The Official AVS Antenna and Related Hardware Topic! - Page 58

I recently bought and installed my CM 4228. When it arrived I noticed that two of the elements on two of the bowties were missing. The missing ones were on the second bowtie down on the right and te third bowtie down on the left, so it looked symmetrical, and I thought maybe it was suppose to be like this. But I have seen pictures and all eight bowties had all four elements. Do you think this is messing up the antenna reception. I only get channels some of the time, but I also live in an area which is notoriously hard to recieve signals.

VMsat - well it certainly is not helping matters. Can you see any obvious signs of damage where the elements attach (i.e. evidence of forceful removal)? I'd exchange it for a "complete" antenna.

I would send it back too.

According to antennaweb.org, I live about 12 miles from the closest station and 15.5 miles from the farthest one, at ground level, with no obstructions of importance. All stations come from the same quadrant (50-52 degrees). With a non-amplified Terk HDTVi indoor antenna we only get one station (at about 12 miles) reliably and with good signal strength; the rest are either not received at all or very rarely. I would like to stick to an indoor antenna if possible. Would switching to an amplified Terk TV5 or Radio Shack 15-1880 solve my problem? What about adding an amplifier to my current antenna?

Thanks,

Val

For a good small indoor antenna, I don't know that you can beat antennas direct DB2. I think they're currently on back order though, excellent little UHF antenna, (most likely) outperform the Terk antennaes and the Radio Shack.

http://www.antennasdirect.com/db2_bowtie_antenna.htm

Of course both the HDTVi and this one are directional, so, if you're in the middle of a couple stations you'd want something multi-directional.

At that distance you do not want any amplifiers. In fact you may need an attenuator if anything. Radio Shack has a cheap variable one. One of the best indoor antennas is the Zenith Silver Sensor (sold by Sears and others). It is somewhat directional. You do NOT want a "multi-directional" or "omni-directional" antenna. All they do is pick up reflected signals and cause the receiver to bounce around trying to lock on to one of them (unsuccessfully). Terk is not highly rated around AVS. Also, indoor antennas in general are problematic. You have to contend with your house and all nearby house's effects on signals. One of the best indoor setups is a CM 4221 in the attic. Works very well for many even if it is a little big and ugly for the living room. Although some have stuck them in a window behind a curtain. It certainly wouldn't hurt to try the 15-1880 since you can easily return it.

Hi guys, I'm back

I've got a couple more Qs.

Here's some pics from my attic. Can anybody ID or give opinion?
(Note: My first time posting pics and making my webpage, plus I changed a handful of burned out light bulbs while I had the ladder out! You guys are slave drivers

Here's the UHF, looks like it's not a CM 4221 remember that it's from 1990.

http://hometown.aol.com/newsgroupjohn/images/uhf.jpg

http://hometown.aol.com/newsgroupjohn/images/combo.jpg

VHF is good except chn 9 CBET from Windsor, Ontario eh?
It's in different direction and farther than others, but no hockey now

http://hometown.aol.com/newsgroupjohn/images/vhf.jpg

http://hometown.aol.com/newsgroupjoh...s/vhfvjobs.jpg

These are combined in attic (no or minimal loses???)
I gave the UHF a twist based on compass. I went a long time w/o dropouts/freezes but lately some on chn 4 (45), WDIV @210deg. Didn't troubleshoot a lot, because I was watching another channel that was rock steady. Now, I have a plan to check analog UHF if possible when it acts up.

Have read in Detroit thread that when I had DOs, cable AND satellite also did. This had led me to wonder if problems may not be OTA reception

Also have noticed UHF analog appears to me to be more ghosty than snowy, even if ghosts are weak, stable and generally look "OK" although I've heard "static" in sound even when picture is quite good (analog). Does this imply MP or weakness, or does it depend?

