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Date: Wed, 18 Jun 2003 18:11:22 +0100
To: rsgb_lf_group@blacksheep.org
From: "James Moritz" <j.r.moritz@herts.ac.uk>
In-reply-to: <Law15-F65HjqGeLb5Pv00035381@hotmail.com>
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Subject: Re: LF: Ghana test - "Doppler"
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At 07:41 18/06/2003 -0800, you wrote:
>If the attachment works its a shot of DCF39 during the heat of the day and 
>gives a good view of what the spread is (same looking signal at night 
>except stronger)- and it looks about the same in Alaska too on XraY events etc.
Dear Laurence, LF Group,

I think this spreading of the DCF39 signal is what has been observed before 
at shorter distances - although the carrier frequency is stable, the phase 
of the carrier returns to a different value after each FSK data burst. The 
"wide" line is due to the random -ish phase modulation of the carrier this 
produces (actually, it isn't entirely random as it appears there are a 
finite number of possible phase jumps - presumably due to data clock and 
carrier frequency being derrived from the same reference frequency?). Thus, 
the speckled effect in your screen shot is actually generated by the FSK 
modulation bursts, and occurs wherever the signal is received - a pity 
really, since if it were a pure CW signal, it would be easy to observe much 
smaller frequency shifts, while as it is, it is difficult to see any change 
much less than about 0.1Hz due to the spreading of the spectral line.

I will be running the beacon signal again tonight - I think 137 772.8 Hz 
was clear of the other sigs, so will stick to this.

Cheers, Jim Moritz
73 de M0BMU