Return-Path: Received: (qmail 10175 invoked from network); 13 Dec 2002 11:56:54 -0000 Received: from netmail01.services.quay.plus.net (212.159.14.219) by mailstore with SMTP; 13 Dec 2002 11:56:54 -0000 Content-Transfer-Encoding: 8bit Received: (qmail 28797 invoked by uid 10001); 13 Dec 2002 11:57:47 -0000 X-Priority: 3 X-MSMail-Priority: Normal Received: from post.thorcom.com (193.82.116.70) by netmail01.services.quay.plus.net with SMTP; 13 Dec 2002 11:57:47 -0000 X-SQ: A X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Received: from majordom by post.thorcom.com with local (Exim 4.10) id 18MoOB-00070K-00 for rsgb_lf_group-outgoing@blacksheep.org; Fri, 13 Dec 2002 11:53:55 +0000 Received: from [147.197.200.9] (helo=hestia.herts.ac.uk) by post.thorcom.com with esmtp (Exim 4.10) id 18MoOB-00070B-00 for rsgb_lf_group@blacksheep.org; Fri, 13 Dec 2002 11:53:55 +0000 Received: from gemini ([147.197.200.44] helo=gemini.herts.ac.uk) by hestia.herts.ac.uk with esmtp (Exim 3.22 #1) id 18MoMy-0001Oz-00 for rsgb_lf_group@blacksheep.org; Fri, 13 Dec 2002 11:52:40 +0000 Received: from [147.197.232.252] (helo=rsch-15.herts.ac.uk) by gemini.herts.ac.uk with esmtp (Exim 3.33 #1) id 18MoMv-0005CD-00 for rsgb_lf_group@blacksheep.org; Fri, 13 Dec 2002 11:52:38 +0000 Message-ID: <5.1.0.14.0.20021213111720.00ae06f8@gemini.herts.ac.uk> X-Sender: mj9ar@gemini.herts.ac.uk X-Mailer: QUALCOMM Windows Eudora Version 5.1 Date: Fri, 13 Dec 2002 11:52:36 +0000 To: rsgb_lf_group@blacksheep.org From: "James Moritz" In-reply-to: References: <002301c2a1fb$c711f020$0504210a@c.scope> MIME-Version: 1.0 X-MailScanner: No Virus detected Subject: RE: LF: Antenna tests Content-Type: text/plain; charset=us-ascii; format=flowed X-Spam-Status: No, hits=-0.4 required=5.0tests=DEAR_SOMEBODY,IN_REP_TO,REFERENCES,SPAM_PHRASE_00_01version=2.42 Sender: Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Dear Hugh, Gary, LF Group, I have used basically 2 methods to measure the loss resistance of an antenna. First is a straightforward "noise bridge" type of impedance measurement where the impedance of the antenna is compared to a reference resistor/capacitor combination. At LF, a CW source is a better idea than a noise source for the bridge excitation, due to the narrow bandwidths. A normal receiver can be used as null detector, but I use the SPM3 level meter with PS3 tracking generator - the ideal tools for the job. I resonate the antenna with a series L, and measure the resistance, rather than trying to balance the resistance and capacitance with the bridge. The main advantage of this is that the resonant antenna stops the poor SPM3 being blasted by the very strong MF broadcast signals at my QTH. The second method is an "on line"method, where I use a dual trace oscilloscope to measure the voltage and current (via a current transformer) at the feed point while transmitting - I also use this as a tuning aid. Of course, this gives you the total of the loss resistance of the antenna, the loading coil resistance, and the radiation resistance. The coil AC resistance can be measured in a separate experiment, and subtracted from the total. The radiation resistance is so small that it has no effect on the overall resistance. Rrad can either be determined by calculations using the antenna geometry, (see ON7YD's web pages, or use an antenna simulator like EZNEC), or inferred from field strength measurements - unfortunately, the latter shows that the former usually gives optimistic results! Cheers, Jim Moritz 73 de M0BMU