gregg75 said:
WANN 32 in Atlanta that has all the sub channels has suddenly moved to channel 29. Wikipedia
says 29 is the physical channel and 32 is their virtual channel.
Do any of you tech people on here know why they have suddenly moved to channel 29? Are
they in the process of upgrading channel 32? How are stations able to flip flop like that?
THANKS
(I apologize for the length of this post.....)
WANN broadcasts an analog signal on channel 32, and a digital signal on channel 29. Until last summer, Atlanta's larger stations did something similar. WGCL broadcast analog on channel 46 and digital on channel 19; WSB on analog channel 2 and digital channel 39; etc...
These stations also transmit a datastream -- a "Virtual Channel Table" -- that tells your TV what channel to tell you the station is broadcasting on. WSB broadcasts on channel 39 but tells you they're broadcasting on channel 2. Until recently, WANN was broadcasting on channel 29 but telling you they were on channel 32. etc., etc., etc...
The Virtual Channel Table is also responsible for handling subchannel numbers & names. Here in Nashville, WTVF carries CBS programming on channel 5.1, a local talk channel on 5.2, and ThisTV on 5.3. The Virtual Channel Table is responsible for keeping track of the .1, .2, and .3 designations and the names of those subchannels.
(the purpose? Threefold. For one, WSB-TV has been "channel 2" for 60 years. Forcing them to change their name to "channel 39" would be like forcing McDonalds to change their name to "BurgerMax" - it would throw out decades of brand-building.
For another, WSB-TV actually has four transmitters (and has applied for a fifth) on different frequencies. Without the Virtual Channel Table, the channel you'd select to watch WSB would depend on whether you were in Atlanta, Gainesville, Athens, Rome, or Newnan. With the Table, WSB-TV is *always* channel 2.
Finally, many stations changed digital frequencies during the transition process. Without the Virtual Channel Table, PBS channel 8 would have been channel 8, then channel 12, then channel 8 again. Even more confusing transitions happened in Los Angeles and Chicago, among other places.)
It seems WANN has stopped broadcasting the Virtual Channel Table. They stopped telling your TV to tell you they're channel 32. According to the DTV standard, WANN shouldn't work at all now. However, most TV sets aren't that picky. If they don't see a Virtual Channel Table, they'll make one up. They'll show the physical channel -- in WANN's case, channel 29 -- and the MPEG "program number" -- which is usually .3 for the first subchannel. If you're receiving, on channel 29.3, the same thing that used to be on 32.1, you can reasonably assume WANN is not broadcasting a Virtual Channel Table, and your TV is making one up instead.
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WANN's frequency has not changed to 32. (they do have a permit to change frequency, but to 50, not 32. They have not yet implemented this change -- they're still on 29.)
For full-power stations, FCC regulations require transmission of a proper Virtual Channel Table. Dropping the table & switching from 32 to 29 like WANN has would not be permitted. Violations are not unheardof.
I'm not entirely certain it's required for low-power stations like WANN. Many of the regulations that apply to full-power stations also apply to low-power stations, but some don't.
