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-   -   Pixelation on subchannels (http://www.videokarma.org/showthread.php?t=267554)

lnx64 08-12-2016 04:45 PM

Pixelation on subchannels
 
I'm having a really weird issue, and I hope this is the right spot to ask this. So, I built my own home made UHF antenna, and mounted it in the attic. It's fed to a 10dB amplifier, and the amp is only 1ft away from the antenna. The coax came with the house, and just goes straight from the amp, right down the wall and to the TV. I'd say maybe 40ft of RG59/U. My father won't let me change it to RG-6.

I did what I could, from the cable jack, I fed it straight into my SDR, and there's literally no multipath distortion whatsoever on the signal, and it's strong too! But the TV it's plugged into, one with a built in digital tuner, all main channels seem to work with minor distortion, but occasional pixelation, but the subchannels, they pixelate so much worse, even if the main channel it's off, is perfect.

What's also weird, is the TV will even show 3/4 - 4/4 bars for the channel, while it's pixelating. One channel, oddly will go from 4/4 straight to 1/4 (or 0/4). I don't get it, it's one thing for me to understand a minor swing in quality, but the major swings too? The major swings are coming from 1 channel, and all subchannels and main do go out. But on the minor swings, that's all around the board.

I have another TV, which is going through a splitter for two bedrooms, which are also off the amp (so 10dB going to -3.5dB loss, not counting coax loss), and get this, the digital stream DTA on it, hardly ever pixelates, it works perfectly fine!

I would think the TV plugged straight into the amp would be the one getting the best signal.

lnx64 08-12-2016 05:10 PM

2 Attachment(s)
Well, I stand corrected, it affects main channels too, even on other TV's, and they all swing the same way. I captured a pic showing the difference, just a second apart.

I'm so much at a loss. I never had issues like this with analog.

WISCOJIM 08-12-2016 07:03 PM

Quote:

Originally Posted by lnx64 (Post 3168313)
there's literally no multipath distortion whatsoever on the signal,

How was this determined?

Edit: I guess this was a function of your SDR?

.

Electronic M 08-12-2016 07:04 PM

If the amp is not a low noise DTV type, that can screw with reception. You can have tons of signal, but if it has noise your scotched.

vts1134 08-12-2016 08:14 PM

Two notes:

1- Replace your RG59. When I moved into my house the only thing that was run was RG 59. I put an antenna in the attic and connected it to my tuner in the basement via the RG 59 and received seven channels at best. I lived with that for a few months after which I fished RG6. Doing nothing but replacing that wire, I went from seven to over 30 channels

2- How old is the DTV tuner you are using?

old_tv_nut 08-12-2016 08:32 PM

This may be a classic case of overload - try putting the set(s) that have problems on the splitter output. If that improves it, replace your 10 dB amp with a lower gain one or put in an attenuator right after the amp.

lnx64 08-13-2016 08:07 AM

Quote:

Originally Posted by WISCOJIM (Post 3168317)
How was this determined?

Edit: I guess this was a function of your SDR?

.

I look at the spectrum analyzer on it, and looked at where two channels began and ended (we have two stations literally next to each other on frequency), and there was no overlay, nice and clean. I also checked on FM radio, and compared to where the HD radio sidebands were, they were literally clean and perfect.

I then also transmitted a low power analog TV channel and looked for ghosting, no matter where the antenna was positioned, and nope, no ghosting, which would normally be a sign of multipath.

lnx64 08-13-2016 08:09 AM

Quote:

Originally Posted by Electronic M (Post 3168318)
If the amp is not a low noise DTV type, that can screw with reception. You can have tons of signal, but if it has noise your scotched.

The amp is indeed for digital TV, but who knows, it could be noisy. It seems to actually only mostly be just two channels though, and to be honest, I'm starting to notice me more end getting pissed at the reception, right when a storm is moving in. I may have just completely forgot about the clouds causing problems with the reception on certain frequencies.

EDIT: Nope, sunny and blue skies this morning, still intermittently breaks up. Turns out my neighbors though have the same issue, on their cheap flat antennas they hang on the walls, on the same channel.

It makes no sense, this is WKMG, they have their towers close by WESH, and WESH comes in perfect. So does WFTV. :/ I don't get why WKMG is so hard to get.

lnx64 08-13-2016 09:06 AM

Ok this honestly sucks. This is how WKMG comes in on the SDR, as compared to a good station that never breaks up, WFTV.

