Red herring, again. AM radio does the same suppression effect if the
signals are widely differing in power (google "AGC" or "AVC" for an
explanation). The odds of two signals being absolutely equal in time is
close to zero. True, they can start simultaneously, but the ending time is
generally measured in multiseconds. One side or the other always gets the
tag end of one conversation or the other and can figure out that a second
station is trying to get a message across.

The squeal when two nearly equal power signals is not the sum of the
frequencies, it is the difference.


Jim



"James Robinson" wrote in message
. ..
Mxsmanic wrote:

Perhaps this is a naive question, but: Why don't voice radio
communications for aviation use FM radio instead of AM radio?

I understand it is because of a characteristic of FM called "capture
effect" that blanks out weaker transmissions when two radios transmit at
the same time. The listener would have no idea that a second, weaker
transmission was being made.

With AM, when two radios transmit on close frequencies, you either hear
both signals poorly, or you get squeal, which is the sum of the two
signals. This characteristic is considered important when you have
elevated
transmitters that can be hundreds of miles away, like on aircraft.