I used to have a fairly nice Rotel preamp that would receive CB radio transmissions sometimes. Whatever it was that was behaving as an AM detector must have been near the output of it because the intensity was unaffected by the volume control.

That was almost certainly the result of illegal transmitters, but it was annoying. One time I heard a man shouting through the stereo and the signal was hot enough in RF land that it made my X10-controlled lights flash on and off.

Later, I got DirecTV and it became differently-annoying: The noise of the satellite receiver switching bias voltage to select between different LNB polarities was sufficient to make a loud pop through the speakers (again, unaffected by the volume control). This made channel surfing very noisy. I was able to reduce it rather substantially with some very deliberate choices in audio cabling construction.

But with better gear (and with the differential[1] signalling that every avenue of pro audio seeks to use by default), this kind of stuff is usually a complete non-issue.

[1]: We popularly call this kind of connection "balanced," but we're wrong about that since there's usually hardly any concern about impedance matching. But it's definitely consistently differential, so I find this less-popular nomenclature to have the right amount of specificity to ~fit reality.

Land-mobile radio stuff. Analog, voice communication.

Our sales guy had sold a remote node for a voter system to improve receive coverage for a central dispatch system. (Signal-to-noise voters are pretty neat: They can continuously compare two or more related audio signals and [ideally!] pick the one that is best for use while discarding the others.)

That node wasn't all that far away as the crow flies, but it was a very long way out in telephone cabling miles. It spread across two different telco LATAs.

So we rented this very long series of bits of wire held together by scotchloks and punch blocks and whatever else in telephone world to use, and we used it. It was not a conditioned circuit: Just wire.

The specific endpoints of that wire were kind of neat, too: There was some basic EQ that could be used to help compensate, and (IIRC) some impedance adjustment to dial in the circuit itself.

And there was a continuous pilot tone used to set gain: Apparently, when wire gets really long like that, atmospheric conditions can dynamically change its attenuation.

Putting a pilot tone near the middle of the voice range (to be notched it out later) and using its level to set gain helps to improve consistency.

That wireline stuff all worked pretty well.

(The remote node was ultimately a bust. The sales guy also tried to cram too much shit into one feedline and antenna, and the gear to combine and separate all of those signals ate too much energy to make any of it an improvement over doing nothing at all.

Which is... well, that's exactly what the engineering told him would happen, but he did it anyway.

No part of this was inexpensive.)