Question: Sub-channels have interference and color wash - not a reception issue

reybo

DTVUSA Rookie
#1
We use a roof antenna to get PBS, ABC, CBS & NBC in Charlottesville, VA.

Since they digitized, all the stations have a main and 1 or 2 sub channels. All the main channels come in with a great picture, but the subs have interference and color wash. This includes WVIR, one of the most powerful stations in the state whose tower is located 10 miles LOS. So this is not a reception issue.

Anyone know what's going on, and if there's a cure for this? The TV is a Samsung LN-S4096D but a smaller, newer TV in our guest apartment with a similar roof antenna behaves the same.

Appreciate any insight.
 

MrPogi

Moderator, , Webmaster of Cache Free TV
Staff member
#2
Primary channels tend to be HD (720p, 1080i) while subchannels tend to be lower resolution SD (480i) - I suspect that this is why your subchannels appear to be of lower quality.
 

MrPogi

Moderator, , Webmaster of Cache Free TV
Staff member
#4
No, this is the way Digital TV works. You see, digital TV can only support a maximum of 2 HD subchannels without seriously degrading picture quality. I have several locally that run two 720p subchannels, and one also runs a third 480i SD channel - although the quality of that third channel suffers a bit. So broadcasters must walk a fine line between picture quality and content choices. Some broadcasters are happy to broadcast a single, uncompressed 1080i HD channel, while others try to squeeze more choices into their allotment of spectrum.

This makes owning a TV station more profitable by taking full advantage of their bandwidth. For example, Fox and ABC both broadcast HD in 720p. Most local affiliates choose to run an additional one or two 480i SD subchannels. Most of these channels (AntennaTV, Cozi, MeTV, RetroTV, etc) broadcast classic TV shows that were originally broadcast and recorded in analog SD - even lower video quality than digital SD. It would make no sense to broadcast this content in HD.

Some stations have taken this a step further and broadcast up to 20 subchannels - for example, KAXT in San Francisco KAXT-CD SAN FRANCISCO-SANJOSE, CA has 12 video channels and 8 audio channels. It is mostly ethnic programming. Sure, the video quality suffers - but if KAXT did not broadcast these subchannels in low quality, they wouldn't be seen at all. The channel's goal is to serve multiple under served populations who would have no access to these channels otherwise.

Given the choice, most broadcasters would prefer to broadcast in HD, but it's a fact of physics that there is only so much radio spectrum available - and that's after the FCC took away channels 51-69 from TV in the 2009 digital transition. Cell phone companies and the FCC are still trying to take more of it from TV broadcasters so we can all watch cat videos on you-tube on our little 4" cell phone screens.
 
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#5
We use a roof antenna to get PBS, ABC, CBS & NBC in Charlottesville, VA.

Since they digitized, all the stations have a main and 1 or 2 sub channels. All the main channels come in with a great picture, but the subs have interference and color wash. This includes WVIR, one of the most powerful stations in the state whose tower is located 10 miles LOS. So this is not a reception issue.
Can you describe what you mean by "interference"? Since the transition, "interference" has been pixelation (parts of the screen blocking out to single colors) or the video or audio cutting completely out. It's an all or nothing proposition. If the video or audio cuts out, it's a reception problem by definition. If you just feel the picture is less well defined, or "washed out" then it's probably the subchannel resolution.

On WVIR, Wikipedia gives the following information:
29.1 1080i 16:9 Main WVIR-TV programming / NBC
29.2 480i NBC 29 Weather Plus
29.3 720p The CW Plus

So the resolutions are definitely different on the subchannels. Have you tried different aspect ratios in the TV menu?

I don't know if you were alive when everyone got TV with an antenna, but the worst digital picture is much better than the best analog channels used to be.

Rick
 

reybo

DTVUSA Rookie
#6
<font color="blue">"I don't know if you were alive when everyone got TV with an antenna, but the worst digital picture is much better than the best analog channels used to be."</font>

I've been watching TV since 1948 and can't say I agree with that. IMO 480i is worse than any local channel on antenna, and 720p is about equal.

This set has no settings for aspect ratio I can find. It does have a signal enhancer control for each channel, set high by default and still that way. Changing it reduces the picture quality.

Is it possible to find a TV that can boost 480i picture quality to acceptable?
 
