Message-ID: <26767.200104301458@gemini>
From: "James Moritz" <j.r.moritz@herts.ac.uk>
Organization: University of Hertfordshire
To: rsgb_lf_group@blacksheep.org
Date: Mon, 30 Apr 2001 15:59:05 +0000
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Subject: LF: Wolf Tests
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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