Isn't the FCC supposed to exist to prevent just this kind of interference? Since this could be a safety of flight issue, I would call the FCC and the FSDO and ask them to investigate whether this facility is in compliance with their permit. I wouldn't assume it to be your equipment if this is the only place you have a problem.
FCC dictates the limits of spurious emmisions for various classes of transmitters.
Unfortunately it is not technically possible to create a signal at a few hundred or thousand watts that is spectraly clean (i.e. only transmitts at the intended frequency).
Typical limits range from -40 to -60db allowable harmonics - to put that in easier numbers - between 100th and 1000th of the main transmitted power. So if you have a shortwave transmitter (as example, these tend to be VERY powerful and have big antenna arrays) at say, 50.000 Watts power and it transmits at 30Mhz then it is likely you will get 500 Watts of signal at 60Mhz and somewhere around 100W perhaps at 120Mhz.
Now, if you are flying close to that transmitter, even if your radio is not tuned to 120Mhz, it is quite likely that the 120Mhz signal is simply going to flood the mixer in your receiver and render it useless. Depending on the construction it will now receive just about anything it sees at its input. This is often recognized as static but you can often hear partly demodulated sound like music or voice.
Now, having said this - your transmitter at perhaps 6-10W is also a problem. It also generates harmonics and it can interfere with nearby TV receivers. Of course, you would have to transmit and fly very low over the TV arial. Perhaps you can try this next time you have an argument with your neighbour and he wants to watch the game...
Does not work so well with cable or sat TV though...
The FCC regulates what is reasonably possible using current technology but does not make impossible demands.
I recall an accident related to this - this was in Germany, Bavaria of all places. The then new fly-by-wire Tornado spun out of control whilst flying close to a powerful radio antenna. It was quickly learnt then what kind of havock a powerful radio signal can do with any kind of sensitive electronics (not just radios).
On a second, similar note, I performed an emergency landing on a field as both CHT and EGT readings all of a sudden went way out of bounds. At the time I had two sets of electronic gauges (no, not made by us - MGL was still in the distant future then).
Once on the ground, everything was just normal and eventually I decided to risk a take-off (it was a good field). Just after take-off the same thing happens but this time I looked at my fuel flow - normal and also the engine sounded just fine so I pressed on. a few minutes later the problem went away. How strange. On another flight in the same area the same thing happened (except this time I ignored it). Behold, close by was a very large short-wave transmitter array. So that was it...
Once MGL was founded and we made our first instruments back in 2000 - guess where I would take them for a good, practial RF interference test...
Rainier
CEO MGL Avionics