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Dad
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chefwong said:
Found this old thread...
http://www.dbstalk.com/showthread.php?t=177724

I've got strong signals. Metro NYC area.....

On a couple channels, it just tends to pixelate every 5 seconds.

HR21 paired with a AM21.
What would be causing it just short of not having a good signal......
Most likely, you are suffering from multipath. Pretty likely in NYC. When you are experiencing this on say channel 7, go to Sat and Ant, and go to Ant Setup and Edit Off Air channels. Go to Signal Meter and step up to ch 7. Watch the tuner sign strengths. If they are bouncing around by more than 1 or 2%, that's multipath.

An example when I had it it would be at 98, then 85, then 96, then 77 etc. If you get that variation, you need to reposition your antenna to avoid the multipath.
 

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chefwong said:
Perfect. The solid shannels were 100% locked.

The 3 offending ones were 100%, then 0 then 100%.
I guess I'll tweak come warmer months..
This is classic multipath or too strong a signal. You dont need 100%, but you cant have bouncing like that.
 

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Dad
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CCarncross said:
This is classic multipath or too strong a signal. You dont need 100%, but you cant have bouncing like that.
Agree, its rare to see 100 then 0 but I have seen it. As you are in NYC near the antennas, could be either too strong or really bad multipath.

Easy to determine.
Go to Radio Shack and buy a simple attenuator. They probably have 10db or 20db in line attenuators. 10 may be enough. Put it in line and see if you can get the signal below 100 on the problem channels. If it is say 90 and then you still have bouncing signals, its multipath.

No doubt NYC is going to be tough to solve. I live 2 miles from some high power tv stations and have had to use a directional antenna facing 90 degrees away from the towers to solve my problem. But on one channel at times I still get some multipath but it is rare.
 

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Legend
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Discussion Starter · #7 ·
Here is something odd.....
While watching SB yesterday, I decided to check 4-1 (OTA channel).

Afterwards, proceed to check signal status as well.
All solid 100%s with no dithering as per previous post to 0.

Do you suppose something was ~fixed~ in the HD firmware that was problamatic in the priors.


No cabling, connector, etc changed.
 

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Legend
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Discussion Starter · #8 ·
Been giving the OTA channel a workout after uncovering a ~fixed~ bug.
It's been solid on all the channels.

Strange no one else PRE HD FW update had similar issues.
 

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This thread is the closest I can find to an issue I'm having with the AM21, so thought I'd post here...

I get acceptable OTA signals - a couple of channels 65-67 and a couple of channels 75-77.

Everything worked fine for several days, then one night I started getting period pixelation (like a few little sparkles every 3 seconds or so). It was borderline unwatchable. Reset the DVR and AM21 and when things came back up everything was fine.

Everything stayed good for a day or two, then same thing happened again. I tried changing the resolutions on the DVR and that didn't have any effect. On a lark, I changed to another OTA channel, and it seemed to take an exceptionally long time to make the channel switch - maybe 15 or 20 seconds. That channel looked fine, and when I switched back to the one that was pixellating... it was fine to. It's like changing the channel reset something in the AM21. So changing the channel fixed it and that was way quicker than reseting everything.
 

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Try rewinding backwards and see if the pixellation reoccurs the second time its playing back the same scenes. If it doesnt, its possibly the DVR's playback system getting behind (to slow to keep up) and not the AM21. If it does reoccur, it could be either either a multipath problem where the decoder in the AM21 is losing lock on the stream due to bit rate errors (try moving the antenna a little), or any number of other things in the DVR.
 

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budaunder said:
This thread is the closest I can find to an issue I'm having with the AM21, so thought I'd post here...

I get acceptable OTA signals - a couple of channels 65-67 and a couple of channels 75-77.

Everything worked fine for several days, then one night I started getting period pixelation (like a few little sparkles every 3 seconds or so). It was borderline unwatchable. Reset the DVR and AM21 and when things came back up everything was fine.

Everything stayed good for a day or two, then same thing happened again. I tried changing the resolutions on the DVR and that didn't have any effect. On a lark, I changed to another OTA channel, and it seemed to take an exceptionally long time to make the channel switch - maybe 15 or 20 seconds. That channel looked fine, and when I switched back to the one that was pixellating... it was fine to. It's like changing the channel reset something in the AM21. So changing the channel fixed it and that was way quicker than reseting everything.
Go into the setup for antenna and look at the signal bars. Do you see a lot of bouncing around of the bars, or are they very stable? If you have a lot of bounce (say more than 3 percentage points), you are watching multi-path, which is very hard on digital broadcasts. It will cause pixellation, and if bad enough, complete loss of signal.

