Return-Path: <owner-rsgb_lf_group@blacksheep.org> Received: (qmail 59165 invoked from network); 19 Jan 2004 13:56:18 -0000 Received: from unknown (HELO ptb-mxscan03.plus.net) (212.159.14.237) by ptb-mailstore01.plus.net with SMTP; 19 Jan 2004 13:56:18 -0000 Received: (qmail 42161 invoked from network); 19 Jan 2004 13:56:18 -0000 Content-Transfer-Encoding: 8bit X-Filtered-by: Plusnet (hmail v1.01) X-Spam-detection-level: 11 X-Priority: 3 X-MSMail-Priority: Normal Received: from ptb-mxcore03.plus.net (212.159.14.217) by ptb-mxscan03.plus.net with SMTP; 19 Jan 2004 13:56:16 -0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore03.plus.net with esmtp (Exim) id 1AiZt2-000Aqg-Jp for dave@picks.force9.co.uk; Mon, 19 Jan 2004 13:56:16 +0000 X-Fake-Domain: majordom Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1AiZsO-00034i-2i for rs_out@blacksheep.org; Mon, 19 Jan 2004 13:55:36 +0000 Received: from [134.58.240.42] (helo=rusty.kulnet.kuleuven.ac.be) by post.thorcom.com with esmtp (Exim 4.14) id 1AiZsN-00034V-5V for rsgb_lf_group@blacksheep.org; Mon, 19 Jan 2004 13:55:35 +0000 Received: from localhost (localhost [127.0.0.1]) by rusty.kulnet.kuleuven.ac.be (Postfix) with ESMTP id EC3E91D773F for <rsgb_lf_group@blacksheep.org>; Mon, 19 Jan 2004 14:55:04 +0100 (CET) Received: from octavianus.kulnet.kuleuven.ac.be (octavianus.kulnet.kuleuven.ac.be [134.58.240.71]) by rusty.kulnet.kuleuven.ac.be (Postfix) with ESMTP id 2D3021D7739 for <rsgb_lf_group@blacksheep.org>; Mon, 19 Jan 2004 14:55:04 +0100 (CET) X-Fake-Domain: dell-rik.fys.kuleuven.ac.be Received: from dell-rik.fys.kuleuven.ac.be (pc-10-33-165-177.fys.kuleuven.ac.be [10.33.165.177]) by octavianus.kulnet.kuleuven.ac.be (Postfix) with ESMTP id 07D4EAEF49 for <rsgb_lf_group@blacksheep.org>; Mon, 19 Jan 2004 14:55:04 +0100 (CET) Message-ID: <5.1.0.14.0.20040119140000.03714bf0@u0019445.kuleuven.be> X-Sender: u0019445@u0019445.kuleuven.be X-Mailer: QUALCOMM Windows Eudora Version 5.1 Date: Mon, 19 Jan 2004 14:57:53 +0100 To: rsgb_lf_group@blacksheep.org From: "Rik Strobbe" <rik.strobbe@fys.kuleuven.ac.be> In-reply-to: <C75A388845B4B54B9CF5E2ADB589B0E3031AEFDE@btss.siemens-pse. sk> MIME-Version: 1.0 X-Virus-Scanned: by KULeuven Antivirus Cluster Subject: Re: LF: Test failed... Content-Type: text/plain; charset=us-ascii; format=flowed 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: <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@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-PN-SPAMFiltered: yes X-Spam-Rating: 1 Hello Rich, According to MMAMA the antenna capacitance should be something like 2.7nF, thus a loadingcoil of +/- 500uH would be needed. I assume that at least one of the variometers covered this range. It is a wild guess, but maybe the power is "DC grounded" using a coil from the antenna base to ground. If this coil is dimensioned for a much higher frequency (MF) it can cause rather strange effects on LF. Eg. : Assume the original use of the tower was a lambda/4 antenna at MF, for a 135 m tower that would be +/- 550 kHz. Antenna impedance (at 550kHz) would be +/- 36 Ohm, so "good engineering" would require a DC path to ground (for safety) with a Z of at least 10 times the antenna impedance = 360 Ohm. At 550 kHz this would mean a +/- 100 uH inductor. So, instead of seeing the antenna as a 2.7nF capacitor to ground it should be seen as a L-C parallel circuit (100 uH // 2.7 nF). Or in terms of reactances (at 136 kHz) : +j85 Ohm // -j433 Ohm = +j106 Ohm (= +/- 124 uH at 136 kHz). To get the antenna tuned (brought to resonance) you would need a series capacitor (not inductor !) with a reactance of -j106 Ohm at 136 kHz = +/- 11 nF. This kind of tuning will also cause impedance transformation : If the resistive component (radiation resistance + loss) is 20 Ohm it will be transformed to 1.2 Ohm and the "system Q" will rise from 22 to 108 (making tuning rather critical). 73, Rik ON7YD >We will try tu tune the antenna with your help, if anybody can help me. >I'll be very happy. >I'll give you all necessary datas: > >Vertical is 135m high with 170cm in diameter (no cap hat), there are 120 >radials in range from the base and 50m, after that are 240 radials between >range 50-130m. Each radial is from 6mm Cu wire about 30cm under the ground >level. Ground conductivity is 14,3mS.