[ntp:questions] Slightly OT: Looking for good GPS PCI time sources

Richard B. Gilbert rgilbert88 at comcast.net
Fri Jul 6 20:39:34 UTC 2007

Perry E. Metzger wrote:
> I'm building a system for a client to measure network latencies in a
> distributed system very accurately -- microsecond accuracy is desired
> (though I suspect in practice we'll end up doing a bit worse). To do
> this, I need to get high quality clock sources for the machines doing
> the measurement. One obvious choice would be PCI cards that
> synchronize to GPS.
> I figure if any group has significant experience with such devices,
> this one would -- anyone have any recommendations? Also, can anyone
> think of another reasonable way to get this sort of accuracy on stock
> PC hardware?
> One consideration might be whether the cards in question allow readout
> of the time as a single atomic operation -- if they don't, one can't
> (for example) read the time without worrying about locking...
> Perry

PCI cards that synchronize to GPS are available.  Meinberg Funkuhren 
sells one such.  Another is the BC637PCI from Symmetricomm.  They are 
rather expensive; the Meinberg card sells for over $1000 US.  I don't 
know what list price for the BC637 is but I saw a used one sold for over 
$400 US on e-Bay a few years ago.  I believe that both of these cards 
feature a GPS disciplined OCXO, at least as an option.  If you buy one 
and get tired of it, all donations are gratefully accepted! :-)

There is one GPS receiver, whose brand name I have forgotten, that will 
give you the time stamp for the leading edge of a pulse you supply. The 
name "Palisade" just bubbled up from the sludge at the bottom of my 
mind. http://www.leapsecond.com/museum/palisade/ It does this trick via 
a serial port so you can forget about time stamping two pulses a few 
microseconds, or even milliseconds apart.

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