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
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