[ntp:questions] best gps receiver for time synchronization

Unruh unruh-spam at physics.ubc.ca
Mon Mar 9 21:47:41 UTC 2009

"Richard B. Gilbert" <rgilbert88 at comcast.net> writes:

>jack wrote:
>> Hi all,
>> I am trying to sync my Windows box to an external GPS source. I
>> currently have BU353, whose output is not very periodic. I read up on
>> ntpd implementation that uses PPS signal but I don't even have an RS
>> 232 port on my computer.
>> My questions:
>> 1) what's the best GPS antenna (and protocol) in terms of
>> consistencies in its output?
>> 2) what kind of accuracy can i expect?
>> Thanks to all.
>> Jack

>The first thing to do is to take great care to get a GPS receiver 
>designed for timing service.  The output of a timing receiver is usually 
>RS-232C serial plus the Pulse Per Second (PPS) output.  USB has 
>unpredictable latencies that make it unsuitable for timing.

>Just about any GPS timing receiver is accurate to within about 50 
>nanoseconds using the PPS signal.  Getting this time into any "vanilla" 

No. The GPS18LVC is claimed to about 1usec. But you cannot get the
interrupt service routines to do better than that anyway. So 1usec is about
the limit. 

>computer is going to degrade the time by an unpredictable and difficult 
>to determine amount of time.

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