[time-nuts] Fury Interface Board: 5MHz needed?

Bruce Griffiths bruce.griffiths at xtra.co.nz
Thu Nov 8 16:32:29 EST 2007


Hal Murray wrote:
>> An illustration of what I meant would be what happens when someone
>> opens the door to the lab where the GPSDO is located. The room
>> temperature may change by a few degrees over a few minutes time,
>> causing the oven to kick in (or out). That kind of change is too fast
>> for the GPS to compensate for, and the increased (or decreased) oven
>> current will drive a frequency change.
>>     
>
> What's the typical time constant for a GPSDO?  Is a single hard-wired number 
> appropriate or should the software adapt as conditions change?
>
> What's the cycle time of a typical bang-bang air conditioner cooling a room 
> full of computers?
>
> Here is one data point.  
>   http://www.ijs.si/time/temp-compensation/
> The graph about 1/3 of way down looks like about an hour.
>
> It's a fun read if you like NTP.
>
>
>
>   
Hal

Typical time constant ranges from 100 sec to 1000 sec or more in a well
designed and optimised GPSDO.
Most are not adaptive but the better ones allow the time constant can be
adjusted by the user to best suit the OCXO and receiver.

Bruce



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