Return-Path: Received: (qmail 83681 invoked from network); 2 Mar 2005 15:44:13 -0000 Received: from unknown (HELO ptb-spamcore01.plus.net) (192.168.71.1) by ptb-mailstore02.plus.net with SMTP; 2 Mar 2005 15:44:13 -0000 Received: from mailnull by ptb-spamcore01.plus.net with spamcore-l-b (Exim 4.32; FreeBSD) id 1D6W2V-0009Uu-QM for dave@picks.force9.co.uk; Wed, 02 Mar 2005 15:45:37 +0000 Received: from [192.168.67.2] (helo=ptb-mxcore02.plus.net) by ptb-spamcore01.plus.net with esmtp (Exim 4.32; FreeBSD) id 1D6W2D-0009SA-Rd for dave@picks.force9.co.uk; Wed, 02 Mar 2005 15:45:14 +0000 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore02.plus.net with esmtp (Exim) id 1D6W0U-0009Iy-5x for dave@picks.force9.co.uk; Wed, 02 Mar 2005 15:43:26 +0000 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1D6VzP-0007BG-6h for rs_out_1@blacksheep.org; Wed, 02 Mar 2005 15:42:19 +0000 Received: from [193.82.116.30] (helo=relay.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1D6VzH-00074T-Fo for rsgb_lf_group@blacksheep.org; Wed, 02 Mar 2005 15:42:11 +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 1D6VzC-0002Zj-NB for rsgb_lf_group@blacksheep.org; Wed, 02 Mar 2005 15:42:08 +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 <0ICQ008VOE9X1J50@cas-mta3.mgmt.casema.nl> for rsgb_lf_group@blacksheep.org; Wed, 02 Mar 2005 16:41:59 +0100 (CET) Date: Wed, 02 Mar 2005 16:43:46 +0100 From: Dick Rollema In-reply-to: <4225CA7F.15619.BBCBA7@localhost> X-Sender: dickrollema@casema.nl@mail.casema.nl (Unverified) To: rsgb_lf_group@blacksheep.org Message-id: <6.1.0.6.2.20050302162804.02a13ea0@mail.casema.nl> MIME-version: 1.0 X-Mailer: QUALCOMM Windows Eudora Version 6.1.0.6 References: <4225CA7F.15619.BBCBA7@localhost> X-SPF-Result: relay.thorcom.net: 83.80.1.28 is neither permitted nor denied by domain of casema.nl X-Spam-Score: 0.8 (/) X-Spam-Report: autolearn=no,FORGED_RCVD_HELO=0.05,HTML_20_30=0.504,HTML_FONT_BIG=0.232,HTML_MESSAGE=0.001 Subject: Re: LF: Lost current in a coil 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=0.1 required=5.0 tests=HTML_FONT_BIG,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 To Mike and All

At 15:15 2-3-05, G3XDV wrote:
A useful test to see whether radiation causes the loss, would be to
completely screen the loading coil.
Because the size of the coil is so small, expressed in wavelength,  radiation is negligible.

I have never understood why, if the current is thought to stay the
same from top to bottom of a coil, the voltage is much bigger at the
top? Is this a phase thing?

The voltage at the bottom is equal to the output voltage of the transmitter; at e.g. 100W this is 70V over 50 ohm.

As an example let the inductance of the coil  be 5mH. Then its reactance at 136kHz is 4270 ohm.
With an aerial current of for instance 2A flowing through the coil the voltage at the top of the coil will be
2 * 4270 = 8541V higher than at the bottom. 
So total voltage at the top will be 70 + 8541 = 8610V.

73, Dick, PA0SE