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Date: Wed, 21 Mar 2001 09:35:21
To: rsgb_lf_group@blacksheep.org
From: "Rik Strobbe" <rik.strobbe@fys.kuleuven.ac.be>
Subject: Re: LF: DFCW
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Hello Wolf,

>The problem is, PC clocks (though called 'Real Time Clocks') can be quite 
>bad, much worse than the cheapest wristwatch you can buy in a coffee-store. 
>So setting the clock for an accuracy of 0.1 sec or better only lasts for a 
>few MINUTES (!) on some nasty PCs (like the one I have to use sometimes). 

When I was thinking of implementing 'time synchronisation' in QRS I did
some tests with 5 different PC's : I set the clock to DCF77, let them run
for 16 hours and checked the difference between the PC clock and DCF77.
The differences turned out to be between +10 and -8 seconds, so a 'drift'
of about 0.6 seconds/hour.
Taking into account that 5% error in the 'time synchronisation' equals a
0.2dB loss (seems acceptable to me) would mean that for 30 sec./dot a 1.5
second timing error is acceptable. Taking worst case (PC clocks drifting in
different directions) this would mean that the time for a QSO is about 70
minutes.
If there is some real interest in this 'time synchronized' stuff I will
have a closer look a the drift of the PC clock, if it tends to be a (more
or less) linear drift it could even be compensated in QRS.

>What really helps would be a GPS (costly, only works if satellites visible) 
>or a cheap DCF receiver connected to the serial port (if not already
occupied 
>by mouse, modem, PIC, TRX control, DSP board etc etc).
>You have to readjust the clock continously, if you want 'reliable' second 
>markers for recording intervals of an hour or so. A possible workaround
would 
>be using the soundcards "calibrated" sample rate as a timebase.

Using the soundcard may be more 'user friendly' that using a GPS. A good idea.


73, Rik  ON7YD