Return-Path: Received: (qmail 6547 invoked from network); 21 Nov 2001 09:10:09 -0000 Received: from unknown (HELO murphys-inbound.services.quay.plus.net) (212.159.14.225) by excalibur.plus.net with SMTP; 21 Nov 2001 09:10:09 -0000 Content-Transfer-Encoding: 8bit Received: (qmail 1239 invoked from network); 21 Nov 2001 09:10:09 -0000 X-Priority: 3 X-MSMail-Priority: Normal Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by murphys.services.quay.plus.net with SMTP; 21 Nov 2001 09:10:09 -0000 Received: from majordom by post.thorcom.com with local (Exim 3.33 #2) id 166TJn-00016t-00 for rsgb_lf_group-outgoing@blacksheep.org; Wed, 21 Nov 2001 09:05:19 +0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Received: from bob.dera.gov.uk ([192.5.29.90]) by post.thorcom.com with esmtp (Exim 3.33 #2) id 166TJm-00016o-00 for rsgb_lf_group@blacksheep.org; Wed, 21 Nov 2001 09:05:18 +0000 Received: by bob.dera.gov.uk; (8.8.8/1.3/10May95) id JAA11395; Wed, 21 Nov 2001 09:13:03 GMT Received: (qmail 1313 invoked from network); 21 Nov 2001 09:55:45 -0000 Received: from gauntlet.mail.dstl.gov.uk (192.168.9.10) by baton.dstl.gov.uk with SMTP; 21 Nov 2001 09:55:45 -0000 Received: by gauntlet.mail.dstl.gov.uk; id JAA13506; Wed, 21 Nov 2001 09:29:52 GMT Received: from unknown(172.17.128.171) by gauntlet.mail.dstl.gov.uk via smap (3.2) id xma013383; Wed, 21 Nov 01 09:29:10 GMT Received: from FRN-MAIL-R3.dstl.gov.uk (unverified) by mailguard.dstl.gov.uk (Content Technologies SMTPRS 4.1.5) with ESMTP id for ; Wed, 21 Nov 2001 09:08:13 +0000 Received: by frn-mail-r3.dstl.gov.uk with Internet Mail Service (5.5.2650.21) id ; Wed, 21 Nov 2001 09:03:54 -0000 Message-ID: <7D653C9C42F5D411A27C00508BF8803D55C636@PDW-MAIL-R1> From: "Talbot Andrew" To: rsgb_lf_group@blacksheep.org Subject: LF: RE: Measuring Q Date: Wed, 21 Nov 2001 09:03:46 -0000 MIME-Version: 1.0 X-Mailer: Internet Mail Service (5.5.2650.21) Content-Type: text/plain; charset=iso-8859-1; format=flowed Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: If you use a larger capacitance resonance will naturally be at a lower frequency so you will be measuring the Q there instead. Selectivity will be higher, but when the bandwidth at the 3dB points is divided into the centre frequency the Q will still come out at the right value, albeit at this new, lower, freq. Incidently, when measuring low Qs you should use the geometric centre frequency in this calculation rather than the mid point between the two 3dB points. ie. Fc = SQRT(Fu * Fl) where Fl and Fu are the 3dB frequencies. It won't make much difference when the Q is in the hundreds, but will be noticable when used on small coils. Andy 'JNT > Is this the right way of going about it? If I use a larger > capacitor across > the coil won't this give a sharper selectivity and improved > apparent Q? > > Regards, > Peter, G3LDO > > e-mail > > Web > > > -- The Information contained in this E-Mail and any subsequent correspondence is private and is intended solely for the intended recipient(s). For those other than the recipient any disclosure, copying, distribution, or any action taken or omitted to be taken in reliance on such information is prohibited and may be unlawful.