From: "James Moritz" <j.r.moritz@herts.ac.uk>
Organization: University of Hertfordshire
To: rsgb_lf_group@blacksheep.org
Date: Mon, 21 May 2001 13:53:47 +0000
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Subject: Re: LF: Wimborne talk on Wolf
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Dear Stewart, LF group,

Nice to see everyone again at Wimbourne yesterday. Hope 
everyone had a good trip home.

In response to Stewart's points, As far as I know, BPSK is good 
because you can use, indeed have to use, a coherent detection 
scheme. If you were using an FSK modulation scheme, presumably 
you would have to find a way of making the two tones have a fixed 
phase relationship to some reference to achieve similar advantage.

Generating BPSK at 13.6MHz and dividing it down to 136k would 
also divide down the phase modulation from 180degrees to 
1.8degrees, which I don't think would do much for the demodulated 
SNR.

Using the normal CW keying shaping to amplitude modulate the 
BPSK transitions would result in a BPSK signal with roughly the 
same bandwidth as the CW signal. However, the amplitude keying 
transitions for CW are normally much faster (5 -10ms) than those I 
am using for BPSK (=1 bit period = 100ms), otherwise the CW 
keying sounds excessively "soft" for aural reception. Looking at 
typical CW spectra on the air, they usually have a bandwidth of 
around 1-200Hz, wheras my current BPSK signal has about 20Hz 
BW.

Cheers, Jim Moritz
73 de M0BMU