Message-ID: <10758.200104121659@gemini>
From: "James Moritz" <j.r.moritz@herts.ac.uk>
Organization: University of Hertfordshire
To: "RSGB LF Group" <rsgb_lf_group@blacksheep.org>
Date: Thu, 12 Apr 2001 17:59:41 +0000
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Subject: Re: LF: Tech - Alan's Aerial Diplexer
In-reply-to: <coR9vCAbeb16MwZX@telemetry.demon.co.uk>
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Dear Tom, LF Group,

It should be pointed out that the series tank circuit in the Decca PA 
amongst other things isolates the PA devices from changes in the 
load impedance. It removes a lot of spikyness from the current 
waveform in the PA. Another effect is to reduce switching losses, 
and therefore heating of the MOSFETs. It definitely is an asset .

I tried simulating Alan's circuit using PSpice. It certainly evens out 
impedance variations at high frequencies, however, when 
combined with a resonant load at 136k (ie. the LF antenna), rather 
sharp parallel resonances lead to rapid swings of impedance 
around the operating frequency. I have not investigated exactly 
what effect this would have, but I guess it would make the tuning 
rather unpredictable. It is a bit more civilised if the cross-over 
frequency is increased by a factor of 1.5 to 240kHz (ie, divide all L 
and C by 1.5).

I have no access to the university e-mail system over the Easter 
break, but hope to be QRV for some of the time at least. Hope 
everybody enjoys the holiday :-)

Cheers, Jim Moritz
73 de M0BMU