Sleuthing Digital TV Signal Problems

[Ben Zonia]

The other day, I was watching WDIV 4/Physical 32, and it was frequently breaking up off air. I checked with a small portable with just a bowtie, and it was solid. I looked up WDIV on rabbit ears with Longley Rice, and there is a slight terrain hole next to a creek/drain, not far away from where I was, in the AUX facility, lower HAAT, different pattern, and higher ERP, so I suspect they were on AUX facilities. If this was analog on Physical Channel 4, you wouldn't even have known it, unless you were way out in the fringe areas.

Anyone else know of situations like this?

[km1125]

For about a week or so I was having that kind of problem with Channel 2 a couple months ago. Not sure if they were on an AUX or just running low power, but nothing had changed on my end and the problem went away.

[Ben Zonia]

It used to be if you knew somebody at the stations, they would tell you if something like that was going on and why. Now they are likely forbidden to tell anything like that, for fear that advertisers would freak out and ask for discounts, etc. It's not like everyone is watching off air though. One FM was down between 30 and 40 dB from normal on my Technics Tuner signal readout, and I called a friend who worked there with an old First Phone and told him my suspicion that they were running the exciter directly into the antenna, and he said that was "probably" it.

[k8jd]

recently , while watching a network local signal thru our Comcast cable, I have seen digital video signal breaking up. (Pixelating) quite often, No way to tell if the on-air signals were also breaking up or it was in the cable system.
I am thinking of adding an antenna and a switch to select air or cable , just because of that. (My curiosity)

[k8jd]

It used to be if you knew somebody at the stations, they would tell you ..... I called a friend who worked there with an old First Phone and told him my suspicion that they were running the exciter directly into the antenna, and he said that was "probably" it.

Yes back in the 60's and 70's , when I worked in BC engineering, The 2nd or 1st FCC Phone licenses were gold. I had the 1st !

It has been a while since FCC commercial licenses have been discounted.
When I was in two way radio repair work, I had to get recertified thru a testing orginazation that gave exams in state of the art electronics. THEN I had to take Mororola's exams geared to products.
The broadcast industry also had N.A.B recertifications, I heard !!

[SolarMax]

recently , while watching a network local signal thru our Comcast cable, I have seen digital video signal breaking up. (Pixelating) quite often, No way to tell if the on-air signals were also breaking up or it was in the cable system.
I am thinking of adding an antenna and a switch to select air or cable , just because of that. (My curiosity)

WDIV via Xfinity had some problems at my location a few times last week.
Pic and audio complete freeze, for a good minute or more. Happened a number of times, have not seen a repeat so far this week. Had also seen some breakup and tiling ahead of the freezeup.
Over the Air was OK so it was not a transmission or Hub thing.
I've noted this earlier, it is really annoying that the Xfinity feeds of all the local broadcasters are more delayed than ever from OTA.
WDIV is the worst, it seems. There is about a TWO MINUTE delay. If you see WDIV's lower right corner time stamp, and look at a correctly-set clock, you will see how far behind it is.

[km1125]

Comcast (Xfinity) picks up most of the local broadcasters via fiber rather then off-air. They do it for a couple reasons. One to eliminate any off-air interference (even temporary) from local noise sources. The other is to allow a different set of commercials to be inserted. Much of that processing is done at the station, and they just send a different (but similar) feed to Comcast via the fiber. Theoretically, they could actually send a higher-definition (or just less compressed) feed to Comcast, but none do.

[tapeisrolling]

Question.... If Comcast gets local feeds via fiber, why the delay I've seen up to 30 sec. between OTA and cable Hi-def?

[km1125]

Question.... If Comcast gets local feeds via fiber, why the delay I've seen up to 30 sec. between OTA and cable Hi-def?

There is actually more delay in the fiber than getting the signal off air (VP+.68 vs maybe .98+), but not anywhere near enough to cause a 30 second delay. Not sure what's causing that. The station might be sending out a delayed feed (for who knows what reason, but one could have to do with that "extra" commercial insertion) and Comcast does a LITTLE processing once they receive it (to combine/incorporate with other feeds into a common QAM transport stream).

However, that's just assuming you're viewing the channel on Comcast via their "real-time" QAM channels. They're migrating away from those to streaming all video via IP over DOCSIS, so if that's how you're receiving it then there would be a LOT more processing happening to prepare it for the IP stream. That could definitely explain a 30 second (or more) delay.