57 PM

MORE NEC DIY INFORMATION:

When looking at Ham antenna designs, bear in mind you can easily rescale to desired frequency.
Simply divide the center design frequency for the Ham design (e.g. 51 MHz for 6 meters)
by the desired new center frequency (say 510 MHz for UHF CH20).
Then scale down all of the dimensions by 51/510 = 0.1.
All the gain and VSWR results will stay the same....until you see that the element diameters
may be unrealistic after scaling....in which case tweak the NEC input files and rerun.

Everything you ever wanted to know at the unofficial NEC Archives:
http://www.si-list.org/swindex2.html
XLNEC.ZIP includes Excel source file utility for LPDA, Yagis with Parabolic, etc.

And WTMI for the over-achiever:
http://www.ac6v.com/antprojects.htm
Unfortunately, very few Ham antenna projects are wideband designs, such as are needed for TV.

=========================================================
Modern optimized Yagi designs don't follow the Yagi-Uda textbook rules.
To achieve a wider bandwidth, lots of tricks are used to "de-tune" the antenna.
Here is a good example of one process:
http://ic.arc.nasa.gov/people/jlohn/Papers/ices2001.pdf

=========================================================
The fol. includes NEC input files for VHF LPDA and UHF LPDA TV Antennas:
http://www.qsl.net/zs6bte/Antennas_for_the_TV_DXer.html
Note that gain is in dBi (vs dBd).

holl_ands

09-18-05, 08:08 PM

I posted updates to spread sheets summarizing specs and sometimes measurements for
PREAMPS, BALUNS, RG-6/11 CABLE and ATSC_NTSC TUNERS_PCI_STBs.

I also posted an update to the DTV ANTENNAS spread sheet,
which compares manufacturer specs to NEC Simulation results and (for a few) actual measurements:
http://hdtv.forsandiego.com/messages/1/2846.html?1126998999

The ANTENNAS spread sheet now includes many non-U.S. antennas.
Note that outside North America, many different channel spacing and number schemes are used.
Fortunately, most specs use frequency rather than channel number:

==========================================================
I was underwhelmed by remaining Parabolic Reflector antenna gain specs, not to mention pathetic F/R ratio.
Only at the high end of the UHF band do they finally outperform the usual assortment of high gain antennas.

BarnacleBill

09-18-05, 09:31 PM

deconvolver

09-18-05, 11:32 PM

BarnacleBill

09-19-05, 12:54 AM

Deconvolver, thanks for all the very good information. After looking at some test results here (http://antennasdirect.com/HDTV_antenna_review.html) I think I will try the silver sensor first, then the square shooter. The graph seems to indicate that the silver sensor does surprisingly well with VHF.

holl_ands

09-19-05, 04:17 AM

There seems to be agreement that the silver sensor is the best indoor HDTV antenna. I have found two different models that use the name.

This (http://www.zenith.com/sub_prod/product_Display.asp?cat=49&id=131) is the most common, with the arrow shape (ZHDTV1). But I also found this (http://shopper.cnet.com/Philips_Silver_Sensor_PHDTV3_TV_antenna/4014-6509_9-31467513.html) triangular shaped flat disk antenna with the same name (PHDTV3). Which one gets all the raves?

Also, would this help get high-band VHF channels 11-12? or would I be better off with the Terk HDTVi, which seems to be the same as the first silver sensor plus VHS? I am less than a mile from the main tower for most stations and about 4 miles in another direction for channels 11-12, which are unwatchable with rabbit ears because of hills.

Thanks for any help you can give me.

The unamplified Silver Sensor reportedly came from UK manufacturer Antiference:
http://www.antiference.co.uk/indoor.htm
http://www.electricshop.com/invt/4000spa111805a
They claimed to have "launched" the Silver Sensor in 1984:
http://www.antiference.co.uk/profile.htm

Note that Antiference also offers a similiar looking Power Sensor model which includes
an external preamp module (that plugs into 220 VAC).

=====================================================
Gemini Industries is a division of Philips:
http://www.gemini-usa.com/gemini/index.asp
They sell the original, unamplified Silver Sensor under the Gemini, Philips, Magnavox and Zenith
brand names....all with similar model numbers.

Zenith Silver Sensor model is ZHDTV1:
http://www.gemini-usa.com/a5/modelDetail.asp?PkgID=369621&User=GemAntennas
http://www.zenith.com/sub_prod/product_Display.asp?cat=49&id=131

Philips Silver Sensor Model PHDTV1:
http://www.walmart.com/catalog/product.gsp?product_id=2625055

Philips-Magnavox Silver Sensor model is PM-HDTV1:
http://gemini-usa.com/a5/ModelDetail.asp?CtgID=1371&User=GemAntennas&PkgID=369620&Rnd=200

and I've seen that the Gemini model is GHDTV1.

