Return-Path: Received: from rly-de10.mx.aol.com (rly-de10.mail.aol.com [172.19.170.146]) by air-de04.mail.aol.com (v123.4) with ESMTP id MAILINDE043-50c49ff50e2e3; Mon, 04 May 2009 16:33:01 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-de10.mx.aol.com (v123.4) with ESMTP id MAILRELAYINDE107-50c49ff50e2e3; Mon, 04 May 2009 16:32:38 -0400 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1M14pV-0006tM-Rv for rs_out_1@blacksheep.org; Mon, 04 May 2009 21:32:01 +0100 Received: from [83.244.159.144] (helo=relay3.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1M14pV-0006tD-5d for rsgb_lf_group@blacksheep.org; Mon, 04 May 2009 21:32:01 +0100 Received: from [193.252.22.191] (helo=smtp6.freeserve.com) by relay3.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1M14pR-0003Ax-Pw for rsgb_lf_group@blacksheep.org; Mon, 04 May 2009 21:32:01 +0100 Received: from me-wanadoo.net (localhost [127.0.0.1]) by mwinf3619.me.freeserve.com (SMTP Server) with ESMTP id 62D067000086 for ; Mon, 4 May 2009 22:31:50 +0200 (CEST) Received: from AGB (unknown [91.109.16.142]) by mwinf3619.me.freeserve.com (SMTP Server) with SMTP id D0E917000084 for ; Mon, 4 May 2009 22:31:49 +0200 (CEST) X-ME-UUID: 20090504203149855.D0E917000084@mwinf3619.me.freeserve.com Message-ID: <109DCE3D58BE4C3DAD93CFE7859DA29B@AGB> From: "Graham" To: References: <260286.17766.qm@web28508.mail.ukl.yahoo.com> <8bf118410905040810m1fb41016pab9a1c0a7c79bf06@mail.gmail.com> <106017.93017.qm@web28508.mail.ukl.yahoo.com> In-Reply-To: <106017.93017.qm@web28508.mail.ukl.yahoo.com> Date: Mon, 4 May 2009 21:31:37 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal Importance: Normal X-Mailer: Microsoft Windows Live Mail 14.0.8064.206 X-MimeOLE: Produced By Microsoft MimeOLE V14.0.8064.206 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="----=_NextPart_000_0065_01C9CCFF.B55DCD00" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.6 required=5.0 tests=HTML_20_30,HTML_MESSAGE, MISSING_OUTLOOK_NAME 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 ------=_NextPart_000_0065_01C9CCFF.B55DCD00 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Chris Its not the battery is it ... assume the supply voltage / regulated volta= ge is holding constant ? G ..=20 From: Chris Osborn=20 Sent: Monday, May 04, 2009 9:23 PM To: rsgb_lf_group@blacksheep.org=20 Subject: LF: Field Strength Meter - advice needed 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 availa= ble components, the differences being: a) I have used a small variable capacitor instead of the published varicap= s. 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 publi= shed LW coil. I have made a decent Helmholtz coil which gives a stable magnetic field ye= t the=20 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 spe= nt hours trying to correct it. 73 Chris G3XIZ --=20 G3YXM IO92BK Birmingham UK ----------------------------------------------------------------------------= ---- No virus found in this incoming message. Checked by AVG - www.avg.com=20 Version: 8.5.287 / Virus Database: 270.12.17/2095 - Release Date: 05/04/09 0= 6:00:00 ------=_NextPart_000_0065_01C9CCFF.B55DCD00 Content-Type: text/html; charset="utf-8" Content-Transfer-Encoding: quoted-printable
Chris
 
Its not the  battery is it ... assume=20 the  supply  voltage / regulated voltage  is holding =20 constant ?
 
G ..
 

Sent: Monday, May 04, 2009 9:23 PM
Subject: LF: Field Strength Meter - advice needed

Thanks again Dave and Alan,

I've spent a few more hours on the F= /S=20 meter today and still have not found the problem.
I can blow with a drink= ing=20 straw on any component and= =20 there's very little
output change yet with time there's a slow drift with= =20 temperature - the output goes up
with increased temperature.

I tho= ught=20 I'd found the problem as by squeezing the ferrite rod 's screening tube
I= =20 could get a fair change in the output (about 10 %).
The tube's metal is n= ot=20 aluminium but I guess an aluminium alloy.
In any case I changed it for a=20 proper aluminium tube - no difference !

From the shack's temperature=20 of  23 degrees and taking the F/S meter outside to an ambient
13=20 degrees the meter's output changed from  0.48 volts to 0.35 volts=20 !!

I have run out of ideas now and am thinking maybe it's even the=20 permeability of the die cast box
that's changing or maybe the perspex end= =20 caps of the ferrite rod. . . . I'm getting desperate !

73 Chris=20 G3XIZ

From: Dave Pick=20 <daveyxm@googlemail.com>
To:= =20 rsgb_lf_group@blacksheep.org
Sent:= Monday, 4 May, 2009=20 16:10:26
Subject: Re: LF:= Field=20 Strength Meter - advice needed

Chris

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

Dave 'YXM

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

I've just rebuilt PA0SE's field strength meter (LF=20 Experimenters' Handbook),
modified for use on the 500 kHz band.

= I've=20 followed the published circuit as near as possible considering available=20 components,
the differences being:
a) I have used a small variable=20 capacitor instead of the published varicaps.
b) I used a JFET 2N3819 in= the=20 front end instead of dual gate mosfets.
c) Obviously I now use the MW c= oil=20 of the ferrite rod instead of the published LW coil.

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

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

73 Chris=20 G3XIZ







--
G3YXM IO92BK Birmingham UK


No virus found in this incoming message.
Checked by AVG -=20 www.avg.com
Version: 8.5.287 / Virus Database: 270.12.17/2095 - Release=20 Date: 05/04/09 06:00:00
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