A few years ago I coordinated 48 channels of wireless for a theater in Houston. The house had 16 channels of installed Shure ULX-D, the production rented 16 more, and we borrowed 16 channels of older Shure systems that could not be networked. Houston is like most major metro areas. It's an RF nightmare so finding 48 clean frequencies was rough, and I used every bit of spectrum available to get there.
The RF coordination plan held through rehearsals and through Friday and Saturday performances. Sunday afternoon my phone started ringing. About a third of the mics had gone to noise and dropouts. I wasn't there in person so there wasn't much I could do to help. We had a handful of backup frequencies but not enough to get all the missing channels working again, and even some of the backups didn't work.
On Monday I figured out the cause. A low-power religious TV station a few miles away only transmits on Sunday. It was not on the air when I scanned, and it was not in the TV channel list I had loaded, so my plan had a group of mics sitting inside its 6 MHz. I found it in SoundBase, which pulls the FCC low-power listings, and rebuilt the coordination that week with tighter spacing, a few frequencies I would not have accepted the first time, and lower transmitter power to limit the intermods. The second weekend ran better but the RF wasn't quite as reliable as the first coordination.
Wireless Multichannel Audio Systems, WMAS, are the most interesting change in this corner of the industry in years. Where a conventional rig spaces 48 narrow carriers across the band, a single 6 MHz block can carry dozens of mic and in-ear links, in both directions on some systems, and the system schedules the links inside the block itself. For a show like that one, coordination becomes a search for a few clean blocks instead of 48 clean slots.
It does not make the Sunday station go away. A WMAS block parked on that channel would have lost every link in it at once, the same way my group of mics went down. For years to come most of the wireless in the field will still be conventional narrowband systems, often running beside a WMAS block, and even an all-WMAS rig needs someone to decide which blocks are clean on the day the show runs.
Scan on every day of the week the show will run, check the low-power listings along with the full-power stations, and start the coordination at the first site visit instead of the week of load-in. RF coordination isn't just about hitting the calculate and deploy buttons. It takes research and planning. You have to understand the environment, the equipment, and the use. The spectrum you measured on Friday is not the spectrum you get on Sunday.