Given that they are all from the same company, they are probably all the same.

================================================
Philips (aka Gemini) now sells an amplified Silver Sensor model PHDTV3:
http://www.gemini-usa.com/gemini/pressDetail.asp?ID=36
http://www.walmart.com/catalog/product.gsp?product_id=3904686&cat=4536&type=19&dept=3944&path=0%3A3944%3A3964%3A133270%3A4536

Looks like they put the Silver Sensor inside a protective plastic case to make it more kid proof,
built-in an adjustable 10 dB Preamp and added some Rabbit Ears to improve the VHF performance.

They now have an amplified, Rabbit Eared model that can compete directly with the Terk HDTVa.
(The unamplified model is the Terk HDTVi, which also has Rabbit Ears for VHF.)

======================================================
Kerry Cozad reported test results for on-air gain, VSWR and antenna pattern measurements
for the Gemini-Philips-Zenith Silver Sensor, Terk HDTVi and other models:
http://hdtv.forsandiego.com/messages/1/3476.html?1118216319

There wasn't much difference, although each had good...and bad VHF channels.
Your better choice for an indoor LPDA type antenna would probably be the Terk HDTVi (unamplified) LPDA,
which comes with collapsible Rabbit Ears for optimizing VHF reception,
(not included in the unamplified Silver Sensor).

======================================================
Being so close to the broadcast towers, you should not use an amplified antenna of any kind, even if it is adjustable.
You want to rely on the tuned RF stage in your HDTV Tuner to suppress strong signals as best as it can.
You also might need to insert a Variable RF Attenuator (see Radio Shack) to prevent overloading your HDTV.
If there are any VHF stations on your nearby tower, they may be preventing reception of CH11 due
to excessive signal causing intermodulation distortion.
Try tweaking the Variable RF Attenuator to see if CH11 comes in.

====================================================
Winegard Square Shooterspecs say 4.5 dBd average gain for UHF, but don't give any VHF gain specs (so how bad is it???)
Kerry Cozad did VSWR and pattern tests, but didn't include the SS in the gain curves (why was that???)
It probably provides less VHF gain than Rabbit Ears, since the spiral log periodic structure is inherently a UHF antenna.

I don't know how well the new (overpriced) Winegard SS-3000 SharpShooter indoor antenna works for VHF,
but spec sheet shows only -5 dBd gain for VHF, which is worse than Rabbit Ears.
And where would you put this 4x5x27 inch monster indoors so that it's pointed in the right direction?

=====================================================
But once you bite the bullet and decide on an outdoor (or attic) antenna,
the CM-4228 (note it's excellent VHF performance) or a purpose build VHF antenna become viable options.
An RF switch (or maybe a simple antenna signal combiner) could be used to either switch or merge the outdoor signal
with the indoor UHF antenna, which would be pointed in the opposite direction.

A cheap $20 antenna should be all that's required for UHF when you can probably see the towers from the roof of the building.
For VHF in the other direction, maybe something in the attic??? But first try the RF Attenuator trick.

BarnacleBill

09-19-05, 04:54 AM

cpcat

09-19-05, 07:17 AM

The arrow shaped Zenith silver sensor is the antenna that is considered a good indoor UHF antenna. The Terk HDTVi just has rabbit ears for VHF so if they don't work for you now then the HDTVi probably won't work either. For a bit more performance on VHF you could try the Winegard Squareshooter-1000 or -2000 (a -1000 with a built in amplifier) which has some front to back selectivity. You will need to try different antenna locations to find the spot with the best reception. To do better than the Squareshooter on VHF-high you would probably need to add a real antenna designed for outdoor use to your UHF antenna. .

I disagree with this. Rabbit ears appropriately extended and positioned should give better performance than either the Silver Sensor alone or the Square Shooter (in the same location, obviously it would have an advantage outside) for VHF both high and low.

Tips on using rabbit ears: http://www.kyes.com/antenna/rabbitear.html

VHF gain for all three: http://www.hdtvprimer.com/ANTENNAS/comparing.html
(bottom graph)

sregener

09-19-05, 08:21 AM

What I need is an antenna that will have much higher gain for the Twin Cities towers, and I'd like to pick up the Eau Claire channels on the back side.

Speaking from experience, the 91XG would be a poor choice, as the reflector screen is very good - it would completely block the signal from behind. You might do better with a Channel Master yagi like the 4248.

deconvolver

09-19-05, 10:19 AM

thr3

09-19-05, 05:01 PM

I'm second guessing the placement of the in line coax grounding block for my new antenna. Based the layout and the grounding rod location, it was easiest to have the interrupt near the antenna where the balun is connected. This leave most of the cable run to the house downstream of the ground point. The references suggest the ground point should be right before the coax enters the house. Is this a serious safety issue? The circuit should be equivalent, but static electricity tends to run counter to my intuition.

