Hi Wolf this may not be the case with the properly tuned Class-E stage which
has relatively low distortion. It does not output a square-wave as some
think. See The QST article by Nat Sokal.
Bear in mind filters complicate things further since they can transform
mis-matches and only really work if resistively terminated. Even more reason
to get your antenna right first. Loaded diplexor filters are a little more
forgiving if you have harmonic problems but should not be necessary on
Class-E a simple low-pass half-wave filter works well but use air cored
coils, not toroids.
Alan G3NYK
----- Original Message -----
From: "Wolf Ostwald" <[email protected]>
To: <[email protected]>
Sent: Wednesday, November 25, 2009 3:25 PM
Subject: LF: instability on MosFet amps
> Hello group !
>
> I found that almost all amp configurations generate harmonics. In case of
a
> homebrewed HF amp, with a push -pull design, I had to build hi-pass
filters
> with a resistive termination, so called split filters, for each band.
> Without dissipating the harmonic energy the stage will have to cope with
> excess voltages and thus bury the MosFets .
>
> My last amp stage for the DI2BJ-beacon is followed by a hi-pass that opens
> at 750 kcs . This way the first harmonic and all the higher ones go into
> thermal dissipation.
>
> A T-type adjustable low-pass is used to match and reduce harmonics
further.
>
> Have fun de wolf df2py
>
>
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