Green Pixels Problem

[Mike88]

Every once in a while I get several rows of green pixels at the bottom of the screen when watching a CBS OTA recording. In Chicagoland that is WBBM, 1080i on real channel 12, and it has no sub-channels.

Originally I thought maybe a weak OTA signal might be causing this. I realize digital is supposed to either work or not work, but I don’t know what else could cause this. Perhaps the green pixels were the signal not being strong enough at a certain point in time.

However I recently read somewhere that Dish DVRs might struggle somewhat when recording some OTA content because of their high bitrate signals. IOW the DVR might not be designed for these “excessive” bitrates.

CBS OTA typically uses 80-90 minutes of HDD capacity when recording a 60 minute program, which is about double compared to recording CBS satellite. Due to the high bitrate, does anyone think this may be the cause of the problem?

 

[rocket69]

sounds like low signal or other such as passing plane or hick up at the main station through the broadcast tower and not the ip feed they give cable/sat.

 

[TG2]

not necessarily weak signal, but could infact be corrupted ... there's CRC's and other technological forethought in there for lines and frames of data ... you would hope that its good enough that only a portion of the data might be unrecoverable and the result would be pixelation and that green streak possibly too. I've seen them, and when I captured one it didn't start at the beginning or end of the line, but just before the end of one of them, and it was much like I've seen with bad JPG photographs, in that a "square/rectangulish" area if you broke the line into character boxes.. was partially shaded, and then the solid bits of color.for the rest of that line and the next...

a couple of good examples..
http://www.fortunecity.com/millenium/tulip/655/img/corrupted-org.jpg
nice defined "cut off" .. decompression of the frame happened up to that point and then <blat> so the picture went black

another showing attempts for recovered data, notice before the green area, some of the picture looks like larger "blocks" of data..
http://imageshack.us/photo/my-images/228/cpbild2jq8.jpg/sr=1

 

[Mike88]

not necessarily weak signal, but could infact be corrupted ... there's CRC's and other technological forethought in there for lines and frames of data ... you would hope that its good enough that only a portion of the data might be unrecoverable and the result would be pixelation and that green streak possibly too. I've seen them, and when I captured one it didn't start at the beginning or end of the line, but just before the end of one of them, and it was much like I've seen with bad JPG photographs, in that a "square/rectangulish" area if you broke the line into character boxes.. was partially shaded, and then the solid bits of color.for the rest of that line and the next...

a couple of good examples..
http://www.fortunecity.com/millenium/tulip/655/img/corrupted-org.jpg
nice defined "cut off" .. decompression of the frame happened up to that point and then <blat> so the picture went black

another showing attempts for recovered data, notice before the green area, some of the picture looks like larger "blocks" of data..
ImageShack® - Online Photo and Video Hosting

The first link does not work for me. The second one is sort of what I've experienced. I only had green & it appeared to be just one shade, medium green. The blocky green lines did fluctuate and only lasted a few seconds.

 

[sethwell]

Bypass the DVR and hook your OTA antenna directly to your tv and see if it still shows up. If it does then it's not the dvr. Might help you determine if it is the dvr, tv, or the OTA feed.

Sent from my iPhone using SatelliteGuys

 

[Mike88]

Bypass the DVR and hook your OTA antenna directly to your tv and see if it still shows up. If it does then it's not the dvr. Might help you determine if it is the dvr, tv, or the OTA feed.

Sent from my iPhone using SatelliteGuys

Then I'd have to watch live TV!

I never had the problem until I got Dish. Previously I had Comcast cable & even if I watched live on the TV it was Comcast clear QAM. I never used the OTA antenna until I got Dish. At this point I can't make a fair comparison, other than the HDTV is OK.

What I could do in order to avoid watching commercials is simultaneous record OTA using my DVD recorder. It has an ATSC tuner & down converts to DVD quality. However if the OTA signal is poor I should still get green pixels. If I see a problem while watching a Dish OTA recording I can then go to the same point in time on the DVDR and see what it looks like.

 

[whatchel1]

Every once in a while I get several rows of green pixels at the bottom of the screen when watching a CBS OTA recording. In Chicagoland that is WBBM, 1080i on real channel 12, and it has no sub-channels.

