Alan and Co
I am using a LPF consisting of 2 x T200 type material with no adverse
effects and insertion loss virtually nil.
It works well with my class E PA and 1/4 wave inv L antenna.
de mal/g3kev
----- Original Message -----
From: "Alan Melia" <[email protected]>
To: <[email protected]>
Sent: Wednesday, November 25, 2009 3:45 PM
Subject: LF: Re: instability on MosFet amps
> 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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