X-GM-THRID: 1203391928636500792 X-Gmail-Labels: rsgb lf X-Gmail-Received: 4f2ca5f344da79897710222cd7eea597af0b2061 Delivered-To: daveyxm@gmail.com Received: by 10.54.72.5 with SMTP id u5cs8877wra; Sun, 14 May 2006 14:59:35 -0700 (PDT) Received: by 10.48.217.20 with SMTP id p20mr3018431nfg; Sun, 14 May 2006 14:59:34 -0700 (PDT) Return-Path: Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mx.gmail.com with ESMTP id m15si4884614nfc.2006.05.14.14.59.34; Sun, 14 May 2006 14:59:34 -0700 (PDT) Received-SPF: neutral (gmail.com: 193.82.116.20 is neither permitted nor denied by best guess record for domain of owner-rsgb_lf_group@blacksheep.org) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1FfOb8-00038b-Nz for rs_out_1@blacksheep.org; Sun, 14 May 2006 22:57:58 +0100 Received: from [193.82.59.130] (helo=relay2.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1FfOb8-00038Q-7A for rsgb_lf_group@blacksheep.org; Sun, 14 May 2006 22:57:58 +0100 Received: from smtp809.mail.ukl.yahoo.com ([217.12.12.199]) by relay2.thorcom.net with smtp (Exim 4.51) id 1FfQ6q-0004D0-V9 for rsgb_lf_group@blacksheep.org; Mon, 15 May 2006 00:34:53 +0100 Received: (qmail 34361 invoked from network); 14 May 2006 21:56:48 -0000 Received: from unknown (HELO lark) (alan.melia@btinternet.com@213.122.39.214 with login) by smtp809.mail.ukl.yahoo.com with SMTP; 14 May 2006 21:56:47 -0000 Message-ID: <004a01c677a1$50793ac0$d6277ad5@lark> From: "Alan Melia" To: References: <000f01c67791$b365e300$2102000a@ibm> Date: Sun, 14 May 2006 22:25:30 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.00.2615.200 X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2615.200 X-Spam-Score: -1.0 (-) X-Spam-Report: autolearn=disabled,AWL=-0.997 Subject: LF: Re: 'meter problem' Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: * X-Spam-Status: No, hits=1.1 required=5.0 tests=MAILTO_TO_SPAM_ADDR 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 Status: O X-Status: X-Keywords: X-UID: 6409 Dick, I may be wrong about this but the "power" linearity of the meter in the SWR circuit depends upon the diodes bring operated in their square law region. This requires the right range meter, because this supplies the load to the diodes....they are usually fairly easily obtainable these days from flea-markets though they may not always be scaled as you might expect. You may put an amplifier in the circuit but you must be sure the meter amplifier is linear and provides the correct load to the diodes. I would suggest you really should use an op-amp but I appreciate there is then a supply problem. I think it unlikely you will be able to retain the linear power calibation with just a single FET or BJT.....but is it important ?? you really only need an indication, and a indication of the tuning. Cheers de Alan G3NYK ----- Original Message ----- From: Dick To: Sent: 14 May 2006 20:58 Subject: LF: 'meter problem' > Hello all, > > I almost finished my new 136kHz transmitter, and after several hours of > fault-finding it seems to work upto > 600-700Watt DC input. > > However, I do have a 'problem' .......... > > Instead of using a 200uA meter for the forward and returned power, I'm using > a 10mA meter. > This 10mA meter needs 53mV for full scale, internal resistance somewhere > around 6 Ohm. > When I put this meter into the G0MRF design it is a to heavy load for the > measurement circuit. > Open voltage drops from 13V to almost 0 V due to the low internal > resistamce. > This also effects the SWR protection circuit........ > > So, I did some experiments by using a FET or transistor as a driver for the > meter. > The measurment circuit voltage is almost not effected by the meter circuit > now, however > it is very difficult to find a good setpoint for the meter....... > > i.e when doubling the power, the meter must read also twice the power. > Somehow I'm not able to get the right linearity or what ever. > > Anyone out there with a circuit diagram that does work? or suggestions. > > It is difficult to exchange the meter because I cannot easily reach the > mountingscrews anymore..... > So I have to use this 10mA meter........ > > 73 > > Dick, PA4VHF > > > >