BobRoss said:
Even though most digital TV channels differ from the old analog channel assignments, digital TV signals embed "virtual channel" data in their signals. Digital TVs and converter boxes get the virtual channel data, and convert it back. So, for the case of WSYR-DT, the signal is broadcast and received on channels 17.1 and 17.2, but most people don't know it's really channel 17. Thanks to the virtual channel data, viewers can access WSYR-DT by punching the more "familiar" numbers (9.1 and 9.2) into their remotes instead.
This idea that virtual channels 9.1 and 9.2, when broadcast over RF channel 17, are "really" 17.1 and 17.2 is a common misconception, but it's wrong.
What's being broadcast over RF channel 17 is a 19.39 Mb/second data stream configured according to some fairly complex standards that are set by the ATSC (Advanced TV Systems Committee) and incorporated into FCC rules by extension.
To grossly simplify: within the RF channel there are multiple programming streams that are carried. Some are pure data, some are video and audio, some can be audio-only. For whatever reason, and I honestly don't know the reason, most stations - but not all of them - carry their main program ("9.1," in WSYR's case) as program stream 3, with the additional subchannels in sequence after that...so 9.2 is probably actually being carried as program stream 4.
In there with all that data is a conversion table that tells the receiver how to display each stream - so that when you punch in "9.1" on your tuner, it's tuning to RF channel 17, program stream 3.
But there's no requirement, at least none that I can see, that makes that particular relationship official. So "9.1" could just as easily be program stream 5, or 6, or 23. But it's not "really" 17.1, and it's not really right to say it's "17.3," either, since that confuses the idea of virtual subchannels with the reality of multiple program streams on a single RF channel.
(Some tuners - Sony TVs, for instance - can tune the program stream number directly, so I can punch in "28.3" on my TV here in Rochester and get WUHF's 31.1 channel, which is transmitted as program 3 on RF channel 28. This can allow reception of "hidden" channels for which no virtual channel is transmitted, like "16.7" here in Rochester, which is an audio stream on WXXI-TV that backhauls radio programming to two of our WXXI radio services, WRUR-FM in Rochester and WXXY in Houghton.)
As for the legal ID requirements, the current wording of the FCC rules is actually the opposite of what you've posted here. It reads:
DTV stations, or DAB Stations, choosing to include the station's channel number in the station identification must use the station's major channel number.
"Major channel number," in this context, refers to an ATSC standard (that has the force of FCC rules) that specifies the first part of the virtual channel number. In general, the "major channel number" - the 2 in WKTV's 2.1, for instance - must be the old analog channel number, assuming the station in question existed in the analog era. For stations that signed on as digital - WSKG's relay in Corning, WSKA, for instance - the major channel number is usually the RF channel number, unless the station is using an RF channel that was previously occupied by an analog station in the market. If someone were to fire up a new signal on RF channel 9 in Syracuse, for instance, they'd actually have to use virtual "17.x" as their major channel number.
(Here, too, there are a handful of exceptions: licensees controlling more than one station in a market can choose to use the same major channel number across multiple RF streams. If WNED in Buffalo still owned WNEQ, it could put 17.1 and 17.2 on the WNED transmitter and 17.3 and 17.4 on the WNEQ transmitter, rather than having the WNEQ channels be 23.1 and 23.2, for instance.)
If WSYR's news opens still read "WSYR-DT 17 Syracuse," that's not a proper legal ID for two reasons: first, because the rules say that the "major channel number" that must be used is "9" - and second, because the callsign on the station's license is
not "WSYR-DT."
When the DTV transition took place in June 2009, the FCC reverted all digital TV stations' callsigns back to their previous "-TV" suffixes (or lack of any suffix, in the case of stations like WTVH and WSYT), unless they specifically requested to retain the "-DT" suffix. None of the stations in the Syracuse market asked to keep "-DT."