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Date: Thu, 11 Apr 2002 12:41:42 +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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Dear Wolf, Alan, LF Group,

I think I can set up this kind of experiment and leave it running fairly 
easily - but a couple of queries:

Signals like MSF have on-off keying.  Feeding this signal into a digital 
divider , the counting process will come to a stop when the signal level 
falls below some threshold, so output from the divider will start and stop 
at points in the cycle which depend on the amplitude of the input. So the 
effect of dividing this signal to an audio frequency will be to introduce 
more or less random jumps in phase each time the signal is keyed, even 
though the original signal is phase coherent. Can the calibration software 
cope with this? If not, a signal with a continuous carrier will be needed 
for the reference - perhaps Droitwich on 198kHz will do.

Also, what signals do you plan to monitor? I expect the FSK and PSK signals 
would be quite difficult, because both receiving stations would have to 
track all the phase variations at the modulation rate, and store a vast 
amount of data to allow the relative phase to be compared - a high degree 
of timing accuracy (<1ms) would also presumably be required. Stations like 
DCF39 would be much easier since they are CW most of the time, but even 
here there is a jump in the phase every few seconds, so timing accuracy of 
the order of 1 second would be required for the two RX stations to compare 
the phase - still needing some work to achieve.

Cheers, Jim Moritz
73 de M0BMU