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Message-ID: <5.1.0.14.0.20020108111413.00a6cdf0@gemini.herts.ac.uk>
Date: Tue, 08 Jan 2002 11:54:43 +0000
To: rsgb_lf_group@blacksheep.org
From: "James Moritz" <j.r.moritz@herts.ac.uk>
Subject: LF: RE: GPS Coherent PSK Transmission / Mystery signal
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Dear LF Group,

Got G4JNT's PSK signal sequence again, quite straightforward once I had 
figured out it was 30 bits long. The spectrogram method is definitely 
easier than the oscilloscope phase comparison since you don't have to watch 
it constantly. The phase transitions are quite clear so long as the signal 
is strong enough compared to the streaks caused by QRN - I used Spectrum 
Lab with a resolution of about 0.04Hz (ie what I would use for QRSS30 
reception). With this, the signal appears as a steady line with a series of 
"beads" on it corresponding to the phase transitions - think of a strong 
QRSS signal, then fill in the spaces between dots with a carrier and you 
get the idea. Wider resolution(ie shorter dot lengths) shows the 
transitions more sharply if the signal is strong enough, but higher 
resolution blurs the transitions too much.The display lags behind the 
actual phase transitions by about 10 or 15s - I suppose it takes this long 
for the FFT data to accumulate.

I also investigated the "south coast mystery signal" - I got a carrier on 
136646.7Hz, drifting perhaps 0.1Hz low overnight. The bearing obtained with 
a loop was roughly 55/235 degrees - which on my map is a line through my 
QTH passing through Lowestoft to the NE, and Dorchester to the SW. The 
signal level did not change by more than a couple of dB between night and 
morning, so probably not a DX signal.

Cheers, Jim Moritz
73 de M0BMU