The Class-E AM folks are doing some interesting things
-- Tee the RF input -- one side to an added envelope
detector, output of this to PWM your power supply to
the ClassE amp module, other side of the tee to
through a VGA/limiter, then into the class-E final
section (phase is preserved, amplitude is constant
INTO the amplifier), and you have the basics of an
EER system; (oh, don't forget the output filters) --
that's for SSB. For CW, well, just use class E. With
the ebb of the high bands, the time may be right for
encouraging a bunch of experimentation with these
devices which are more suited (in versions published
to date) for frequencies below 14MHz. Looks like the
major class-E issue is tuning of the output network to
ZVS.
http://www.classeradio.com
Some of their circuits (paralleling the FETs for more
juice, etc.) remind me of some diagrams I've seen of
the early days of radio and doing this with some of
the new-fangled vacuum devices just available at that
time.
-Brian N9ADG
(caveat: While I have the parts gathered to experiment
with what I mentioned above, time hasn't allowed me to
do so yet. I would welcome comments from those that
have built some of this stuff. )
--- Dave Haupt <emailw8nf@yahoo.com> wrote:
> The documentation part is done. Check out the
> textbooks and articles written over the years by
> W1FR,
> Fritz (aka Frederick) Raab. He has built and
> documented an envelope removal and restoration high
> efficiency amplifier which he has, indeed, operated
> on
> the ham bands. Fred's work would be system-level,
> encompassing the interplay of the RF portions,
> modulated power supplies, amplitude and phase
> feedback
> systems, requisite filtering, etc. Fred used to run
> a
> company called Green Mountain Radio Research, but I
> do
> not know if that is still the case.
>
> For extremely detailed discussions and theories of
> the
> Class D, E, etc, portions of the RF deck, look for
> writings by Nate Sokal (WA1HQC).
>
> Neither gentleman tends to use his callsign with his
> works, so it is prudent to limit your searches to
> name
> only. Any of the trade magazine website, plus the
> usual tech book publishing houses (Artech,
> Prentice-Hall, etc) are reasonable places to search
> for the works of these two gentlemen.
>
> A web site sounds like a fine idea. I should like
> to
> do just such a thing, when it is notably higher on
> my
> priority list.
>
> 73,
>
> Dave W8NF
>
>
> --- "R. Measures" <r@somis.org> wrote:
> > ** Dave -- Why not design a 90% efficient linear
> > amplifier for the HF
> > Ham bands, document the construction process, and
> > show us how to on your
> > Web site.
> >
> > >In the late 1980s, one of the engineers I worked
> > with
> > >had recently come from Continental Electronics of
> > >Dallas, TX. The most recent transmitter design
> on
> > >which he had worked at Continental was a
> > multi-hundred
> > >kW rig. It used a solid-state switchmode
> > plate/screen
> > >modulation, with loop feedback to keep the
> > distortion
> > >low. The transmitter was capable of operation
> from
> > AM
> > >BC (not legal in the US at that power level) to
> in
> > >excess of 20MHz. Because of the custom nature of
> > such
> > >large transmitters, it was, of course, not
> > >band-switched. Rather, the purchaser specified
> the
> > >operating frequency.
> > >
> > >However, the techniques, without question, could
> > lend
> > >themselves to a band-switched design. And
> there's
> > >nothing preventing such techniques when the RF
> > devices
> > >are solid state.
> > >
> > >There is nothing inherent in a high efficiency
> > >broadcast design that renders it narrowband.
> > >
> > >Complex? Yes. Technically difficult? No.
> > >
> > >73,
> > >
> > >Dave W8NF
> > >
> > >__________________________________
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> > >
>
>
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