Return-Path: Received: from rly-da04.mx.aol.com (rly-da04.mail.aol.com [172.19.129.78]) by air-da03.mail.aol.com (v123.4) with ESMTP id MAILINDA031-a6349ff05b42bd; Mon, 04 May 2009 11:11:58 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-da04.mx.aol.com (v123.4) with ESMTP id MAILRELAYINDA043-a6349ff05b42bd; Mon, 04 May 2009 11:11:50 -0400 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1M0zoR-0006E4-4J for rs_out_1@blacksheep.org; Mon, 04 May 2009 16:10:35 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1M0zoQ-0006Dv-Mx for rsgb_lf_group@blacksheep.org; Mon, 04 May 2009 16:10:34 +0100 Received: from mail-ew0-f180.google.com ([209.85.219.180]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1M0zoO-0007rl-BN for rsgb_lf_group@blacksheep.org; Mon, 04 May 2009 16:10:34 +0100 Received: by ewy28 with SMTP id 28so4377142ewy.4 for ; Mon, 04 May 2009 08:10:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=googlemail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:content-type; bh=m+oc2yzqRA6DVfQwU4NG2RGV6okOxwp/sdLFr95reeM=; b=p33U8saB9+QKqK+OT2Vlj+lg4+O3svegvmF2qxu7LHihqKxdjaSdVFh9ViezgfhKmi Rw7UgdlspZ1kPVYFcqnUb8g2CEpm6V/OulnVl4B/htGdyGyRGRXVX7NHGPZzsoofFSRV P7QOdXdSbEngZI6m00QoF7oquw90x7sSUHYxY= DomainKey-Signature: a=rsa-sha1; c=nofws; d=googlemail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=bFjmwk9H7Y5A1oMg7IMX6FOITqKvZ29ApfoCqRqFcTPnBNa5WyDmWFyFnrDQZDyuTk GoxRVaWL6yDaH/kVeOjgGXU3S1copFIeEsy7EqL0nO24YaFegZRuTjl+lky2lVYCcKGd E/qVK9Lnhlsx+DpO16Vew369cp6rip2UoC4ts= MIME-Version: 1.0 Received: by 10.216.11.138 with SMTP id 10mr1736186wex.51.1241449826681; Mon, 04 May 2009 08:10:26 -0700 (PDT) In-Reply-To: <260286.17766.qm@web28508.mail.ukl.yahoo.com> References: <260286.17766.qm@web28508.mail.ukl.yahoo.com> Date: Mon, 4 May 2009 16:10:26 +0100 Message-ID: <8bf118410905040810m1fb41016pab9a1c0a7c79bf06@mail.gmail.com> From: Dave Pick To: rsgb_lf_group@blacksheep.org X-Karma: unknown: DomainKey-Status: good (testing) X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: Re: LF: Field Strength Meter - advice needed Content-Type: multipart/alternative; boundary=0016367d6f14ed05e70469178fb5 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 X-AOL-IP: 193.82.116.20 X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-d243.2 ; domain : googlemail.com DKIM : pass X-Mailer: Unknown (No Version) --0016367d6f14ed05e70469178fb5 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Chris Have you tried a can of "freezer" spray to identify where the problem lies? 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-decoupled 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 > available 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 > published LW coil. > > I have made a decent Helmholtz coil which gives a stable magnetic field yet > the > field strength meter's output voltage is very dependent on temperature and > can 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 > > > > > -- G3YXM IO92BK Birmingham UK --0016367d6f14ed05e70469178fb5 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Chris

Have you tried a can of "freezer" spray to identify w= here the problem lies? Is it the ferrite aerial or is it the FET amplifier?=20= If you have enough gain then a little negative feedback on the FET stage may= help, add some un-decoupled source resistor.

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=20= band.

I've followed the published circuit as near as possible considering=20= available components,
the differences being:
a) I have used a small va= riable capacitor instead of the published varicaps.
b) I used a JFET 2N38= 19 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=20= magnetic field yet the
field strength meter's output voltage is very= dependent 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
--0016367d6f14ed05e70469178fb5--