That was a photo caption, but the article gave a bit more detail further down:
As constructed, in addition to a transmitter and ATSC 3.0 encoder/exciter, there’s also a large combiner/filter network to allow multiple TV carriers to share the broadband antenna.
“We keep talking about these sites as a trial test, but we’re actually building them out to go commercial,” said Starke. “It isn’t going to be build, test, and then tear down. They will eventually go commercial. Depending on ERP or antenna input power, each could handle up to possibly 10 to 12 stations.”
He observed the initial DFW SFN trial calls for the airing of programming from Cunningham Communication’s KTXD-TV outlet (RF Ch. 46) and UniMás’s KSTR-DT (RF Ch. 48). (Sinclair has no broadcast properties in the DFW market). Starke noted that since both stations fall above the latest TV broadcast spectrum upper bound, they will be moving to lower channels (RF Ch. 34 & 23) as the nationwide repack initiative reaches the DFW market. (Interestingly, there’s another television operation mixed into the broadband antenna shared by the KTXD-TV and KSTR-DT SFN transmitters, and this one—Ch. 56 (722-728 MHz)—will not be moving as it’s owned by Dish Network, which secured this slot in the earlier 700 MHz spectrum auction.)
Those are currently ATSC 1.0 channels (well, except of course RF 56, which the article said is owned by Dish although I don't know what they're doing with it - the article called it a "television operation" but nothing more specific) and AFAIK
those channels have never gone off the air, even briefly.
I didn't find the article entirely clear, but the impression I got from the quote above was that the combiner in the photo (and presumably similar equipment at the other SFN sites) would be used to combine those signals so they can all share one antenna when KTXD and KSTR convert to ATSC 3.0 "for real." (That would also imply that KTXD and KSTR will convert to ATSC 3.0 before
repacking; hence the need to tune the combiner to RF 46 and 48 for now, then retune it to the new frequencies when repacking happens. If so, channel sharing on KDAF and KUVN will begin earlier than the phase 3 repacking timeline.)
I figured a different frequency would be used for the test to avoid disrupting existing broadcasts. But now that you mention it, I checked and see a small drop in SQ on RF 46 which began around 11 AM Thurs., 7/5. Could that be interference from the tower near my home? Are they running an ATSC 3.0 test on RF 46 while simultaneously broadcasting on the same frequency in ATSC 1.0 from Cedar Hill? Doesn't seem like that would be a very useful test.