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The Official AVS Antenna and Related Hardware Topic! - Page 470

post #14071 of 16082
Quote:
Originally Posted by woodgab View Post

This link is a good read for us folk:


In it, Mr. Putman provides a solution to multipath using two Yagi style antenna's. I didn't even think multipath could be a rural problem until Steve's post above (trees). My dropouts do correlate with wind.

I have a CM 4228 coming and look forward to posting in this sticky. Great idea, Ken!
My sitch:
-5.5 miles from towers at 40 and 51 degrees carrying all desired UHF stations.
-Despite relative short distance a Silver Sensor can't give decent strength on frequencies 56 and 30 (WB, CBS)
-A current question would be what's better: A 150-200ft run of rg6 and a clear line of site, or a 50ft run with the threat of multipath and a less than clear line of site? I have a berm behind my house and could mount the, somewhat omni-directional, CM 4228 high up on a tree.

thanks for the link
post #14072 of 16082
I am looking for some decent feed back on combining two antennas to one down lead.

First my tvfool report.

http://www.tvfool.com/?option=com_wr...60b5ae88bf9131

Now this report is based on an antenna height of 50 feet, and although my antenna is basically 25 feet above ground level, a few of the channels listed in the pink and purple rings come in at 70% signal strength, specially WUNI 29.1 Worcester MA, WBZ 30.1 Boston MA and WHDH 42.1 from Boston MA all come in around 60 % signal strength, so the TVfool is a bit incorrect.

I currently have two four bay home made antennas, one pointed at 288 degrees (west-north-west) for WTIC 31.1 Hartford and the other Hartford CT stations. WTIC comes in at 70 to 80 % signal strength, my weakest station is WVIT 35.1 comes in at 45 to 50 % signal strength.

The other antenna is roughly pointed between 39 degrees and 50 degrees for Boston and Providence R.I.

Each antenna has its own down feed, one is designed for both uhf and vhf, it is 8" whiskers spaced at 9", this points towards the north-east and picks up VHF 12.1 and 13.1 and various UHF stations.

The other antenna is 7" whiskers spaced at 5 1/2", it is mainly for UHF and helps guard against over load from VHF station WEDN 9.1 Norwich, which is located 4 miles away at 271 degrees.

At the moment, I am currently switching between each antennas coax on my indoor signal amplifier.

What I would like to do is design a setup that allows both antennas to be combined together so that all the channels will come in without switching anything.

The only co-channel I would experience is with WTIC 31.1 Hartford CT and WFXT 31.1 Boston MA, the DTV receivers I have are pretty good dealing with two different stations on the same RF frequency, because it lists both WTIC and WFXT in the channel line up after a scan is done, when I press 61, or 25 one station does not show up on the others branded channel number.

Keep in mind WTIC used to be on CH 61 and WFXT used to be on CH 25.

My quest is to set up an antenna distribution system such as an MATV system without the use of multiple receivers and transmitters such as how CATV does it.

I have seen distribution system amplifiers on the web from companies such as SolidSignal and was wondering how well they worked.

The one I would need would only be for UHF and VHF signals, not one that includes Dish network or Direct TV, so those types are not what I would need.

I need one that will combine each antenna without canceling out the other one and perhaps one that isolates the antennas as well, to prevent out-of-phase issues between the antennas.

On the output, I would like to feed at least 3 televisions with minimal signal loss.

Do those distribution amplifiers work? I know combining both antennas using a splitter caused signals at 50% signal strength to drop right out of sight.

I wish not to use any type of A/B switch if it is at all possible to do this another way.

Below is an older image showing both of my antennas, the one on the right now has a reflector, both antennas are currently outdoors on my roof attached to my chimney.

I can add an updated photo of those two antennas tomorrow when it is daylight.

Attachment 223537


Thanks in advance for any suggestions or advice.


Bruce.
LL
post #14073 of 16082
The distribution amps work fine. The problem is that you can rarely combine signals from two such antenna systems without complications.

Using a reversed splitter works sometimes, but, it usually fails.


You could contact someone like Tin Lee to design and build a custom filter-combiner, but it would likely cost more than the rest of your system plus a new TV set.
post #14074 of 16082
Currently, you are stuck with separate antennas & an RF Switch.

