Return-Path: Received: (qmail 57519 invoked from network); 20 Jul 2004 18:19:05 -0000 Received: from unknown (HELO ptb-spamcore01.plus.net) (192.168.71.1) by ptb-mailstore01.plus.net with SMTP; 20 Jul 2004 18:19:05 -0000 Received: from [192.168.67.2] (helo=ptb-mxcore02.plus.net) by ptb-spamcore01.plus.net with esmtp (Exim 4.32; FreeBSD) id 1BmzCv-000LKB-MX for dave@picks.force9.co.uk; Tue, 20 Jul 2004 19:19:17 +0100 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore02.plus.net with esmtp (Exim) id 1BmzCg-000DIG-Uw for dave@picks.force9.co.uk; Tue, 20 Jul 2004 18:19:03 +0000 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1BmzCN-0004pJ-RS for rs_out_1@blacksheep.org; Tue, 20 Jul 2004 19:18:43 +0100 Received: from [193.82.116.30] (helo=relay.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1BmzCN-0004pA-Cr for rsgb_lf_group@blacksheep.org; Tue, 20 Jul 2004 19:18:43 +0100 Received: from mk-smarthost-8.mail.uk.tiscali.com ([212.74.114.47]) by relay.thorcom.net with esmtp (Exim 4.34) id 1BmzCJ-0003D1-Pn for rsgb_lf_group@blacksheep.org; Tue, 20 Jul 2004 19:18:43 +0100 Received: from ppp-1-118.carl-a-1.access.uk.tiscali.com ([80.225.129.118]:3192 helo=taylormade) by mk-smarthost-8.mail.uk.tiscali.com with smtp (Exim 4.30) id 1BmzBg-0001DR-9a for rsgb_lf_group@blacksheep.org; Tue, 20 Jul 2004 19:18:00 +0100 From: "Gary - G4WGT" To: rsgb_lf_group@blacksheep.org Date: Tue, 20 Jul 2004 19:17:37 +0100 Message-ID: MIME-Version: 1.0 X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook IMO, Build 9.0.2416 (9.0.2910.0) Importance: Normal In-Reply-To: <001e01c46dcf$34e50a60$d6537ad5@rogersservices> X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 X-Spam-Score: 0.7 (/) X-Spam-Report: autolearn=no,HTML_20_30=0.474,HTML_FONTCOLOR_BLUE=0.1,HTML_MESSAGE=0.001,RCVD_IN_SORBS=0.1 Subject: LF: RE: Re: TX output circuit Content-Type: text/html; charset=windows-1252 X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Status: No, hits=0.6 required=5.0 tests=HTML_20_30,HTML_FONTCOLOR_BLUE, HTML_MESSAGE autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-Spam-Filtered: by PlusNet SpamCORE (v3.00) Content-transfer-encoding: 8bit

Hi Jim,

Thanks for the offer of the modified G0MRF PA details, please send to g4wgt@tiscali.co.uk

Regards

Gary - G4WGT

-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org]On Behalf Of James Moritz
Sent: 19 July 2004 21:29
To: rsgb_lf_group@blacksheep.org
Subject: LF: Re: TX output circuit

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