[time-nuts] E1938A aging

SAIDJACK at aol.com SAIDJACK at aol.com
Fri Aug 31 01:55:29 EDT 2007

Hi guys,  

wanted to share something:
attached are several days of data capture from GPSCon showing how the  E1938A 
oscillator warms up after presumably several years or more of being  
turned-off. My unit's date-code was 1999, so it may have been off for almost a  decade.
The oscillator is locked to GPS using our Fury GPSDO. You can see it locks  
to GPS very quickly (took less than one hour to <20ns), then ages  gracefully.
I thought the EFC curve (red curve) was such a perfect, beautiful asymptote  
that I had to share these pics.
This shows very well how a crystal ages very quickly over the first 3 to 5  
days after turn-on.
The green line is essentially ambient temperature. There was a warm-start  
after about 12 hours of operation, visible as a negative jump in the TI  offset.

The second plot is a zoomed in version showing the last 25 hours of  lock. 
There is no phase offset anymore due to the fact that the Fury has  measured the 
aging, and is compensating for it.
The red EFC plot is in voltage (0V to 5V) so one other fascinating  
data-point is that the aging over slightly less than 3 days is only 2.3mV, and  the EFC 
voltage is converging upon 2.9V.
[Second file in separate email]

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