RF Combiner Loss is AT LEAST 4 dB...which can not be recovered.
Combining AFTER separate Preamps doesn't overcome this loss, cuz their
internal noise ADDS together, resulting in 3 dB lower SNR.
Two Mast-Mounted Preamps (with separate cables) or one Preamp preceded
by an RF Combiner, CAN overcome most of the downlead and RF Splitter Losses,
which can be quite high, so it's certainly worth doing.

Since you only have ONE strong VHF and ONE strong UHF station, Overload
(Intermodulation Noise) won't be much of a problem (until a second UHF
transmitter comes on-line).
To prevent single channel overload problems, preceed a High Gain Preamp,
such as CM7775 (UHF Only) with a Ch26 single channel filter/attenuator.
Without Ch26 filter, a LOW-GAIN Preamp model must be used, e.g. W-G HDP-269
(UHF + VHF) or W-G AP-4700 (UHF + VHF Bypass). Might also want a Ch9 Filter.

====================================================
Your small 4-Bay (similar to CM4221) and WAY TOO SMALL "Babblin5" 4-Bay are
esp. losing Gain on the lower UHF channels.
Upgrading to a higher Gain model may or may not overcome the Combiner's 4+ dB loss:
http://m4antenna.eastmasonvilleweath...Data/Data.html
http://m4antenna.eastmasonvilleweath...d%20tests.html
http://m4antenna.eastmasonvilleweath...d%20Tests.html

4nec2 Simulation Results:
http://m4antenna.eastmasonvilleweath...%20models.html
http://m4antenna.eastmasonvilleweath...dels%20M8.html
http://imageevent.com/holl_ands/multibay/4bayrefl/m4swp
http://imageevent.com/holl_ands/multibay/compare

Note that these 8-Bay and Super-4-Bay antennas ALSO pick up Hi-VHF, so you
might want to use an inexpensive UVSJ Combiner as a filter/attenuator
(use a 75-ohm terminator on the unused VHF port).

PS: dBi = dBd + 2.15
post #14075 of 16082
Quote:
Originally Posted by holl_ands View Post

wrote: http://m4antenna.eastmasonvilleweath...Data/Data.html

Holl_ands, do you know who the guy is who runs the site ?
post #14076 of 16082
>>> I've never had a situation in which an HLSJ was inadequate
>>> to attenuate FM overload.
>>
>> IIRC the HLSJ provide about 20-22 dB. I used to use 20 dB FM traps,
>> and one helped, but using 2 or more was better. So one HLSJ might
>> not be enough.....
>
> I just tested a garden variety HLSJ with no brand name on it, and it
> attenuated the FM band by 27dB. When Konrad used 20dB FM traps, were
> they the conventional 93-108 Mhz traps, as nearly all were? Those roll
> off between 88 and 93, and so many FM signals will be attenuated much
> less than 20dB by those traps, whereas the HLSJ attenuation is a flat
> over the entire band.

Good point. I have traps marked 88 and some marked 95 MHz. I was probably
using the 95 for that experiment.

Also, there was (probably still is) a strong 88.3 FM that trashed the
audio on a then NTSC ch6. One 88 trap wasn't enough to kill the FM and
two 88 traps killed ch6. The 95 ones didn't help either (not a big
surprise). These were just cheap FM traps, nothing fancy from tinlee or
similar. It wasn't worth pursuing further since ch6 was going away.

Nice to hear that the HLSJ exceeds the specs. I no longer have any
VHF-LO stations that I care about, so I'm using multiple HLSJs to
kill everything below VHF-HI. And UVSJ filters on the UHF antenna
before combining the antennas. And LPF-216 and LPF-700 and ferrite.
post #14077 of 16082
> You might try wrapping the unshielded Winegard amplifier case in
> aluminum foil to see if that additional shielding helps.

Make sure that the foil doesn't make the amp overheat
before leaving it that way long term. Each 10 degree C
rise in temp reduces the expected life of semiconductors
by half.

I've seen interference come in through the power injector
for a preamp.

If you have "common mode" interference, a HLSJ or other
filter will not remove it. That's a job for ferrite.
post #14078 of 16082
Quote:


Make sure that the foil doesn't make the amp overheat
before leaving it that way long term.

Hmm, since the Winegard case is dark colored, the aluminum foil may actually make it run cooler as long as the same ventilation is maintained.
Preamps are low wattage, so not a lot of internal heat is generated.
post #14079 of 16082
Quote:
Originally Posted by holl_ands View Post

To prevent single channel overload problems, preceed a High Gain Preamp,
such as CM7775 (UHF Only) with a Ch26 single channel filter/attenuator.

