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
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