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Old 7-Jan-2012, 4:05 PM   #1
ChrisAntennahead
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Cool STRANGE: WEDW 49(Bridgeport PBS) Frozen green/pink picture at 90-100%

The above situation has just started happening yesterday, Friday. Also yesterday channel 21 WLIW(Long Island PBS) signal strength dropped from a usable steady 50-60% down to 10-20%.

BACKGROUND:

My Location: 35miles NE of NYC, 20miles ESE of Bridgeport CT.
Setup: Antennacraft HBU-55 on SW corner of house handling NY Metro, combined with Antennacraft DB8 on NE corner handling greater Bridgeport.

TVF resume for my location: http://www.tvfool.com/?option=com_wr...7fb9eea020a99f

DETAILS:
Above setup has for the full month it has been up pulled in the following:
-All major NY Metro(2.1-13.1 plus 21.1 WLIW and 31.1-4 iOnTV)
-All Spanish Channels
-The following "fringers": WGCN 17(Religious), WSAH 43(Bridgeport), WNJB 58(NJ), and WMBC 63.

Yesterday afternoon, I tune in WEDW 49(PBS Bridgeport), the screen is frozen with bands of green and pink on the bottom and intermittent audio. Signal strength is still where it's always at - between 90-100%. Simultaneously, WLIW 21(PBS Long Island) signal strength dropped to practically unusable. LIW has since slowly recovered to it's "usual" strength(50-60%).

Intermezzo: I have checked all connections and positions of antennae, all tight and normal, no damage to outside or inside RG6. Weather, calm and clear low to mid 40s F.

This morning(Saturday), EDW 49 was also visible for about a half hour between 8 and 9am, but soon froze back up and this time signal strength went at times down to 0%.

I must emphasize: All other stations mentioned above are reporting normally per my location and per TV Fool. The issue affects only PBS stations, and as of now only WEDW 49 Bridgeport. Hopefully this will head off any suggestions here of "equipment issues".

Thanks for any suggestions you can give me as to the channel 49 dilemma.

Signed,

PBS/NPR Addict
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Old 8-Jan-2012, 3:09 AM   #2
Electron
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Tv antennas and Tv reception

http://forum.tvfool.com/showthread.php?t=2930
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Old 8-Jan-2012, 3:22 AM   #3
GroundUrMast
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How are the two antennas combined? (Reversed splitter, UVSJ, Jointenna...)


What happens when you connect just the DB-8 directly to the CM-7000 STB?
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Old 9-Jan-2012, 3:15 PM   #4
ChrisAntennahead
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Originally Posted by GroundUrMast View Post
How are the two antennas combined? (Reversed splitter, UVSJ, Jointenna...)


What happens when you connect just the DB-8 directly to the CM-7000 STB?
Reverse splitter.

I have not experimented with connecting just one antenna or the other since as stated above no other channels were affected by this sudden phenomenon. Everything is aimed where it should be and all connects are tight. Weather past 4 days has been mostly calm & clear, mid 40s.

Again, setup as I described has worked well for over a month now, since beg. of December. On Friday Jan 6, channel 49 displayed what other sources have described to me as "overload" or multipath reflectivity conditions.

As of this post, both PBS channels are back to relative normal. We'll wait and see what happens next.

-Chris
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Old 9-Jan-2012, 6:55 PM   #5
Dave Loudin
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Each antenna you have retains some sensitivity to stations "from behind," so your NYC antenna is picking up some small amount of signal from Bridgeport and vice versa. Apparently, under normal circumstances, there aren't enough "other market" signals in each antenna to cause problems. Normally, we do not recommend combining antennas the way you have because it is hard to predict the outcome.

The issue is how well in phase the signals combine. There are two sources of phase delay in your setup. Focussing on the Bridgeport direction, the signals from that direction arrive at the HBU-55 later than the DB-8. Those signals then have to travel back down the coax to the reverse splitter, adding more delay. (The reverse applies to the NYC signals, where they arrive later at the DB-8.)

