[time-nuts] Question on crystal jumps

[Brooke Clarke]

Hi Said:

All kinds of things effect the crystal including gravity.  Some time ago I 
wrote a Labview program to look at the control voltage then rotated the PRS10 
resting it on each of four faces, see:
http://www.prc68.com/I/Images/FC_ROT.jpg
So, just as gravity effects pendulum clocks, it's also effecting crystal 
oscillators, just on a smaller scale.

There also was a LV screen for the physics package, see:
http://www.prc68.com/I/Images/Phy.jpg

The PRS10 is at:
http://www.prc68.com/I/PRS10.shtml

Have Fun,

Brooke Clarke
http://www.prc68.com/P/Prod.html  Products I make and sell
http://www.prc68.com/Alpha.shtml  All my web pages listed based on html name
http://www.PRC68.com
http://www.precisionclock.com
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SAIDJACK at aol.com wrote:
> Hi Bob,
>  
> they should and do, and if it jumps the Rb will pull-in the OCXO  frequency 
> correcting for the error. This pull in time is determined by the loop  time 
> (cut-off frequency) of the Rb PLL loop. I expect this loop time to be much  
> shorter than a GPSDO's loop time, so the effect is probably much less visible.  One 
> should still be able to see it as a distinct offset when plotting the  EFC 
> control voltage of the OCXO.
>  
> Considering that jumps often hit 1ppb offset, I am surprised how many folks  
> on this forum have discussed that their oscillators jump, and how little  
> research actually has gone into figuring out how to minimize these jumps. I  would 
> not be a big fan of contraptions that use two or three OCXO's to minimize  
> the impact since all three could potentially jump at the same time. I would  
> rather attack the problem at the source - most of the time its the  crystal.
>  
> There is probably something that can be done to minimize jumps, such as the  
> crystal cut, modifying the crystal operating temperature, modifying the 
> current  through the crystal, comparing different mounting methods, changing the  
> direction (orientation) the crystal is mounted in, etc etc.
>  
> Here is a hint for experimentation: I once had an OCXO that jumped all the  
> time (many times per hour). Since this was a reject part (definitely a factory  
> RMA), I took a large screwdriver and gave the OCXO a good bang. The jumping 
> was  immediately mitigated down to a couple of times per day. That causality 
> was a  real eye opener, whatever stresses were on the crystal were released by 
> the  shock.
>  
> bye,
> Said 
>  
>  
> In a message dated 10/23/2008 08:39:18 Pacific Daylight Time,  
> quenbob5 at pacbell.net writes:
> 
> So why  would they not show the same kind of jumps as plain OCXO's?  Rick K.  
> mentioned atomic standards avoid jumps.
> Bob  Q.
> 
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