[time-nuts] Newbie question - what use is a Ruby?
Magnus Danielson
magnus at rubidium.dyndns.org
Mon Oct 5 19:12:12 UTC 2009
Scott Burris wrote:
> Murray Greenman wrote:
>> 4. They are a handy adjunct to the GPSDO. Use the latter to calibrate
>> the former, and then you've a reference even if GPS is unavailable. The
>> Rb units also have very good short-term stability.
>>
> So, how would you go about calibrating your Rubidium against your GPSDO?
>
> Presumably you would wait until your GPSDO has not gone into holdover
> for some
> "good" amount of time, whatever that would be.
>
> Then my way would be to use the GPSDO as the external frequency
> reference to
> either my Racal-Dana 1998 or HP5328A, apply the rubidium as input, and
> adjust
> the C field for 10.00000* Mhz.
> But I'm sure that's not the time-nuts way of doing this. :-) So what's
> the right way?
Use the time-interval mode of the counters, log the time-interval over
time and adjust the C field until the long-term drift in time interval
between the reference and the oscillator cancels out.
Requires some divide-down thing, like the TADD-2 divide-box. Use the 100
kHz output when comparing to the PPS signal of say a Thunderbolt or
whatever is available.
Cheers,
Magnus
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