Return-Path: Received: (qmail 26867 invoked from network); 20 Jan 2001 21:24:32 -0000 Received: from unknown (HELO murphys-inbound.servers.plus.net) (212.159.14.225) by 10.226.25.101 with SMTP; 20 Jan 2001 21:24:32 -0000 Received: (qmail 9814 invoked from network); 20 Jan 2001 21:27:59 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by murphys with SMTP; 20 Jan 2001 21:27:59 -0000 Received: from majordom by post.thorcom.com with local (Exim 3.16 #1) id 14K5SU-0008Tp-00 for rsgb_lf_group-outgoing@blacksheep.org; Sat, 20 Jan 2001 21:22:02 +0000 Received: from phobos.unica.co.uk ([208.239.240.147] ident=root) by post.thorcom.com with esmtp (Exim 3.16 #1) id 14K5SS-0008Tj-00 for rsgb_lf_group@blacksheep.org; Sat, 20 Jan 2001 21:22:01 +0000 Received: from [212.1.130.1] (helo=smtp-1.visp.telinco.net) by phobos.unica.co.uk with esmtp (Exim 3.13 #2) id 14K5SD-0000Kl-00 for rsgb_lf_group@blacksheep.org; Sat, 20 Jan 2001 16:21:45 -0500 Received: from [212.1.152.166] (helo=g4jnt) by smtp-1.visp.telinco.net with smtp (Exim 3.16 #1) id 14K4pc-00061v-00 for rsgb_lf_group@blacksheep.org; Sat, 20 Jan 2001 20:41:52 +0000 Message-ID: <002601c08322$5f071400$a69801d4@g4jnt> From: "Andrew Talbot" To: rsgb_lf_group@blacksheep.org Subject: LF: Re: Re: Loading Coils Date: Sat, 20 Jan 2001 20:48:40 -0000 MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 4.72.3110.1 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: >From G3LDO >>>From this it would appear that vector potential is a mathematical device to >simplify electromagnetic calculations rather than an entity generated by the >loading coil itself. Exactly ! Only the maths of antennas is complicated, an engineer looks at then in a much simpler way and ends up with the same results ! There are three fields generated by any electromagnetic system with a time varying component. Electric, magnetic and radiation. Vector potential is just a tool applied with Maxwell's equations to calculate the components of each of these in the three dimensions. Textbooks usually show these equations in great detail, because most students need the maths. The best textbooks don't just regurgitate the same equations repeatedly, they actually manage to explain how antennas can be made to work ! On the subject of coverings for loading coils, I have yet to find any plastic that absorbs any energy at 137kHz (although I haven't tried any of the black building materials that just may be loaded with carbon). So I was rather surprised the other day when someone mentioned that the RF had melted their antenna covering. Could it have been an arc over the surface caused by wet and dirt. It is very straightforward to find if any material intended for an insulator or for placing near loading coils is itself lossey. Just put it in a microwave cooker for a few minutes. If it gets hot or catches fire it may absorb something at 137k. I've yet to find ANY plastic that gets warm. Plywood is terrible, it got too hot to touch after 20 seconds Andy G4JNT