The degree of phase difference between the signals at the splitter depends on frequency (as frequency increases, wavelength decreases - so a fixed physical distance is a different amount of wavelengths at RF 49 than at RF 42, for example.) So, for some channels, signals from the two antennas will add in phase (good!) and, for other channels, signals from the two antennas will add out of phase (bad!).

Again, under normal circumstances, you seem to be OK. However, when propagation conditions change (and they will from time to time), the NYC antenna is now getting enough signal strength to cause problems to the Bridgeport channels. Note that WEDW is the strongest station from the Bridgeport direction, so the likelihood of getting some signal in the HBU-55 is greater than for others. It also means that the spacing between your two antennas probably leads to destructive signal combinations at the splitter.

The same argument in reverse could be made for WLIW. Remember that the effects, positive or negative, are frequency-dependent in this scenario. The only way to test for sure is to remove one antenna from the splitter and replace it with a terminator.
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Old 9-Jan-2012, 7:11 PM   #6
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Combining two dissimilar antennas with a reversed splitter is not always successful. The common experience is that some signals are improved and one or more, and in some cases all, are less reliable. This I believe is due to the combined antenna array being more susceptible to multipath and signals combining out of phase an average of 50% of the time based on the random relationship between antenna spacing and cable lengths. Because each signal source is traveling a different path and is a unique span of frequencies, the performance of the combined antenna array is different for each channel. Your experience is exceptional in positive sense, but does not prove to me that it can not be improved on or that it does not have fault(s) which will appear intermittently to the viewer.

In my 30+ years of paid trouble shooting, I have been humbled on several occasions after having closed my mind to one or more possible causes of trouble that I was attempting to resolve. It gets even more challenging to keep an open mind when there are multiple faults contributing to the same symptom(s).

By connecting just one antenna I was hoping to obtain evidence that the problem was with the station, or, local to the receive antenna array. But, with symptoms no longer present, this test would not provide much if any conclusive information.

You're certainly free to dismiss any and all suggestions of how to diagnose or trouble shoot.

*** Hi Dave you posted a bit before me... sounds like we're one the same page though. Cheers ***
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Last edited by GroundUrMast; 9-Jan-2012 at 8:27 PM. Reason: Ack. DL ... not wanting to step on his post.
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Old 9-Jan-2012, 7:32 PM   #7
ChrisAntennahead
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Quote:
Originally Posted by Dave Loudin View Post
Each antenna you have retains some sensitivity to stations "from behind," so your NYC antenna is picking up some small amount of signal from Bridgeport and vice versa. Apparently, under normal circumstances, there aren't enough "other market" signals in each antenna to cause problems. Normally, we do not recommend combining antennas the way you have because it is hard to predict the outcome.

The issue is how well in phase the signals combine. There are two sources of phase delay in your setup. Focussing on the Bridgeport direction, the signals from that direction arrive at the HBU-55 later than the DB-8. Those signals then have to travel back down the coax to the reverse splitter, adding more delay. (The reverse applies to the NYC signals, where they arrive later at the DB-8.)

The degree of phase difference between the signals at the splitter depends on frequency (as frequency increases, wavelength decreases - so a fixed physical distance is a different amount of wavelengths at RF 49 than at RF 42, for example.) So, for some channels, signals from the two antennas will add in phase (good!) and, for other channels, signals from the two antennas will add out of phase (bad!).

Again, under normal circumstances, you seem to be OK. However, when propagation conditions change (and they will from time to time), the NYC antenna is now getting enough signal strength to cause problems to the Bridgeport channels. Note that WEDW is the strongest station from the Bridgeport direction, so the likelihood of getting some signal in the HBU-55 is greater than for others. It also means that the spacing between your two antennas probably leads to destructive signal combinations at the splitter.

The same argument in reverse could be made for WLIW. Remember that the effects, positive or negative, are frequency-dependent in this scenario. The only way to test for sure is to remove one antenna from the splitter and replace it with a terminator.
Actually my antennae are spaced quite a bit apart - one is on the roof aiming southwest, and the other(the DB8) is in the front yard, facing east-northeast, on top of an 8ft pole. LOL! The setup has worked fine for me actually, and I think if the two were within 10 ft of each other at the same altitude I'd be in real trouble.

