Return-Path: Received: from mtain-df07.r1000.mx.aol.com (mtain-df07.r1000.mx.aol.com [172.29.64.219]) by air-md02.mail.aol.com (v127_r1.1) with ESMTP id MAILINMD022-8b794b87c31ee9; Fri, 26 Feb 2010 07:48:30 -0500 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-df07.r1000.mx.aol.com (Internet Inbound) with ESMTP id 9BCFB380000FF; Fri, 26 Feb 2010 07:48:28 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Nkzau-00051k-3i for rs_out_1@blacksheep.org; Fri, 26 Feb 2010 12:47:00 +0000 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Nkzat-00051b-Oa for rsgb_lf_group@blacksheep.org; Fri, 26 Feb 2010 12:46:59 +0000 Received: from mx.omskcity.com ([79.133.160.2]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1Nkzaq-00053S-VQ for rsgb_lf_group@blacksheep.org; Fri, 26 Feb 2010 12:46:59 +0000 Received: from noname.nodomain.nowhere (host209.161-133-79.sotline.ru [79.133.161.209]) by mx.omskcity.com (8.13.6/8.13.6) with ESMTP id o1QCkpUN090633 for ; Fri, 26 Feb 2010 18:46:52 +0600 (OMST) (envelope-from fitec@omskcity.com) Received: from localhost (fitec@localhost) by noname.nodomain.nowhere (8.8.5/8.8.5) with SMTP id TAA00249 for ; Fri, 26 Feb 2010 19:51:53 GMT X-Authentication-Warning: noname.nodomain.nowhere: fitec owned process doing -bs Date: Fri, 26 Feb 2010 19:51:52 +0000 (GMT) From: "Alexander S. Yurkov" To: rsgb_lf_group@blacksheep.org In-Reply-To: <931424D0B09442018D818E6AD1E5A63A@White> Message-ID: MIME-Version: 1.0 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-3.1.8 (mx.omskcity.com [79.133.160.2]); Fri, 26 Feb 2010 18:46:54 +0600 (OMST) X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,none Subject: Re: LF: Re: 9kHz noise level Content-Type: TEXT/PLAIN; charset=US-ASCII 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: 3039ac1d40db4b87c31c1385 X-AOL-IP: 193.82.116.20 X-Mailer: Unknown (No Version) > Subject: LF: Re: 9kHz noise level > > Dear LF, > > sometime back in 2000 I attempted to measure the daytime noise background at 9 kHz (see http://www.qru.de/vlf-theorie.html). I was using my regular LF antenna at my suburban QTH. The effective height is ~ 9 m, calibrated on LF by comparison to a small loop, and assuming that it would depend only little on frequency. Using good old Spectrogram with moderate averaging and placing the cursor between the visible impulsive spherics, I arrived at a background noise of about 5 dBuV/m referenced to 1 Hz (equivalent to 142 dB kTo). Seems noise level depend strong on the location. Anyway it is obvious for industrial noise. > Empiricaly I found that some noise limiting or blanking was essential to > maximize SNR for narrow bandwidth reception. Theory confirm this empirical rule. Few years ago i do some a theoretical study of optimal signal recieption in the condition of strong spherics noise. Such a noise is substantialy nongaussian then conventional theory assumed gaussian noise is not adequate. The study show conventional filtering (or FFT, it is the same) is not optimal. To get optimal SNR one should do some nonlinear processing before filtering. This processing is very similar to limiting. There is some an article on the subject on my web page www.qsl.net/ra9mb but unfortunely it is in russian. And it is very theoretical:-) I wonder if such a processing really improove SNR on 9 kHz. Such a processing was realized in GLFER program as author told to me. But i don't test it. Regards, Alexander/RA9MB