[time-nuts] FE-5680A arrived

GandalfG8 at aol.com GandalfG8 at aol.com
Thu Jan 12 01:32:53 UTC 2012


My observations are that the RS232 offset on these needs to be  considered 
as very much a fine adjustment only, and presumably just  intended to pull 
the frequency on to 10 MHz rather than to provide a  usable offset.
 
I did try pushing my first unit to the extremes of the adjustment range  
shown in the manual and it didn't like it, the frequency was highly unstable 
and  at one extreme it just gave up and rejected the offset.
 
Observations on three units so far indicate that none seem to have had any  
offset programmed in the field but all are less stable the further they are 
from  being set to 10MHz.
 
I haven't recorded any long term data as yet, just observed the short  term 
stability on an HP 53132A and Tek FCA3100 clocked against one of three  
T'bolts, but am getting a definite impression that 10MHz is a sweet spot and  
that anything either side is just begging to be corrected:-)
 
Regards
 
Nigel
GM8PZR
 
 
 
 
 
In a message dated 12/01/2012 01:04:03 GMT Standard Time, smither at c-c-i.com 
 writes:

More  observations.  My unit is S/N 0316 61953, UN 63983.  If I try to  
change the
offset count (using RS232) by more than about 131,000 counts  (0x20000) at 
a time
it sometimes loses the 1PPS and the lock signal goes  high.

By bringing the offset count up slowly (increments of 0x10000) I  recorded 
the
following drift rates versus offset count:

0 usec / sec  at 0
1 usec / sec at 1441792 (0x160000)
2 usec / sec at 2949120  (0x2D0000)
3 usec / sec at 4390912 (0x430000)
4 usec / sec at 5898240  (0x5A0000)

The offset count was incremented in units of 0x10000  (65,536) counts so the
drifts are approximate.

A plot of these  results is here:

http://c-c-i.com/node/161

My unit  appears to have an adjustment resolution of about 6.8E-13 / count -
close  to what has been reported here  before.





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