Luke Militello wrote:
> You need a great circle calculator to calculate the propagation delay
> between the radio source and your location. This is true for all radio
> time sources using NTP. On this site...
>
> http://williams.best.vwh.net/gccalc.htm
>
> ...set the 'distance' to 'km' and the 'Earth model' to 'WGS84/NAD83/GRS80'.
> Then enter the radio source's location (Lat/Long -- Can be gotten from
> WikiPedia) and your location. Hit compute. Then take the distance value
> output and multiple it by 1000 to get it in 'm'. Lastly divide this value
> by the speed of light in 'm/s' (299792458). This will give you the
> propagation delay in seconds. Take that value, verbatim, as is and use it
> for your fudge time offset!
>
> <OFFSET/DELAY> = (<DISTANCE IN KM> * 1000) / 299792458
Luke,
what you wrote is correct, but I bet it won't help in this case.
As I said earlier, decoding of the DCF77 AM modulation usually provides much
jitter and delay anyway. Then the receiver is connected via USB, which
provides additional jitter and delay.
The OP said he is located near Frankfurt, i.e. very close to the transmitter,
so the propagation delay can be neglected compared to the inaccuracies
provided by the DCF77 AM signal.
If the receiver would decode the Phase Noise modulation from DCF77 there was
much more accuracy in decoding, and in this case the propagation delay due to
the distance could be relevant.
To the original poster (sorry I don't see his real name anywhere):
In your initial email you wrote:
remote refid st t when poll reach delay offset jitter
==============================================================================
xGENERIC(0) .DCFa. 0 l 20 64 377 0.000 -11.980 7.579
*ntp2.rrze.uni-e .PPS. 1 u 129 256 377 16.380 4.990 1.111
+time.fu-berlin. .PPS. 1 u 116 256 377 23.770 4.349 1.287
-ntp1.as34288.ne .PPS. 1 u 174 256 377 20.779 5.490 0.911
-ptbtime1.ptb.de .PTB. 1 u 35 64 377 27.754 7.891 3.220
The offsets are from -12 to +5 or +8, so this means the difference is about 17
to 20 ms which need to be added to fudge time1 (or subtracted, I'm not sure
out of my head).
Anyway, the default fudge time1 value may not be 0, so you should first set
fudge time1 0, let ntpd settle, check the difference between the offsets, and
then set the fudge time 1 to the correct value, with the appropriate sign,
e.g. +0.018 or -0.018 with the numbers above.
Martin
--
Martin Burnicki
Meinberg Funkuhren
Bad Pyrmont
Germany
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