If I knew I could use a 4228 to solve problems I think I'd try it. Might have to do some disassembly to get it thru opening and it would be a pain to add a rotor, I'm not sure what the consensus is w/ or w/o rotor. This would be under the assumption I could cut down MP, and still have strength, but maybe I'd be fooling myself.

Thanks
John

Original post>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
I got a new Pio plasma and hooked it up to the attic antenna (condo) I had installed when it was built about 15 yrs ago. I don't know what it is and haven't been up there yet to look.

I get from the high 70s to low 90s on sig strength screen, which is not easy to monitor when watching. I've seen some dropouts or freezes for up to a few seconds which I think *may* be associated with rain or possibly wind or fog(!)? When conditions are right for this, the signal goes down to 40 or 50 briefly. (Is it likely that this is multipath?)

This is what antennaweb shows:

DTV Antenna

* red - uhf WWJ-DT 62.1 CBS DETROIT MI 200° 14.1 44
* red - uhf WTVS-DT 43.1 PBS DETROIT MI 200° 14.1 43
* red - uhf WXYZ-DT 7.1 ABC DETROIT MI 218° 14.1 41
* red - uhf WKBD-DT 50.1 UPN DETROIT MI 230° 15.3 14
* red - uhf WDWB-DT 20.1 WB DETROIT MI 200° 14.1 21
* red - uhf WJBK-DT 2.1 FOX DETROIT MI 210° 13.9 58
* red - uhf WDIV-DT 4.1 NBC DETROIT MI 210° 12.3 45
* red - uhf WADL-DT 39.1 IND MOUNT CLEMENS MI 126° 12.9 39

From what I've read here, I get the impression that:

1. Multipath may be my problem vs. signal "strength".
2. An amp may cause a problem instead of solve it.

I haven't seen much about how directional antennas are and I wonder if I don't have a highly directional one, would one be likely to solve my problem since these stations that I'm interested in are within 30 deg?
(Any recommendations, assuming I can fit it in.)

Is there any easy way to verify the coax and connectors are good? (With ohm meter etc?)

Would it be foolish to try a preamp halfway between the antenna and TV, where I have a coupling for the coax already?
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

From sregner)

1. Probably. But diagnosing reception problems with digital meters is never easy. If you have UHF analog stations broadcasting from the same towers at the same relative power (take digital and multiply by 5 for analog equivalent) then watching them can tell you what the problem is. Does the picture get very snowy? Or do you get moving ghosts? The answer to that question will tell you the answer to your problem. Snow = weak signals. Ghosts = multipath.

2. 30 degrees is not a directional antenna. A directional antenna should have an acceptance angle of less than 10 degrees. Examples include the Channel Master 4228 and the Antennas Direct 91XG. Either of these would probably require a rotor.

3. If you're getting signals that are routinely in the 70s+, your coax is most probably good. If you consistently had problems above or below a certain frequency, things would be different.

4. Foolish? If you've got snow on the analog test in answer #1 above, no. If you've got any ghosting now or when you have issues, yes.

(From cpcat)
You need to get up there and take a picture of the antenna and post it here. At your distance, a CM 4221 should work and has a beamwidth of around 60 degrees. If you're already using something equivalent though, you'll have to go bigger. Sometimes attics can really block the signals. If you can't get the pic at least desribe what it looks like.

Originally posted by JLaamanen

Here's some pics from my attic. Can anybody ID or give opinion?
(Note: My first time posting pics and making my webpage, plus I changed a handful of burned out light bulbs while I had the ladder out! You guys are slave drivers

Here's the UHF, looks like it's not a CM 4221 remember that it's from 1990.
-----------------------------------------------------------------------


Whether it is a CM or not is moot. The design is similar to the 4221. Have you tried an attenuator? If not, go to Rat Shack and buy their cheap variable attenuator and stick it right behind your receiver so you can adjust it while watching the screen. You are so close to the towers that you may have *too much* signal (not to mention reflections). The attenuator will reduce all of them and hopefully just the main signal will get through.

