[1000mp] Test IMD vs actual IMD

[lhlousek]

Hi Joe, K4IK and Jeffrey, WA6KBL

You make interesting points and I'd be more willing to accept them on face value if the generation of third order
products was a linear process.  Certainly receivers are a different thing but third order products are characterized by
an intercept point, the theoretical point at which the power in the third order products is equal to the desired signal,
exactly because it is not a linear effect.  The 3rd order products increase faster than the applied level and they also
decrease faster than the applied signal level.  Depending on the nonlinear mechanism that causes the generation of
higher order products it is conceivable that a typical vocal audio envelope puts substantially less power into the
higher order products than do two equal tones at max rated PEP.  I guess, on the other hand, it is also conceivable that
the audio envelope could be worse.  So far, I'm not convinced either way.

Don't get me wrong.  I think transmitter should be a clean as technically and economically feasible but the measurement
of cleanliness that counts it what they produce in actual use and not under a contrived test condition.  The question
is, how well does the two tone test reflect actual IMD performance.  The two tone test has been a standard because it
was easy to generate and measure two tones.  With current digital technology it is now possible to define and generate a
standard audio envelope that could be used for IMD testing and that might better reflect actual IMD performance

Lou W7DZN