Return-Path: Received: from rly-df03.mx.aol.com (rly-df03.mail.aol.com [172.19.156.16]) by air-df05.mail.aol.com (v123.4) with ESMTP id MAILINDF051-53a49fe9a7b92; Mon, 04 May 2009 03:34:27 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-df03.mx.aol.com (v123.4) with ESMTP id MAILRELAYINDF033-53a49fe9a7b92; Mon, 04 May 2009 03:34:22 -0400 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1M0sgN-0005cq-BL for rs_out_1@blacksheep.org; Mon, 04 May 2009 08:33:47 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1M0sgM-0005ch-RD for rsgb_lf_group@blacksheep.org; Mon, 04 May 2009 08:33:46 +0100 Received: from web28512.mail.ukl.yahoo.com ([87.248.110.191]) by relay1.thorcom.net with smtp (Exim 4.63) (envelope-from ) id 1M0sgM-0002W7-8R for rsgb_lf_group@blacksheep.org; Mon, 04 May 2009 08:33:46 +0100 Received: (qmail 7393 invoked by uid 60001); 4 May 2009 07:32:40 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yahoo.co.uk; s=s1024; t=1241422360; bh=InQVWE6KC1lwUViI63XzOC/wW/gAb5vhUD8k7qR5c9s=; h=Message-ID:X-YMail-OSG:Received:X-Mailer:References:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=xkkderpPHUQVr4+mcvKvbLFHOX268/Emq3lFeZdBVArQeqBiWOmLP864Trp2ewmf2+S1a676gvwdk6oocub+Ek16DkTqbNATP+KRenCJ6xkvWnghIWaYX9/0KQWvRCJqsO8YawFCygPMxNS8QNZi01HdtfLhnyh6gj0uO2e3c8c= 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=opcQ1GU3orNuvOOmtmO688TxWSMeX9RSi+hrCz0IukebpdljX5xSiyNc1k+brNN7fczTIz4NAgC/vyqioXY6tc4FvOD/HFV359EHohqL3Kpd9x9bBOr3hKfLHoKPDx0bE5PQMu4Mug7ZaXEfX2oPD1el7qpV/9TGIMsssibZStU=; Message-ID: <161871.7382.qm@web28512.mail.ukl.yahoo.com> X-YMail-OSG: 9N3n0ywVM1nqCveLzDzQzrZ9qr73Sj1CRHN3RKkBtuZJZ_GXSZateJt1JdS6Mjh8uk2A78Hlcf1KpKop_F8897ohE47uwyvwkV38hllbwYNGd3GPTfZmUqr4_oyKqRCVfmm.knG4fJ2UVZtcadqMfGDXqlJZUquwWLmn99xgh7ieRTeVsHOWss9KtsrskmiugwpQ69RsELhRj05Dyn4wrQdpNkkrr7Cql2vl8EjbvoFJS0o84KDY_jJAFNqG9VRzP2OJUsVxO1FG0e6iS1O2YXviAacjJhFyRSFKTCeOF192B6D_0JHymVI- Received: from [80.6.43.68] by web28512.mail.ukl.yahoo.com via HTTP; Mon, 04 May 2009 07:32:39 GMT X-Mailer: YahooMailRC/1277.35 YahooMailWebService/0.7.289.1 References: <260286.17766.qm@web28508.mail.ukl.yahoo.com> Date: Mon, 4 May 2009 07:32:39 +0000 (GMT) From: Chris Osborn To: rsgb_lf_group@blacksheep.org In-Reply-To: MIME-Version: 1.0 X-Karma: unknown: DomainKey-Status: good (testing) Subject: Re: LF: Re: Field Strength Meter - advice needed Content-Type: multipart/alternative; boundary="0-241418580-1241422359=:7382" 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-d221.1 ; domain : yahoo.co.uk DKIM : pass --0-241418580-1241422359=:7382 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Many thanks for all advice Jim, I'll have another happy day experimenting and implementing your suggestions. I've blown on the ferrite rod through the slot in the screening tube using a drinking straw but the output seems quite steady as a result of this= exercise. The oscillator output seems stable in both frequency and ampitude. Re the clipping of the AF stages, this seems not to be the problem and even=20= a flattish PP3 battery doesn't cause any significant change in output. Thanks again for your help. 73 Chris G3XIZ ________________________________ From: James Moritz To: rsgb_lf_group@blacksheep.org Sent: Sunday, 3 May, 2009 20:23:43 Subject: LF: Re: Field Strength Meter - advice needed Dear Chris, LF Group, Looking at the circuit, there are not that many possibilities for varying ga= in with temperature. The NE/SA 602/612 devices should be quite stable with temperature - the Phil= ips data shows less than 1dB variation over 0 - 70 degrees. But if the oscil= lator level is marginal, gain might vary more. The 741 output amplifier is working at high gain, and low supply voltage, so= might possibly be marginal. This would be worse if it were driven into clip= ping - unlikely if output V less than 1V RMS or so. The 2N3819 gain might vary quite a lot with temperature, depending on how it= is biased, and the particular specimen of 2N3819. The RC low-pass filter might show significant variation with temperature if=20= high-K ceramic capacitors with particularly wild temperature coefficients we= re used. The ferrite rod antenna is a possibility, especially if the tuning is fixed=20= as shown in the circuit diagram. The Q and temperature coefficient of these=20= can be quite high, so a temperature change could cause it to drift off frequ= ency and change the signal level - with a Q of 200, about 1kHz change in fre= quency would be sufficient. I would suggest doing a bit of signal tracing - for example, disconnecting t= he RF stage and injecting a signal directly into the mixer would eliminate t= he ferrite rod and 2N3819. Another possibility would be to try heating up co= mponents individually, e.g. with a fingertip or a soldering iron, to see whe= re large changes occur. Or, with the ferrite rod, try re-peaking the tuning=20= after changing the temperature to see if there has been a shift in the tunin= g. Hope this is helpful, Cheers, Jim Moritz 73 de M0BMU ----- Original Message ----- From: "Chris Osborn" To: "LF Group" Sent: Sunday, May 03, 2009 6:13 PM Subject: LF: Field Strength Meter - advice needed =20 --0-241418580-1241422359=:7382 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable
Many thanks for all advice Jim,