i was just curious if the antenna direct db2 is better then the silver sensor indoors? I live about 45 miles from the stations and want to pull in cbs hd which is 21.6 kw.

sf49 - impossible to say. Each will work better than the other in certain circumstances. Each antenna has its own gain profile with high & low gain areas going around the compass points. These lobes & nulls can be "skinny" or "wide" in shape as well as differing in number. So each accepts and rejects signals a little different from the other. In your living room it is impossible to know beforehand which combination will work best. The best one can do is guess at a good starting point based on anecdotal data, design data and user's experiences. Eventually you find that the SS works well more often than others like Terk. That is not to say that Terk never works, just statistically it is less likely when starting from scratch. The DB2 is a proven double-bowtie design and works well in some places, I'm sure.

At 45 miles it will be tough to pull in a 21.6 kW signal indoors, but anything is possible! All of the major networks in our area are at 600kW or more. I certainly hope that CBS station is planning to boost power soon - what are the call letters?

quarque,

I picked up one of those antenna-u-ators and hooked it up on the DTV input. Was surprised how low I could dial "signal strength" down and maintain pic (at least in a short test, but will do more investigation). What I need now is a channel acting up. What concerns me a little is the report that cable and satellite was having problems w/ "West Wing" when I saw them too. I hope I'm not trying to fix network feed problems. Maybe I should move it to work on the analog input too, hmmmm.

Thanks,
John

In general an outdoor is always better then an indoor antenna. 45 miles you'll need a mid size outdoor for reliable DT reception.

I am now without HD having ditched my RS 15-1880 indoor beastie. I am now looking at either the CM3016 or RS 15-2152 to reach two antenna farms, one about 16 miles away and the other at 34 miles.

As I live in an area susceptible to hurriances I don't want an outdoor mount so would be looking for an attic install. I can accomodate an 80" boom (just) with about 45 degrees of turning radius for adjustments. The two antenna farms are about 100 degrees apart.

My question is about expected attenuation due to the attic root. It is a clay-tile roof with felt underneath then plywood on the inside. I will mount high enough to clear the A/C ducting but still expect some attenuation but don't know how much.

On a similar vein what attenuation would one expect from 50' of RG-6 ?

Any insight from people with similar experience appreciated.

Cheers,
Tony

how does anyone go about stacking 2 uhf antennas? i.e. using a combiner or ? does it serve to boost a signal or just try to gather more signal? i am about 90 air miles from the towers of the stations i would like to try to receive and i can get 1 of them about 65% of the time but it breaks up and one of them about 45% of the time but one i can get almost all the time. i am currently trying 2 different antennas 1: is the winegard i have asked questions about ( dedicated UHF ) and 1: is the radioshack VU90XR. i have also thought about getting the xg91 but haven't quite decided if it's worth it or not! i live in Lehigh Acres,Florida 33936 and the stations are in Miami and West Palm Beach. last weekend i had approximately 13 HDTV channels but now only 2.

any info on the possibility of stacking antennas (if it would help) is greatly appreciated.

no hills or mountains to interfere with reception

At 90 miles, it isn't the hills or mountains that get in the way - it's the earth itself! The earth is curved and for an antenna mounted about 330 meters above average terrain, UHF signals run "aground" at 60 miles.

Whatever signal you are getting is a result of the troposphere helping you out. You're lucky in that Florida often gets a lot of tropospheric help, but it's not the kind of thing you can count on.

Stacking theoretically increases gain by 3db. While that doesn't sound like much, 3db is a doubling of the signal received by the receiver (this will not mean that you get an increase of 50% on your signal strength meter.) Stacking also increases directionality of your antenna, which is useful if multipath is the problem.

In my experience, one really good antenna is the ideal for long-distance reception. But nothing can overcome a bad location or extreme distances. AntennasDirect has a good return policy, so it may be worth a shot. But otherwise, I'd skip the stacking.

