Return-Path: Received: (qmail 85758 invoked from network); 1 Mar 2005 11:34:06 -0000 Received: from unknown (HELO ptb-spamcore01.plus.net) (192.168.71.1) by ptb-mailstore02.plus.net with SMTP; 1 Mar 2005 11:34:06 -0000 Received: from mailnull by ptb-spamcore01.plus.net with spamcore-l-b (Exim 4.32; FreeBSD) id 1D65f1-0009Sv-6v for dave@picks.force9.co.uk; Tue, 01 Mar 2005 11:35:34 +0000 Received: from [192.168.67.1] (helo=ptb-mxcore01.plus.net) by ptb-spamcore01.plus.net with esmtp (Exim 4.32; FreeBSD) id 1D65el-0009Kz-NC for dave@picks.force9.co.uk; Tue, 01 Mar 2005 11:35:16 +0000 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore01.plus.net with esmtp (Exim) id 1D65fF-0005rL-QI for dave@picks.force9.co.uk; Tue, 01 Mar 2005 11:35:47 +0000 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1D65cq-00057J-E9 for rs_out_1@blacksheep.org; Tue, 01 Mar 2005 11:33:16 +0000 Received: from [193.82.116.30] (helo=relay.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1D65co-00056D-Uq for rsgb_lf_group@blacksheep.org; Tue, 01 Mar 2005 11:33:14 +0000 Received: from cas-mta3-fe.casema.nl ([83.80.1.28] helo=mta.casema.nl) by relay.thorcom.net with esmtp (Exim 4.43) id 1D65cn-0002BN-6m for rsgb_lf_group@blacksheep.org; Tue, 01 Mar 2005 11:33:14 +0000 Received: from s9z5i6.casema.nl ([83.85.106.243]) by cas-mta3.mgmt.casema.nl (Sun Java System Messaging Server 6.1 HotFix 0.11 (built Jan 28 2005)) with ESMTP id <0ICO00N3Z8364X20@cas-mta3.mgmt.casema.nl> for rsgb_lf_group@blacksheep.org; Tue, 01 Mar 2005 12:33:07 +0100 (CET) Date: Tue, 01 Mar 2005 12:34:58 +0100 From: Dick Rollema X-Sender: dickrollema@casema.nl@mail.casema.nl (Unverified) To: LF-Group Cc: "W.F. Oorschot" Message-id: <6.1.0.6.2.20050301115700.03662eb0@mail.casema.nl> MIME-version: 1.0 X-Mailer: QUALCOMM Windows Eudora Version 6.1.0.6 X-SPF-Result: relay.thorcom.net: 83.80.1.28 is neither permitted nor denied by domain of casema.nl X-Spam-Score: 0.1 (/) X-Spam-Report: autolearn=failed,FORGED_RCVD_HELO=0.05 Subject: LF: Current "lost" in loading coil Content-type: text/plain; charset=us-ascii; format=flowed Content-transfer-encoding: 8bit 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=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 X-Spam-Filtered: by PlusNet SpamCORE (v3.00) To All from PA0SE Several amateurs have found that the current at the bottom end of the loading coil is higher than at the top (aerial side) of the coil. In my station the difference is of the order of 10%. William, PA0WFO, has a large coil of 8 mH and a 23 m long wire as aerial. He measures 1.5 A at the bottom of the coil en 0.6 A at the top. My theory is that the "lost current" flows via the capacitance of the coil to its surrounding (even a metal object in free space has capacitance). The current at the bottom of the bottom of the coil divides between the capacitances of coil and aerial. I suggested to William he measure the capacitance of the coil and of the aerial. For the coil he found 150 - 200 pF, depending upon the position of the coil and for the aerial 210 pF. But these values do not explain the large difference in current at bottom and top of the coil. In a transmitting aerial the current increases going from the end of the radiator towards the coil. Now to my question: does this increase in current also occur in the winding of the coil? My feeling is that the current at the beginning and end of a coil should be the same; apart from the current that flows via its capacitance to the surrounding. I also have read that the coil should be considered as an aerial with a length equal to the length of the coil. But on 2 km that would be an extremely small aerial, reckoned in wavelength. So radiation by the coil must be negligible. There are certainly experts on the reflector who know the answers. I welcome their views. 73, Dick, PA0SE