Return-Path: Received: (qmail 11636 invoked from network); 21 Oct 2002 19:51:42 -0000 Received: from murphys.services.quay.plus.net (212.159.14.225) by mailstore with SMTP; 21 Oct 2002 19:51:42 -0000 Received: (qmail 11912 invoked from network); 21 Oct 2002 19:50:26 -0000 Received: from post.thorcom.com (193.82.116.70) by murphys.services.quay.plus.net with SMTP; 21 Oct 2002 19:50:26 -0000 X-SQ: A Received: from majordom by post.thorcom.com with local (Exim 4.10) id 183iZ2-00054w-00 for rsgb_lf_group-outgoing@blacksheep.org; Mon, 21 Oct 2002 20:50:12 +0100 Received: from [210.86.15.146] (helo=mta203-rme.xtra.co.nz) by post.thorcom.com with esmtp (Exim 4.10) id 183iZ2-00054i-00 for rsgb_lf_group@blacksheep.org; Mon, 21 Oct 2002 20:50:12 +0100 Received: from mta3-rme.xtra.co.nz ([210.86.15.141]) by mta203-rme.xtra.co.nz with ESMTP id <20021021194940.HWRM3817.mta203-rme.xtra.co.nz@mta3-rme.xtra.co.nz> for ; Tue, 22 Oct 2002 08:49:40 +1300 Received: from xtr743187 ([210.54.99.39]) by mta3-rme.xtra.co.nz with SMTP id <20021021194936.CNUK5415.mta3-rme.xtra.co.nz@xtr743187> for ; Tue, 22 Oct 2002 08:49:36 +1300 Message-ID: <000001c2793a$fcd867a0$276336d2@xtr743187> From: "Vernall" To: rsgb_lf_group@blacksheep.org References: Date: Tue, 22 Oct 2002 08:45:50 +1300 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.00.2919.6600 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Subject: LF: Drooping top loading Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Status: No, hits=0.2 required=5.0tests=QUOTED_EMAIL_TEXT,SPAM_PHRASE_00_01,USER_AGENT_OEversion=2.42 Sender: Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Bill, > My experience with many shapes of top hats is that it DOES reduce the > radiation measured in the far field. The theoretical explanation I have seen > is that the effective height is reduced due to the current foldback. I have an LF antenna that uses a telescopic mast for one part of multiple top loading (three masts in all). The mast is parked in the down position, and cranked up for LF transmitting. The far field is definitely lower (from S meter reports of several others) when the wire is below the "full" height. The situation may well depend on how good the ground conductivity is, as a "drooping" part of top loading means higher field strength to ground over the droopy part, and higher field strength means higher ground current and consequent I squared R losses. In other words, RF warm spots can arise under drooping wires. If the antenna is built over an immaculate ground system with hundreds of ground radials (as per a text book design), then the likes of an umbrella antenna would not be as lossy as one built over average soil with perhaps a few radials. 73, Bob ZL2CA