Return-Path: <owner-rsgb_lf_group@blacksheep.org> Received: (qmail 38224 invoked from network); 25 Nov 2004 17:51:55 -0000 Received: from unknown (HELO ptb-spamcore01.plus.net) (192.168.71.1) by ptb-mailstore01.plus.net with SMTP; 25 Nov 2004 17:51:55 -0000 Received: from mailnull by ptb-spamcore01.plus.net with spamcore-l-b (Exim 4.32; FreeBSD) id 1CXO4n-000MQL-34 for dave@picks.force9.co.uk; Thu, 25 Nov 2004 18:10:52 +0000 Received: from [192.168.67.2] (helo=ptb-mxcore02.plus.net) by ptb-spamcore01.plus.net with esmtp (Exim 4.32; FreeBSD) id 1CXO4m-000MQC-QG for dave@picks.force9.co.uk; Thu, 25 Nov 2004 18:10:40 +0000 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore02.plus.net with esmtp (Exim) id 1CXNmQ-000BEn-Ox for dave@picks.force9.co.uk; Thu, 25 Nov 2004 17:51:43 +0000 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1CXNlo-00057I-87 for rs_out_1@blacksheep.org; Thu, 25 Nov 2004 17:51:04 +0000 Received: from [193.82.116.30] (helo=relay.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1CXNln-000579-S2 for rsgb_lf_group@blacksheep.org; Thu, 25 Nov 2004 17:51:03 +0000 Received: from hestia.herts.ac.uk ([147.197.200.9]) by relay.thorcom.net with esmtp (Exim 4.41) id 1CXNlk-00015C-C5 for rsgb_lf_group@blacksheep.org; Thu, 25 Nov 2004 17:51:03 +0000 Received: from altair ([147.197.200.45] helo=altair.herts.ac.uk) by hestia.herts.ac.uk with esmtp (Exim 3.22 #1) id 1CXNip-0000Ry-00 for rsgb_lf_group@blacksheep.org; Thu, 25 Nov 2004 17:48:00 +0000 Received: from [147.197.164.230] (helo=RD40002) by altair.herts.ac.uk with esmtp (Exim 3.36 #1) id 1CXNip-0003gi-00 for rsgb_lf_group@blacksheep.org; Thu, 25 Nov 2004 17:47:59 +0000 From: "james moritz" <j.r.moritz@herts.ac.uk> To: rsgb_lf_group@blacksheep.org Date: Thu, 25 Nov 2004 17:47:59 -0000 Message-ID: <000001c4d316$e7330bc0$e6a4c593@RD40002> MIME-Version: 1.0 X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.4510 Importance: Normal In-Reply-To: <41A5F930.6070602@usa.net> X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1165 X-UH-MailScanner: No Virus detected X-SPF-Result: relay.thorcom.net: 147.197.200.9 is neither permitted nor denied by domain of herts.ac.uk X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=no, Subject: LF: RE: Re: Linear amplifiers , MSK, and 500kHz Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Status: No, hits=0.0 required=5.0 tests=none 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-Spam-Filtered: by PlusNet SpamCORE (v3.00) Dear Alberto, LF Group, With OFDM being a fashionable form of modulation for all sorts of things (DAB, DTTV, DRM, next generation wireless widgets of all shapes and sizes), there is a huge amount of interest in reducing the crest factor so that PAs can be made more efficient, or less linear - if you do an internet search with words like ofdm, cofdm, peak, mean, power, crest, factor, reed, muller, pmepr you will find huge amounts of info on this topic - probably more than you wanted! In a cursory search, I did not find any useful, easy-to-understand articles, but that does not mean there aren't any. A few of the professional journal papers I skimmed through were: http://www.kmutt.ac.th/itc2002/CD/pdf/19_07_45/FA2_OD/2.pdf http://www.rennes.supelec.fr/ren/rd/scee/ftp/articles/melecon2000.pdf http://www.rennes.supelec.fr/ren/rd/scee/ftp/articles/cscc2000.pdf These are ally highly abstract, and confirmed that I know almost nothing about the subject, but do appear to say that peak-to-mean power ratio can be reduced to 3dB, or less, by clever coding. Most systems using OFDM seem to limit the crest factor in one way or another, so I think it is likely suitable techniques already exist out there, somewhere... how applicable they are to LF is another matter, of course. An intriguing idea is the "single frequency network" capability of COFDM, where the same signal can be transmitted by multiple transmitters, and received without suffering greatly from selective fading type problems that would happen with most signals. This reminds me of the talk there was a while back of using multiple LF transmitters for "beam forming", and multiple receivers for "diversity". Cheers, Jim Moritz 73 de M0BMU