It appears this CM7775 model is no longer available on most reputable web sites.

One web site has this statement: The Channel Master 7775 is no longer available for purchase.

It has been replaced by the Winegard AP-4800 Pre-Amplifier!!!!


http://www.summitsource.com/product_...oducts_id=6912

Okay so I try looking up that amplifier and see this:

This item is no longer available for purchase.

It has been replaced by the AntennaCraft 10G202 Amplifier!!!!



http://www.summitsource.com/winegard...00-p-4661.html

Then finally I get a product that exists :

http://www.summitsource.com/antennac...02-p-6053.html


Any feed back on this amp?

Bruce.
post #14080 of 16082
Well, the CM-0068 preamp is still available, and has lower UHF noise. And it uses the reliable over-built CM-0747 power unit.

http://www.summitsource.com/channel-...sb-p-5721.html
post #14081 of 16082
>> Make sure that the foil doesn't make the amp overheat
>> before leaving it that way long term.
>
> Hmm, since the Winegard case is dark colored, the aluminum
> foil may actually make it run cooler as long as the same
> ventilation is maintained. Preamps are low wattage, so not
> a lot of internal heat is generated.

I once tried wrapping a preamp in aluminum foil and it
ran significantly warmer to the touch. Your mileage may vary.
post #14082 of 16082
Quote:
Originally Posted by JoeM View Post

Holl_ands, do you know who the guy is who runs the site ?

That is mclapp's website for M2, M4, M8. Here is his latest post on this forum:
http://www.avsforum.com/avs-vb/showt...php?p=19231072
He is also very active on the Canadian forum for OTA & Antenna R&D:
http://www.digitalhome.ca/forum/forumdisplay.php?f=81

He is in New York and I'm in California, so we haven't actually "met", other than on-line.
post #14083 of 16082
Quote:
Originally Posted by MrBruce View Post

The Channel Master 7775 is no longer available for purchase.
It has been replaced by the Winegard AP-4800 Pre-Amplifier!!!!

http://www.summitsource.com/product_...oducts_id=6912

Okay so I try looking up that amplifier and see this:
This item is no longer available for purchase.
It has been replaced by the AntennaCraft 10G202 Amplifier!!!!


http://www.summitsource.com/winegard...00-p-4661.html

Then finally I get a product that exists :
http://www.summitsource.com/antennac...02-p-6053.html

Any feed back on this amp?

Bruce.

Antennacraft doesn't provide any Overload specs, so we have NO CLUE how strong
the signals on the input can be before they start degrading weak signals reception.
I also would not recommend 29 dB Gain for VHF unless you were perhaps 100 miles
from any VHF transmitters (Aussie Outback???)...YIKES!!!!!

W-G AP4800 has 28 dB Gain for UHF and 0 dB Gain (Bypass) for VHF.
Google Product Search shows it being available from numerous sources,
incl. www.solidsignal.com, located in Maine, they may have lower shipping.

==================================================
CM-0068 overload specs are significantly worse than AP4800:
http://imageevent.com/holl_ands/files/ota
See Preamp Comparison Chart - Rev A, which I updated to reflect W-G change
to HDP-269 Max Input Spec. Be sure to read NOTE at bottom re using TVFool
"Receive dBm" levels, including if Digital TV, ADD 7 dB to derive PEAK value.
post #14084 of 16082
A minor detail, but Solid Signal is located in Novi, Michigan, a suburb of Detroit.
post #14085 of 16082
Okay so looking at the TvFool chart, the NMdb is basically the signal quality needed over the noise margin.

So lets say if we were to look at my TvFool report and go down the list and concentrate on the NM, WLNE DT 49.1 is at 2.6 db and the next one down the list is WSBE DT 21.1 at -1.0 db and so on down the list until it reaches WNJB DT 8.1 at -26.1.

So what I am actually attempting to do here is to get the signal to go above 1.0 to overcome the noise ratio, is this correct?

Where would I factor in the power ebm versus the NM?

What I see for my strongest channel is WHPX DT 26.1 at NM=65.4db and power dbm=-25.4. What is meant by the power dbm and why is it at minus 25.4?

