X-GM-THRID: 1235627619996633221 X-Gmail-Labels: rsgb lf Delivered-To: daveyxm@gmail.com Received: by 10.78.172.1 with SMTP id u1cs116734hue; Sat, 5 May 2007 10:32:06 -0700 (PDT) Received: by 10.66.242.5 with SMTP id p5mr1111444ugh.1178386326202; Sat, 05 May 2007 10:32:06 -0700 (PDT) Return-Path: Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mx.google.com with ESMTP id 32si7703815ugf.2007.05.05.10.32.02; Sat, 05 May 2007 10:32:06 -0700 (PDT) Received-SPF: neutral (google.com: 193.82.116.20 is neither permitted nor denied by best guess record for domain of owner-rsgb_lf_group@blacksheep.org) DomainKey-Status: bad (test mode) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1HkO4k-0000cP-6b for rs_out_1@blacksheep.org; Sat, 05 May 2007 18:29:42 +0100 Received: from [83.244.159.144] (helo=relay3.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1HkO4i-0000cG-HJ for rsgb_lf_group@blacksheep.org; Sat, 05 May 2007 18:29:40 +0100 Received: from web86408.mail.ird.yahoo.com ([217.146.188.125]) by relay3.thorcom.net with smtp (Exim 4.63) (envelope-from ) id 1HkO4h-0008DE-Oo for rsgb_lf_group@blacksheep.org; Sat, 05 May 2007 18:29:40 +0100 Received: (qmail 30917 invoked by uid 60001); 5 May 2007 17:29:34 -0000 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=btinternet.com; h=X-YMail-OSG:Received:Date:From:Subject:To:MIME-Version:Content-Type:Content-Transfer-Encoding:Message-ID; b=I62UTkTHbCuj9GG79MrtrY0+/zkm1tRkQ0CUG0rz7b9rJiZ5dLVknEK8XfVMHB9R+w+HBAnf5ublj4aGUbatW1YAmx5cthhyOheQ6v3dlnfysfc008FuLsc6ojChXIyZI279go9M3J1H0z+SeMRRua6rAJ9fotpXuxc0KzGzwxU=; X-YMail-OSG: LpbjYcUVM1nN2SENpf.WRPVOkS46KTDbqU4T8nfebEWU6PkQmhpJCUOpxMGd.ZjTuU.vSS_BeTEUFvis6rsp8wBtLt.ml29mk9qvDT1ZQWoyOrIv Received: from [80.6.40.58] by web86408.mail.ird.yahoo.com via HTTP; Sat, 05 May 2007 18:29:34 BST Date: Sat, 5 May 2007 18:29:34 +0100 (BST) From: CHRISTOPHER OSBORN To: LF group MIME-Version: 1.0 Message-ID: <405452.30291.qm@web86408.mail.ird.yahoo.com> DomainKey-Status: good (testing) X-Spam-Score: 0.9 (/) X-Spam-Report: autolearn=disabled,HTML_10_20=0.945,HTML_MESSAGE=0.001 Subject: LF: Field Strength Meter Content-Type: multipart/alternative; boundary="0-1120525625-1178386174=:30291" Content-Transfer-Encoding: 8bit X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=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: 1647 --0-1120525625-1178386174=:30291 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Has anyone built the field strength meter from the 'LF Experimenter's Handbook' (p 83) ? I intend to make a similar one but for the 500 kHz band, however a couple of things in the artical are confusing me: (1) The formula (3) for a Helmholtz coil pair gives H = I / (1.40 * r ) where I is the coils' current in Amperes and r the coils' radii in metres. Looking on the internet the Helmholtz formula also includes the permeablility of free space - 4 * PI * 10 ^ -7 !! so is there a misprint ? (2) The artical gives the required magnetic field to equate to an electric field strength of 5 mV / m as being 13.3 uA / m I follow the working for this ok but if the Helmholtz coils are being fed from a signal generator with a series 50 ohms resistor surely the output voltage setting would be impracticably low - about 540 uV ( I think ) I can make the Helmholtz coils as per the artical (i.e. with radii of 0.292 m) so what signal generator setting would I need to generate the required field strength of 13.3 uA / m and how would I achieve this ? Any lessons learned by members of LF Group while making this meter would be much appreciated. 73 Chris G3XIZ --------------------------------- Yahoo! Mail is the world's favourite email. Don't settle for less, sign up for your freeaccount today. --0-1120525625-1178386174=:30291 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Has anyone built the field strength meter from the 'LF Experimenter's Handbook' (p 83) ?
I intend to make a similar one but for the 500 kHz band, however a couple of things in the artical are confusing me:
(1)
The formula (3) for a Helmholtz coil pair gives  H = I / (1.40 * r )
where I is the coils' current in Amperes and r the coils'  radii in metres.
Looking on the internet the Helmholtz formula also includes the permeablility of free space  -  4 * PI * 10 ^ -7  !!    so is there a misprint ?
(2)
The artical gives the required magnetic field to equate to an electric field strength of  5 mV / m as being 13.3 uA / m
I follow the working for this ok but if the Helmholtz coils are being fed from a signal generator with a series 50 ohms resistor surely the output voltage setting would be impracticably low  -  about  540 uV ( I think )

I can make the Helmholtz coils as per the artical (i.e. with radii of 0.292 m) so what signal generator setting would I need to generate the required field strength of 13.3 uA / m and how would I achieve this ?
Any lessons learned by members of LF Group while making this meter would be much appreciated.

73 Chris G3XIZ


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