(For stacking, you need two identical antennas, connected to a splitter using cables of exactly the same length. If you use coax, you have to make sure the baluns also are "in phase" or you'll cancel the antennas out. For maximum gain, they should be stacked one above the other, at somewhere between 36" and 48".)

Re: Indoor and Attic UHF Signal Attenuation.

I've been doing some searching for information on this subject.

If your house is made of RF shielding material, such as a mylar aluminum "heat shield" or foil backed insulation material or aluminum siding, then the signal leaks in via windows and may be attenuated by 20 dB. People walking in front of the antenna may cause another 3-6 dB of attenuation.

During an on-the-air statistical gathering test of the Brazilian ATSC system, the MEDIAN indoor attenuation was 12.5 dB, which means that some homes have a lot more attenuation to make up for those of more typical tropical open construction.

So far in my search, I haven't seen much information wrt real-world attic attenuation, but I did run across a laboratory test that measured attenuation for basic building materials:
http://fire.nist.gov/bfrlpubs/build97/art123.html

A few germaine measurements:
500 MHz, 10000 MHz
0.4 dB, 2.6 dB, Double thickness, wood planking
0.35 dB, 0.75 dB, Single thickness, 3/4 in Plywood
0.2 dB, 0.8 dB, Single thickness, 1/4 in Glass

It appears that the roofing material attenuation for UHF is about 1 dB for low channels and 2 dB for high channels.
Of course, in a real attic there are metal nailing plates, wood struts and other objects that can perturb the antenna gain pattern and generate multipath reflections.
So the total reduction is probably 2-3 dB.

Re: RG-6 Attenuation.

Depends on the part number.
Belden makes over a dozen different part numbers with attenuation per 100 feet of cable
ranging from 4 to 9 dB for the high UHF channels and 3.5 to 6 for the low UHF channels.
The Quad Shield products tend to be in the middle of this range.
Of course, cable from your local home outlet may be different....

All the more reason to use a preamp, which does several things to improve the overall sensitivity:
1) replaces the HDTV's tuner with the much more sensitive (5-10 dB) preamplifier,
2) overcomes the reduction in sensitivity due to the cable downlead and RF splitters (another 5-10+ dB)
and 3) minimizes the DTV signal degradation due to VSWR reflections (another 2-6 dB).

If signal levels are high enough to overload a preamp, an attenuator may need to be used prior to the preamp, such as is integrated into the R-S model, which should yield a considerable portion of the above improvements.

In document at link below which among other things describes results of 2600 field tests(some indoors, all in U.S.) of ATSC reception : They found typical outdoor to indoor signal attenuation to be in the range of about -9~-13db ... see table 7 in section 5.3 and paragraph immediately below table 7 on page 20 of PDF file at link below :

http://www.atscforum.org/doc/FieldTestReport.pdf

In addition to srenger's excellent info, here is an excellent article on stacking antennas :

http://pages.cthome.net/fmdx/stackant.html

VSWR doesn't cause that much loss. The formula for attenuation due to VSWR is:

K = (VSWR - 1) / (VSWR + 1)

attenuation in dB = 10 log (1 - K^2)

A very high VSWR of 6:1 only causes 3 dB of attenuation. A more typical VSWR
of 2:1 causes 0.5 dB of attenuation.

Ron

i just revisited antennaweb and added my address and info,according to what was found for my location,with the right antenna it's showing that i can receive stations from 68 miles to 84.2 miles away. keep in mind it doesn't say digital,just gives a list of stations that can be received. one of those station ( 84.2 miles away ) i do get the digital feed occassionally.
the other i can get analog only reception.

i went to antennaweb typed in this info

121 highview ave
lehigh acres,fl
33936
no towers
no tall buildings
click on submit
and it returns the info i spoke of

Tony,
Attics take a huge toll on the signal you get. The few that I have measured so far have been in the 20 dB range of attenuation. Those attics are made of standard asphalt shingles, over roofing felt, over plywood type construction. I have not been in an attic like yours.

