OTA channel misassignment. HELP!

[tigerdriver]

I reported in my post yesterday that CBS-HD had disappeared (channel 7, freq 18). T'is still true...BUT, the mystery deepens. Today, I found CBS on channel 18. The signal is clear; unfortunately, the guide information still shows it as channel 7. (Is it just coincidental that the channel number is remapped to the frequency? Hmmm.)


Since neither Antenaweb nor AVS reports anyone broadcasting on channel 18, I believe that the HD Tivo must have its head wedged somehow. I've tried: (1) a power-off reboot; (2) clearing (then rescanning) the channel mapping in Settings-Channels-Off Air Channels. All to no avail. CBS always shows up on channel 18 instead of Channel 7.


Thanks.

[JimSpence]

I believe that this is a problem with your local station. They send out what is called PSIP which tells the receiver to map the actual frequency from 18 to what you are used to see as 7.

[tigerdriver]

I believe that this is a problem with your local station. They send out what is called PSIP which tells the receiver to map the actual frequency from 18 to what you are used to see as 7.

Aha! Thanks. I just scanned a technical white paper on PSIP. Surely it can't be legal to spontaneoulsy remap yourself into the FCC-owned spectrum? Also, one of the benefits of PSIP is to "maintain the user's tuning paradigm." So, wouldn't fixing this be super prioirty for the engineering department? It's lasted for over 24 hrs now.

Also, doesn't the PSIP contain the guide info as well (or does OAT come from D* by satellite)? If so, wouldn't that be showing up on channel 18?

[tbb1226]

HD TiVo ignores any guide data that might be in the broadcast PSIP data (which, if I'm not mistaken, is not mandatory or consistently provided).

The "remapping" only occurs inside your receiver. The signal is broadcast on channel 18, and your receiver gives it to you on a "virtual" channel 7.

I suggest contacting the station's engineering department to ask if they're aware of the issue, and when it might be resolved.

[TyroneShoes]

HD TiVo ignores any guide data that might be in the broadcast PSIP data (which, if I'm not mistaken, is not mandatory or consistently provided).

The "remapping" only occurs inside your receiver. The signal is broadcast on channel 18, and your receiver gives it to you on a "virtual" channel 7.

I suggest contacting the station's engineering department to ask if they're aware of the issue, and when it might be resolved.
A good suggestion. But, speaking from experience, this is the kind of problem that frequently does not get fixed over a weekend. The higher-level engineers usually don't work weekends. I would try a rescan as the first step.

I have seen it happen where the PSIP generator burps and puts the mapping on a completely random channel, but losing the mapping altogether is a much more common occurence. That may be what's going on here, or there may be something inconsistent in the TMS info, or the local STB may simply have a corrupted lookup table necesitating a rescan.

PSIP mapping isn't mandatory, but broadcasters are motivated to help your tuner find the physical channel, so it is a priority.

Tivo ignores the guide info within PSIP because it is not a standalone ATSC tuner. Being instead a hybrid that includes a method of acquiring TMS info from the sat for all sat channels, Tivo has opted to get the information that way for all channels, including OTA.

"Remapping" actually occurs at the TV station, where metadata is included in PSIP that tells the tuner, including those in the HR10, what virtual channel to display when tuning the physical channel (or tells the tuner to go to the physical channel when a user enters the virtual number). The TV station always broadcasts only on the physical channel, so there is no FCC violation involved if the virtual number gets dropped or changed somehow. But if the TMS info is inconsistent with that, the HR10 could get confused.

But PSIP problems at the station is a much more common occurence. The net effect is that if the PSIP mapping changes, or if your STB somehow loses the lookup table it creates during original scan, that tuning to the virtual channel does nothing but confuse the tuner. A rescan tells it the secret handshake once again (I.E., "BTW, I found 7.1 on 18.1 during the scan", for instance) and the lookup table is updated so that it can once again find the physical channel. Otherwise, when you ask for the virtual channel, it not only doesn't know what physical channel to go to, but it also doesn't know where to get the information telling it where the physical channel actually is, which is why you need an original scan in the first place, so that a local lookup table can be created so that the STB knows where to go the next time.

The moral of that story is to do a rescan if a channel is missing, but that brings a caveat that if other channels are not broadcasting at that time, they will come up missing on the rescan, so avoid doing this during off hours (at least until 2-17-2009).

[tigerdriver]

TyroneShoes, <great name/handle, by the way>

Thanks for the technical info. The first thing I tried was a clear/rescan on the HD Tivo. It still got the station on its UHF frequency 18. Then I plugged it directly into my TV and got the same results.

Even though yesterday was Sunday, on a lark I called the station anyway. The girl that answered said that she would leave a message for engineering. While composing the message (and I'm not making this up), she asked me how to spell "UHF."

Anyhow, the station is back at 7 this morning. And, FWIW, I didn't have to do a rescan on the HD Tivo.

..
Joe

[phox_mulder]

Being in TV as I am, I know that the PSIP computer is not one that is checked on a regular basis.
It usually sits covered in dust until someone calls the station and complains, at which time it gets rebooted and all is well for another couple weeks.


phox

[tigerdriver]

Being in TV as I am, I know that the PSIP computer is not one that is checked on a regular basis.
It usually sits covered in dust until someone calls the station and complains, at which time it gets rebooted and all is well for another couple weeks.



Suspicion confirmed!

..
Joe