Return-Path: X-Spam-DCC: paranoid 1233; Body=3 Fuz1=3 Fuz2=3 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 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 u1H9x3QN014644 for ; Wed, 17 Feb 2016 10:59:04 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1aVymQ-00089w-PO for rs_out_1@blacksheep.org; Wed, 17 Feb 2016 09:52:18 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1aVymQ-00089n-Go for rsgb_lf_group@blacksheep.org; Wed, 17 Feb 2016 09:52:18 +0000 Received: from brian.netcom.co.uk ([217.72.171.64]) by relay1.thorcom.net with esmtp (Exim 4.86) (envelope-from ) id 1aVylW-0001tT-9a for rsgb_lf_group@blacksheep.org; Wed, 17 Feb 2016 09:52:17 +0000 Received: from sb.abelian.org (i-194-106-52-83.freedom2surf.net [194.106.52.83]) by brian.netcom.co.uk (Postfix) with ESMTP id 3021B320085 for ; Wed, 17 Feb 2016 09:29:03 +0000 (GMT) Received: from [127.0.0.1] (localhost [127.0.0.1]) by sb.abelian.org (Postfix) with ESMTP id F24CD28A0851 for ; Wed, 17 Feb 2016 09:50:51 +0000 (UTC) Message-ID: <56C4427B.3020402@abelian.org> Date: Wed, 17 Feb 2016 09:50:51 +0000 From: Paul Nicholson User-Agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130106 Thunderbird/17.0.2 MIME-Version: 1.0 To: rsgb_lf_group@blacksheep.org References: <0316b41f8f3e4ce4adbe1cd88daa2063@kabelmail.de> In-Reply-To: <0316b41f8f3e4ce4adbe1cd88daa2063@kabelmail.de> X-Scan-Signature: 66d07794ca19cd68f7d6cc289cd4ac18 Subject: Re: AW: AW: Re: AW: Re: VLF: 8270.000 Hz and forest VLF grabber preparations... Content-Type: text/plain; charset=ISO-8859-1; 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 10.1.3.10 Status: O X-Status: X-Keywords: X-UID: 6859 Uwe wrote: > message follows at > 2016-02-1700 02:30:00 > same settings No problem, decoded with Eb/N0 = +6.7, a bit weaker thanks to the nighttime noise but would still do 10 second symbols. Stefan wrote: > Some decodes appeared but with 2 characters it could > be wrong. These are false decodes, just random noise which happens to have a correct CRC. The default list length of 20000 is too long for 2 chars, probably 1000 is enough. I'm still working on the difficult problem of finding the optimum list size and CRC strength for each message length. As you use longer list length, the chance of a decode increases (with rapidly diminishing benefit) but the chance of a false decode increases (roughly linearly). A false decode is more serious than a failed decode because there's no way to know if 'GT' or 'NI' was the correct message! At least with no decode, you know where you stand. So to make use of longer lists, it is necessary to send with stronger CRC, but the extra CRC bits is more inner code overhead which reduces the chance of a decode (for a fixed signal strength and duration). If CRC and list size are both increased by the right amounts, the decode chance overall increases, but only up to a limit corresponding to around 3dB coding gain from the outer code. The best settings could be determined by a lot of brute-force trials but the permutations to be tested are many and the computing time would be huge, so I try to reduce the number of trials by some performance calculations. For now, stay with 16 bit CRC and use list length 1000 or less for 2 chars. -- Paul Nicholson --