X-GM-THRID: 1210064181903762437 X-Gmail-Labels: rsgb lf X-Gmail-Received: 0903e6de030f5e3cb97826ff56cfcf9005d46607 Delivered-To: daveyxm@gmail.com Received: by 10.64.250.6 with SMTP id x6cs307276qbh; Thu, 27 Jul 2006 06:32:13 -0700 (PDT) Received: by 10.49.1.9 with SMTP id d9mr1760261nfi; Thu, 27 Jul 2006 06:32:11 -0700 (PDT) Return-Path: Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mx.gmail.com with ESMTP id o53si2927705nfa.2006.07.27.06.32.10; Thu, 27 Jul 2006 06:32:11 -0700 (PDT) Received-SPF: neutral (gmail.com: 193.82.116.20 is neither permitted nor denied by best guess record for domain of owner-rsgb_lf_group@blacksheep.org) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1G65pV-0003KH-9a for rs_out_1@blacksheep.org; Thu, 27 Jul 2006 14:23:09 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1G65pU-0003K8-Hi for rsgb_lf_group@blacksheep.org; Thu, 27 Jul 2006 14:23:08 +0100 Received: from hestia.herts.ac.uk ([147.197.200.9]) by relay1.thorcom.net with esmtp (Exim 4.62) (envelope-from ) id 1G65pQ-0006Hf-8V for rsgb_lf_group@blacksheep.org; Thu, 27 Jul 2006 14:23:08 +0100 Received: from [147.197.215.113] (helo=tucana.herts.ac.uk) by hestia.herts.ac.uk with esmtp (Exim 3.22 #1) id 1G65f5-0007U3-00 for rsgb_lf_group@blacksheep.org; Thu, 27 Jul 2006 14:12:23 +0100 Received: from [147.197.164.230] (helo=RD40002) by tucana.herts.ac.uk with esmtp (Exim 4.44) id 1G65ey-0002VP-IO for rsgb_lf_group@blacksheep.org; Thu, 27 Jul 2006 14:12:16 +0100 From: "james moritz" To: Date: Thu, 27 Jul 2006 14:12:16 +0100 Message-ID: <000001c6b17e$4823a8d0$e6a4c593@RD40002> MIME-Version: 1.0 X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.4510 Importance: Normal In-Reply-To: <000d01c6ab39$8ebd6420$0300a8c0@lark> X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2869 X-UH-MailScanner: No Virus detected X-UH-MailScanner-Information: X-H-UH-MailScanner: No Virus detected X-UH-MailScanner-From: j.r.moritz@herts.ac.uk X-Spam-Score: -0.7 (/) X-Spam-Report: autolearn=disabled,AWL=-0.755,HTML_40_50=0.086,HTML_MESSAGE=0.001 Subject: LF: Tapped loading coil design spreadsheet Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C6B186.A9EA81D0" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.9 required=5.0 tests=HTML_30_40, HTML_FONTCOLOR_UNKNOWN,HTML_MESSAGE autolearn=no version=2.63 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 Status: O X-Status: X-Keywords: X-UID: 4872 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C6B186.A9EA81D0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Dear LF Group, =20 I have been doing some investigation into the design of tapped loading = coils for LF antennas - specifically, where to put the tap for the TX = connection to achieve matching to 50 ohms. As far as I can see, there is no simple formula that gives a realistic result, and generally the tapping point = is selected by trial and error. But it would be nice to know at least approximately where the taps should be, to take the guesswork out of = making a coil. =20 It appears that the tapping point can be calculated reasonably = accurately (within about 10% resistance, or +/- 1 turn or so - assuming the antenna loss resistance is known), but it is quite a complicated and tedious process. So I have made an Excel spreadsheet that does all the coil = design calculations, the user just has to enter the coil diameter, winding = pitch and some other details, and the antenna capacitance, and gets a graph of matched antenna resistance vs. tapping point turns (and some other info, like the overall number of turns needed). I have tested the spreadsheet results against measurements of 3 real loading coils with different geometries, with the kind of results mentioned above. It is also quite = easy to "reverse engineer" an existing loading coil. =20 Some interesting results arose that I was not aware of previously. There = is a definite upper limit to the antenna resistance that can be matched, = which depends on the winding pitch and diameter of the coil. "Short, fat" = loading coils, with large diameter and closely spaced turns, can match higher antenna resistances than "long, thin" coils. Any tapped coil can match resistances below the TX output resistance, if it has enough turns. But = for lower antenna resistance, a "long, thin" coil offers the advantage of a smaller change in resistance between each tap, leading to a more = accurate match.=20 =20 I have written a short article as a pdf file that explains how to fill = in the spreadsheet, and showing the measured coil data, to go with the spreadsheet itself. These files are too big for the reflector, but let = me know if you would like me to email them direct. I would be interested to know if others get reasonable agreement between the spreadsheet results = and their loading coils - if you don't have Excel on your PC, let me know details of your coil (diameter, length, number of turns or winding = pitch), and I can run the calculations for you. =20 Cheers, Jim Moritz 73 de M0BMU ------=_NextPart_000_0001_01C6B186.A9EA81D0 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

Dear LF Group,

 

I have been doing = some investigation into the design of tapped loading coils for LF antennas = – specifically, where to put the tap for the TX connection to achieve = matching to 50 ohms. As far as I can see, there is no simple formula that gives a = realistic result, and generally the tapping point is selected by trial and error. = But it would be nice to know at least approximately where the taps should be, = to take the guesswork out of making a coil.

 

It appears that the = tapping point can be calculated reasonably accurately (within about 10% = resistance, or +/- 1 turn or so – assuming the antenna loss resistance is known), = but it is quite a complicated and tedious process. So I have made an Excel = spreadsheet that does all the coil design calculations, the user just has to enter = the coil diameter, winding pitch and some other details, and the antenna = capacitance, and gets a graph of matched antenna resistance vs. tapping point turns = (and some other info, like the overall number of turns needed). I have tested = the spreadsheet results against measurements of 3 real loading coils with = different geometries, with the kind of results mentioned above. It is also quite = easy to “reverse engineer” an existing loading coil.

 

Some interesting = results arose that I was not aware of previously. There is a definite upper limit to = the antenna resistance that can be matched, which depends on the winding pitch and = diameter of the coil. “Short, fat” loading coils, with large diameter = and closely spaced turns, can match higher antenna resistances than = “long, thin” coils. Any tapped coil can match resistances below the TX = output resistance, if it has enough turns. But for lower antenna resistance, a = “long, thin” coil offers the advantage of a smaller change in resistance = between each tap, leading to a more accurate match.

 

I have written a = short article as a pdf file that explains how to fill in the spreadsheet, and showing = the measured coil data, to go with the spreadsheet itself. These files are = too big for the reflector, but let me know if you would like me to email them = direct. I would be interested to know if others get reasonable agreement between = the spreadsheet results and their loading coils – if you don’t = have Excel on your PC, let me know details of your coil (diameter, length, = number of turns or winding pitch), and I can run the calculations for = you.

 

Cheers, Jim = Moritz

73 de = M0BMU

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