From: jannsen <0482183881-0001@t-online.de>
To: rsgb_lf_group@blacksheep.org
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	 <004b01c46cc0$0d40fce0$07d98351@rogersservices> <001e01c46dcf$34e50a60$d6537ad5@rogersservices>
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Date: Tue, 20 Jul 2004 19:18:34 +0200
Message-ID: <1BmyGA-11XwkC0@fwd11.sul.t-online.com>
Subject: Re: LF: Re: TX output circuit
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James Moritz schrieb:
> Dear Scott, LF Group,
>
> To save long-winded explanations, I have drawn a circuit diagram of my
>  modified version of the G0MRF PA output circuit, with some details of the
>  output transformer. It is too big to send via the reflector, but if anyone
>  wants it, let me know and I will e-mail it direct.
>
> My unit gives 400W out with 37V supply - for 300W out with a 48V supply, I
>  reckon the primary windings of the output transformer should be changed from
>  4 to 6 turns. The value of the choke in the DC supply is not critical - the
>  iron dust cores can often be found in old PC SMPSUs. The most significant
>  change to the original circuit was to remove the decoupling capacitor from
>  the centre tap of the transformer primary, and increase the inductance of
>  the choke, converting the circuit into a "current feed" class D
>  configuration. This means the DC supply has a high impedance at 137kHz,
>  which prevents high transient currents into the low pass filter capacitors
>  when the MOSFETs switch. The ideal drain voltage waveform would be a half
>  sine wave, allthough in practice there is still considerable ringing at the
>  switching transitions, allthough much reduced. The value of the damping
>  resistors and capacitors is a compromise; reducing R and increasing C
>  reduces the amount of HF ringing, but increases dissipation in the resistors.
>
> Cheers, Jim Moritz
> 73 de M0BMU 
>
>
>
Hi Jim,

pse send the diagram direct: dj8wx@qsl.net or 0482183881-0001@t-online.de

tks in advance

Uwe/dj8wx