I can share with you a little history: The AntennaCraft did stand alone for about 1 week before I put the DB8 in the front yard. The only differences then were that WEDW 49 barely peaked at 30% in strength, WSAH 43 10%, and everything else(NY Metro & Spanish) was about the same.

The marriage of the HBU555 and DB8 has now lasted 1 month, and Friday's weirdness with the two PBS channels(21 and 49) was the first such weirdness and hopefully the last.
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Old 9-Jan-2012, 7:50 PM   #8
ChrisAntennahead
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Quote:
Originally Posted by GroundUrMast View Post
Combining two dissimilar antennas with a reversed splitter is not always successful. The common experience is that some signals are improved and one or more, and in some cases all, are less reliable. This I believe is due to the combined antenna array being more susceptible to multipath and signals combining out of phase an average of 50% of the time based on the random relationship between antenna spacing and cable lengths. Because each signal source is traveling a different path and is a unique span of frequencies, the performance of the combined antenna array is different for each channel. Your experience is exceptional in positive sense, but does not prove to me that it can not be improved on or that it does not have fault(s) which will appear intermittently to the viewer.

In my 30+ years of payed trouble shooting, I have been humbled on several occasions after having closed my mind to one or more possible causes of trouble that I was attempting to resolve. It gets even more challenging to keep an open mind when there are multiple faults contributing to the same symptom(s).

By connecting just one antenna I was hoping to obtain evidence that the problem was with the station, or, local to the receive antenna array. But, with symptoms no longer present, this test would not provide much if any conclusive information.

You're certainly free to dismiss any and all suggestions of how to diagnose or trouble shoot.

*** Hi Dave you posted a bit before me... sounds like we're one the same page though. Cheers ***
Part of my troubleshooting technique as of late is a good dose of "wait n' see". And so I waited until Saturday(Jan 7th) and sure enough both PBSers(21 WLIW and 49WEDW) returned to normal. During the phenomenon no other channels(from NY or Bridgeport directions) were effected.

I'd like to think, in a humorous sense, that some intern at EDW pressed a wrong button and somehow screwed up something, and that it took some time & doing before someone with seniority caught and corrected it. Problem is there is no way(on the weekends at least) to contact the station engineer or PD directly to report a problem.

I have also been told that a 90-100% signal strength but frozen green/pink pixellated picture and intermittent = severe multipath reflection(is that source correct?), so I guess whatever was causing this has moved on.

-Chris
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Old 9-Jan-2012, 8:20 PM   #9
Dave Loudin
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That's GUM's and my point. Your multipath comes from using two antennas. It does matter how far apart the antennas are, but only in the sense of what channels might be affected. So long as the HBU-55 picks up some WEDW, it has the chance to cause problems no matter where it is installed.
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Old 9-Jan-2012, 8:40 PM   #10
ChrisAntennahead
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Originally Posted by Dave Loudin View Post
That's GUM's and my point. Your multipath comes from using two antennas. It does matter how far apart the antennas are, but only in the sense of what channels might be affected. So long as the HBU-55 picks up some WEDW, it has the chance to cause problems no matter where it is installed.
Understood. I just hope that the 12 hours that my phenomena persisted are the last 12 hours of it that I see. It has not happened before or since. I personally cannot blame my setup for something that reared its head for such a brief span of time, that's all.

Have I just been lucky? Given all you and Ground Your Mast have said so far, I guess so! LOL! What I do need to ask, since combining antennae is probably going to become more common in the digital OTA environment, is what is the correct way to do what i'm doing?

#1. Do the lengths of RG6 from both of my antennas need to be the same, even though the DB8 is just outside the room where the TV is located?

#2. Should I be using something other than just a reverse-split method to combine the antennae?

#3. Should I be using something to limit what frequencies either antenna is capable of picking up - I.E. confine the DB8 to channels over, say 30?

These are steps I may be willing to take for the sake of all concerned partie- err - antennas!

