[time-nuts] GLONASS receiver

Chris Albertson albertson.chris at gmail.com
Sun Aug 5 20:07:00 EDT 2012


On Sun, Aug 5, 2012 at 4:27 PM, Bob Camp <lists at rtty.us> wrote:

> Hi
>
> If the OCXO is off by 200 ppb, it will slip time by 200 ns per second.
>
> It will be off by a *lot* more than 200 ns at the end of a year. Compared
> to the spec's on a cell tower OCXO, 200 ppb per year isn't very good...
>
>
Cell towers typically are spec'd for only 24 hours hold over from a GPS
outage.  The idea is that you can get a repair person to a tower within 24
hours.   But I think in real life they can handle a longer than 24 hour
period.

A YEAR of holdover would be nuts.  Who would want to pay for a clock like
that?

I'm very slowly working on getting my Rb oscillator to be disciplined by
the t-bolt.  The $40 Rb unit is roughly a "1E-10 level" oscillator but if
used to drive my NTP server I only really need 1E-3 level accuracy.    So
this means I have 1E7 seconds or about 100 days before my clock looses a
millisecond.  I think this is exactly what the OP was asking for.

For this kind of months long outage OCXO is not the best. But if you are
worried about minutes or an hour of holdover OCXO is the best.

Chris Albertson
Redondo Beach, California



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