Return-Path: Received: from mtain-dd01.r1000.mx.aol.com (mtain-dd01.r1000.mx.aol.com [172.29.64.141]) by air-db08.mail.aol.com (v129.4) with ESMTP id MAILINDB081-85f44d9e0ca323c; Thu, 07 Apr 2011 15:12:35 -0400 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-dd01.r1000.mx.aol.com (Internet Inbound) with ESMTP id 89B9F380000DB; Thu, 7 Apr 2011 15:12:30 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Q7uOO-00068v-6l for rs_out_1@blacksheep.org; Thu, 07 Apr 2011 19:57:20 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Q7uON-00068m-Qu for rsgb_lf_group@blacksheep.org; Thu, 07 Apr 2011 19:57:19 +0100 Received: from out1.ip08ir2.opaltelecom.net ([62.24.128.244]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1Q7uOL-0006Uu-BF for rsgb_lf_group@blacksheep.org; Thu, 07 Apr 2011 19:57:19 +0100 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: ArkCAOsHnk1OlmeT/2dsb2JhbAAMmGnQHYVtBJFI X-IronPort-AV: E=Sophos;i="4.63,317,1299456000"; d="scan'208";a="485786918" Received: from unknown (HELO [192.168.2.2]) ([78.150.103.147]) by out1.ip08ir2.opaltelecom.net with ESMTP; 07 Apr 2011 19:57:11 +0100 Message-ID: <4D9E0904.8040502@talktalk.net> Date: Thu, 07 Apr 2011 19:57:08 +0100 From: qrss User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9.2.15) Gecko/20110303 Thunderbird/3.1.9 MIME-Version: 1.0 To: rsgb_lf_group@blacksheep.org References: <4D9DE551.9020508@talktalk.net> <695A83CA124D4749BE18FDA582116731@JimPC> In-Reply-To: <695A83CA124D4749BE18FDA582116731@JimPC> X-Spam-Score: 1.4 (+) X-Spam-Report: autolearn=disabled,RATWARE_GECKO_BUILD=1.426 Subject: Re: LF: VLF QRM puzzle - why not the same in a split screen on SL? Content-Type: text/plain; charset=ISO-8859-1; format=flowed 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=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-aol-global-disposition: G x-aol-sid: 3039ac1d408d4d9e0c9e1dda X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none X-Mailer: Unknown (No Version) Interesting, thanks Jim. Eddie On 07/04/2011 19:33, James Moritz wrote: > Dear Roger, LF Group, > > These vertical stripes are indeed due to harmonics of the mains > frequency, specifically the 179th harmonic at nominally 8950Hz. If you > watch these harmonics with, say, "QRSS3" spectrogram settings, you > will see wandering "carriers" at multiples of 50Hz, that drift around > in a range of a few 10s of Hz near 9kHz, and may change frequency at a > rate of several Hz per minute. However, with a millihertz-resolution > spectrogram, this drift rate is fast enough that some energy appears > in most of the displayed FFT bins on the screen during one FFT window > period, then drifts completely out of the displayed range. Hence the > result is a vertical streak of noise. 8970Hz/179 is apparently close > to the limit of how far the mains frequency is allowed to drift; I > usually see these bands of noise a few times a day around 8970Hz, but > it rarely reaches 8976Hz > > Cheers, Jim Moritz > 73 de M0BMU > >