Return-Path: Received: (qmail 24716 invoked from network); 29 Apr 2003 20:09:58 -0000 Received: from murphys.services.quay.plus.net (212.159.14.225) by mailstore with SMTP; 29 Apr 2003 20:09:58 -0000 Received: (qmail 23988 invoked from network); 29 Apr 2003 20:09:45 -0000 Received: from post.thorcom.com (193.82.116.70) by murphys.services.quay.plus.net with SMTP; 29 Apr 2003 20:09:45 -0000 X-SQ: A Received: from majordom by post.thorcom.com with local (Exim 4.14) id 19AbPp-0000PF-U4 for rsgb_lf_group-outgoing@blacksheep.org; Tue, 29 Apr 2003 21:09:25 +0100 Received: from [212.135.6.10] (helo=smarthost0.mail.uk.easynet.net) by post.thorcom.com with esmtp (Exim 4.14) id 19AbPl-0000P6-1f for rsgb_lf_group@blacksheep.org; Tue, 29 Apr 2003 21:09:21 +0100 Received: from tnt-5-122.easynet.co.uk ([195.40.200.122] helo=erica) by smarthost0.mail.uk.easynet.net with smtp (Exim 4.10) id 19AbPj-0008ms-00 for rsgb_lf_group@blacksheep.org; Tue, 29 Apr 2003 21:09:19 +0100 Message-ID: <000601c30e8c$01f2b740$7ac828c3@erica> From: "g3ldo" To: rsgb_lf_group@blacksheep.org References: <5.1.0.14.0.20030429145925.00ae4c60@gemini.herts.ac.uk> Date: Tue, 29 Apr 2003 21:14:10 +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: Re: LF Tuning meter Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Status: No, hits=-9.8 required=5.0tests=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 Hi Jim > For tuning LF antennas, I have for some time been using an oscilloscope to > monitor the current and voltage waveforms at the TX output. Resonance > occurs when V and I are in phase, and the load resistance is 50ohms when > V/I = 50. This is very easy to use provided a scope is to hand, but not > very useful if it isn't. An SWR bridge can be used, but it only indicates > the degree of mismatch, so tuning is still a matter of trial and error. So > with a mind towards future /P operations, I have built a self-contained > tuning meter. > Although I included a description of your ScopeMatch Tuning Aid in the LF book (as built by Lech G3KAU) I never did get round to building one myself. The reason is that I never had a transmitter that had a 50ohm output system. With the BK amplifier I went straight from 4ohms to the multi-tap toroid transformer at the base of the antenna system. Resonance is indicated by maximum antenna current and matching by the current to the amplifier FETs. The amplifier was coupled to the antenna matching transformer with a length of heavy duty mains cable. When I moved on to the Decca transmitter I changed the antenna antenna loading toroid transformer to an auto transformer arrangement because I didn't need the isolation. This system is 70ohms and for some time I used the same mains cable transmission line. I recently changed it to 50ohm coax (because it seemed not quite right to be using mains cable for such an application) but it had no effect on the transmitter performance. The question is would your tuning aid be of any use in my system? I can see a use when I use the LF transmitter at Amberley Museum, where resonance and antenna feed impedance are totally different to the home QTH but is your latest meter for 50ohms only? I would be grateful if you could send me a copy of the PDF. Regards, Peter, G3LDO e-mail Web