AFC = Automatic Frequency Control
Some radios have AFC circuits that cannot be switched off. They can be faulty.
My Part 15 FM transmitter is about 8-feet away from a Panasonic 1970's table radio which has one of those "always on" AFC circuits. The KDX signal tunes in very nicely but after a few minutes the AFC tries to switch to the 90 kW station nearby on both the dial and physically in the neighborhood.
It ruins everything.
Have you tried to go into the radio and physically by-pass the AFC circuit? I'd think that it would eliminate the issue facing you.
Ya But How?
gamewell makes it sound easy: "physically by-pass the AFC circuit"
I wouldn't know how to do that even if there was a schematic.
You can always get the schematic (most likely on line) and call up the company and get hold of a tech support person who'll be able to point out the circuit to you. If you own a soldering iron and a pair of wire cutters/needle nose pliers it should be a snap.
Carl, First of all what you are having happen with the Panasonic radio with AFC is NORMAL functioning of AFC that's doing what it should, at the expense of close much weaker signals beside. Better radios/tuners have it switchable just for this reason. The AFC basically, without getting technical broadens the bandwidth of a station so to speak and will lock on to that going over other adjacent weak ones....With a decent receiver like the GE super if you turned off the AFC you'd find maybe 2 stations in between two strong ones that you wouldn't get with the AFC on.
Older radios especially Panasonic, Sony, Radioshack, etc used to have service manuals, not to be confused with owners manuals that had all the technical things like alignment, schematics, sensitivity and selectivity specs, parts replacement, etc. and if you search your model number for the service manual on Ebay, or just generally you will come up with sites to get these.
Or else use a different radio like the Tecson or other radio.
Of course if any electrolytic caps. are used in the AFC circuit after 50 years they can go bad which would maybe explain why it works the way you are getting it.
Otherwise your part 15 signal is received at first but it's fighting with the AFC trying to get the stronger adjacent station that all you have to do is walk around and affect the signal as you move which causes the stronger station to overpower yours.
Not likely something is wrong with it.
I don't think Carl said anything was wrong. Just annoying.