Return-Path: Received: (qmail 27345 invoked from network); 17 Mar 2001 13:45:20 -0000 Received: from unknown (HELO murphys-inbound.servers.plus.net) (212.159.14.225) by extortion.plus.net with SMTP; 17 Mar 2001 13:45:20 -0000 Received: (qmail 16527 invoked from network); 17 Mar 2001 13:45:17 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by murphys with SMTP; 17 Mar 2001 13:45:17 -0000 X-Priority: 3 Received: from majordom by post.thorcom.com with local (Exim 3.16 #2) id 14eGw0-0001cP-00 for rsgb_lf_group-outgoing@blacksheep.org; Sat, 17 Mar 2001 13:39:56 +0000 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 14eGvz-0001cK-00 for rsgb_lf_group@blacksheep.org; Sat, 17 Mar 2001 13:39:55 +0000 Received: from [147.197.200.44] (helo=gemini) by hestia.herts.ac.uk with esmtp (Exim 3.16 #4) id 14eGve-000387-00 for rsgb_lf_group@blacksheep.org; Sat, 17 Mar 2001 13:39:34 +0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Message-ID: <18498.200103171339@gemini> From: "James Moritz" Organization: University of Hertfordshire To: rsgb_lf_group@blacksheep.org Date: Sat, 17 Mar 2001 13:44:19 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 8bit Subject: LF: Test signals 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 interest in the "Wolf" BPSK trials. To make a start, I intend to transmit a test signal this evening, in order to make available a real signal for people to record and experiment with. Mr. Murphy has intervened as usual, and I have to fix a problem with my synthesiser, but I hope to be QRV around 2000utc. The format of the signal will be: Frequency: 137.5000kHz. If occupied, I will QSY up or down by 50Hz. Power: about 300mW ERP ID: Normal CW at 6wpm, approximately on every hour and half hour, followed by a few minutes of carrier for frequency measurement purposes. The rest of the time, the signal will be BPSK in the Wolf format. This is 10 bits/second, and consists of 96 second frames that repeat continuously. The Wolf program can operate on a signal of length up to about 25 minutes, so if you record from 5 minutes past the hour/half hour, for 25 minutes, you will have a full set of data. However, if the signal is reasonably strong at your QTH, only a few minutes of recording is required. The web pages contain a fair amount of info, but here are some hints from my experience. The signal must be recorded at 8000 samples/sec - I used DL4YHF's Spectrum Laboratory to do this; it also produces a spectrogram at the same time. Most sound editing software seems to offer a choice of sample rate too. The program expects a nominal audio frequency of 800Hz. It does not work well with a very strong signal; I found that with a local signal it was neccessary to reduce signal level to 20 or 30dB below the sound card's overload point to get good results. KK7KA says that signal level should be -20 to -50dB below full scale. The noise level should be at least -6dB on full scale. You can alter this on a recorded signal using sound editing software if neccessary. It is neccessary to calibrate the soundcard sample rate accurately. This can be done by feeding an audio signal with accurately known frequency into the soundcard, recording a few minutes, and then running Wolf in the -m (frequency measure) mode; the true sample rate is then (true f / measured f) x nominal sample rate. In my case, this worked out to 7954.801 samples/sec. It is essential to do this on receive, although the web page info could be interpreted to suggest it isn't You can do a similar thing to determine the frequency error in the receiver; receive an accurately known frequency, run it through Wolf in measure mode, which gives you the frequency offset. Using the Spectrum Lab spectrogram to measure the apparent audio frequency gave very similar results, but with less resolution than the Wolf software. If it does not work first time, you can use the same recorded signal as many times as you like, until the settings are right. Once I had level, sampling rate, and frequency offset correctly set, I got perfect decoding straight away. Hope this is some help - please let me know if you have queries, suggestions for improvements, flames, etc. Cheers, Jim Moritz 73 de M0BMU