[time-nuts] GLONASS receiver

Bob Camp lists at rtty.us
Sun Aug 5 20:16:17 EDT 2012


Hi

Your typical CDMA cell tower is spec'd for a 1 us / 24 hours holdover. Weather that's actually going to matter is open to some debate. They try to apply the spec within 3 to 5 days after power up. 

Bob

On Aug 5, 2012, at 8:07 PM, Chris Albertson <albertson.chris at gmail.com> wrote:

> 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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