Bruce.
post #14086 of 16082
I quote from tvfool at
www.tvfool.com/?option=com_content&task=view&id=57

Quote:


NM(dB)
This is the predicted Noise Margin (NM) of each channel "in the air" at your location, specified in dB. You must add/subtract any gains/losses you get from your antenna, building penetration, amps, cables, splitters, and other factors present in your situation. Hypothetically speaking, you need to end up with an NM value above 0 in order to pick up a station.

Pwr(dBm)
This is the predicted signal power of each channel at your location, specified in dBm. Note that the relationship between NM and Pwr depends on the type of signal being detected. Analog stations require more power than an equivalent digital station to achieve the same level of NM.

Don't confuse NM with SNR (signal-to-noise ratio). The noise margin is the difference, in dB, between the signal in question and the minimum required signal (NM 0 dB). The minimum required signal includes the minimum SNR for that type of transmission which for 8VSB OTA signals is about 15.5 dB to be free of pixelation or picture freeze. TVfool assumes a standard noise level for all locations, but your local noise level at your site might be higher, requiring a stronger signal for reliable reception. This would mean less margin-to-dropout than predicted by measurement of the signal strength alone.

In order to make an estimate of the signal strength delivered to your tuner or preamp by the antenna (in the open air), you add the antenna gain (a plus added to a minus makes the minus less minus) to the dBm value given by tvfool. Most tuners will dropout a weak signal at about -84 dBm, so you need a signal stronger than that to obtain lock, and need a signal even stronger (about -74 dBm, allowing a safety factor of 10 dB) for reliable reception.

And to quote Andy Lee (creator of tvfool.com) from one of his earlier posts:
Quote:


Difference between SNR and NM

SNR is generally defined as the ratio between desired signal power and the power of the noise floor. The minimum required SNR for any communication system depends on the details of its design and signal structure. Modulation type, symbol rate, error correction codes, Turbo codes, Viterbi encoding, and dozens of other design considerations ultimately affect what SNR is needed to make the system work.

For example, ATSC requires a theoretical minimum of about 15 dB SNR in order to get a TV picture. NTSC requires about 27 dB SNR (with analog, it's a very subjective matter to decide what is "watchable", but this is roughly where you get a picture with "some snow").

There are other systems (like GPS) that can work even when the SNR values are negative. These signals have a very high "processing gain" that make it possible to decode it even when it is buried well below the noise floor. The desired signal can actually have less power than the ambient thermal noise and still be used.

NM, on the other hand, is generally defined as the amount of signal relative to the minimum threshold for operation. On a dB scale, the 0 dB point is at the theoretical boundary between working and not working. Positive dB numbers mean the system should work with some margin for error. Negative dB numbers mean the system should not work because the signal level is deficient by that many dB.

If we used SNR to compare ATSC and NTSC, we'd have two different number scales to deal with. We'd have to mentally keep track of the minimum SNR thresholds for each signal type and do a lot of quick math in our heads.

If we use NM to compare ATSC and NTSC, it's a lot easier to tell how well we're doing relative to the minimum operating thresholds. It also reduces some of the confusion caused by the differences in power levels. Many people believed that digital coverage was going to be worse than analog coverage because a lot of transmitters were broadcasting with significantly less power. However, less power does not mean less coverage.

The average person will not know the different operating thresholds for each signal type, so providing numbers for field strength, dBm, SNR, or ERP often leads to increased confusion for some people.

Besides the above quote by Andy from his earlier post, there are also two excellent diagrams showing what happens to a TV signal on its way from the transmitter to your receiver.

Back to MrBruce:
Quote:


What I see for my strongest channel is WHPX DT 26.1 at NM=65.4db and power dbm=-25.4. What is meant by the power dbm and why is it at minus 25.4?

The dBm scale is a power scale. The reference level of 0 dBm is defined as a power of 1 mW (0.274 Vrms across 75 ohms, but the dBm scale is NOT a voltage scale). A signal of 0 dBm doesn't mean no signal, it means a signal that is the same strength as the reference level.

Signals stronger than the reference level have a plus sign (stated or implied). Signals weaker than the reference level have a minus sign. A signal of -25.4 dBm is considered a very strong signal that might overload a preamp.
post #14087 of 16082
I used a commercial RFI Shielding Spray paint on the inner surface of a Blonder-Tongue "home" preamp, and it de-tuned everything so badly that it went in to oscillation.
Had to wire-brush it all out.
post #14088 of 16082
After correcting NM with Antenna Gain & various Losses, what remains is the FADE MARGIN.
Ideally, for long term reliability, you would like to have 10 dB or MORE of Fade Margin
to overcome Multipath Fading, Man-Made Noise, Clutter Loss, seasonal/daily signal
strength variations, etc. On the other hand, in some locations, on some days, signals
can be received when the Fade Margin is somewhat negative...but don't count on it....