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#7
Rickideemus said:
...the worst digital picture is much better than the best analog channels used to be.
I've been watching TV since 1948 and can't say I agree with that. IMO 480i is worse than any local channel on antenna, and 720p is about equal.
Are we talking about the same thing?? I'm talking about analog -- e.g. from the 90's. You know -- static, ghosts, snow, fading, crackling, horizontal out of control, vertical gone batty? There's a whole generation of kids who don't know what the opening monologue in "The Outer Limits" was about: "We control the vertical. We control the horizontal..."

Bottom line is, unless there's a problem with your TV, you're getting exactly the picture they sent from the transmitter.

This set has no settings for aspect ratio I can find. It does have a signal enhancer control for each channel, set high by default and still that way. Changing it reduces the picture quality.
I found a copy of the user manual online. There are all kinds of settings that affect picture quality. The aspect ratio would change with the P.MODE button. They say to press it repeatedly until you're satisfied. There's a low noise amplifier (LNA) switch for each channel. You probably want that OFF for a station 10 miles away. There's a "home mode" as opposed to some kind of showcase mode. You can tweak the individual colors, contrast... all kinds of stuff. You might want to start with the factory defaults. It tells you how to do that too.

http://downloadcenter.samsung.com/content/UM/201105/20110502111839569/BN68-01047F-00-110502.pdf

Rick
 

MrPogi

Moderator, , Webmaster of Cache Free TV
Staff member
#8
If you have the showroom mode selected instead of the "home" setting, it will be much brighter and have more contrast - both of which will degrade SD.
 

reybo

DTVUSA Rookie
#9
This week we installed a new roof antenna, a 1 HD Stacker Antenna VHF/UHF/FM/ Digital HDTV from Denny's Antenna Service. . Big.

First thing we noticed was that the very powerful WVIR with its antenna about 12 miles line-of-sight SE was less satisfactory than it had been when we had a simple 3' Channel Master. There were vertical flutter lines 1/3 and 2/3 thirds in from the left margin. Before I had a chance to cut the power boost to WVIR, that settled down.

The TV seems to have adapted itself to the new antenna. Reception on Ch 6 WTVR has always been iffy, being 65 or so miles SE. When the station switched to digital, its reliable coverage dropped. As did it's tall tower, which went from 1138 ft. to 843.

We tested reception on Ch. 6 right away. No viewable signal. But within an hour it did come in, and has been reliable ever since.

A website history says WTVR re-broadcasts here in Charlottesville but we have seen no evidence of a local transmission. Two PBS channels echo here, one from Richmond, one from Harrisonburg.
 
#10
This week we installed a new roof antenna, a 1 HD Stacker Antenna VHF/UHF/FM/ Digital HDTV from Denny's Antenna Service. . Big.
Congratulations! Has this resolved your problem with interference + color wash on sub-channels?

First thing we noticed was that the very powerful WVIR with its antenna about 12 miles line-of-sight SE was less satisfactory than it had been when we had a simple 3' Channel Master. There were vertical flutter lines 1/3 and 2/3 thirds in from the left margin. Before I had a chance to cut the power boost to WVIR, that settled down.
Did Denny advise you to use an amplifier on such a strong signal? Sounds like you overloaded your tuner.

The TV seems to have adapted itself to the new antenna. Reception on Ch 6 WTVR has always been iffy, being 65 or so miles SE. When the station switched to digital, its reliable coverage dropped. As did it's tall tower, which went from 1138 ft. to 843. We tested reception on Ch. 6 right away. No viewable signal. But within an hour it did come in, and has been reliable ever since.
Very nice! It also has some terrain in the way, apparently. I did a TV Fool report to a zip code in Charlottesville, and WTVR comes up as a 1edge station (not line-of-sight). We could tell you more if you did a TV Fool report by going here and entering your exact address and antenna height. Copy the link that appears toward the top of the page and share it with us here. I'd really be curious to know just how deep in the weeds that signal is, to get an idea of the power of the HD stacker. Also curious to know if the signal disappears when you take out the amp.

A website history says WTVR re-broadcasts here in Charlottesville but we have seen no evidence of a local transmission.
Maybe there were re-broadcasts in the past, but the FCC database reports WTVR has no retransmitters.

Rick
 
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