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https://en.wikipedia.org/wiki/Tropospheric_propagation

Li'l story. Wireless microphones, of the kind used in television production, use the same radio frequencies as VHF television broadcasts. Because transmitters interfere, these frequencies are allocated by the FCC to not overlap - this is why Albuquerque has channels 4, 5 and 7 while Denver has 3 and 6. So if you work in television production, you get good at learning what frequencies are likely to work, how to determine what frequencies work and what you need to do in order to get Miss Hotness on lav without being crushed by Geraldo Rivera.

We've got a lot of cast on a lot of mics in a highly intense radio environment and we pay experts several hundred dollars an hour to make sure everything works all the time. They come out, hem and haw for several days every season, and then we go for thousands of hours in a row without any problem.

Except for Bob.

About four years back, round about midnight-1am, Bob would start snatting and hissing and being otherwise unusable for no particular reason. We'd swap him to the spare mic, which was on a different frequency, and leave him there until morning. By morning, Bob's mic was fine again.

"What about Bob" became the game we all played at night. We had a bitchin' frequency scanner, we had a dozen seasoned RF professionals, we had everything. But it wasn't until I looked up recent license grants that we had an answer.

As it turns out, Bob's mic was at a harmonic of a religious TV station that had just started broadcasting... 120 miles away. And while we were normally fine, when the weather was just so and the thermal inversion hit (at about midnight), all of a sudden the tropospheric propagation from Jesus Television would bounce off the troposphere and squash Bob's transmitter like a bug. Once I knew that, I pulled up the spectrum wide enough to see JesusTV and Bob and looked at 'em at 11 and looked at 'em at 1. Sho'nuff, JesusTV clobbered the shit out of Bob.

We swapped frequencies between Bob and the spare such that Bob was on the spare frequency and the spare was using Bob's. It meant we didn't really have a spare after midnight when the weather was wrong... but then we re-freq'd everything the next season and it all worked out.

But yeah. High frequency RF is fuckn' voodoo.