Terry, N4TZ/9 has touched on an important point that has long been a
priority on my list of receiver specifications that are relevant and those
that are less relevant. Two tone IMD is not at the top on my list. A related
parameter which is similar but not identical is receiver desensitization.
This requires only one off freqeuncy signal, not two. And there is not a
precise frequency requirement as with two tone IMD. In adddition, I have
also noticed that often a still more pernicious phenomena is transmitted
broadband phase noise. Several field day operations have been ruined
primarily by these two types of interference and not two tone IMD. I also
wish to add that two tone IMD is more serious on CW becaue both signals are
always transmitted at full power. On the other hand, with SSB, both
transmittiers must hit peak power simultaneoulsy for a third order product
to be generated in the receiver. Due to the instantaneous peaks of speech
that occur at a sporatic manner, the probability of this happening is
greatly lessened and when it does happen, the interference is an extremely
short spurt.
73, AL, w6wqc
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