Return-Path: Received: (qmail 13097 invoked from network); 16 Dec 2003 08:55:52 -0000 Received: from unknown (HELO ptb-mxscan01.plus.net) (212.159.14.235) by ptb-mailstore01.plus.net with SMTP; 16 Dec 2003 08:55:52 -0000 Received: (qmail 28840 invoked from network); 16 Dec 2003 08:55:52 -0000 Received: from ptb-mxcore01.plus.net (212.159.14.215) by ptb-mxscan01.plus.net with SMTP; 16 Dec 2003 08:55:52 -0000 X-MSMail-Priority: High X-SQ: A X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore01.plus.net with esmtp (Exim) id 1AWAzg-0007Ut-L2 for dave@picks.force9.co.uk; Tue, 16 Dec 2003 08:55:52 +0000 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1AWAyp-0002EM-5s for rs_out@blacksheep.org; Tue, 16 Dec 2003 08:54:59 +0000 Received: from [212.1.130.141] (helo=smtp-1.visp.telinco.net) by post.thorcom.com with esmtp (Exim 4.14) id 1AWAyo-0002ED-KY for rsgb_lf_group@blacksheep.org; Tue, 16 Dec 2003 08:54:58 +0000 Received: from [80.40.60.97] (helo=standalone) by smtp-1.visp.telinco.net with smtp (Exim 3.36 #1) id 1AWAyn-0004lY-00 for rsgb_lf_group@blacksheep.org; Tue, 16 Dec 2003 08:54:57 +0000 Received: by localhost with Microsoft MAPI; Tue, 16 Dec 2003 08:52:42 -0000 Message-ID: <01C3C3B1.F78B6000.g4jnt@thersgb.net> From: "Andy talbot" To: rsgb_lf_group@blacksheep.org Date: Tue, 16 Dec 2003 08:52:38 -0000 Importance: high X-Priority: 1 X-Mailer: Microsoft Internet E-mail/MAPI - 8.0.0.4211 MIME-Version: 1.0 Subject: RE: LF: Related Technical Query - Soundcard calibrator Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Checker-Version: SpamAssassin 2.60 (1.212-2003-09-23-exp) on post.thorcom.com X-Spam-Status: No, hits=0.5 required=5.0 tests=X_PRIORITY_HIGH autolearn=no version=2.60 X-SA-Exim-Scanned: Yes Sender: Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-PN-SPAMFiltered: yes OK, Thanks to all for replies on the noise generator calculations. I'm now quite convinced its a simple SQRT(2*BW / Fclock) power division from the total calculated from peak waveform voltage. The lack of any PI seems obvious now, provided both clock and bandwidth are specified in the same units. Now need to just make up a 32 bit shift register clocked at 4MHz for a PRN sequence that generates spectral lines 0.93mHz apart (17.9 minutes repeat interval) - enough for most LF modes used - so far. BTW, I found a web page listing ALL the shift register taps for maximal length sequences up to 32 stages. If anyone is interested it is http://homepage.mac.com/afj/taplist.html Andy G4JNT -----Original Message----- From: James Moritz [SMTP:J.R.Moritz@herts.ac.uk] Sent: 2003/12/12 11:17 To: rsgb_lf_group@blacksheep.org Subject: RE: LF: Related Technical Query - Soundcard calibrator Dear Andy, LF Group I hate to throw a spanner in the works, but... A noise source of exactly this type is discussed in Horowitz & Hill "The Art of Electronics" 2nd ed., section 9.34. This gives the formula (in the form Andy has used) Vrms^2 = Vpk^2 * 2 * BW /Fclock, (giving 224mV rms) which is different by a factor of sqrt(pi) from the value Andy gets. I spent some time last night trying to figure out which one is correct, and came out with a reasonably convincing case for Horowitz & Hill's formula - if anyone is interested, I will put it into an e-mail compatible form Cheers, Jim Moritz 73 de M0BMU