On Jun 13, 5:25*pm, walt wrote:
However, interference to the amp from radiation from
an antenna driven by another amp will not be phase or frequency
coherent with the tx receiving the interference. Perhaps that's the
reason the interfering signal gets through while the waves reflected
from a mismatch don't?

Measurements made of broadcast transmitters in the engineering test
lab at Harris Broadcast Division show that power reflected from a
mismatched load does indeed enter the PA plate output circuitry, and
change the amount of power dissipation and cooling requirement for the
transmitter.

That is the reason why virtually every modern manufacturer of
broadcast transmitters specifies a maximum value of load VSWR for
which their maximum rated powers are permissible.

For Harris FM transmitters that value is 1.7:1 (any phase angle). As
the load VSWR exceeds that value the transmitter progressively "folds
back" its output power to protect itself from component damage.

RF