Message-ID: <000201bfcc19$7d40a320$405301d5@default>
From: "Alan Melia" <Alan.Melia@btinternet.com>
To: "rsgb_lf_group" <rsgb_lf_group@blacksheep.org>
Subject: LF: QRS, BPSK and diversity
Date: Thu, 1 Jun 2000 20:19:04 +0100
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Hi all, I monitored Dave G3YXM's attempts to make a PSK31 with Reino OH1TN
earlier in the year (or was it last year now). I could see the signal from
Reino easily on FFTDSP4 (not one of the most sensitive of DSP waterfall
displays available these days) but using the soundcard PSK31 decoder I could
not copy a signal at all from Reino, though I had a perfect copy of Dave so
the system was working. It may be that the soundcard decoder is not the most
sensitive, but that test showed that Dave (with a better aerial than me)
could only get PSK31 copy when Reino was fully R5 on hand-keyed morse (not
even QRS).  I suspect the power output from both Dave and Reino was probably
down about 3dB on their normal CW power, due to the need to use a linear
system for PSK31.  I await Andy's experiments with interest.

Several of us have recently copied a QRS beacon from Marco running an
estimated 1mW ERP south of the Alps (900kms from me) I think this is well
into the area of powers being radiated by the Lowfer beacons allowing for
their frequency 50% higher, so their aerials are twice as efficient. Also I
suspect the Lowfer beacon keepers who radiate BPSK may be the more technical
ones who have the more efficient stations.

I think it may be a case of 'horses for courses' and it all depends what you
wish to achieve.

On the diversity topic, strangely enough I related it to the astronomers
correlation proceedures as well Jim, but am I wrong or is it a case of
diminishing returns? I suspect you have to double the number of aerials for
each 3dB. Four aerials is feasible but gives only 6dB and we would need
eight aerials for 9dB which would be a bit of an epic. I did once write a
simulation of this using an FFT writen in Basic (a sort of Slow Fast Fourier
Transform!) with uncorrelated random noise masking the wanted signal. It
certainly works but got the feeling that it was a lot of effort for a fairly
small return. We are not interested in locating a source accurately, as are
the astronomers so we do not use one of the main points of the VLBA, its
spatial resolution.

All interesting stuff.
Cheers de Alan G3NYK    JO02PB
Alan.Melia@btinternet.com