Attics also cause reflections that the HDTV tuner has to equalize out and there is only so much equalization that is available. So that means there is less equalization available for the 'real world' multipath that is arriving over your house.

Some folks have good luck with the Channel Master CM7777 preamp. Inside the attic it is pretty hard to overload the front end of that particular amp. (Outside it can happen quite easily.) Given the right conditions, preamp will not overload but the output of the amp can overload the HDTV tuner . That is just one of the good reasons for using an attenuator at the receiver.

RG6 cable has a loss of about 4 dB per 50 ft in the UHF band. That 4 dB loss is one of the few planing factors the FCC got right when they made the table of allocations for HDTV.

I've attached a PDF of the measurements I did in my attic. All of the outside antenna gains are referenced to a Scala log-periodic antennas performance. The attic measurements are referenced to each antennas' own outside performance. So if you look at the green lines, the upper one is how the CM4221 compared to the Scala outside. The lower green line is what the attic did to the antenna. The difference between them is the loss that the attic caused.

Bob Chase
KHWB-TV

 

2004-12-11 testing attic antenna performance v03.pdf 129.5986328125k . file

Ron,
You are correct if you only look at attenuation as a factor of 'degradation'. No argument there. You are also right about 2:1 VSWR being typical. In fact, you might even be too generous, as antennas have worse VSWR characteristics than tuners.

VSWR also causes reflections. A tuner with a VSWR of 2:1 will reflect a signal that is -10 dB compared to the original signal back to the antenna. If the antenna also has a VSWR of 2:1, then it will reflect the 'reflection' back at the tuner. Assuming that there is 4 dB of cable loss, the reflection caused by tuner VSWR will arrive back at the tuner about 28 dB down (-28 dB) from the original and a little bit later than the original. To the tuner, it will look like a VERY strong multipath signal and the tuner will expend some of its equalizer on removing it, leaving less equalization available for the real signal.

VSWR reduction is one the reasons that attenuators help HDTV tuners improve reception. A 3 dB pad attenuates the VSWR reflection by 6 dB, a 10 dB pad attenuates the reflection 20 dB, and so on. Many people attribute the affect the attenuator has on reception only to the reduction of strong signals. I see time after time folks writing to say that "The attenuator worked, there must be a really strong signal that was killing me". While it is often really the weak, time delayed, signals that kill reception.

How VSWR affects TV reception is also one of the least understood things in the broadcast industry. See Dr. Charlie Rhodes articles on the TV Technology website for an in depth look HDTV reception. He is a huge proponent of attenuators, preamps, and wide-band AGC in tuners.

Bob Chase
KHWB-TV

Hi,
I've had the Silver Sensor for a few months now and for the most part, its been great. Recently, however, a few channels have started to drop in and out. Namely FOX and NBC and PBS (WTTW where I live). The tuner is having a hard time "latching" onto the signal - sometimes after a few minutes, it'll find it and the strength will go from 40% to 80-90% - but sometimes if just stays at 40-50% and therefore can't lock in.

Funny thing is, up until a few weeks ago, FOX and NBC were the strongest signals (and CBS was weak). Now, I get CBS OTA (at about 80%) and I have the aforementioned FOX/NBC issues!

Even weirder is that I haven't moved my antenna at all from the general area its been at for the last few months (which at the time, I found to be the "sweet spot" in my condo). I've also rescanned many times, manually added the channels, and scooted the antenna a tad to the left/right.

So... question: how can I improve the my signal strength (for FOX/NBC)? I can pick it up at times so I know I can get it, but how can I keep it consistent? Any suggestions? Amp, pre-amp, etc? (btw, I'm sort of new in the antenna world).

I live in CHicago about 5 miles from the towers according to antennaweb.

THANKS!!!

