Return-Path: X-Spam-DCC: paranoid 1170; Body=2 Fuz1=2 Fuz2=2 X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on lipkowski.org X-Spam-Level: X-Spam-Status: No, score=-0.5 required=5.0 tests=BAYES_00,DNS_FROM_AHBL_RHSBL, FORGED_RCVD_HELO,RATWARE_GECKO_BUILD,SPF_PASS autolearn=no version=3.1.3 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by paranoid.lipkowski.org (8.13.7/8.13.7) with ESMTP id u3K6XsD9008028 for ; Wed, 20 Apr 2016 08:33:54 +0200 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1asla3-0006p2-UK for rs_out_1@blacksheep.org; Wed, 20 Apr 2016 07:25:43 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1asla3-0006ot-3Q for rsgb_lf_group@blacksheep.org; Wed, 20 Apr 2016 07:25:43 +0100 Received: from parrot.netcom.co.uk ([217.72.171.49]) by relay1.thorcom.net with esmtp (Exim 4.87) (envelope-from ) id 1asla0-00077Y-Mf for rsgb_lf_group@blacksheep.org; Wed, 20 Apr 2016 07:25:41 +0100 Received: from pn.abelian.org (i-194-106-52-83.freedom2surf.net [194.106.52.83]) by parrot.netcom.co.uk (Postfix) with ESMTP id 73C483273F6 for ; Wed, 20 Apr 2016 07:24:41 +0100 (BST) Received: from [127.0.0.1] (localhost [127.0.0.1]) by pn.abelian.org (Postfix) with ESMTP id 0BB44400446 for ; Wed, 20 Apr 2016 06:25:39 +0000 (UTC) To: rsgb_lf_group@blacksheep.org References: <8D3687799046F9F-15C4-93AEC4@webmail-vm170.sysops.aol.com> <04cf01d19a81$4f3950b0$edabf210$@comcast.net> From: Paul Nicholson Message-ID: <571720E2.6010306@abelian.org> Date: Wed, 20 Apr 2016 06:25:38 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: <04cf01d19a81$4f3950b0$edabf210$@comcast.net> X-Scan-Signature: 4b5b5ebe37a4c4f430f59bc35c1947b0 Subject: Re: LF: RE: 8270.0025 Tuesday Apr 19 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit 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-Scanned-By: MIMEDefang 2.56 on 10.1.3.11 Status: O X-Status: X-Keywords: X-UID: 7791 I wrote: > http://abelian.org/vlf/tmp/160419a.gif Another plot from the same pipeline, all same settings but with the sferic blanker removed http://abelian.org/vlf/tmp/160419b.gif DF6NM is lost in the noise without sferic blanking. Average noise per 139uHz bin: 0.02 fT with blanker : 0.14 fT without blanker Blanker is reducing the background by about 17dB in these quiet afternoon conditions. Around 20dB is typical. 0.14 fT in 138uHz is 12 fT in 1Hz, reasonable for daytime background. I did some blanking trials in 2010 when Stefan first began VLF transmissions, see the rough notes at http://abelian.org/vlf/blanking.html The trials examine clipping and blanking with a range of thresholds, smoothing factors and dwell times. The settings I have used since then correspond closely to the last graph of Test 1. Typically between 30% and 40% of the incoming signal is blanked when the threshold is set to 1.2 times the moving mean amplitude. Sometimes I can improve the S/N by raising the threshold to 1.8 or 2.0. Estimating the effect of the blanker on flux density measurements is difficult so I just guess. I normally use a factor of 1/0.7 amplitude gain to correct for the blanking effect. If I want an accurate measurement I have to mix in a simulated weak carrier before the blanker and measure that as a reference. -- Paul Nicholson --