Return-Path: Received: (qmail 28455 invoked from network); 2 Jun 2000 19:16:23 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by grants.core.plus.net.uk with SMTP; 2 Jun 2000 19:16:23 -0000 Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8bit Received: from majordom by post.thorcom.com with local (Exim 3.02 #1) id 12xwns-0002na-00 for rsgb_lf_group-outgoing@blacksheep.org; Fri, 02 Jun 2000 20:08:20 +0100 X-Priority: 3 X-MSMail-Priority: Normal Received: from finch-post-11.mail.demon.net ([194.217.242.39]) by post.thorcom.com with esmtp (Exim 3.02 #1) id 12xwnr-0002nV-00 for rsgb_lf_group@blacksheep.org; Fri, 02 Jun 2000 20:08:19 +0100 Received: from pickmere.demon.co.uk ([158.152.117.143]) by finch-post-11.mail.demon.net with smtp (Exim 2.12 #1) id 12xwno-000JEM-0B for rsgb_lf_group@blacksheep.org; Fri, 2 Jun 2000 19:08:17 +0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Message-ID: Date: Fri, 2 Jun 2000 16:08:39 +0100 To: rsgb_lf_group@blacksheep.org From: "M.J.Powell" Subject: Re: LF: Re: Aerial tests. References: <4.2.0.58.20000601105903.0097a890@mail.pncl.co.uk> <000301bfcc87$d6d381a0$9dd699d4@w8k3f0> In-reply-to: <000301bfcc87$d6d381a0$9dd699d4@w8k3f0> MIME-Version: 1.0 X-Mailer: Turnpike Integrated Version 4.02 S Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: In message <000301bfcc87$d6d381a0$9dd699d4@w8k3f0>, Dick Rollema writes >To All from PA0SE > >Walter Blanchard quoted the RACAL expert who has in the past designed the >Decca antennas as follows: > >>(...) If the small one has an assymetric horizontal component (flat-top) >> this will complicate matters considerably since it will radiate both >> vertical and >> horizontally-polarised and there will be interaction between them that >> will affect the radiation pattern. So it would be unlikely to have a >circular >> polar pattern and this might account for some of the observed variations. > >This is not confirmed by computer simulation. > >Computer program AO by Brian Beezley, K6STI, shows for the L-antenna over >medium ground an almost perfect omnidirectional radiation pattern. The >deviation >from a circle is no more than about 0.1dB. > >The program also shows that the maximum of the horizontally polarised wave >is straight up and 21.1dB down on the maximum of the vertically polarised >wave. >The latter maximum occurs under an angle of 12 degrees (direct + reflected >wave). >In the region where the inverse distance law is applicable the space in the >vertical radiation pattern between zero degrees and the lobe under 12 >degrees is filled by the surface wave. And yet did not Marconi use a vertical antenna with a long horizontal wire to obtain directivity from Cape Race? When the original aerials came down in a gale he found equal or stronger signal strengths using an inverted 'L' with the arm pointing the right way. Mike -- M.J.Powell