Re. Receive Antenna VSWR Degradation to DTV Receiver Sensitivity
(frequently expressed as an increase in the Noise Figure):

The issue is not the signal loss due to VSWR, but the degradation to the DTV signal (mostly envelope delay) due to delayed reflections up and down a long antenna cable.
Some DTV transmitters reportedly compensate for this degradation by pre-distorting the transmit waveform in accordance to information from a local feedback receiver.
At the receive end, connecting a preamp via a short cable greatly minimizes this not so well known problem.

The issue of DTV signal degradation due to antenna VSWR has been discussed in Doug Lung's TV Technology on-line column:
http://www.tvtechnology.com/features...dl-ieee2.shtml
http://www.tvtechnology.com/features...-receive.shtml
http://www.tvtechnology.com/features...antennas.shtml

A more complete description is found on pg 63+ in the fol. ATSC Report: "Performance Assessment of the ATSC Transmission System, Equipment and Future Directions", Rev. 1.0, 12 April 2001 available from:
http://www.atsc.org/news_information/papers.html

And Dielectric's website has O. Bendov's paper: "On the Validity of the Longley-Rice Propagation Model for HDTV Coverage and Interference Analysis":
http://www.dielectric.com/broadcast/longley-rice.asp


So we should all hope that the antenna manufacturers are trying to reduce VSWR in order to claim that they are especially "For DTV".
Unfortunately, very few of them mention VSWR in their spec sheets (SquareShooter is exception).


A paper presented by Kerry Cozad at Oct04 IEEE Broadcast Technology Society re. DTV antenna VSWR and Gain measurements is cited in the fol., but I have not yet seen it. I would appreciate a copy if anyone has it.
http://www.tvtechnology.com/features...features.shtml


Anyone know of any DTV Antenna VSWR measurements....or NEC simulation results?

Bob: Thanks for the valuable "real world" measurement re attic loss.
I'm surprised as how much more you measured for your attic compared to the statistical numbers found for a large number of lower, indoor locations in the above ATSC Field Test Report.

Could you remark on construction materials, esp roof and proximity of foil backed insulation either in the line of fire or below the antenna as well as any other nearby metal objects?
Also, how did you measure signal strength?

I'm surprised by how well the mast mounted CM4221 4-Bay performed compared to ANY of the presumably higher gain models....and how poorly the CM4248 Yagi performed both outside and in the attic.

And why did the Scala 1469 Log Periodic have 7+ dB less attenuation at mid to high frequencies in the attic than ALL of the other antennas, but was right in the middle of the pack outdoors? Very strange....

An amplifier is never a good idea inside of 10 miles from the transmitters, and rarely a good idea even 20 miles away. You might want to try a variable attenuator (Radio Shack sells one) and see if that makes a difference.

Your location, as I'm sure you know, is less than ideal for today's receiver technology. You probably have plenty of signal strength, but lots of multipath.

I am also thinking of a Channel Master 4228 8-Bay Bowtie UHF Antenna. I entered my information at www.antennaweb.org and it indicated that the channels that I am interested in are either 19.8 or 20.1 miles from me at either 355 or 357 degrees. The antenna will be in the attic above the garage. Do you guys think that this antenna will be adequate without an amplifier or should I just get an amplifier right away? I am thinking of just ordering from www.solidsignal.com Does anyone know if they are a good dealer to buy from?

From Figure 23 in the reference that holl_ands cited:

http://www.atsc.org/news_information...Assessment.pdf

It would appear that a -28 dB echo doesn't have much effect (especially
considering the it would take about 350 feet of feedline to generate a 1
microsecond VSWR induced echo).

Ron

Twenty miles is well within the 4228's capabilities. Of course, if you've followed the attic discussions much, you know that those aren't the best places to put your antenna. Nevertheless, I don't recommend anyone purchase a preamplifier until they've determined that their reception problems are related to weak signal strength rather than multipath.

I haven't personally done business with Solid Signal, but others here have spoken highly of them. You can read independent reviews here:
http://www.resellerratings.com/seller8101.html