-Chris

Last edited by ChrisAntennahead; 9-Jan-2012 at 8:40 PM. Reason: spelling
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Old 9-Jan-2012, 8:59 PM   #11
Dave Loudin
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Lucky? Yes, but over time you will see how often this will be a true problem. You can convince yourself that our theory (and that's all we can offer) is correct the next time it happens. I hope you won't have to test it, though!

Matching lengths of RG-6 won't eliminate the problem, just move it to a different channel (well, that actually might be a solution!) The antennas are still physically separated, so one signal path to the combiner will always be longer than the other.

There is no way to guarantee constructive combination of separate antennas that cover the same frequency band. There are special combiners that combine UHF frequencies from one port with VHF frequencies on another port and there is a special device, called a JoinTenna that can insert one channel from one antenna into the wideband feed of another.

The most reliable way to feed the signals from two antennas where their frequency ranges overlap is to NOT combine them. Run separate cables to an A/B switch by the TV. Like having to use a rotor, this has operational disadvantages for recording programs.
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Old 9-Jan-2012, 9:09 PM   #12
ChrisAntennahead
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Originally Posted by Dave Loudin View Post
Lucky? Yes, but over time you will see how often this will be a true problem. You can convince yourself that our theory (and that's all we can offer) is correct the next time it happens. I hope you won't have to test it, though!

Matching lengths of RG-6 won't eliminate the problem, just move it to a different channel (well, that actually might be a solution!) The antennas are still physically separated, so one signal path to the combiner will always be longer than the other.

There is no way to guarantee constructive combination of separate antennas that cover the same frequency band. There are special combiners that combine UHF frequencies from one port with VHF frequencies on another port and there is a special device, called a JoinTenna that can insert one channel from one antenna into the wideband feed of another.

The most reliable way to feed the signals from two antennas where their frequency ranges overlap is to NOT combine them. Run separate cables to an A/B switch by the TV. Like having to use a rotor, this has operational disadvantages for recording programs.
I did need a UVSJ combiner at my apartment where the DB8 handled UHF and a dipol handled VHF-Hi, so I'm familiar with that type of combiner.

I'm also wondering if, based upon what i read in those links, if my antennas were closer together(on same or adjacent masts) would some of the phasing issues be resolved - or just shifted around on the spectrum. This is ineresting!
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Old 9-Jan-2012, 9:49 PM   #13
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Quote:
Understood. I just hope that the 12 hours that my phenomena persisted are the last 12 hours of it that I see. It has not happened before or since. I personally cannot blame my setup for something that reared its head for such a brief span of time, that's all.
All I would suggest is, be on guard against assumptions.

Quote:
Have I just been lucky?
Quite possibly.


Quote:
#1. Do the lengths of RG6 from both of my antennas need to be the same, even though the DB8 is just outside the room where the TV is located?
Changing coax length would likely 'fix' one problem at the expense of causing trouble for other channels.

Quote:
#2. Should I be using something other than just a reverse-split method to combine the antennae?
Excellent question. There are more effective and reliable methods worth consideration.

Quote:
#3. Should I be using something to limit what frequencies either antenna is capable of picking up - I.E. confine the DB8 to channels over, say 30?
You and I are not likely to be able to afford the commercial grade equipment used in CATV head-ends. But you can be sure, the owner of a CATV head-end does not spend money without reason. It's common for a CATV operator to demodulate each signal source, analog or digital. Then they use the base-band video and audio to modulate a locally generated RF carrier which can be combined with the other RF signals in their system. This gives them comprehensive control over virtually all aspects of the signal.

Though CATV has displaced many, MATV operators still exist (apartment, hotel and hospital antenna systems for example). These systems don't have a large base of paying subscribers so they are usually limited to RF filtering techniques. Products from companies like tinlee.com may be pricey for you or I, but they can often provide the level of filtering needed to limit undesired signal from a second antenna.

In the consumer grade (price range) market, Channel Master has limited filter options. And there are some other methods: http://forum.tvfool.com/showthread.php?t=2882 & http://forum.tvfool.com/showthread.php?t=820
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