Originally I thought maybe a weak OTA signal might be causing this. I realize digital is supposed to either work or not work, but I don’t know what else could cause this. Perhaps the green pixels were the signal not being strong enough at a certain point in time.

However I recently read somewhere that Dish DVRs might struggle somewhat when recording some OTA content because of their high bitrate signals. IOW the DVR might not be designed for these “excessive” bitrates.

CBS OTA typically uses 80-90 minutes of HDD capacity when recording a 60 minute program, which is about double compared to recording CBS satellite. Due to the high bitrate, does anyone think this may be the cause of the problem?

It's one station only? What type ant are you using? Can tell you it isn't a excessive bit rate problem. Have you checked TV Fool to see if it is coming from an entirely different direction than other channels. If you are comparing the size of sat to OTA then you are comparing apples & oranges so to speak. OTA is MPEG2 and HD sat is MPEG4, so size will be much larger for OTA. BTW which unit do you have?

 

[kwindrem]

Every once in a while I get several rows of green pixels at the bottom of the screen when watching a CBS OTA recording. In Chicagoland that is WBBM, 1080i on real channel 12, and it has no sub-channels.

Originally I thought maybe a weak OTA signal might be causing this. I realize digital is supposed to either work or not work, but I don’t know what else could cause this. Perhaps the green pixels were the signal not being strong enough at a certain point in time.

However I recently read somewhere that Dish DVRs might struggle somewhat when recording some OTA content because of their high bitrate signals. IOW the DVR might not be designed for these “excessive” bitrates.

CBS OTA typically uses 80-90 minutes of HDD capacity when recording a 60 minute program, which is about double compared to recording CBS satellite. Due to the high bitrate, does anyone think this may be the cause of the problem?

I doubt DVR bandwidth is the issue. There's enough bandwidth on/off the drive for 4 records and 2 playbacks.

If the green pixels are in blocks or a row of 8 or 16 lines, then it's an issue before the decoder. Satellite dropout is one possibility but you normally get a freeze rather than blocks/streaks of green.

If the green you are seeing is in one line streaks, it's most likely on the output side of the decoder, e.g., the HDMI connection to your TV. You might try replugging the connection or a different cable. It's more likely to see this on all channels/signals but there are many things (image composition, ...) that can add up to a link failure if you have a marginal connection.

 

[sethwell]

Then I'd have to watch live TV!

I never had the problem until I got Dish. Previously I had Comcast cable & even if I watched live on the TV it was Comcast clear QAM. I never used the OTA antenna until I got Dish. At this point I can't make a fair comparison, other than the HDTV is OK.

What I could do in order to avoid watching commercials is simultaneous record OTA using my DVD recorder. It has an ATSC tuner & down converts to DVD quality. However if the OTA signal is poor I should still get green pixels. If I see a problem while watching a Dish OTA recording I can then go to the same point in time on the DVDR and see what it looks like.

I was trying to help you determine if your DVR is the problem. If you hook your OTA antenna up to your tv and you still have the green lines then it is either your tv or the signal coming into it.

Sent from my iPhone using SatelliteGuys

 

[Mike88]

I have a 722k DVR, and the antenna is in the attic. I know that’s not the best place but I’m in a townhouse & don’t know what it would take to get approval to put it on the roof. That being said my signal strength is good, at least when I’m checking it. If it drops in the middle of recording I would have no way of knowing this.

I’d have to freeze frame the image when this happens, but it definitely is not one line streaks. It covers about the bottom inch of screen on a 42” HDTV and the rows are jaggedy. IOW the upper portion may not extend the full width.

It’s definitely not satellite dropout because it only happens on OTA CBS, which comes from the same direction as the other major stations - the Sears/Willis Tower.

