[ntp:questions] Home Time Server

Terje Mathisen terje.mathisen at hda.hydro.com
Wed Oct 10 19:18:26 UTC 2007


David L. Mills wrote:
> In regards to how the clocks work, all the above WWV clocks use the 
> munutes and seconds pulses as well as he 100-Hz subcarrier modulation. 
> The PSTI/Traconex clock uses a comb filter for the seconds pulse and 
> brute force for the subcarrier demondulation. The NTP WWV driver is a 
> mathematically optimum linear receiver with a ton of DSP algorithms.
> 
> I have no experience with European and Japanese broacasts but assume the 
> DCF-77, MSF, HBG and JJY services are equivalent to WWVB. It looks like 

DCF-77 is not equivalent at all, it is in fact much better! :-)

With the right gear, you can sync to the gps-like pseudorandom 
modulation of the DCF-77 carrier phase, this allows you to determine 
pulse transitions at approx 15-30 us level.

You still have to correct for transmission delay, which means that such 
a fancy receiver is only useful when you're close enough to the 
transmitter that the direct ground wave dominates the received signal.

Terje
-- 
- <Terje.Mathisen at hda.hydro.com>
"almost all programming can be viewed as an exercise in caching"




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