[time-nuts] Tuning a Trimble Thunderbolt

Charles Steinmetz csteinmetz at yandex.com
Mon Apr 20 22:25:12 EDT 2015

Pete wrote:

>On a related note, is it possible to extract any data regarding the
>training from the unit?

Not as far as the time-nuts community knows, no (other than looking 
at the DAC voltage and temperature reporting during holdover and 
attempting to reverse engineer the prediction algorithm by 
correlating those with the long-term DAC voltage -- good luck).

>Also, are there any published details about how the training works?

Not as far as the time-nuts community knows, no.

>Are the training parameters saved periodically to non-volatile memory,
>or are they purely stored in RAM and so will be lost if powered down?
>If the latter, does the RAM have any provisions for backup power

I doubt it -- mine always act as if they are training from zero if 
they have been powered down.  Because of the lack of precise retrace 
of quartz crystals, I don't think you'd want old (pre-power-down) 
data, anyway.  Some crystals will even come up drifting in the 
opposite direction after being powered down, and they all take some 
time (days, at least) to settle down after any disturbance (including 
power interruptions, however brief).

>Alas, the location for the antenna is suboptimal: in the best location
>available to me (an outdoor balcony) I have a clear view of the
>southern sky from 150-300 degrees (az) and from horizon to zenith with
>only a few low-elevation obstructions. However, this is only
>accessible in warm months
>      *   *   *
>The surveyed position is within about 10 meters of the actual location
>according to Google Maps and local building information.

That's a problem.  Every meter is approximately 3.3nS, so 10m 
introduces a +/- 33nS error in the raw data (as much as 33nS closer 
to some satellites and 33nS farther from others).  Add in the 
uncertainty due to noise, and you get easily hundreds on nS of error 
in the computed solution.

Unfortunately, you are unlikely to do any better than this with the 
antenna location you described.  Time to buy a house, with no tall 
trees nearby.  (You may already have heard that time-nuttiness can be 
expensive....  ;-)

Best regards,


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