TV stations that synchronize to avoid ATSC into analog interference use
GPS as well. *They have to be within 6 Hz of each other.

For that matter, there is an ATSC standard for broadcasting television
on a single-frequency network within an area of license. That is, a
station would have multiple transmitters (lower power, of course) all
broadcasting in sync and on the same frequency (the assigned TV
channel). The advantage, besides potentially less expensive
transmitter facilities, is that a broadcaster can put up antenna in
such a way as to ensure better coverage over their entire market.

Yes, there would be destructive interference in places, but since the
signal is 6 MHz wide and at 600 MHz, only a small portion of the
entire band would be affected at any given location. The error
correction takes care of it.

The timing requirement for this is quite tight.

- Jonathan