The mast is also grounded to the same rod.

Can some one elaborate on this point?

greywolf

09-19-05, 05:34 PM

It's a code issue. I believe the purpose is to prevent the possibility the coax breaking and contacting a power line or losing its grounding and becoming a lightning attractor during a storm. If the break happened between the grounding block and the house, the coax lead into the house could deliver power line voltage or lightning through the coax. The exposure between the block and the house is therefore supposed to be as short as practicable for the least likelihood of damage.

The bigger real issue is that a separate equipment grounding rod must be bonded to the main building ground with 6ga copper wire or its equivalent. Otherwise, a potential difference could occur between the two ground points and ground loops and/or heavy damage from any nearby lightning strike could result.

holl_ands

09-19-05, 06:26 PM

Holl_ands, good grief, you are amazing. That must have taken a lot of work. Thank you so much. It will take me a while to absorb everything you wrote and it's time for bed. I love this board.

I bought the RS variable attenuator yesterday, but it did not seem to do much good. I think I need a more directional VHF antenna. Thet's why I was considering the SquareShooter. It may not be any "better" than rabbit ears for VHF, but if it is more unidirectional, then it will help suppress the strong signals from nearby Sutro tower, so it won't swamp channels 11-12. I can disconnect the antenna completely and still pick up the Sutro stations.

LOCATIONS:

So it appears that you are about a mile South of Sutro Towers in S.F.
And about 4 miles North of KNTV (NBC Analog and Digital),which sits atop a 1000 foot hill
with presumably a more or less unobstructed line-of-sight path
(give or take some local buildings that may be in the way).
From that close, their signals should be nearly as strong as from Sutro Tower.
[In which case moving the antenna around should have found a sweet spot free of multipath.]

Do you know for sure whether A-KNTV (CH11) and/or KNTV-DT (CH12) are broadcasting
from their new location 4 miles away (per Change Proposal in FCC database),
or whether they are still broadcasting from their old Licensed position 55 miles
away in the mountains South of San Jose???

Maybe they're still using the Licensed location and after the move,
NBC reception problems will go away???

=====================================================
SECURE THE HATCHES (AARRRGHHH!!!): [Just couldn't help myself...]

Fabricate a Type F connector with a short in it.
Attach the short to the HDTV Receiver's input and see how much VHF leakage you get.
The stations should be very weak, if at all.
If the VHF stations look real strong, you might have HDTV Tuner leakage problems.

Progress up the line to include any RF Splitters and HDTV interconnection cables
and then the downlead coax to see if there is much of a difference.
You may find that one of the connectors needs replacement or is simply dirty
(I clean the center wire with emory paper) or perhaps the coax itself is leaking in nearby signals.

Are you using (at least) double shielded coax for the ENTIRE run?
Maybe you are jumping to standard single shield cable closer to the HDTV?
If so, it may need to be replaced.

Also make sure to bypass any distribution amplifiers, since they can also overload.

=====================================================
re ANTENNAS (just in case you need to bring in a distant station):

A more directional VHF antenna may be needed, but the most important thing to look at
in your situtation is the Front-to-Back Gain Ratio (F/B in dB).
Only some of the purpose built VHF antennas will provide significant F/B >20 dB:
http://www.hdtvprimer.com/ANTENNAS/comparing.html
And some of them actually have a significant response lobe towards the rear.

W-G SquareShooter specs show VHF F/B of 6 dB for CH7 but only 2.6 dB for CH10.
(So is it better or even worse for CH11/22???)
Also note that the VHF pattern is skewed counterclockwise by about 45 degrees!!!
And the VHF gain???? W-G has "NO COMMENT".
It's not really intended to be a VHF antenna.....you get what you get....

W-G SharpShooter specs claim average VHF CH7-13 F/B of 11.3 dB.
But if you blow up their on-line polar plots, the tiny type sez it's only 7.5 for CH13.
Can we presume that CH11/12 is probably closer to this value???.
But since the SS-3000 is amplified, it's probably a non-starter a mile away from the broadcast towers.
[And I didn't see anything on how the 1 db Noise Figure Preamp might be bypassed.]

Rabbit Ear models are dipoles that presumably can be positioned to attenuate the undesired
local VHF signals....give or take bouncing off nearby objects.
But NEC Sim results don't support this common conjecture:
www.hdtvprimer.com/ANTENNAS/RabbitEars.html