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[195.171.43.25]) by mx.google.com with ESMTP id ba7si2099031wjc.192.2014.05.15.10.41.42 for ; Thu, 15 May 2014 10:41:43 -0700 (PDT) Received-SPF: none (google.com: owner-rsgb_lf_group@blacksheep.org does not designate permitted sender hosts) client-ip=195.171.43.25; Authentication-Results: mx.google.com; spf=neutral (google.com: owner-rsgb_lf_group@blacksheep.org does not designate permitted sender hosts) smtp.mail=owner-rsgb_lf_group@blacksheep.org Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1WkzCR-0005as-D1 for rs_out_1@blacksheep.org; Thu, 15 May 2014 18:12:07 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1WkzCQ-0005aj-T7 for rsgb_lf_group@blacksheep.org; Thu, 15 May 2014 18:12:06 +0100 Received: from parrot.netcom.co.uk ([217.72.171.49]) by relay1.thorcom.net with esmtp (Exim 4.82) (envelope-from ) id 1WkzCP-00050l-C9 for rsgb_lf_group@blacksheep.org; Thu, 15 May 2014 18:12:05 +0100 Received: from sb.abelian.org (i-194-106-52-83.freedom2surf.net [194.106.52.83]) by parrot.netcom.co.uk (Postfix) with ESMTP id CB8CB327565 for ; Thu, 15 May 2014 18:09:07 +0100 (BST) Received: from [127.0.0.1] (localhost [127.0.0.1]) by sb.abelian.org (Postfix) with ESMTP id E1D0F28A0300 for ; Thu, 15 May 2014 17:12:04 +0000 (UTC) Message-ID: <5374F564.9030605@abelian.org> Date: Thu, 15 May 2014 17:12:04 +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: <536F1A51.3060806@abelian.org> <078901cf6d1b$4179a730$c46cf590$@comcast.net> <5370FABB.8020500@abelian.org> <53711C3E.4040207@gmail.com> <53724676.20309@abelian.org> In-Reply-To: <53724676.20309@abelian.org> X-Spam-Score: 0.7 (/) X-Spam-Report: Spam detection software, running on the system "relay1.thorcom.net", has identified this incoming email as possible spam. The original message has been attached to this so you can view it (if it isn't spam) or label similar future email. If you have any questions, see the administrator of that system for details. Content preview: I completed some trials with rate 1/8 K=25 and it works very well indeed. I use 15 second symbols and a near-field source set to the give same flux density at the rx as the signal from DF6NM. The results are considerably better than 1/4 K=21 and I look forward to trying the stronger code over a long distance. [...] Content analysis details: (0.7 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [217.72.171.49 listed in list.dnswl.org] 0.7 SPF_NEUTRAL SPF: sender does not match SPF record (neutral) X-Scan-Signature: 4e3b1488273adbbe9757d6bdd5adf219 Subject: Re: VLF: Coherent BPSK at 8270 from DF6NM 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=0.9 required=5.0 tests=FROM_ENDS_IN_NUMS 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 I completed some trials with rate 1/8 K=25 and it works very well indeed. I use 15 second symbols and a near-field source set to the give same flux density at the rx as the signal from DF6NM. The results are considerably better than 1/4 K=21 and I look forward to trying the stronger code over a long distance. The signal also decodes with 10 second symbols but is marginal, ranking a few hundred down the Viterbi list and tolerant of only about 20 degrees of phase error. Nevertheless the code was able to correct 213 errors in 560 symbols. I tried to find a better set of polynomials for K=25 but without success. It becomes exponentially more difficult as K increases. To illustrate, I set 128 CPU cores to search for polynomials and let them run for 36 hours. They turned up a couple of thousand possible codes and a further 16 cores tested these. None produced a better distance spectrum than my existing top performer although one came close. Now I am motivated to test rate 1/16 and have started a search for K=21 and K=25 codes. K=21 is a practical decode limit for domestic computers and K=25 is the limit with AWS EC2 32 core VMs. Decode time is around 10 seconds but it takes 5 mins or so to search for the phase if the signal phase is steady, and maybe 40 mins to an hour if there is significant Doppler. I guess that's not unreasonable for a message that takes a few hours to send. Ready in a day or two for more far-field tests. -- Paul Nicholson --