Return-Path: Received: (qmail 54669 invoked from network); 10 Nov 2004 19:53:27 -0000 Received: from unknown (HELO ptb-spamcore02.plus.net) (192.168.71.3) by ptb-mailstore02.plus.net with SMTP; 10 Nov 2004 19:53:27 -0000 Received: from mailnull by ptb-spamcore02.plus.net with spamcore-l-b (Exim 4.32; FreeBSD) id 1CRyV8-0002OU-58 for dave@picks.force9.co.uk; Wed, 10 Nov 2004 19:51:31 +0000 Received: from [192.168.67.1] (helo=ptb-mxcore01.plus.net) by ptb-spamcore02.plus.net with esmtp (Exim 4.32; FreeBSD) id 1CRyV7-0002OQ-Tg for dave@picks.force9.co.uk; Wed, 10 Nov 2004 19:51:29 +0000 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore01.plus.net with esmtp (Exim 4.30; FreeBSD) id 1CRyWz-0007gF-86 for dave@picks.force9.co.uk; Wed, 10 Nov 2004 19:53:25 +0000 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1CRyWK-0007mI-Ie for rs_out_1@blacksheep.org; Wed, 10 Nov 2004 19:52:44 +0000 Received: from [193.82.116.30] (helo=relay.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1CRyWK-0007m9-3V for rsgb_lf_group@blacksheep.org; Wed, 10 Nov 2004 19:52:44 +0000 Received: from smtp809.mail.ukl.yahoo.com ([217.12.12.199]) by relay.thorcom.net with smtp (Exim 4.41) id 1CRyVx-0008UU-8n for rsgb_lf_group@blacksheep.org; Wed, 10 Nov 2004 19:52:41 +0000 Received: from unknown (HELO jgtdiynm) (james.moritz@213.122.171.187 with login) by smtp809.mail.ukl.yahoo.com with SMTP; 10 Nov 2004 19:52:14 -0000 Message-ID: <000f01c4c75e$a00d5ca0$bbab7ad5@jgtdiynm> From: "James Moritz" To: rsgb_lf_group@blacksheep.org References: Date: Wed, 10 Nov 2004 19:51:08 -0000 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-SPF-Result: relay.thorcom.net: 217.12.12.199 is neither permitted nor denied by domain of btopenworld.com X-Spam-Score: 0.1 (/) X-Spam-Report: autolearn=no,HTML_MESSAGE=0.001,RCVD_IN_SORBS=0.1 Subject: Re: LF: Loading coil - suggestions 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 Chris, LF group,

When I first started running QRO on LF, I had problems with loading coils overheating. So I made a big loading coil using ex-Decca litz wire and a 500mm diameter plastic "sectional manhole" as a former. This has a Q of about 700 and significantly improved antenna current over the original, with a Q of about 200. Since it is outdoors, I built a shelter for it out of 2" x 2" timber covered in plastic sheet. I was alarmed to discover the Q had gone down to 200 again when I put the coil in the shelter. Some investigation showed that this was because of the timber frame - the wood was pressure-treated with preservative, and was quite damp inside. Replacing it with some kiln-dried timber restored the Q, but it seems to be slowly deteriorating again after a few years outdoors. The frame is quite well spaced away from the coil, perhaps 150mm or more at the nearest point, so obviously wood is not the best of dielectrics...

Having said that, GBR worked for decades with a loading coil wound on a wooden former - this with around 200kV and half a megawatt going through it - so some wood must be OK!

Cheers, Jim Moritz

73 de M0BMU