ORIGINAL: MO_Radio_Tech
Two transmitters on the same frequency in close proximity (say at the same flying field) will always cause failure.
Au contraire!
Two transmitters on the same frequency in close proximity will very often cause problems, but if you're using one of the more modern PPM receivers with advanced features such as transmitter signal recognition (TSR) then you'd be surprised at just how much you might get away with.
I tested a Berg DSP II receiver the other day against two transmitters (a Hitec Eclipse 7 and an Airtronics).
Just out of curiosity, I registered the signature of the Airtronics with the Berg (by turning the Airtronics Tx on then the Berg) and it worked fine. Then, the Airtronics transmitter was turned off and the Hitec turned on -- nothing. The receiver simply would not respond to the Hitec -- which actually didn't surprise me because the Airtronics was is positive shift and the Hitec is negative.
However, when the Airtronics was turned back on, it still had full control with no glitching or anything -- even though there were now *two* transmitters operating on the same channel and they were both equidistant from the receiver.
In that case you could be pretty much guaranteed that a PCM receiver would have gone into failsafe and left you with no control from either transmitter.
These new "smart" decoders aren't perfect -- but they're damned impressive!
And another important benefit (to some) is that receivers like the Berg and FMA M5 are much smaller/lighter than *any* PCM receiver I've seen. This means that even the smallest/lightest models can gain the benefits.