X-GM-THRID: 1198117983831384937 X-Gmail-Labels: rsgb lf X-Gmail-Received: bbf7f4f80f47dba7a87ee8fa02e895288b0ea4c1 Delivered-To: daveyxm@gmail.com Received: by 10.54.70.14 with SMTP id s14cs3003wra; Fri, 17 Mar 2006 08:52:29 -0800 (PST) Received: by 10.64.193.9 with SMTP id q9mr610033qbf; Fri, 17 Mar 2006 08:52:28 -0800 (PST) Return-Path: Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mx.gmail.com with ESMTP id e15si1215516qbe.2006.03.17.08.52.27; Fri, 17 Mar 2006 08:52:28 -0800 (PST) Received-SPF: neutral (gmail.com: 193.82.116.20 is neither permitted nor denied by best guess record for domain of owner-rsgb_lf_group@blacksheep.org) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1FKI8s-00051b-SL for rs_out_1@blacksheep.org; Fri, 17 Mar 2006 16:49:34 +0000 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1FKI8s-00051S-GC for rsgb_lf_group@blacksheep.org; Fri, 17 Mar 2006 16:49:34 +0000 Received: from smtp810.mail.ukl.yahoo.com ([217.12.12.200]) by relay1.thorcom.net with smtp (Exim 4.51) id 1FKJj1-0002IT-1S for rsgb_lf_group@blacksheep.org; Fri, 17 Mar 2006 18:31:15 +0000 Received: (qmail 89192 invoked from network); 17 Mar 2006 16:49:13 -0000 Received: from unknown (HELO LAPTOP) (peter.martinez@btinternet.com@86.135.51.50 with login) by smtp810.mail.ukl.yahoo.com with SMTP; 17 Mar 2006 16:49:13 -0000 Message-ID: <060401c649e2$b85e4460$0300a8c0@LAPTOP> From: "Peter Martinez" To: References: <001a01c649df$5981a0c0$57e8fc3e@your4105e587b6> Date: Fri, 17 Mar 2006 16:49:12 -0000 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 X-Spam-Score: -0.6 (/) X-Spam-Report: autolearn=disabled,AWL=-0.578 Subject: LF: Re: LOPT CORES Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=original Content-Transfer-Encoding: 7bit X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=none 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 Status: O X-Status: X-Keywords: X-UID: 6413 >From G3PLX: Ferrite cores in TV line output and switchmode power supplies often have an air gap. This means that the effective permeability is not very high. This is done because the transformers in these circuits are used as inductive energy storage devices, not as true transformers. The inductance of the winding is much lower than the winding of a true transformer with the same number of turns. For LF transmitter use, we don't want to store the energy, just have a transformer with a high inductance which doesn't shunt the load, so we don't want a gap in the core. In the case of TV line output transformers, the gap is usually formed by means of two thin mylar spacers between the two halves. Unscrew the clamp and the two spacers will fall out and can be discarded. In the case of 'E and I' cores in switchmode PSUs, the same spacer idea may be used, so if you are recycling one of these for LF transmitter use, just remove the spacers. But in some cases the gap is built into the centre limb of the 'E' part, and if you examine the E core carefully you will see that the centre limb is shorter than the outer limbs and there's an air gap when you clamp the E to the I. Cores like this will be no good for our purposes! 73 Peter