[time-nuts] Some More questions

Rob Kimberley time.bandit at btinternet.com
Thu Jan 19 14:25:01 EST 2006

Oh yes they do......

Extract from Zyfer CSII Manual.....

"In the Time Locked mode the GTF module's output signals and the system's
time are
synchronized to UTC. The 1 PPS output from the GPS receiver is used as
reference to
discipline the module's oscillator and to align the 1 PPS output pulse."


"2.1.6 Discipline in Time Locked Mode

The first time a module enters the Time Locked mode after power is applied,
the time
and frequency output signals are "jam" synchronized to GPS, and are phase
frequency corrected as needed to maintain the specified accuracy of the
output signals.
The Frequency Discipline Machine (FDM) continuously compares the module's
receiver 1 PPS output with the generated 1 PPS derived from the module's
oscillator to
determine the correction necessary to discipline the oscillator. The FDM
filters out the
short-term variations inherent in the GPS 1 PPS".

If you want more, then http://www.zyfer.com/prod_manuals/385-8000V.pdf


Rob K 

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Matt Ettus
Sent: 19 January 2006 19:01
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Some More questions

On 1/19/06, Hal Murray <hmurray at suespammers.org> wrote:
> > Then, I am not sure all GPS receivers actually use their internal 
> > crystal oscillator in a PLL as the timebase. I have read that some 
> > work  by removing or adding pulses in a discrete fashion rather than 
> > phase  locking, and this offers significant jitter, making the 1 PPS 
> > only  useable to phase lock a reference oscillator with a very long 
> > integration period to eliminate the jitter.

To my knowledge, nobody tunes the frequency of the oscillator in their GPS


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