Pwr & NM are STATISTICAL averages. Some locations may do significantly better (or worse),
esp. if Tropospheric Scatter propagation conditions are frequently encountered....YMMV....

================================================
If OVERLOAD CALCULATIONS (see signature below) permit, a Mast-Mounted Preamp
can significantly improve overall sensitivity by reducing contribution of post-Preamp
losses (incl TV Tuner Noise Figure): [Loss is reduced by the amount of Preamp Gain.]
https://docs.google.com/spreadsheet/...Hc&hl=en#gid=0
http://www.digitalhome.ca/forum/showthread.php?p=888368
post #14089 of 16082
In my humble opinion, the FCC has really made a mess of things when it comes to over the air broadcasts, makes you think they were in on some kind of a deal with Cable television and dish/direct TV to get people to give up with OTA and purchase their limited services.

Trust me when I say, before the digital transition, an on roof antenna brought in more broadcast channels than dish or cable did and no blackouts on out of market stations.

The quality of HDTV is fantastic, don't get wrong. However it should have been organized and put together so that if a station reached 75 miles away came in with a viewable snow free picture, it should be the case now.

Instead the FCC had TV stations lower their PEP and share frequencies with stations that are well under 200 miles apart.

In my area of Connecticut, the two markets that shared the same RF frequencies was Boston Mass Vs. New York City, Providence R.I. Vs. Philadelphia PA.

Now you have Boston Mass Vs. Hartford CT, Hartford CT Vs. New York City.

What a mess they have created and what it boils down to, is the OTA person gets so frustrated with the pixelization and drop-outs, they end up going back paying for cable or dish again.

Both cable and dish antenna are a joke, they have more premium channels than they do OTA channels and limit the number of same network affiliates, they also require you to rent their equipment by placing most of the HDTV channels on frequencies above 800 Mhz, where most home owned HDTV equipment does not tune to. Cable ready HDTV tuners usually stop at channel 99, cable places them on channels like 700 and above, dish requires their tuners because home entertainment systems are not dish or directTV ready!

What a monopoly this has become!

We used to get all of the Providence R.I, Boston and Connecticut stations here in my area of Connecticut.

Now WTNH 10.1 New Haven CT which used to be on VHF CH 8 is impossible to receive here and it only moved from 180-186 Mhz to 192-198 Mhz, a perfectly viewable station is now a zero signal reading in my area, not even a fluctuation on my RF meter above 0% on a good day when tropo happening.

I am curious how Cable television in my area can carry WCVB 20.1 Boston and WCCT 20.1 Hartford from the same tower and never get co-channel interference.

Both receiving aerials are on the same tower, yet they get no drop-outs or co-channel interference.

Is there anyone out there with a membership to this forum board who is a head-end tech at a cable company have any secrets to share with us?

Oh by the way, here is a picture showing both my 4 bay antennas up on my roof, that one facing you is pointed towards Hartford CT and the one on the left is pointed towards Boston and Rhode Island.

Attachment 223782


I described both antennas in an earlier post, I am just curious about the center frequency for Mclapps 10 inch whiskers and 9 1/2 spacing?

Also I realize having wood as an insulator appears to be a bad idea, so I will be looking for some PVC to attach to the wood and add the whiskers to that, but how much db loss is estimated with wood and what is the primary factor for wood being a poor insulator?

Bruce.
LL
post #14090 of 16082
Quote:
Originally Posted by MrBruce View Post

In my humble opinion, the FCC has really made a mess of things when it comes to over the air broadcasts, makes you think they were in on some kind of a deal with Cable television and dish/direct TV to get people to give up with OTA and purchase their limited services.

Trust me when I say, before the digital transition, an on roof antenna brought in more broadcast channels than dish or cable did and no blackouts on out of market stations.

The quality of HDTV is fantastic, don't get wrong. However it should have been organized and put together so that if a station reached 75 miles away came in with a viewable snow free picture, it should be the case now.

Instead the FCC had TV stations lower their PEP and share frequencies with stations that are well under 200 miles apart.

