It's a problem or a blessing depending on which way you look at it. Two diffrent fquencys will add together to make a third,or subtract from each other to make a fourth freqemcy. That is the way the IF (Intermediate Frequency) part of your receiver works. The receivercrystal generatesa frequency that iscombined with all of the received frequencys the the first stage can accept. The result is two different frequencys, the two added together or the two subrracted from each othe give to greatly different frequencys. The IF stage can narrow down the signals to a more precise frequency. A single conversion receiver does this once, buta dual conversion does it twice and the desiredmix is 425KC IfI remember correctly. Two strong TX signals will bleed into the IF(mixed frequencys in the receivers) to come up withthird frequency.When that mix happens to match one of the receivers IF frequencies, then the signal will get through.This is what you are seeing.

I remember seeing a post on this some time back that detailed theinteractive frequencys, but I don't have a linkfor you

This is the reason most RX's are dual conversion,each mixing helps refinethe mix to a verynarrow possibilty of usable signals. The 425khz is a frequency that gave the least mix of twoTransmitted signals on allbands that woud feed through to the final signal. Ijust noticed that I used a 40 year old term, KC for KilloCycles vs todays KHZ Killo Hertz .It's just a nominclature difference, not a practical one. The 425Khz If is an old holdover from the early AMbroadcast radio days. I suspect that that if you do the math, it is a frenquecy that is less likely to be duplicated with a random mix of frequncys so the true signal will be the result.

Bottom line, there are acouple channelsin the 72mhz bandthat can beat together and over power the RX IFfrequency and cause problems. It is usually only a problem when the TX's are close to each other andproduicingnearequal signal strength. If oneTX signal is dominate, the problem goes away.

I hope this makes sense. It's late and added to that are a couple glasses of old grape juice.

Don