Return-Path: X-Spam-DCC: paranoid 1290; Body=2 Fuz1=2 Fuz2=2 X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on lipkowski.org X-Spam-Level: X-Spam-Status: No, score=-2.0 required=5.0 tests=BAYES_00,DNS_FROM_AHBL_RHSBL, HTML_30_40,HTML_MESSAGE autolearn=no version=3.1.3 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by paranoid.lipkowski.org (8.13.7/8.13.7) with ESMTP id t9UJONNl010188 for ; Fri, 30 Oct 2015 20:24:23 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1ZsFEp-0000u5-B9 for rs_out_1@blacksheep.org; Fri, 30 Oct 2015 19:21:23 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1ZsFEp-0000tw-0I for rsgb_lf_group@blacksheep.org; Fri, 30 Oct 2015 19:21:23 +0000 Received: from mail-wi0-f172.google.com ([209.85.212.172]) by relay1.thorcom.net with esmtps (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) (Exim 4.86) (envelope-from ) id 1ZsFDp-0007vY-QU for rsgb_lf_group@blacksheep.org; Fri, 30 Oct 2015 19:21:21 +0000 Received: by wikq8 with SMTP id q8so17444460wik.1 for ; Fri, 30 Oct 2015 12:20:05 -0700 (PDT) X-DKIM-Result: Domain=gmail.com Result=Good and Known Domain DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; bh=jAees7ihRWlsXXL7331xE7VtTgBmpTYFnp5B7tCm51Q=; b=xiHlysuRgjPYOEz/ZkqfFxR8k+qQCSKYvf3z3yhc+PKajgHCIqmuVnK4yGH1hTmufd B75a73Jn3wrlI2ZRqpwvylT4PIvOjmrWVfOA9p9zBWAICREmDElIxsoDOlElYPSh7DMZ KH0K58gcpQbnU52dZZ6CXseNhBkix+hxQCGLoNv6LSdEkQ60xeOF+EpHiyDEGwzRc5Be UGWsUPEP2NAXG1iPBMgmhE2vAmdIi41zDCHhwJ9/nj3vPGRuDNyi8eYgZmHl7htdJp0h qgpk+/JJz4/XFG+YxVLIW/ck6fIyTX8pLlsBQNT7X1rpbTeelwbLdpCmdmxC9csK0SFq Rtcw== MIME-Version: 1.0 X-Received: by 10.194.116.42 with SMTP id jt10mr10397006wjb.117.1446232805635; Fri, 30 Oct 2015 12:20:05 -0700 (PDT) Received: by 10.28.183.139 with HTTP; Fri, 30 Oct 2015 12:20:05 -0700 (PDT) In-Reply-To: <56328B1F.2080901@posteo.de> References: <1981852865.20151017122027@chriswilson.tv> <1530BFEB-9BC2-4CA2-A7A3-338629A98202@me.com> <308511169.20151029202607@chriswilson.tv> <56328B1F.2080901@posteo.de> Date: Fri, 30 Oct 2015 19:20:05 +0000 Message-ID: From: Andy Talbot To: rsgb_lf_group@blacksheep.org X-Scan-Signature: 84016abdd353c82964b6d256164a353f Subject: Re: LF: Automatic variometer circuit Content-Type: multipart/alternative; boundary=001a1130d382a489690523575055 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-Scanned-By: MIMEDefang 2.56 on 10.1.3.10 Status: O X-Status: X-Keywords: X-UID: 4707 --001a1130d382a489690523575055 Content-Type: text/plain; charset=UTF-8 Can I warn against one feature shown in the circuit diagram The two 10uF electrolytics connected from the output of the first opamp to the supply rails should not be there. They cause instability as opamps are not designed to drive capacitive loads and frequently go unstable. If an opamp is used to deliver a mid voltage rail like this, the temptation to add extra decoupling should be avoided. The opamp output gives a very low source impedance that will not benefit from any extra decoupling. If you do not get nay instability using that circuit as it stands, then you are very lucky - or perhaps it is oscillating and not noticed I recently fell into this trap quite accidentally. It is so "natural" to want to decouple supply rails with capacitors placed everywhere that I placed several 100nF caps on a PCB without thinking. All of them had to be removed to stabilise the resulting circuitry. Andy G4JNT On 29 October 2015 at 21:09, DK7FC wrote: > Hi Chris, > > Am 29.10.2015 21:26, schrieb Chris Wilson: > >> [...] albeit my loading coil needs manual >> tweaking to move to the right part of the band. Not sure of the best >> way to remote tune it, it would be nice to have the ability to move >> about the band without running outside in the dark. I may start a >> thread about what alternatives there are, thanks again Erwin >> >> > > I'm using a motor driven variometer which uses the phase meter circuit of > the M0BMU LF tuning meter. It is working well on LF, where my antenna > resonance is so sharp that i have to re-tune when doing QSY by 7 Hz. > See: > https://dl.dropboxusercontent.com/u/19882028/LF/LFtunemeter.pdf > > https://dl.dropboxusercontent.com/u/19882028/LF/DK7FC%20Automatic_variometer_tuner%20.jpg > > https://dl.dropboxusercontent.com/u/19882028/LF/automatic_variometer_board.jpg > > https://dl.dropboxusercontent.com/u/19882028/LF/LF_variometer_drive_engine_arrangement.jpg > https://dl.dropboxusercontent.com/u/19882028/LF/phase_meter.jpg > > 2011 was a nice LF year for me!! :-) > > 73, Stefan > > > --001a1130d382a489690523575055 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Can I warn against one feature shown in the circuit diagra= m=C2=A0
The two 10uF electrolytics connected from the output of the fir= st opamp to the supply rails should not be there. =C2=A0 They cause instabi= lity as opamps are not designed to drive capacitive loads and frequently go= unstable.

