>The mixers in my FT-1000, however, are cleaner than the class A
>push-pull FET's used in the preamplifier to drive the mixers.
>
>The mixers in your SSB transmitter are also likely very much
>cleaner than the various "linear" stages in the transmitter.
Absolutely. I agree 100%. THe FET's will be over-driven before the
mixer is. That's why you can turn the preamp-off and get a tremendous
improvement in IP3 performance.
>
>Cross modulation and IMD also occurs in nickle plated coax
>connectors. The problem is what the rest of the system does with
>IMD, not how many angels (or devils) we can fit on the head of a
>pin.
Agreed.
>
>I think this all got started because it is easy (and a natural
>mistake) to confuse harmonic distortion that does NOT affect
>signal quality with IMD distortion that does affect signal quality.
True again as well.
>
> The closest harmonic distortion product that would
>affect our 14 MHz rig appears on ten meters.
So while harmonic distortion doesn't affect your signal it might piss off
someone trying to work a DX station on 10M that is on your harmonic! :-)
So we want to minimize it but you're absolutely right, the cause and
solution to harmonic distortion is totally different that the solution to
intermod.
>Some class C amplifiers, when operated at levels outside
>the crossover distortion point, can even produce acceptable IMD
>performance in non-critical applications.
Agreed again.
>
>Hopefully all the time on this thread is worth it, and some old wive's
>tales will die. It isn't what happens over a single RF cycle that
>causes problems in narrow band PA's. It is what happens as the
>envelope level is changed, and the slope of the response to that
>change.
That is correct. The variation of the envelope in a non-linear system is
what causes IM. Nothing else, not distorted audio, etc. While distorted
audio might sound bad, it doesn't create the intermod. FM modulation is
a constant envelope which is why you can use a Class C brick with it.
All good points.
73,
Jon
KE9NA
--------------------------------------------------------------------------
The Second Amendment is NOT about duck hunting!
Jon Ogden
jono@enteract.com
www.qsl.net/ke9na
"A life lived in fear is a life half lived."
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