Return-Path: Received: from rly-mg06.mx.aol.com (rly-mg06.mail.aol.com [172.20.83.112]) by air-mg07.mail.aol.com (v123.4) with ESMTP id MAILINMG073-a1a49ff4eeb307; Mon, 04 May 2009 16:24:41 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-mg06.mx.aol.com (v123.4) with ESMTP id MAILRELAYINMG064-a1a49ff4eeb307; Mon, 04 May 2009 16:24:14 -0400 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1M14hM-0006mV-Gc for rs_out_1@blacksheep.org; Mon, 04 May 2009 21:23:36 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1M14hM-0006mM-18 for rsgb_lf_group@blacksheep.org; Mon, 04 May 2009 21:23:36 +0100 Received: from web28508.mail.ukl.yahoo.com ([87.248.110.187]) by relay1.thorcom.net with smtp (Exim 4.63) (envelope-from ) id 1M14hL-0003BZ-DL for rsgb_lf_group@blacksheep.org; Mon, 04 May 2009 21:23:35 +0100 Received: (qmail 98269 invoked by uid 60001); 4 May 2009 20:23:29 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yahoo.co.uk; s=s1024; t=1241468609; bh=VLNrnKOoDb1xXk/mMkb02lMNvcBvmsFzWdLAf7u56c4=; h=Message-ID:X-YMail-OSG:Received:X-Mailer:References:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=hoHVISBeCgpyiM/0q7T09ymoWGxfTDOqrQnb6PG6/tOU3exwYFjtsdf5M+oeBPkgduRSHl2Xf7VG2mnmgRx+ryCPp7GNiotiFQKwPJ10JlMID3N6KnjawSJ1F7yxwfMCaNotKzwyK0WTncwJiCnUoFx7uQ1VuU2pyRTwLaiShZk= DomainKey-Signature:a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.co.uk; h=Message-ID:X-YMail-OSG:Received:X-Mailer:References:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=jIF58XIr3/mgH0NG19aM6m7+v/HgN1SBi9LijMul+Pw5GyGFkll5nCIXJREWw7RoF4skYrDFB7xqQaZUnFpnmM5P1htecz3eZCtiV8dn0ZWZxvp6cBK+cjmAwEehpfhev+6vuY9alw09BldMr3AY5XeS2UB7eBq43yWXT0rOoLg=; Message-ID: <106017.93017.qm@web28508.mail.ukl.yahoo.com> X-YMail-OSG: mWHjvEkVM1mDnkV.M.n0m6mHtVZBktQzmIkBJRgpjws9bXkOmCFd2r5.ChWRlQKUzDtYSnAw2krlfR4KcasWA0hC5Qc7pDC12iXfFo.dy368YZkBQX0PJlSLmW80oCOTHYfaug5ZvtGEgkDuavUUnnWdT6yHOr7G8lVcBn8FPXLDjA2vdd8xVsmZGM5fjIsVwyIyX_uGejSZN1QmSc2MYpkzf1hjoZV4gPDPq8dYLxLGkS37SJ5pqz5grCVJUOOAA_VhugDoDg7YoB3m7CzKyuV2gyms2ZqgeNuLyzvSSmwagNAAYgJKmA-- Received: from [80.6.43.68] by web28508.mail.ukl.yahoo.com via HTTP; Mon, 04 May 2009 20:23:28 GMT X-Mailer: YahooMailRC/1277.35 YahooMailWebService/0.7.289.1 References: <260286.17766.qm@web28508.mail.ukl.yahoo.com> <8bf118410905040810m1fb41016pab9a1c0a7c79bf06@mail.gmail.com> Date: Mon, 4 May 2009 20:23:28 +0000 (GMT) From: Chris Osborn To: rsgb_lf_group@blacksheep.org In-Reply-To: <8bf118410905040810m1fb41016pab9a1c0a7c79bf06@mail.gmail.com> MIME-Version: 1.0 X-Karma: unknown: DomainKey-Status: good (testing) Subject: LF: Field Strength Meter - advice needed Content-Type: multipart/alternative; boundary="0-264717085-1241468608=:93017" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.5 required=5.0 tests=HTML_20_30,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 X-AOL-IP: 193.82.116.20 X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-d230.1 ; domain : yahoo.co.uk DKIM : pass --0-264717085-1241468608=:93017 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Thanks again Dave and Alan, I've spent a few more hours on the F/S meter today and still have not found=20= the problem. I can blow with a drinking straw on any component and there's very little output change yet with time there's a slow drift with temperature - the outp= ut goes up with increased temperature. I thought I'd found the problem as by squeezing the ferrite rod 's screening= tube I could get a fair change in the output (about 10 %). The tube's metal is not aluminium but I guess an aluminium alloy. In any case I changed it for a proper aluminium tube - no difference ! >From the shack's temperature of 23 degrees and taking the F/S meter outside= to an ambient=20 13 degrees the meter's output changed from 0.48 volts to 0.35 volts !! I have run out of ideas now and am thinking maybe it's even the permeability= of the die cast box that's changing or maybe the perspex end caps of the ferrite rod. . . . I'm=20= getting desperate ! 73 Chris G3XIZ ________________________________ From: Dave Pick To: rsgb_lf_group@blacksheep.org Sent: Monday, 4 May, 2009 16:10:26 Subject: Re: LF: Field Strength Meter - advice needed Chris Have you tried a can of "freezer" spray to identify where the problem lies?=20= Is it the ferrite aerial or is it the FET amplifier? If you have enough gain= then a little negative feedback on the FET stage may help, add some un-deco= upled source resistor. Dave 'YXM 2009/5/3 Chris Osborn LF, I've just rebuilt PA0SE's field strength meter (LF Experimenters' Handbook), modified for use on the 500 kHz band. I've followed the published circuit as near as possible considering availabl= e components, the differences being: a) I have used a small variable capacitor instead of the published varicaps. b) I used a JFET 2N3819 in the front end instead of dual gate mosfets. c) Obviously I now use the MW coil of the ferrite rod instead of the publish= ed LW coil. I have made a decent Helmholtz coil which gives a stable magnetic field yet=20= the=20 field strength meter's output voltage is very dependent on temperature and c= an vary up to 30 %. I would be most grateful for any advice on curing this problem as I've spent= hours trying to correct it. 73 Chris G3XIZ --=20 G3YXM IO92BK Birmingham UK =20 --0-264717085-1241468608=:93017 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable
Thanks again Dave and Alan,

