Return to KLUBNL.PL main page

rsgb_lf_group
[Top] [All Lists]

LF: "Wolf" BPSK tests anyone?

To: [email protected]
Subject: LF: "Wolf" BPSK tests anyone?
From: "James Moritz" <[email protected]>
Date: Fri, 16 Mar 2001 13:31:53 +0000
Organization: University of Hertfordshire
Reply-to: [email protected]
Sender: <[email protected]>
Dear LF Group,

Since transatlantic QRSS activity seems to have ceased for the time being, I thought I would give KK7KA's "Wolf" a try. This is essentially BPSK, but the encoding and decoding scheme is designed so that a weak signal can be effectively integrated over a long period. The current version of the software operates with a fixed-length 15 character message; with good SNR, this will decode in 24 seconds, but with a weak signal, the software will operate on up to about 25 minutes of received signal, hopefully leading to a significant improvement in performance. The US Lowfers seem to have been doing quite well with it. There is quite a bit of info on http://www.scgroup.com/ham/wolf.html, and also http://www.highnoonfilm.com/xmgr/updates/wolf.htm .

I have now tested my Decca TX with a specially built BPSK keyer which has the accurate timing required by Wolf. I am able to receive my own signals, and decode them successfully, so I know it works! Both the carrier frequency, and the timing of the data should be within 1 part in 10^7, which seems to be more than adequate.

The requirements for receiving this mode are basically just receiver plus soundcard/PC, but great care is needed in initially calibrating both the system frequency offsets, and the errors in the soundcard sampling rate, in order to successfully decode weak signals. This is critical for successful operation. The software includes some utilities to help do this. The signal processing is "off line"; first you record a period of received signal at 8k samples/sec using the software of you choice (I used DL4YHF's Spectrum Lab, which conveniently allows you to display a spectrogram at the same time). Then, you run the recorded .wav file through the Wolf program, together with the appropriate calibration factors. The program prints the decoded message. This can be repeated if neccessary, until you are happy with the results.

I gather VA3LK is also nearly ready to start trials using this mode, so if anyone is interested in trying some tests, I would be happy to oblige. The most important thing seems to be which frequency to use; from this end, the obvious choice seems to be either in the 135.9 - 136.0kHz, or 137.4 - 137.6kHz ranges. I can vary ERP from about 1W down to 1mW, or less if you like, and set frequency in 0.1Hz steps. Let me know what signal would best suit your needs. I should be able to be QRV most evenings over the next couple of weeks.
Cheers, Jim Moritz
73 de M0BMU


<Prev in Thread] Current Thread [Next in Thread>