Return-Path: Received: (qmail 85014 invoked from network); 1 Mar 2005 12:53:57 -0000 Received: from unknown (HELO ptb-spamcore01.plus.net) (192.168.71.1) by ptb-mailstore01.plus.net with SMTP; 1 Mar 2005 12:53:57 -0000 Received: from mailnull by ptb-spamcore01.plus.net with spamcore-l-b (Exim 4.32; FreeBSD) id 1D66uM-000OvF-2s for dave@picks.force9.co.uk; Tue, 01 Mar 2005 12:55:30 +0000 Received: from [192.168.67.3] (helo=ptb-mxcore03.plus.net) by ptb-spamcore01.plus.net with esmtp (Exim 4.32; FreeBSD) id 1D66uJ-000Ou8-Ja for dave@picks.force9.co.uk; Tue, 01 Mar 2005 12:55:23 +0000 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore03.plus.net with esmtp (Exim) id 1D66uT-0001Qh-Bj for dave@picks.force9.co.uk; Tue, 01 Mar 2005 12:55:33 +0000 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1D66sH-0003Pa-32 for rs_out_1@blacksheep.org; Tue, 01 Mar 2005 12:53:17 +0000 Received: from [193.82.116.30] (helo=relay.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1D66sG-0003PR-KH for rsgb_lf_group@blacksheep.org; Tue, 01 Mar 2005 12:53:16 +0000 Received: from smtp808.mail.ukl.yahoo.com ([217.12.12.198]) by relay.thorcom.net with smtp (Exim 4.43) id 1D66sE-00048N-1N for rsgb_lf_group@blacksheep.org; Tue, 01 Mar 2005 12:53:16 +0000 Received: from unknown (HELO aquarids) (ganymede444@217.42.60.198 with login) by smtp808.mail.ukl.yahoo.com with SMTP; 1 Mar 2005 12:53:08 -0000 From: "Dave G3WCB" To: rsgb_lf_group@blacksheep.org Date: Tue, 1 Mar 2005 12:53:04 -0000 Message-ID: MIME-Version: 1.0 X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook IMO, Build 9.0.2416 (9.0.2911.0) X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1441 Importance: Normal In-Reply-To: <001a01c51e57$6c9ddc00$47540150@p2300> X-SPF-Result: relay.thorcom.net: 217.12.12.198 is neither permitted nor denied by domain of btopenworld.com X-Spam-Score: 1.5 (+) X-Spam-Report: autolearn=no,FROM_ENDS_IN_NUMS=0.516,RCVD_IN_NJABL_PROXY=1.026 Subject: LF: RE: Re: Current "lost" in loading coil Content-Type: text/plain; charset=iso-8859-1; 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=0.9 required=5.0 tests=FROM_ENDS_IN_NUMS 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) Bryan, Dick, LF, I have about 9% more current at the bottom than at the top (1.48A vs 1.37A). Not as great as difference as William. The coil is 50cm tall, and 30cm diameter. My antenna is a 30m "Tee" at 6m height with a two-wire top. I know where some of the RF goes.....I had to remove the fluorescent tube from its fitting in the Coil House (a.k.a. garage) because it was striking every time I keyed up. Bit of a giveaway, that... 73, Dave G3WCB IO91RM -----Original Message----- From: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org]On Behalf Of captbrian Sent: 01 March 2005 12:09 To: rsgb_lf_group@blacksheep.org Cc: W.F. Oorschot Subject: LF: Re: Current "lost" in loading coil I am not an expert at all but a feeling for the answer can often be found by taking a predictable answer to a simple example and moving progressively to the situation under consideration. (A)If you pull the coil out into a straight wire (all in the mind of course ) will the current be less at the remote end than the close end ? Ans. Yes of course If you make a single spiral turn of the original diameter but stretching the full length of the wire will it be less ? Ans. of course it will. How about two spiral turns? Ans, Yes Three turns ? Ye-es. Four ? Five ? Is there some magic number of turns that the current suddenly becomes the same at the top and the bottom? Ans. Never heard of such a thing OK then ,When you have the coil all put back together (in your mind) to the original configuration will there be less at the top than at the bottom? Obviously yes!! How much difference is another matter. (B) I always thought of a short loaded antenna as an inductance in series with the capacitance of the "whip" to make a resonant "acceptor" circuit but I was coaching a nurse for her american radio amateur exam so she could use it on board a far-away sailboat. When talking about bottom loading of a back-stay antenna with a coil of wire she said "well that's obvious , the coil is just a winding up of the rest of the wire which should have been out there in the first place" and ever since I have thought of bottom loading as just a winding up of some of the antenna wire. On that basis the current is sure to be less at the top than at the bottom. G3GVB ----- Original Message ----- From: Dick Rollema To: LF-Group Cc: W.F. Oorschot Sent: Tuesday, March 01, 2005 11:34 AM Subject: LF: Current "lost" in loading coil > 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 > > > >