 

[TG2]

most likely just Digital Transmission or Reception Error .. its only effecting a portion of the signal for a split second in time ... difference in transmission from TV as opposed to Satellite is the encryption and compression on the sat signal ... thus a transmission/reception glitch can have more effect

 

[sethwell]

It’s definitely not satellite dropout because it only happens on OTA CBS, which comes from the same direction as the other major stations - the Sears/Willis Tower.

which is why i say to bypass your dvr and hook it directly to your tv to test to see if it still happens on your tv. if it does, then you could hook it up to another tv to see if it does this on both tvs. if both tv's have the problem then it is the signal coming from the antenna. after that you might contact the station you are having problems with and ask an engineer if they are having any signal problems on thier end. if they are good then you should look at your antenna and cableling as well as any connectors or amps between the antenna and your set.

now if it doesn't show up after that then you might need a new MT2 cartridge from dish. you may have a faulty one. now that i think about it, you might take the cartridge out and re-install it. i recall a thread about doing that to solve some OTA problems.

 

[Mike88]

which is why i say to bypass your dvr and hook it directly to your tv to test to see if it still happens on your tv. if it does, then you could hook it up to another tv to see if it does this on both tvs. if both tv's have the problem then it is the signal coming from the antenna. after that you might contact the station you are having problems with and ask an engineer if they are having any signal problems on thier end. if they are good then you should look at your antenna and cableling as well as any connectors or amps between the antenna and your set.

now if it doesn't show up after that then you might need a new MT2 cartridge from dish. you may have a faulty one. now that i think about it, you might take the cartridge out and re-install it. i recall a thread about doing that to solve some OTA problems.

It only happens once in awhile. IOW I could be watching live TV with commercials for weeks. And I have only one TV. This is why I thought about duplicating the recording on the DVDR. If the Dish DVR shows the problem I can check the DVDR for that same time & see if anything happened. If the DVDR is good that would mean the OTA system is good.

 

[whatchel1]

Maybe you should try splitting the signal between both the TV & the MTA2. If when there is a glich and you are watching live check and see if the TV has it.

 

[Mike88]

Maybe you should try splitting the signal between both the TV & the MTA2. If when there is a glich and you are watching live check and see if the TV has it.

The glitch lasts for only a few seconds at a time. It may happen a couple times during a 1 hr program or not at all. I've been recording some CBS OTA and some sat for several months and have not seen it lately. Maybe the summer/warmer weather's atmospheric conditions make a difference. I don't know. I'll swap more CBS over to the OTA tuner & see what happens.

 

[KKlare]

At least one of the Chicago stations is on low VHF. The low-band VHF (2-6) is usually a problem (I remember it being channel 3--now why would they use that?) If your antenna does not have long enough (like up to 5' across) elements for that channel you would have a weak signal. Conversely most channels are now UHF and require the short elements (a few inches) for those frequencies.

You may be getting multi-path interference, especially with a lot of buildings near the line of sight or with a lack of LOS, especially the VHF channels (2-13). As recommended above, see AntennaWeb for the direction and strengths of the channels. You may have better view of some channels than the others. You should have better luck with the Dish locals. Luck,
-Ken

 

[Mike88]

At least one of the Chicago stations is on low VHF. The low-band VHF (2-6) is usually a problem (I remember it being channel 3--now why would they use that?) If your antenna does not have long enough (like up to 5' across) elements for that channel you would have a weak signal. Conversely most channels are now UHF and require the short elements (a few inches) for those frequencies.

You may be getting multi-path interference, especially with a lot of buildings near the line of sight or with a lack of LOS, especially the VHF channels (2-13). As recommended above, see AntennaWeb for the direction and strengths of the channels. You may have better view of some channels than the others. You should have better luck with the Dish locals. Luck,
-Ken

CBS used to be channel 3 but they changed to channel 12 quite some time ago.

 

[TG2]

At least one of the Chicago stations is on low VHF. The low-band VHF (2-6) is usually a problem (I remember it being channel 3--now why would they use that?)

and now you also know why VCR's came with ch3 or ch4 output... (although it probably should have come with more than that, but the VCR makers were always cheap bastards for the most part)

 

[KKlare]

They choose low channels to use cheaper components for the modulator. With OTA only, adjacent channels are not allowed in any area so a choice of 3 or 4 was sufficient to have a channel that would not interfere (much) with pickup of the locals. Note channels 4-5 6-7 13-uhf are not adjacent, so no beating against the other, i.e., 2-4, 5-6, 7-13 are grouped. An aside, broadcast OTA channel 37 (could be 38) is never assigned because it is reserved for radio astronomy--possibly hydrogen alpha line.
-Ken