Message-ID: <47430398.8000702@telia.com>
Date: Tue, 20 Nov 2007 16:56:08 +0100
From: "Johan H. Bodin" <jh.bodin@telia.com>
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Subject: Re: LF: CLASS E
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Mal,

for proper class E operation, the drain waveform must be allowed to be 
non-symmetrical so you cannot just use a center tapped output transformer. In 
other words, there must be no "hard coupling" between the drains in a class E 
push-pull amplifier. One way is to design two identical class E amplifiers, each 
designed for an output power P into the load R. Note: Each amplifier must have 
its own DC feeding choke - no center tapped stuff here! Then feed these two 
amplifiers with push-pull drive (180 degrees phase shift) and connect the 
primary winding of an output transformer between the outputs of the two 
amplifiers. The output transformer should be designed so that 2*R will be "seen" 
when "looking" into the primary. The total output power will be 2*P. With 
sufficient Q in the series tanks (C2, L), the output current will be almost 
sinusoidal, as in the single ended case, so the two halves of the amplifier will 
not "know" that they are actually operating in push-pull. Since the two series 
resonant tanks of the two amplifiers and the output transformer primary will all 
be connected in series, you can simplify the circuit by using a single resonant 
tank with twice the L and half the C. This may look assymetrical but it gives 
exactly the same result (a few pF stray C can be neglected at these low 
frequencies...). One can say that this is simply two class E amplifiers 
connected in series. However, the even harmonic cancelling property of push-pull 
is still there because of circuit (and drive) symmetry.

I have tried this configuration, for example on 160m QRP, and it seems to work 
very well.

73
Johan SM6LKM


hamilton mal skrev:
> Hi all
> Is anyone else using a class E PA on 500 or 137. Mine is single ended, maybe
> someone has a push pull design.
> 73 de Mal/G3KEV
> 
> 
>