If an opamp is used to deliver a mid vo= ltage rail like this, the temptation to add extra decoupling should be avoi= ded. =C2=A0 The opamp output gives a very low source impedance =C2=A0that w= ill not benefit from any extra decoupling.

If you = do not get nay instability using that circuit as it stands, then you are ve= ry lucky =C2=A0- or perhaps it is oscillating and not noticed=C2=A0

I recently fell into this trap quite accidentally. =C2=A0= It is so "natural" to want to =C2=A0decouple supply rails with c= apacitors placed everywhere =C2=A0that I placed several 100nF caps on a PCB= without thinking.=C2=A0 All of them had to be removed to stabilise the res= ulting circuitry.

Andy =C2=A0G4JNT
=

On 29 October 2015 at 21:09, DK7FC <selberdenken@posteo.de&g= t; wrote:
Hi Chris,

Am 29.10.2015 21:26, schrieb Chris Wilson:
[...] albeit my loading coil needs manual
tweaking=C2=A0 to=C2=A0 move to the right part of the band. Not sure of the= best
way=C2=A0 to=C2=A0 remote=C2=A0 tune it, it would be nice to have the abili= ty to move
about=C2=A0 the=C2=A0 band=C2=A0 without=C2=A0 running=C2=A0 outside in the= dark. I may start a
thread about what alternatives there are, thanks again Erwin
=C2=A0 =C2=A0

I'm using a motor driven variometer which uses the phase meter circuit = of the M0BMU LF tuning meter. It is working well on LF, where my antenna re= sonance is so sharp that i have to re-tune when doing QSY by 7 Hz.
See:
https://dl.dropboxusercontent.com/u/1= 9882028/LF/LFtunemeter.pdf
https://dl.= dropboxusercontent.com/u/19882028/LF/DK7FC%20Automatic_variometer_tuner%20.= jpg
https://dl.dropboxuser= content.com/u/19882028/LF/automatic_variometer_board.jpg
https://dl= .dropboxusercontent.com/u/19882028/LF/LF_variometer_drive_engine_arrangemen= t.jpg
https://dl.dropboxusercontent.com/u/1= 9882028/LF/phase_meter.jpg

2011 was a nice LF year for me!! :-)

73, Stefan



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