Return-Path: Received: (qmail 14549 invoked from network); 1 May 2003 21:26:56 -0000 Received: from marstons.services.quay.plus.net (212.159.14.223) by mailstore with SMTP; 1 May 2003 21:26:56 -0000 Received: (qmail 23889 invoked by uid 10001); 1 May 2003 21:26:55 -0000 Received: from post.thorcom.com (193.82.116.70) by marstons.services.quay.plus.net with SMTP; 1 May 2003 21:26:55 -0000 X-SQ: A Received: from majordom by post.thorcom.com with local (Exim 4.14) id 19BLZ3-0006Qu-8b for rsgb_lf_group-outgoing@blacksheep.org; Thu, 01 May 2003 22:26:01 +0100 Received: from [212.135.6.14] (helo=smarthost4.mail.uk.easynet.net) by post.thorcom.com with esmtp (Exim 4.14) id 19BLYq-0006Ql-2X for rsgb_lf_group@blacksheep.org; Thu, 01 May 2003 22:25:48 +0100 Received: from tnt-1-51.easynet.co.uk ([195.40.206.51] helo=erica) by smarthost4.mail.uk.easynet.net with smtp (Exim 4.10) id 19BLYm-000FIF-00 for rsgb_lf_group@blacksheep.org; Thu, 01 May 2003 22:25:46 +0100 Message-ID: <001701c31029$0888ea40$33ce28c3@erica> From: "g3ldo" To: rsgb_lf_group@blacksheep.org References: <5.1.0.14.0.20030430120518.00ade070@gemini.herts.ac.uk> <001501c31001$6a079780$bee5fc3e@l8p8y6> Date: Thu, 1 May 2003 22:30:32 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.50.4522.1200 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Subject: LF: Mains Cable Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Status: No, hits=-12.9 required=5.0tests=ORIGINAL_MESSAGE,QUOTED_EMAIL_TEXT,REFERENCESversion=2.53 X-Spam-Checker-Version: SpamAssassin 2.53 (1.174.2.15-2003-03-30-exp) X-SA-Exim-Scanned: Yes Sender: Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rsgb_lf_group-outgoing@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false ----- Original Message ----- From: "hamilton mal" > HI Jim. > This looks like a nice tuning aid and judging by your signal it must be > working, the only other signal from the South that moves my S meter is > G3YXM, the others could certainly benefit from your meter. I wonder how it > works with mains electric cable instead of coax to the antenna. Someone > recently mentioned using this cable, and it seems popular on the South > Coast. I have always designed my TX/RX system to use 50 ohms, that way I > know exactly how to measure the performance and it reflects on signals > radiated and received from this QTH. As far as I am aware I am the only one who has confessed to using electrical mains cable as transmission line so I guess the above is aimed at me. The distance from my LF transmitter to the primary loading and tuning coil is about two metres. This makes the length of my "transmission line" about .0009 wavelengths. To put that into perspective that is about 20mm on 14MHz. The impedance of the transmission system is unimportant, although there are certain considerations. For example, the distance from the Decca transmitter site to the antenna loading/tuning building was often a couple of km so a higher impedance system is chosen to reduce I^2 R losses. Early amateur home brew transmitters (and some commercial) using pye tanks were often designed with a nominal 75ohms output due to the availability of cheap television coax. 50ohm systems were chosen by equipment, test gear, coax cable and antenna manufacturers in the interests of standardisation - there is nothing 'magic' about 50ohms systems. There is no point in having an interim 50ohms section between a transmitter (that is other than 50ohms) and the antenna matching/loading system unless you wish to use it with a piece of existing or proposed 50ohm test equipment. Regards, Peter, G3LDO e-mail Web