Return-Path: Received: (qmail 24810 invoked from network); 19 Jul 2004 20:39:16 -0000 Received: from unknown (HELO ptb-spamcore02.plus.net) (192.168.71.3) by ptb-mailstore01.plus.net with SMTP; 19 Jul 2004 20:39:16 -0000 Received: from mailnull by ptb-spamcore02.plus.net with spamcore-l-b (Exim 4.32; FreeBSD) id 1Bmeuu-0008vC-OO for dave@picks.force9.co.uk; Mon, 19 Jul 2004 21:39:21 +0100 Received: from [192.168.67.3] (helo=ptb-mxcore03.plus.net) by ptb-spamcore02.plus.net with esmtp (Exim 4.32; FreeBSD) id 1Bmeuu-0008ue-Kj for dave@picks.force9.co.uk; Mon, 19 Jul 2004 21:39:20 +0100 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore03.plus.net with esmtp (Exim) id 1Bmeun-000IrL-G0 for dave@picks.force9.co.uk; Mon, 19 Jul 2004 21:39:13 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Bmeu1-0001jx-Rl for rs_out_1@blacksheep.org; Mon, 19 Jul 2004 21:38:25 +0100 Received: from [193.82.116.30] (helo=relay.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Bmeu1-0001jj-Da for rsgb_lf_group@blacksheep.org; Mon, 19 Jul 2004 21:38:25 +0100 Received: from smtp814.mail.ukl.yahoo.com ([217.12.12.204]) by relay.thorcom.net with smtp (Exim 4.34) id 1Bmetx-0007iS-VQ for rsgb_lf_group@blacksheep.org; Mon, 19 Jul 2004 21:38:25 +0100 Received: from unknown (HELO rogersservices) (james.moritz@213.122.83.214 with login) by smtp814.mail.ukl.yahoo.com with SMTP; 19 Jul 2004 20:35:42 -0000 Message-ID: <001e01c46dcf$34e50a60$d6537ad5@rogersservices> From: "James Moritz" To: rsgb_lf_group@blacksheep.org References: <002201c46c3d$060963a0$0201a8c0@private.network> <004b01c46cc0$0d40fce0$07d98351@rogersservices> Date: Mon, 19 Jul 2004 21:29:19 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.00.2615.200 X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2615.200 X-Spam-Score: 0.1 (/) X-Spam-Report: autolearn=no,HTML_MESSAGE=0.001,RCVD_IN_SORBS=0.1 Subject: LF: 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=0.0 required=5.0 tests=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

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