[ntp:questions] NTP absolute accuracy?

David Lord snews at lordynet.org
Tue Nov 3 03:17:23 UTC 2009


Unruh wrote:
> John Hasler <jhasler at newsguy.com> writes:
> 

....

> 
>> The 60KHz WWVB signal is synchronously amplitude-modulated at a 1Hz
>> rate.  The exact cycle on which the amplitude changes can be locked in
>> by a digital phase-locked loop.  A VCXO can be phase-locked to the
>> carrier to within a small fraction of a cycle.  Thus with a strong
>> signal the PPS error should be dominated by variations in propagation
>> delay.  In practice accuracies of +-100usec are reportedly achievable,
>> but my very casual research indicate that even the fancy receivers don't
>> bother to include the hardware necessary to do so.
> 
>> Too bad NIST can't find the money for the PRNG phase modulation DCF77
>> has.
> 
> This is of course all made totally redundant by the GPS time delivery--
> even makes up for the transmission delay. It begins to look like like
> Morse code in the days of cell phones. Quaint, but not really useful.
> 

MSF is good for weather forecasting at the moment :-)

<http://www.lordynet.me.uk/pub/ntp/me6000g_ntp-day.png>

(green=+ve/blue=-ve)

With DCF this was almost each night that signal was lost for
maybe thirty minutes then same again early morning. This is
switch between groundwave and skywave. I thought I was close
enough to transmitter at about 160km from Anthorn (MSF) vs
1000km from Frankfurt (DCF), but obviously not.


David




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