Date: Tue, 08 Jan 2002 02:47:40 -0800 (PST)
From: "John Sexton" <computernetworks@go.com>
Subject: LF: RE: GPS Coherent PSK Transmission
To: rsgb_lf_group@blacksheep.org
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Hi Andy,
Yes I should have realised that since it was 30 bits long, the start would be at the 15 min points, not at odd 7.5 minute points. However I saw your transmission start at about 18.53 (or was it 17.53) so perhaps you were a half-cycle out?? I didn't keep a record so I can't check.

I used Jim's method No. 1, using Argo and looking for the beads on the line. There is a small problem with timing however, since the FFT introduces a delay. This appeared to be of the order of 1 bit, which I thought I had allowed for, but perhaps it was 2 bits or approx 0 bits, hence my record slipping 1 bit. Of course if you don't start at the correct zero, the probability of inversion depends on the ratio of 1's to 0's in the sequence.

Anyway great fun. It is interesting that there are alternative simple ways of decoding modulations for which one does not have the standard equipment. This sounds like a new fun area.

73 John, G4CNN


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