Envelope-to: dave@picks.force9.co.uk Delivery-date: Sun, 05 Feb 2006 09:17:43 +0000 Received: by ptb-mxcore01.plus.net with spam-scanned (PlusNet MXCore v2.00) id 1F5g1f-0007pM-Cd for dave@picks.force9.co.uk; Sun, 05 Feb 2006 09:17:43 +0000 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore01.plus.net with esmtp (PlusNet MXCore v2.00) id 1F5g1f-0007pF-7z for dave@picks.force9.co.uk; Sun, 05 Feb 2006 09:17:43 +0000 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1F5g1I-0000qI-Lw for rs_out_1@blacksheep.org; Sun, 05 Feb 2006 09:17:20 +0000 Received: from [193.82.59.130] (helo=relay2.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1F5g1I-0000q9-6p for rsgb_lf_group@blacksheep.org; Sun, 05 Feb 2006 09:17:20 +0000 Received: from olympus.pncl.co.uk ([195.224.180.233] helo=olive.pncl.co.uk) by relay2.thorcom.net with esmtp (Exim 4.51) id 1F5gkx-0006xG-Vu for rsgb_lf_group@blacksheep.org; Sun, 05 Feb 2006 10:04:33 +0000 Received: from AUG2004 (81-6-246-23.dyn.gotadsl.co.uk [81.6.246.23]) (authenticated bits=0) by olive.pncl.co.uk (8.13.4/8.13.4) with ESMTP id k159GDlw024203 for ; Sun, 5 Feb 2006 09:16:13 GMT Message-ID: <007001c62a34$97e808b0$2101a8c0@AUG2004> From: "Walter Blanchard" To: rsgb_lf_group@blacksheep.org Date: Sun, 5 Feb 2006 09:14:30 -0000 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2527 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2527 X-Pinnacle-MailScanner-Information: Please contact the ISP for more information X-Pinnacle-MailScanner: Found to be clean X-MailScanner-From: blanch@pncl.co.uk Subject: LF: {Spam?} Active_antennas Content-Type: text/html; charset=windows-1252 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_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-PN-SpamFiltered: by PlusNet MXCore (v2.00) Content-transfer-encoding: 8bit

The theory behind the "height gain" observed using small LF active antennas at different heights has to do with compression of the near-earth LF potential gradient caused by the grounded "mast" holding the antenna.

The essential bit is that there is a grounded connection between the antenna and receiver, which may be just the outer of the co-ax cable. It would be an interesting experiment to repeat the "height gain" experiment without any connection to ground. This could be done by building an active antenna with a little transmitter to re-radiate the received LF signal (on 2.4 GHz?) and poking it up using a fibreglass mast. If the theory is right then there wouldn't be any height gain. Might do it myself sometime but anyone else interested?

Walter G3JKV.