[ntp:questions] Re: ntp & adsl

Jan Ceuleers janspam.ceuleers at computer.org
Tue Jan 31 19:13:48 UTC 2006


Folkert van Heusden wrote:
> so I need to add an offset of 1.25ms somehow? still less then this 17ms
> offset I saw.
> 
> # mode 14, RAW DCF at 50baud, is 258ms (RAWDCF_BASEDELAY in refclock_parse.c)
> 
> Do I also need to add an extra offset of 258ms since it takes the first
> bit at least 258ms to get in?

Folkert,

I also have a DCF77 receiver and have looked at all of the issues that 
you describe. The approach that I settled for was, rather than a 
bottom-up calculation of the group delay that should be fudged (which I 
found to be quite far removed from the offsets actually observed), a 
top-down measurement of the systematic offset between my DCF77 receiver 
and a selection of internet-based servers.

The way to do this is described (or at least referred to) at 
http://www.eecis.udel.edu/~mills/ntp/html/miscopt.html and 
http://www.eecis.udel.edu/~mills/ntp/html/refclock.html

If I can be bothered I repeat this procedure about twice per year, in 
order to account for the fact that the propagation delay of the DCF77 
signal is reportedly different in winter than it is in summer.

Best regards, Jan




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