TV stations are making another digital transition, very slowly, from the ATSC 1 standard we've been using for over 20 years to a more robust standard called ATSC 3.
This time around, the FCC isn't giving stations a second RF channel during the transition, the way they did for analog and ATSC 1 digital.
Instead, they're leaving it up to the marketplace, depending on station groups to cooperate to introduce ATSC 3 service in each market.
So in Greenville/Spartanburg/Asheville, Sinclair offered up the WMYA transmitter, "channel 40" but now on RF 35, as the ATSC3 "lighthouse" to kick off service. WYFF, WSPA, WLOS, WHNS and WMYA itself all send their .1 streams to the WMYA transmitter to be broadcast in ATSC3. If you had a newer TV in that market with ATSC3 reception, you'd get all of those stations that way (and probably with a much better signal on the NC side for WLOS!)
In return, WYFF, WSPA and WHNS use part of their ATSC1 signals to carry the various WMYA subchannels for viewers with older receivers. If you're watching 40.1 in the market, you're actually seeing a signal coming from the WYFF transmitter. 40.2 rides on WSPA, and so on.
The ATSC3 standard can carry higher definition pictures and more interactive content, as well as data casting. And it works better with on-channel boosters and mobile reception, so in a market like this one, you could eventually have a bunch of smaller shared transmitter sites everywhere from Asheville down to Anderson instead of trying to serve everyone with one big site that still doesn't work.
The idea is that someday when there are enough ATSC3 tuners out there, the shared channels will flip - one signal in the market will carry "lighthouse" ATSC1 channels for anyone who hasn't converted, and everything else will be ATSC3. But that's going very slowly right now. There have been some missteps with getting receivers into the marketplace, and best guess right now is that there are maybe 5 percent of viewers seeing ATSC3, if even that.