WKMG: http://i.imgur.com/mHfTT3p.png
WFTV: http://i.imgur.com/IKs8pnH.jpg

Well without a doubt, this explains why I am having issues with WKMG. It's just so weak. I tried this straight off the amp and the antenna, same results. :/

EDIT: Fixed WKMG link, I was looking at the wrong frequency.

lnx64 08-13-2016 09:09 PM

Well I may have fudged this one up.

The ground wire to the splitter outside the house and to the amp, was not properly grounded. So far since properly grounding it (and hopefully has nothing to do with being night time now), the signal has been FAR better.

http://i.imgur.com/f0EBZ9Y.jpg

EDIT: You know, a lot of websites say grounding an attic antenna is useless, but so far, it's proven to help a lot. I've been watching antenna TV, without one single breakup yet.

earlyfilm 08-26-2016 12:54 PM

Quote:

Originally Posted by lnx64 (Post 3168313)
. . . . UHF antenna . . . . . . mounted . . . in the attic. It's fed to a 10dB amplifier, and the amp is only 1ft away from the antenna.

INX64,

I hope your fix has stayed fixed.

Just a little FYI for anyone looking at this thread in the future with a similar problem.

To feed the power to the booster, you probably have a DC block on the feed line below where the power supply connects or combined with the power supply. These can cause random problems like you described. The first thing I would check is adding a ground on set side of the blocker, and if no improvement, then remove that and it try on the antenna side of that block or booster power supply.

On the old analog system, these issues usually, but not always, showed up as ghosts.

James

lnx64 08-26-2016 02:13 PM

It didn't, but I did find the other part I was missing. Terminators on the unused ports of the amp. When I capped them with proper 75 ohm terminators, it's been working great for the past 10 days without so much as a single hiccup.

http://i.imgur.com/y68qZ8I.jpg

And now WKMG is even more stronger: http://i.imgur.com/UUzdWcQ.jpg

I hadn't realized just how important terminating unused outputs were, I thought it'd only affect 50MHz under, which is the return frequency of the amp if it was used on cable service, but apparently it had more of an impact.

old_tv_nut 08-26-2016 11:46 PM

Now you've got me shaking my head. You didn't say you were using a cable amp! Do you know what the noise figure is? Apparently it doesn't matter now, but really you should be using a low noise figure amplifier specifically designed as an antenna booster, which I assumed. Since you didn't mention it has multiple outputs, no one could have suggested terminating them.

People, when asking for help, you really have to give a complete description of your setup!

Anyway, glad you have it fixed, but I think it could have happened much faster with an accurate description of what you have.

lnx64 08-26-2016 11:57 PM

Quote:

Originally Posted by old_tv_nut (Post 3168982)
Now you've got me shaking my head. You didn't say you were using a cable amp! Do you know what the noise figure is? Apparently it doesn't matter now, but really you should be using a low noise figure amplifier specifically designed as an antenna booster, which I assumed. Since you didn't mention it has multiple outputs, no one could have suggested terminating them.

People, when asking for help, you really have to give a complete description of your setup!

Anyway, glad you have it fixed, but I think it could have happened much faster with an accurate description of what you have.

Complete EDIT: Well the noise figures are not at all what I expected. I must have downloaded the wrong PDF!! The noise figure for the amp I'm using is 4.50 dB. The channel master I was comparing it to, a distribution amp, is less than 2 dB. I was using this amp because it was given to me from a friend who worked in cable. He said it'd work because RF is RF. And I swear I looked up these specs, but I must have download the wrong PDF somewhere.

I am so sorry, I swear I didn't intend to have the wrong information or mislead. Based on what I got, these amps were identical, 1 in, 4 outputs.

Electronic M 08-27-2016 07:58 AM

Quote:

Originally Posted by old_tv_nut (Post 3168982)
Now you've got me shaking my head. You didn't say you were using a cable amp! Do you know what the noise figure is? Apparently it doesn't matter now, but really you should be using a low noise figure amplifier specifically designed as an antenna booster, which I assumed. Since you didn't mention it has multiple outputs, no one could have suggested terminating them.

People, when asking for help, you really have to give a complete description of your setup!

Anyway, glad you have it fixed, but I think it could have happened much faster with an accurate description of what you have.

You never read my post (#4), did you? I asked him if he was using a low noise amp meant for DTV and told him if he was not it could be his problem...


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