[time-nuts] Thunderbolt performance vs temperature sensor

Neville Michie namichie at gmail.com
Sat Mar 7 03:58:23 UTC 2009

further to Thunderbolt holdover performance,
if you had your thunderbolt in a room that only had ± 1 degree  
temperature variation
when you switched it on, then it would only learn a rather weak  
temperature sensitivity.
If it was in a room with a daily swing of 20 degrees it should learn  
a fairly accurate
temperature sensitivity coefficient.
If you switched it on in the ±20 degree environment, then moved it to  
the ±1 degree environment
would it eventually forget the robust tempco number and substitute a  
more noise prone number?
The question I am asking is what is the best strategy to get the best  
holdover performance?
This question is relevant to my plans to put my TBOLT in a ± 0.5  
degree environment to help the

cheers, Neville Michie

On 07/03/2009, at 2:35 PM, SAIDJACK at aol.com wrote:

> Hi there,
> Would you have the EFC plots while in holdover for us?
> You can try to place the unit into your refrigerator. That will  
> drop it  down
> to 3C or so from ambient. That will give you enough of a change so  
> that you
> can see how the EFC changes with the two sensors.. It will also  
> give you a
> good  idea how good the OCXO itself can handle thermal shocks.
> BTW: the drift you described is quite high, it definitely busts the  
> spec in both cases (CDMA: 7us/Day or so). But I am not surprised by  
> this if they
> use the Dallas chip for temp compensation of the OCXO.
> A good GPSDO (with double oven) should not drift more than 1us per day
> typically in holdover after one week of continuous operation.
> bye,
> Said
> In a message dated 3/6/2009 16:04:32 Pacific Standard Time,
> holrum at hotmail.com writes:
> Hello  Said,
> The Tbolt that I used for the test was well aged (several months  of
> operation) and stable prior to the tests.  It was only powered  
> down  for the 10
> minutes or so that it took to swap out the old sensor.
> I  tried to choose data sets that were fairly comparable  
> temperature wise.
> I also chose the basic measurement interval to be 1 hour so that  
> temperature
> would not be changing much over the hour.  I am fairly confident  
> that the
> results reflect changes due to the temperature sensor.
> I wanted to make  the measurement PPS drift / degree C change /  
> hour but the
> later model (low  res) temp sensor chip would seldom produce a  
> recordable
> change in temperature  over a one hour period.
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