Return-Path: X-Spam-DCC: paranoid 1233; 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 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 tADKVtAc030643 for ; Fri, 13 Nov 2015 21:31:55 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1ZxKxq-0001XP-LZ for rs_out_1@blacksheep.org; Fri, 13 Nov 2015 20:28:54 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1ZxKxq-0001XG-AO for rsgb_lf_group@blacksheep.org; Fri, 13 Nov 2015 20:28:54 +0000 Received: from parrot.netcom.co.uk ([217.72.171.49]) by relay1.thorcom.net with esmtp (Exim 4.86) (envelope-from ) id 1ZxKwm-0002dr-2B for rsgb_lf_group@blacksheep.org; Fri, 13 Nov 2015 20:28:53 +0000 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 CACC4327403 for ; Fri, 13 Nov 2015 20:19:00 +0000 (GMT) Received: from [127.0.0.1] (localhost [127.0.0.1]) by sb.abelian.org (Postfix) with ESMTP id 9854128A05BF for ; Fri, 13 Nov 2015 20:27:32 +0000 (UTC) Message-ID: <564647B4.2050800@abelian.org> Date: Fri, 13 Nov 2015 20:27:32 +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: <8D2EABAF0379B74-9084-3D874@webmail-vd017.sysops.aol.com> <8D2EB5632CCBBF3-2188-4C745@webmail-vd012.sysops.aol.com> <9FB2E29A7CB342428BE0AF663FA8A4A8@White> In-Reply-To: <9FB2E29A7CB342428BE0AF663FA8A4A8@White> X-Scan-Signature: fc152e7304849b9a177649b85aea9f41 Subject: Re: LF: VO1NA frequency 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: 5041 Joe VO1NA wrote: > I really messed up the encoded file but ebnaut > still gave the callsign and cat's name. Amazing, > isn't it! Even though I vaguely understand how it works I always find it fascinating to see. By flipping bits in test.txt you are adding binary noise, and the input of 0's and 1's to the decoder effectively forces hard decisions on the signal bits. The decoder does much better with a real signal and Gaussian noise, gaining 3dB by making soft decisions on the analog samples and another 3dB through coherent detection. Given a very weak signal, the demodulator will get about 50% of the signal bits correct purely by chance. The decoder will handle up to about a 35% or 40% bit error rate. So the weak signal itself only has to supply about 10% or 15% correctly demodulated bits. The signal is biasing the random noise in the right direction just enough to raise a 50% random success rate to about a 60 or 65% rate and the decoder does the rest. > the Rpi B takes forever to decode an uncorrupted file. > The university unix machine took several seconds. I've never tried it on the RPi, so that's a first. If you have more than one CPU a -c option will tell the decoder how many cores to use, eg -c4 on a quad core Model 2 RPi. > I'll be on 477.7 for the next 2 days and will get back > to work on this with the tips from you and Markus. Suits me. The pre-amp is in pieces right now and I'm working on improvements to the timing system which is looking a lot better. Currently getting 3 degrees RMS phase jitter at 137kHz which is about 60nS worth. Not bad for a low cost GPS and ancient BT878 video card. -- Paul Nicholson --