[time-nuts] Temperature stability for Thunderbolt: results

Bob Camp lists at rtty.us
Fri Jan 28 12:58:26 UTC 2011


In the case of the TBolt and LH, the EFC sensitivity can be calibrated against GPS. It's a built in function on version 3.0 and it works pretty well. Over the ranges we're talking about observing for temperature, linearity is not likely to be an issue. 

I do have a wonderful example of how badly all this can go wrong. Snow has been piling up on the GPS antenna over the last couple days. The plots on all of the GPSDO's are going absolutely nuts. You could correlate stuff to temperature, but the more likely relationship would be to the thickness of the snow. 

No method is perfect ....


On Jan 27, 2011, at 7:36 PM, Magnus Danielson wrote:

> On 27/01/11 22:37, Tom Van Baak wrote:
>>>> By this (quite possibly imperfect) measure: When the EFC goes down
>>>> 3:1, you have improved the thermals by 3X. If you started at 1 C
>>>> swings, the OCXO is now seeing 1/3 C swings.
>>> Agreed (re: the EFC component that correlates to changes in Tbolt
>>> ambient temperature).
>> A number of posts have mentioned LH measurements and
>> variations in DAC voltage or TI or OSC values. I'm curious
>> how close to the truth this is.
> There are three observables to use:
> time measurements (GPS t measurement)
> frequency measurements (GPS f measurement)
> DAC control values (PLL PI-loop output)
> The last one is scaled by the EFC sensitivity which is uncalibrated and non-linear.
> The time and frequency measures is the observables towards GPS, for the car analogy precision measurements against reference points along the road.
> Cheers,
> Magnus
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