And now the FCC plans to finish their hatchet job on broadcasters by taking away even more channels and repacking everybody even tighter. There must be money changing hands, since nobody could really be that stupid.
post #14091 of 16082
Quote:
Originally Posted by L David Matheny View Post

...There must be money changing hands, since nobody could really be that stupid.

Didn't FCC's Genachowski used to work for Sprint?
post #14092 of 16082
Quote:
Originally Posted by holl_ands View Post

CM-0068 overload specs are significantly worse than AP4800:.

Someone would have to go back into the archives here to find it, but several years ago, I compared overloads of a similarly spec-ed Channel Master Spartan CM-0064 and the Winegard 23dB version of the 4700/4800 that they had made briefly and that had the same overload specs as their higher and lower gain models and the Channel Master outperformed it decisively.

Found it: http://www.avsforum.com/avs-vb/showp...38&postcount=9

Quote:


I have an off-air antenna targeted at Baltimore and located between Baltimore and Washington,...The strongest signal developed by that antenna are my undesired analog channels 22 and 50 (25dBmV) 26 (24dBmV) and 20 (20dBmV). My undesired digital channels 48 and 50 are around 10dBmV, and everything else is weaker.

I have to recover and process Baltimore channels 38 (-18dBmV) and 40 (-23dBmV) even though there is a strong, Washington channel 39 (+2dBmV off this same antenna) in between them. Now, I can tune unamplified channels 38 and 40 with my Radio Shack Accurian tuner and develop signal "strength" percentages of 80% on one and 75% on the other, but if I preamplify them using any Winegard product - even my AP4727, which is supposed to have the same output capability as the AP4700 and AP4800, but with just 23dB of gain - and then bandpass filter and attenuate the single channel outputs, those channel 38 and 40 signals have been decimated by the amplifier beyond recovery.

Believe it or not, I get better performance from a Channel Master 0064DSB than from the Winegard that has identical, 23dB of UHF gain. Winegard's published overload ratings are a bad joke. Yet even with the 0064DSB, my analog channel 24 (about +4dBmV, coming off the antenna) suffers from some other analog picture sliding across it from left to right when it is amplified along with other analog signals that are a little over 20 dB stronger than it is.

Until we get a better handle on the development of intermodulation byproducts, we are going to be frustrated in a lot of situations in which the rated maximum output of an amplifier is not exceeded yet it makes weak signals worse, because a byproduct that is substantially weaker than the carriers it is derived from can still overwhelm a significantly weaker channel, and often does.
post #14093 of 16082
Quote:


makes you think they were in on some kind of a deal with Cable television and dish/direct TV to get people to give up with OTA and purchase their limited services.

They have an eighty year tradition of doing stuff like that, so why do you expect them to change ?
post #14094 of 16082
Quote:
Originally Posted by MrBruce View Post

......
Trust me when I say, before the digital transition, an on roof antenna brought in more broadcast channels than dish or cable did and no blackouts on out of market stations.
...... However it should have been organized and put together so that if a station reached 75 miles away came in with a viewable snow free picture, it should be the case now.....

Bruce.

The question is, what channels were those stations on BEFORE the transition?

We had to laugh at the FCC's "Loss of Service" maps when they came out, because they all pointed out the 3 low-band VHF stations in Salt Lake as "losing" viewership. What they failed to note was, VHF (especially "low-band") flows in to every nook and cranny...most of the "loss" areas were small canyons and shaded areas that really get nothing else. The more-populated ones were already getting service via translators, so the loss of the VHF direct signal didn't make any huge difference.
Also, with UHF channels, you can't expect reliable service beyond about 30-40 miles, typically (given an antenna height of 1000' at the sending end, and 20-30' at the receiver). That's just the physics of it,,,the curvature of the earth and the (slightly farther) Radio Horizon.
So, much of the "loss" was due to the change from VHF (especially "low-band") to UHF.
The FCC maps really compared apples to oranges, and blamed it on "digital".
post #14095 of 16082
Quote:
Originally Posted by MrBruce View Post

......
I am curious how Cable television in my area can carry WCVB 20.1 Boston and WCCT 20.1 Hartford from the same tower and never get co-channel interference.
Both receiving aerials are on the same tower, yet they get no drop-outs or co-channel interference.
Is there anyone out there with a membership to this forum board who is a head-end tech at a cable company have any secrets to share with us?.....
Bruce.