I've spent a few more hou= rs on the F/S meter today and still have not found the problem.
I can blo= w with a drinking straw on any component and there's very little
output change yet with time there= 's a slow drift with temperature - the output goes up
with increased temp= erature.

I thought I'd found the problem as by squeezing the ferrite=20= rod 's screening tube
I could get a fair change in the output (about 10 %= ).
The tube's metal is not aluminium but I guess an aluminium alloy.
I= n any case I changed it for a proper aluminium tube - no difference !
From the shack's temperature of  23 degrees and taking the F/S meter o= utside to an ambient
13 degrees the meter's output changed from  0.48 volts to 0.35 volts !!

I have run out of ideas now a= nd am thinking maybe it's even the permeability of the die cast box
that'= s changing or maybe the perspex end caps of the ferrite rod. . . . I'm getti= ng desperate !

73 Chris G3XIZ

= From: Dave Pick <daveyxm@googlemail.com>
To: rsgb_lf_group@blacksheep.org
Sent: Monday, 4 May, 2009 16:10:= 26
Subject: Re: LF: Fiel= d Strength Meter - advice needed

Chris

Have you tried a= can of "freezer" spray to identify where the problem lies? Is it the ferrit= e aerial or is it the FET amplifier? If you have enough gain then a little ne= gative feedback on the FET stage may help, add some un-decoupled source resi= stor.

Dave 'YXM

2009/5/3 Chris Osborn <g3xiz@yahoo.co.uk>
LF,

I've just rebuilt PA0SE's field strength meter (= LF Experimenters' Handbook),
modified for use on the 500 kHz band.

I've followed the published circuit as near as possible considering avai= lable components,
the differences being:
a) I have used a small variab= le capacitor instead of the published varicaps.
b) I used a JFET 2N3819 i= n the front end instead of dual gate mosfets.
c) Obviously I now use the MW coil of the ferrite rod instead of the publish= ed LW coil.

I have made a decent Helmholtz coil which gives a stable=20= magnetic field yet the
field strength meter's output voltage is very dep= endent on temperature and can vary up to
30 %.

I would be most grateful for any advice on curing this problem=20= as I've spent hours trying
to correct it.

73 Chris G3XIZ







--
G3YXM IO92BK= Birmingham UK

--0-264717085-1241468608=:93017--