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Date: Tue, 16 Apr 2002 12:37:52 +0100
To: rsgb_lf_group@blacksheep.org
From: "James Moritz" <j.r.moritz@herts.ac.uk>
Subject: RE: LF: Phase meter for propagation experiment
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At 11:01 16/04/2002 +0100, you wrote:
>Not sure if the Doppler shift due to orbital wobble  will affect the 
>modulation
>in the same way it does carrier frequency.  Are there any physicists out 
>there
>who can confirm this ?
>
>Andy  G4JNT
>
>
Dear Andy, LF Group,

I'm not a physicist, but it seems to me that however the line sync is 
modulated onto the satellite signal, a change in the path length to and 
from the satellite will change the path delay, and so the arrival time of 
the sync pulse, by 3.3ns per metre. At 15.625kHz, this will cause a change 
in relative phase of 2pi * 3.3ns/64us, which is 3.3*10e-4 radians per metre 
of path length. So if the path length changes by 40m/s as Stewart states, 
the rate of phase change will be 0.013rad/s, or 2.1 millihertz. Multiplied 
up to 136k, this would be about 0.02Hz as Stewart calculates.

How fast is the ionosphere supposed to be moving around? my OCXO reference 
seems to be stable within a few parts in 10^9 over a short period of time 
on a good day, and this amounts to a fraction of a metre per second 
equivalent. So if the effective height of the ionosphere changes by a few 
10s of km in a few hours, the frequency/phase change should be detectable 
without locked oscillators.

Cheers, Jim Moritz
73 de M0BMU