Return-Path: Received: (qmail 15925 invoked from network); 20 Mar 2001 16:09:36 -0000 Received: from unknown (HELO murphys-inbound.servers.plus.net) (212.159.14.225) by 10.226.25.101 with SMTP; 20 Mar 2001 16:09:36 -0000 Received: (qmail 15235 invoked from network); 20 Mar 2001 16:09:36 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by murphys with SMTP; 20 Mar 2001 16:09:36 -0000 Received: from majordom by post.thorcom.com with local (Exim 3.16 #2) id 14fObO-00039W-00 for rsgb_lf_group-outgoing@blacksheep.org; Tue, 20 Mar 2001 16:03:18 +0000 X-Priority: 3 X-MSMail-Priority: Normal Received: from hestia.herts.ac.uk ([147.197.200.9]) by post.thorcom.com with esmtp (Exim 3.16 #2) id 14fObL-00039R-00 for rsgb_lf_group@blacksheep.org; Tue, 20 Mar 2001 16:03:16 +0000 Received: from [147.197.200.44] (helo=gemini) by hestia.herts.ac.uk with esmtp (Exim 3.16 #4) id 14fOau-0002Z1-00 for rsgb_lf_group@blacksheep.org; Tue, 20 Mar 2001 16:02:48 +0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Message-ID: <9881.200103201602@gemini> From: "James Moritz" Organization: University of Hertfordshire To: rsgb_lf_group@blacksheep.org Date: Tue, 20 Mar 2001 16:07:37 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 8bit Subject: LF: Wolf Tests X-Mailer: Pegasus Mail for Win32 (v3.11) Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: Dear LF Group, Thanks for the reports and comments. Some pointers to receiving WOLF mode BPSK- The receive audio must be recorded at 8000 samples/sec., mono. DL4YHF's Spectrum Lab can do this, and generate a spectrogram at the same time. WOLF can operate on up to about 25mins of sampled data; at about 1 megabyte per minute, the files are quite large. With a good SNR, only a few minutes recording is required, but more data is needed for low SNR. In order to decode successfully, 3 parameters need to be set up correctly: -The level: The signal must be about 20-40dB down on the full scale level of the soundcard- WOLF simply does not work properly with a strong signal. If everything else is OK, what you see is that the first 3 lines of output are correct, but the rest is gibberish. The low level can be achieved by reducing the RX gain, or post-editing with sound recorder software. If the signal is down in the noise, KK7KA says you should set the level so that the noise peaks are 6dB below full scale. - The soundcard sampling rate correction (-r switch); The frequency error due to the soundcard is often the biggest frequency error in the whole system (about 4.5Hz in my case). It varies with the particular soundcard, and the particular sample rate it is set to. It also upsets the timing of the decoding process. One way to determine the actual sample rate is to inject an accurately known audio frequency into the sound card, and measure the apparent frequency using the Wolf -m option; the sample rate is then (8000 x real frequency)/apparent frequency. Once determined, the correction seems to be stable. KK7KA describes the neccessary accuracy as being in the parts per million range for optimum performance, ie you are aiming for better than 0.1 samples/second accuracy. -The frequency offset (-f switch): This corrects for frequency errors in TX and/or RX tuning; it can be determined by receiving a signal of known frequency, and measuring the received audio frequency using the Wolf -m option again. This is perhaps less critical than the soundcard sampling rate error; about 0.1Hz or so is tolerable. The obvious problem is how to determine the soundcard error, if you don't have a accurate audio frequency source. I used the reference output of my synthesiser divided doown to 1kHz (and filtered; a fairly clean sine wave seemed to be neccessary to avoid aliasing problems with the soundcard). You could use the RX audio out, but only if you knew what the RX frequency error was to within a small fraction of a Hz. The effect of having the wrong sampling rate is that the first few lines of decoding work OK, but after that you get gobbledygook, so trial and error is a possible, if time consuming method. I think a technique where you measure the difference between two audio output frequencies might work OK, but this needs some further work to check it out. All this is a bit of a pain, but once completed, Wolf seems to work straight away all the time. I'm not sure about the effects of QRM on this signal - obviously, it has been designed to work with low SNR, but does it's performance with gaussian noise also apply to QRM such as carriers, or pulsed waveforms like mains noise and Loran? I intend to run some more tests this evening, starting about 2000utc, at about the 30mW ERP level for an hour or so. Later , I will be running the full 1W ERP for possible transatlantic reception, between at least 0000 - 0200utc. As before frequency will be 137.500kHz. If anyone would like a different frequency, power level, time etc. please let me know. Cheers, Jim Moritz 73 de M0BMU