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[AMPS] Re: Ferrite Rod for 6M Amp

To: <amps@contesting.com>
Subject: [AMPS] Re: Ferrite Rod for 6M Amp
From: W8JI@contesting.com (Tom Rauch)
Date: Tue, 1 Jun 1999 09:05:06 -0400
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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