Return-Path: Received: (qmail 82266 invoked from network); 19 Jan 2004 16:47:20 -0000 Received: from unknown (HELO ptb-mxscan01.plus.net) (212.159.14.235) by ptb-mailstore01.plus.net with SMTP; 19 Jan 2004 16:47:20 -0000 Received: (qmail 45632 invoked from network); 19 Jan 2004 16:47:19 -0000 X-Filtered-by: Plusnet (hmail v1.01) X-Spam-detection-level: 11 Received: from ptb-mxcore01.plus.net (212.159.14.215) by ptb-mxscan01.plus.net with SMTP; 19 Jan 2004 16:47:18 -0000 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore01.plus.net with esmtp (Exim) id 1AicYY-000Bkr-9G for dave@picks.force9.co.uk; Mon, 19 Jan 2004 16:47:18 +0000 X-Fake-Domain: majordom Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1AicYD-00077W-Lg for rs_out@blacksheep.org; Mon, 19 Jan 2004 16:46:57 +0000 Received: from [147.197.200.9] (helo=hestia.herts.ac.uk) by post.thorcom.com with esmtp (Exim 4.14) id 1AicYC-00077N-VM for rsgb_lf_group@blacksheep.org; Mon, 19 Jan 2004 16:46:57 +0000 X-Fake-Domain: gemini Received: from gemini ([147.197.200.44] helo=gemini.herts.ac.uk) by hestia.herts.ac.uk with esmtp (Exim 3.22 #1) id 1AicMl-0004F2-00 for rsgb_lf_group@blacksheep.org; Mon, 19 Jan 2004 16:35:07 +0000 X-No-DNS-For: 147.197.232.252 Received: from [147.197.232.252] (helo=rsch15) by gemini.herts.ac.uk with esmtp (Exim 3.33 #1) id 1AicMk-0000cP-00 for rsgb_lf_group@blacksheep.org; Mon, 19 Jan 2004 16:35:06 +0000 From: "James Moritz" To: rsgb_lf_group@blacksheep.org Date: Mon, 19 Jan 2004 16:35:08 -0000 Organization: University of Hertfordshire X-Bad-Message-ID: no DNS (rsch15) Message-ID: <000001c3deaa$334f56b0$fce8c593@rsch15> MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.2627 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Importance: Normal In-reply-to: X-UH-MailScanner: No Virus detected Subject: LF: RE: AC feeder... Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Checker-Version: SpamAssassin 2.60 (1.212-2003-09-23-exp) on post.thorcom.com X-Spam-Status: No, hits=0.0 required=5.0 tests=none autolearn=no version=2.60 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: rs_out@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-PN-SPAMFiltered: yes X-Spam-Rating: 2 Dear Rich, If the chokes have fairly low inductance (so that XLchoke < XCant; total L < several 100uH) or they are part of some sort of tuned trap resonant at 1097kHz, I guess this arrangement will result in the antenna feed point having an inductive reactance at 136k, so you will need to add capacitance to tune this out. How much capacitance will depend on the choke inductance - you could probably calculate that to a reasonable approximation by measuring the size and number of turns. Or better still, measure the actual impedance if you have the necessary test gear. I guess it would be some nF. It would have to have high RF voltage/current rating. Connecting the resonating C between ant feed and ground would probably give quite a high resistance at 136k; connecting the C between ant feed and TX output a very low resistance. Either way, you would probably need additional matching to the TX output, either using a transformer or by tapping the capacitor. The efficiency of this kind of matching network would depend a lot on the Q of the chokes at 136k, and the other components, and would probably be much lower than if they were not there - but since the AC feed chokes can obviously take quite big RF currents and voltages, they might have reasonably high Q, and since the antenna is so big, you will be able to radiate a good signal even if efficiency is quite low. Cheers, Jim Moritz 73 de M0BMU