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Message-ID: <coR9vCAbeb16MwZX@telemetry.demon.co.uk>
Date: Thu, 12 Apr 2001 15:11:39 +0100
To: "RSGB LF Group" <rsgb_lf_group@blacksheep.org>
From: "Tom Boucher" <tom@telemetry.demon.co.uk>
Subject: LF: Tech - Alan's Aerial Diplexer
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Alan

What a convenient piece of timing! I was intending to play with an
absorbtive load at the third harmonic on my Tx this weekend, so your
diplexer design arrived at the right time.

I gave up on the YXM/MRF style design using a pair of FETs in push-pull
because the FET consumption rate got ridiculous. So I made a copy of the
Decca bridge circuit which works extremely well and so far appears
reliable at the 600 watt level. My intention is to put a few more turns
on the output transformer and get it up to a kilowatt this weekend.
However, I have been investigating the rather nasty looking waveform on
the FET outputs and was wondering if it could be due to reflections of
odd harmonics back into the PA as these will not see a 50 ohm load. I
have a damping R and C across the transformer primary which helps.
(Zobel did Dave call it?)

I should add that, for the moment, I have abandoned the series tuned
tank circuit of the Decca. The bridge feeds directly into a YXM tapped
output transformer, with a single primary, which then feeds a low pass
filter.

All good fun!

73, Tom G3OLB