Hi Mike,
From: Michael Tope <W4EF@pacbell.net>
To: "Amps Reflector (E-mail)" <amps@contesting.com>
Subject: [AMPS] Re: Ferrite Rod for 6M Amp
Date sent: Sat, 29 May 1999 21:29:28 -0700
>
> Tom and Rich,
>
> This whole discussion makes no sense to me.
Actually the only part that doesn't make sense is why a ferrite
material used in hundreds or thousands of harmonic distortion
critical VHF applications apparently failed Rich's test and
certification for use in much less critical applications.
Since no one else has ever reported or ever seems to have a
problem with the same material causing harmonic distortion in
other applications at much higher frequencies, the test method,
test equipment, or perhaps interpretation of the results must be the
real problem.
If I put two sinewaves into
> any kind of nonlinear network, I would expect to see IMD products as well
> as harmonics results. After passing thru the non-linearity, the two sine
> waves will no longer be linearly independent - in essence the two signals
> should begin to cross modulate each other.
Mixers are always non-linear devices, if they aren't they won't
"mix". Why doesn't the mixer in your receiver create close-in IMD
or cross modulate? Many receivers use broadband block
convertors, some systems even use single diode switches for
mixers. Where's the odd-order IMD problem when processing
multiple signal frequencies?
Vacuum tubes or transistors in class AB are non-linear when
viewed at a fractional cycle rate, why do they often provide
acceptable IMD performance?
It's incorrect to think fractional cycle distortion causes performance
shortfalls in the application being discussed.
While the part about the core causing distortion at 14 MHz and not
10 MHz is fantasy enough, the most dazzling part of the sideways
thinking is the implied assumption a ferrite core carrying only a tiny
fraction of the applied RF current driving a tube that conducts just
over 1/2 a cycle will somehow be meaningful in distortion
performance of that PA.
I knew a fellow who wanted to run push-pull tubes in a 75 meter
linear amp to improve the audio. The junk-science about fractional
cycle distortion causing IMD problems fits the same category of
"clueless conclusions".
73, Tom W8JI
w8ji@contesting.com
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