[ntp:questions] time delta between clients

Unruh unruh-spam at physics.ubc.ca
Wed Feb 20 00:39:37 UTC 2008

Steve Kostecke <kostecke at ntp.org> writes:

>On 2008-02-19, Rick Jones <rick.jones2 at hp.com> wrote:

>> Before I did that I borrowed a hand-held GPS receiver (Magellan
>> "Crossover" IIRC) from someone.  Admittedly it will not be a match for
>> the GPS18, and may have a "weaker" receiver.  But given that _all_
>> signal went poof when I entered the building, I suspect the GPS18,
>> unless it is much more sensitive, would have lost all signal too :(

>My GPS18LVC works through a standard US residential roof. But you
>probably have lots of metal in the way. So ... YMWV

>You can extend the serial cable between the GPS and the host system so
>that you can place the receiver where it has a sky view. It may also
>help to place the host system in a location close to the roof. If you
>use a small system which can run off of POE that will simplify the
>cabling a bit.

I run a GPS 18 LVC along 10m of cat5 cable in addition to the 5m cable it
comes with. Not ideal, but it works. While reflections might be a problem,
15m is 50ns and the pps is only good to 1usec anyway, and the "time
reading" is only good for about 3usec as well. So the broadening of the
pulse by a few 10s of nsec is completely lost in the noise. 

(Ie, I use the usb as a power supply for the receiver-- the red and black
wires go to the red and two black wires on the GPS, the pink goes to the
Ack on the parallel port with also a ground connection, and the green and yellow go to the
transmit/receive on the serial port. )

>Steve Kostecke <kostecke at ntp.org>
>NTP Public Services Project - http://support.ntp.org/

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