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LF: Wolf Tests

To: [email protected]
Subject: LF: Wolf Tests
From: "James Moritz" <[email protected]>
Date: Mon, 30 Apr 2001 15:59:05 +0000
Organization: University of Hertfordshire
Reply-to: [email protected]
Sender: <[email protected]>
Dear LF Group,

Have not been very active lately due to visiting relatives, but I have been making regular recordings on 137.79kHz in an attempt to receive VA3LK's Wolf-mode beacon sigs. So far, however, nothing to report - solar activity has been mostly high since I started, so perhaps this is to be expected.
Regarding the noise level at the to edge of the band, it is certainly
true that the "Luxembourg Effect" QRM is stronger than lower down
the band. However, it usually comes in bursts of fairly short
duration, so I would expect it not to have too serious effects on the
Wolf signal, since all the information in this is effectively distributed
over a long period of time. I think there may be more problems due
to the various carriers that exist within the bandwidth occupied by
the Wolf signals - as far as I can tell, these effectively increase the
noise level, and the Wolf signal is too wide to avoid them in the
same way as can be done with QRSS. So it might be worth looking
for a quieter part of the band relatively free from carriers.
I would think the fact that Larry is physically relatively close to CFH
makes it unlikely that his signal would cause QRM to the users of
CFH - I suppose there is an area around Larry's QTH where his
signal is strong enough to cause problems for CFH reception; but
since CFH is much higher power, and the signal bandwidth quite
narrow, this area must be very small. Since Larry is inland of CFH,
I think it is unlikely that his signal is ever going to be a problem to
the Canadian navy, even on an adjacent frequency. There is more
likely to be a difficulty for them from European stations on this side
of the Atlantic, where CFH is relatively weak.
As G3XDV notes, the number of lines of output from Wolf depends
on the length of the recording. Each 96 second frame of Wolf data
generates a line of output, except the first frame, which gives 3
lines. The maximum length of data that can be handled is 1632
seconds, which is 17 frames, or about 27 minutes. If the file is
longer than this, the rest of the data will be ignored. If you want to
decode the later parts of a very long file, the -s parameter
specifies the number of samples that will be ignored by Wolf before
decoding starts, eg. to start 1/2 hour into a recording, put -s
14400000 (30mins x 60secs x 8000samples/sec).
The thing to remember about the figures generated by Wolf is that
they don't mean very much unless a signal really is being decoded.
It is instructive to make a recording of some noise, and run it
through Wolf - as often as not, strings of identical -f and -jm figures
will appear, as they do for a real signal. This means that trying to
optimise Wolf parameters using the numbers generated by Wolf is
unlikely to be helpful unless a signal has already decoded
successfully.
I will run my Wolf-mode beacon again over the next few days if
anyone is interested; the frequency and bit rate of this is accurate
enough to use as a calibration reference for setting up a Wolf
receiving system.

Cheers, Jim Moritz
73 de M0BMU


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