[ntp:questions] Isolated Network Drift Problem

Unruh unruh-spam at physics.ubc.ca
Wed Nov 26 17:31:13 UTC 2008

David Woolley <david at ex.djwhome.demon.co.uk.invalid> writes:

>Unruh wrote:

>> With your 100m setup you really want a buffer amp on the line. At 100m, the
>> one way trip is .3ms, with reflections every .6ms which might make the
>> system a bit weird. To get rid of the reflections you need a 100ohm
>> termination if you use cat5e cable to lengthen the 5m wire on the receiver.

>Round trip time for 100m of velocity factor 2/3 cable is approximately:

>3 * 2 * 100 / (2 * 3E8)

>= 3E2/3E8
>= 1 microsecond.

I was taking the speed to be c. And it is only a one way trip-- from the
GPS to the computer, not round trip. So I will buy your .5us (having no
idea what the velocity factor is of cat 5e cable) but not your
round trip ( which is twice that but is irellevant on a properly terminated

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