[ntp:questions] Questions about joining pool.ntp.org

Chris Albertson albertson.chris at gmail.com
Tue Aug 30 07:15:28 UTC 2011


> The time stuff I understand, even the radio wave propogation stuff,
> though obviously not as well as others here.
> I'm not sure what "cable length", "speed of light delay", or "velocity
> factor" is all about.
>

What I was getting at was that that better GPS receivers are so accurate
with their pulse per second that you have to carefully account for the delay
in a short cable.  In other words the delay due to speed of light down a
wire that is four feet long is greater then the error in the PPS.   I
brought it up to show how insanely small the timing error is.     Then
"velocity factor" is a correction the signal does not move a speed of light
in a real wire.

None of this matters for NTP.  But some people use GPS for other purposes,
like maintaining a frequency standard. or running cell phone towers.  NTP is
actually one of the least demanding uses of GPS timing signals

-- 

Chris Albertson
Redondo Beach, California



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