ORIGINAL: rhklenke
My guess would be that his transmitter was slightly mistuned and your RX was too, and his transmitter basically took over your RX (your RX locked onto his TX more likely). I do not think it would be possible for a second PCM TX to take over PARTIAL control of your aircraft - sending commands to some of the servos, but not all. That would take some pretty fancy synching up to replace/modify some of the bits in a series of packets, but not others.
Not just that - it would have to not only modify certain bits in the primary data section of the frame, it would presumably also have to modify the EXACT correctly corresponding bits in the CRC or whatever error checking mechanism Futaba uses, would it not ?
Assuming even a half-decent CRC algorithm, that IS definitely a possibility in statistically rare cases, but I don't see how it would be reproducable - seems more likely that if you left both TXs and the RX on continuously and recorded every frame sent from both TXs and every frame received by the RX, you'd get maybe ONE bogus-yet-accepted frame every day, or similar large period rather than being able to cause it to happen at will.
Also, if it was a case of the stronger TX being able to take over as suggested above, then this is different than Dave's scenario as I understand it. I believe Dave indicated that the acceptance of bogus info occurred only when the 2nd TX was some distance away - as it came closer (i.e signal strength increasing), the regular failsafe kicked in as expected. If the 2nd TX was stronger and better tuned to the RX, then as it came closer it should have been even MORE able to take control. (Unless I'm misunderstanding the "closer' aspect, and the 2nd TX was only getting closer to the 1st TX, but simultaneously getting SIGNIFICANTLY further away from the model ?)
One last thought ... instead of considering this from the point of view of two signal sources "blending" to create one which the RX works on, is there any chance this is some artifact of TX 1 inadvertantly picking up the signal from TX2 and absorbing that into the data that it's passing to the CRC encoder ? I understand a reasonable amount of DSP, but am not an RF guy by any means, so please don't laugh TOO hard if this is ridiculous. Maybe the fact that the TX circuitry is 'tuned" for the freq in question makes it susceptible to incoming RF of the same freq, which is why only another TX on the same channel causes such issues but all the nearby TXs on other freq's don't ? If that were the case though, it would be susceptible to picking up reflected "bounces" of its own very recently transmitted signal though... so this seems not to be feasible. Sorry - just thinking out loud.
Gordon