Looks like the two stations are about 90-degrees from each other at Norwich. There are some pretty elaborate ways to do this, using yagi antennas and other, highly-directional antennas.
It's also possible to use shielding (buildings, etc), by carefully positioning the antennas...and, hoping nobody builds anything close by that would reflect an unwanted signal in to the antenna.

A very directional antenna is the Kathrein-Scala Paraflector:
http://www.kathrein-scala.com/catalog/PR-TV.pdf
Note that it is single-channel, and it's beamwidth is narrowest toward the curved part of the reflector.

Lindsay also makes a full parabolic, single and paired:
http://www.lindsaybroadbandinc.com/P..._Parabolic.pdf

Other antennas. like long Yagi's can be used:
http://www.lindsaybroadbandinc.com/P...UHF_Series.pdf

And, arrays of antennas can be constructed. The spacing between them can be adjusted for nulls toward the "wrong" station:
http://www.tvcinc.com/headend-equipm...hf-quad-array/
post #14096 of 16082
Quote:
Originally Posted by MrBruce View Post

I am curious how Cable television in my area can carry WCVB 20.1 Boston and WCCT 20.1 Hartford from the same tower and never get co-channel interference.

Both receiving aerials are on the same tower, yet they get no drop-outs or co-channel interference.

Not sure about the specifics of your local channels, but ours are fed to Comcast via Fiber, they feed both the SD and HD versions which Comcast rebroadcast. Sometimes the local transmitter can go off air, but the cable feed is good and vice versa. Handling two different antenna positions then becomes no problem.
post #14097 of 16082
Quote:


I described both antennas in an earlier post, I am just curious about the center frequency for Mclapps 10 inch whiskers and 9 1/2 spacing?

Thats going to peak somewhere around channels 40 - 45. But since the gain curve is upward scaling, it helps the lower channels too compared to shorter whiskers.

Quote:


Also I realize having wood as an insulator appears to be a bad idea, so I will be looking for some PVC to attach to the wood and add the whiskers to that, but how much db loss is estimated with wood and what is the primary factor for wood being a poor insulator?

Bruce.

Wood absorbs moisture. Even dry wood could be 6% water. Impure water is a conductor. (distilled 100% pure H2O isnt though)

Youre catching a LOT of wind with those reflectors.
post #14098 of 16082
Quote:
Originally Posted by MrBruce View Post

I am curious how Cable television in my area can carry WCVB 20.1 Boston and WCCT 20.1 Hartford from the same tower and never get co-channel interference.

I agree with rdoac.

Here is the TVfool report for the Metrocast headend.

http://www.tvfool.com/?option=com_wr...60b54a0a2eca0d

To pick up WCVB on channel 20 reliably an antenna would need about 50 db rejection of WCCT on channel 20. While such an antenna can be designed on paper, the implementation is impractical.
post #14099 of 16082
Quote:
Originally Posted by MrBruce View Post

Okay so looking at the TvFool chart, the NMdb is basically the signal quality needed over the noise margin.

So lets say if we were to look at my TvFool report and go down the list and concentrate on the NM, WLNE DT 49.1 is at 2.6 db and the next one down the list is WSBE DT 21.1 at -1.0 db and so on down the list until it reaches WNJB DT 8.1 at -26.1.

So what I am actually attempting to do here is to get the signal to go above 1.0 to overcome the noise ratio, is this correct?

Where would I factor in the power ebm versus the NM?

Bruce.

My last post about Noise Margin had a LOT of words. Maybe a diagram would be better:



Diagram is repeated in attachment in case the link to my image host is broken.

I quote wiki:
Quote:


In communications system engineering, noise margin is the ratio by which the signal exceeds the minimum acceptable amount. It is normally measured in decibels.

In simple words, Noise margin(in circuits) is the amount of noise that a circuit can withstand. Noise margins are generally defined so that positive values ensure proper operation, and negative margins result in compromised operation, or perhaps outright failure.

en.wikipedia.org/wiki/Noise_margin
LL
post #14100 of 16082
Quote:
Originally Posted by Tower Guy View Post

I agree with rdoac.

Here is the TVfool report for the Metrocast headend.

http://www.tvfool.com/?option=com_wr...60b54a0a2eca0d

To pick up WCVB on channel 20 reliably an antenna would need about 50 db rejection of WCCT on channel 20. While such an antenna can be designed on paper, the implementation is impractical.

It is also possible for Cable Headends to simply make arrangements to
use the DirecTV or Dishnet or C-Band feeds.....YIKES...that's WAY too EASY.....
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