On the AM21, the signal levels (which are NOT measuring strength, but rather signal QUALITY/bit-error-rate variant), should be constant within a very small limit. The farther you depart from this constant signal, the more issues you will have.

In most cases, to solve this, you need a more directional (higher gain/longer boom) antenna, so you will discriminate against the off axis reflection signals. The higher the gain, the narrower the front lobe (beam) of the antenna, so it rejects signals off the sides and back significantly.

I get an absolutely perfect signal (in terms of reliability, at 60% on the signal quality meters, if (and only if), the 60% reading is stable (not bouncing around).
 

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CCarncross said:
budaunder, I really don't find those signal numbers acceptable...I think that anything below a solid 80+ is not really that great, and it cant vary much if any at all...
Since the OP is discussing the AM21, I believe he is referring to the OTA signals - not the satellite signals. I agree that anything below 80 is not acceptable for satellite, but for OTA, you get what you can get. All that matters is that the signal be steady.

I have distant OTA stations that are in the 50s, but very steady, and I never have problems with them. As others have mentioned, multipath can be a major problem. I have one local station where the signal is constantly swinging between 100 and 70, and the picture breaks up every few seconds. Another local station that broadcasts from the same tower and is only one RF frequency different (UHF 48) from the station that is giving me problems (UHF 49) has a steady signal around 90, and I never have problems with the picture on that channel. Multipath with UHF signals can be very perplexing.

In the days of analog television, the symptom of multipath would be ghost images. With digital, multipath can be detected by the signal strengh constantly changing, and the symptom is that the picture freezes or pixellates.

All that matters for OTA is that the signal is steady. Low and steady is better than high and changing.
 

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fleckrj said:
Since the OP is discussing the AM21, I believe he is referring to the OTA signals - not the satellite signals. I agree that anything below 80 is not acceptable for satellite, but for OTA, you get what you can get. All that matters is that the signal be steady.

In the days of analog television, the symptom of multipath would be ghost images. With digital, multipath can be detected by the signal strengh constantly changing, and the symptom is that the picture freezes or pixellates.

All that matters for OTA is that the signal is steady. Low and steady is better than high and changing.
Your post is very similar to mine above, with one minor issue. Multi-path with these boxes is observed by the QUALITY MEASURE (in percent), constantly changing. The signal "strength" is not even being measured by these boxes. Low and steady is most definitely better than high and fluctuating, as you rightly pointed out, but it's important to remember that we are measuring signal quality (a variant of bit-error-rate) and not signal strength (carrer to noise ratio) with these boxes.
 

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An update on another experiment... the "pause trick" did indeed fix the pixellation also. It wasn't a normal pause response - when I hit pause, it kinda hiccuped/flashed and took an extra second or two to freeze the picture. When I rewound and played back the past 30 seconds or so there was no pixellation (even though there was when I was watching it live). When I fast forwarded to the present time, there was no longer any pixellation.

My setup could be ripe for multipath - it's a roof mounted omnidirectional antenna. The signal strength will bounce around a small bit - by two to three points, say from 65 to 68on the channel in question. It's a flat roof with 18 inch parapets and the antenna is only about two feet above the roof floor. I have good clear line of site to the transmitter - literally I can see the tower on a mountain 20 miles away. If I get motiviated I'm going to try and raise the antenna up another couple of feet and see if that makes a difference in the signal meter.
 

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budaunder said:
An update on another experiment... the "pause trick" did indeed fix the pixellation also. It wasn't a normal pause response - when I hit pause, it kinda hiccuped/flashed and took an extra second or two to freeze the picture. When I rewound and played back the past 30 seconds or so there was no pixellation (even though there was when I was watching it live). When I fast forwarded to the present time, there was no longer any pixellation.

My setup could be ripe for multipath - it's a roof mounted omnidirectional antenna. The signal strength will bounce around a small bit - by two to three points, say from 65 to 68on the channel in question. It's a flat roof with 18 inch parapets and the antenna is only about two feet above the roof floor. I have good clear line of site to the transmitter - literally I can see the tower on a mountain 20 miles away. If I get motiviated I'm going to try and raise the antenna up another couple of feet and see if that makes a difference in the signal meter.
If it stays within that 3 point variation (and it doesn't bounce all the time), that is pretty decent and shouldn't cause the problem. However, if you watch it for a longer period of time and all of a sudden it deviates 10 percent or more, then that might correspond to picture breakup.
 
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