I'll have another hap= py day experimenting and implementing your suggestions.
I've blown on the= ferrite rod through the slot in the screening tube
using a drinking stra= w but the output seems quite steady as a result of this exercise.

The= oscillator output seems stable in both frequency and ampitude.

Re th= e clipping of the AF stages, this seems not to be the problem and even a fla= ttish
PP3 battery  doesn't cause any significant change in output.
Thanks again for your help.

73 Chris G3XIZ



From: James Moritz <james.moritz@btopenworld.= com>
To: rsgb_lf_grou= p@blacksheep.org
Sent: S= unday, 3 May, 2009 20:23:43
Subject= : LF: Re: Field Strength Meter - advice needed

Dear= Chris, LF Group,

Looking at the circuit, there are not that many pos= sibilities for varying gain with temperature.

The NE/SA 602/612 devic= es should be quite stable with temperature - the Philips data shows less tha= n 1dB variation over 0 - 70 degrees. But if the oscillator level is marginal= , gain might vary more.

The 741 output amplifier is working at high g= ain, and low supply voltage, so might possibly be marginal. This would be wo= rse if it were driven into clipping - unlikely if output V less than 1V RMS=20= or so.

The 2N3819 gain might vary quite a lot with temperature, depending on how it is biased, and the particular spe= cimen of 2N3819.

The RC low-pass filter might show significant variat= ion with temperature if high-K ceramic capacitors with particularly wild tem= perature coefficients were used.

The ferrite rod antenna is a possibi= lity, especially if the tuning is fixed as shown in the circuit diagram. The= Q and temperature coefficient of these can be quite high, so a temperature=20= change could cause it to drift off frequency and change the signal level - w= ith a Q of 200, about 1kHz change in frequency would be sufficient.

I= would suggest doing a bit of signal tracing - for example, disconnecting th= e RF stage and injecting a signal directly into the mixer would eliminate th= e ferrite rod and 2N3819. Another possibility would be to try heating up com= ponents individually, e.g. with a fingertip or a soldering iron, to see wher= e large changes occur. Or, with the ferrite rod, try re-peaking the tuning after changing the temperature to see if there has be= en a shift in the tuning.

Hope this is helpful,

Cheers, Jim Mo= ritz
73 de M0BMU

----- Original Message ----- From: "Chris Osborn"= <g3xiz@yahoo.co.uk>
To: "LF Group" <rsgb_= lf_group@blacksheep.org>
Sent: Sunday, May 03, 2009 6:13 PM
Sub= ject: LF: Field Strength Meter - advice needed




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