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Message-ID: <3.0.1.16.19990802173940.2ff70aec@mail.cc.kuleuven.ac.be>
Date: Mon, 02 Aug 1999 17:39:40
To: rsgb_lf_group@blacksheep.org
From: "Rik Strobbe" <rik.strobbe@fys.kuleuven.ac.be>
Subject: LF: Re: Class E RF amplifiers
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>Hi all, I dug out a copy of an article by Nathan Sokal (Pres. of Design
>Automation) that was published in Design Electronics on 20 Sept 1977 titled
>"Class E can boost efficiency".
>This turns out to be a very practical article with simple design formulae,
>and a 'build it and play' circuit with example scope traces of current and
>voltage waveforms. The test circuit is to run at 10 MHz but the detail
>looks
>eminently suited to 136kHz. Efficiencies of 82 to 95% are quoted for some
>very ordinary transistors and FETs. There is no formula given for the RF
>Choke but I think that can be scaled from the 10MHz value.

I am using a 'G3YXM' PA, slightly modified from the original. Main changes
are a pair of IRFP350's on each side of the push-pull (running at 56V) and
an extra LC section in the LPF.
With 9.2A draincurrent (= 515W input) I get 2.95A RF current into my 52 Ohm
dummyload (= 452W output). That means 87.8% efficiency.
Seems to be within the range of this famous 'Class E'.
The nice thing on Dave's PA (besides good efficiency) is that is a
straighforward and 'no nonsense' design, if you stick to scematics and
component list it cannot go wrong.
It is absolutely stable (I know an OM who blew more than a dozen FETs on an
oscillating PA) and survives open circuit (no problem, current goes down)
and even shortcircuit if you have a proper current-trip in the PSU.

73, Rik


Rik Strobbe  ON7YD
rik.strobbe@fys.kuleuven.ac.be
Villadreef 14  B-3128 Baal  BELGIUM   (JO20IX)