[ntp:questions] LOCL clock reachability not 377?

Henry Hallam henry at pericynthion.org
Thu Jul 31 23:15:24 UTC 2014

On Thu, Jul 31, 2014 at 12:17 PM, A C <agcarver+ntp at acarver.net> wrote:
> Some of the cheap GPS receivers derive the PPS from the RF carrier sent
> by the constellation.  The PPS output is available if the oscillator is
> still receiving a synchronizing signal from the receiver even if the GPS
> CPU itself has unlocked.  Unlocking is far more frequent than a total
> loss of signal.
> As an example, I have a GlobalSat receiver which uses the satellite
> signal to control the oscillator separate from the time output.
> Occasionally the lock is lost so the time output drifts or stops but the
> receiver still sees RF energy from the satellites at the receiver input
> which keeps the PPS under reasonable control (slight jitter of a up to a
> few milliseconds but not bad).  If I could keep my system ticking with
> the PPS input even though other clocks were dead I'd be ok.

As someone intimately familiar with the design of GPS receivers, this
makes no sense to me.  Could you elaborate?


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