[time-nuts] Tbolt instability (finding Dac gain)

[WarrenS]

Another way to find the 'Dac Gain' that does not take any external Test instruments, 
Just Lady Heather or the TboltMon S/W program

----Part of  Original Message ----- 
From: WB6BNQ 

   >>> 12)  Make sure  the Dac gain is correct, mine is -3.4, not the -5Hz/ volt default
  >>How did you determine this value ? 
 >  One way is with an external counter and with the unit in disable mode;
> You can output various small value changes to the Dac and measure their effect on the freq 
using an external counter 
OR EITHER of the two SOFTWARE PROGRAMS.

OR 
If you do not want to manually change the DAC, You can do the following:
With the TBolt in stable tracking mode, 
1) Place it into the "Disable" mode.  
2) Record S/W Dac Value
3) Turn the unit over or at an angle that will give a large Freq offset, (around 1 to 1.5 e-9,  1 PPB) 
4) Record the Freq change offset using either S/W program.
5) Take unit out of 'Disable' mode and place in Manual 'Hold over' mode for a couple seconds (to enable 'Fast Recovery')
6) And then place the unit back into 'Normal' mode, BUT leave it  tilted as is. 
7) After a couple of minutes or less the unit will 'Recover' and update its Dac value to rezero the offset Freq caused by the tilt.
8) Record the New Dac value, find the voltage difference (Difference = New Dac value - the Old DAC value) , 
9) Using the recorded freq offset that was obtained when unit was tilted (and still is tilted)
This gives you what Dac voltage is needed to change the Freq by the known recorded tilted offset amount.
'Dac gain' = (Delta_Freq in PPB x 1e-9)  /  (Delta_Dac in volts)  x 1e-7  
10) Repeat same procedure starting at step #1, ... disable Mode, .. and tilting unit back to original axis. 
11) Verify the same value is calculated for Dac gain.
12) If both are not about the same value, Redo the test procedure.
13) If answers do not both come out near -5 Hz / Volt,  fix my math.
14) Enter New Dac gain into program and 'save data'.   I used TboltMon for that.
15) When entering the new Dac Gain, it is also a good time to update 
and save the 'Initial starting Dac value' using the The Initial untilted Dac value.

Have fun,
ws