[Amps] Non-linear subharmonics was: Nonsense, AL-1500 parasitic

[jeff millar]

You're quite correct that non-linearities do not directly generate anything
other than integer harmonics 2f, 3f, etc.  But it still possible to generate
sub-harmonics with a non-linear reactance, a passive circuit, and a pump
frequency.  Because there's two kinds of nonlinearity:

    Non-linear resistance...which results in clipping, etc.
    Non-linear reactance...which results in parametric effects

Parametric circuits can have _gain_ at frequencies other than the pump
frequency.  A sub-harmonic arises because the the parametric divice looks
like negative resistance and produces gain which results in oscillation at
f/2 or f/3.

Yes, this is unlikely in typical circuits.  But the effect is real and
documented and interesting.

jeff, wa1hco.



----- Original Message -----
From: "Tom Rauch" <w8ji@contesting.com>
To: "Ron" <w8ron@stratos.net>; "jeff millar" <wa1hco@adelphia.net>
Cc: "'Amps'" <amps@contesting.com>
Sent: Wednesday, May 22, 2002 12:09 AM
Subject: Re: [Amps] Non-linear subharmonics was: Nonsense, AL-1500 parasitic


> > I still think something in the amp or something in the
> > feedline/antenna/tower/guy system can cause the problem.  In response
> > to the initial question, I asked about ferrites in the tank.  But
> > maybe a solid state driver could produce the sub-harmonic. If the
> > measurements are correct, then the spurious is truely a sub-harmonic
> > and it becomes interesting to find the source.
>
> It is especially interesting now that Dave says he duplicated the
> problem with diodes.
>
> I have never been able to generate a submultiple of a signal with an
> form of non-linear system, including saturated ferrites.
>
> I wish it were that simple.
> > from one > cycle to the next to be lower in frequency. To be an odd
> > fraction of the > fundamental would mean that the non-linearity
> > effects one cycle of the rf > fundamental but not the next!
>
> That is correct. Dividing frequency requires more than a simple non-
> linear junction, or a non-linear device like saturated ferrites.
>
> Whatever it is it requires that one point in one cycle is *not*
> treated like the next repeating point. That's why you never find
> subharmonics generated in solid state or tube-type PA's, ferrites, or
> conventional diodes. 73, Tom W8JI
> W8JI@contesting.com
>