[time-nuts] Fury - Rubidium

SAIDJACK at aol.com SAIDJACK at aol.com
Tue Jul 27 15:57:53 EDT 2010


Hi guys,
 
it may help to increase DAC gain to get faster recovery times from "bumps"  
etc.
 
On an OCXO, the frequency recovery from an upset should happen within a  
couple of minutes, definitely less than 15 minutes to achieve frequency  lock.
 
The phase recovery (to 0ns offset) may take a couple of hours to do.
 
If it takes a very long time to recover, then I think increasing the DAC  
gain, or alternatively the EFCS and PHASECO together may help.
 
Wikipedia has some good instructions on how to optimize PID type controller 
 gains to get the fastest response with minimal noise...
 
Also, please make sure to disable temperature compensation when using the  
external source, unless a thermistor is connected to the board, sensing the 
Rb  temperature. Otherwise the temperature compensation may add noise due to 
it  scaling the gain to huge values due to the missing thermistor.
 
bye,
Said
 
 
In a message dated 7/27/2010 09:58:41 Pacific Daylight Time,  
true-cal at swbell.net writes:

My  experience is very similar to Scott's. I ran many hours with both an  
LPRO-101 
and FE-5680A. The disciplining behavior and Fury settings  were the same 
for 
either Rb. My biggest disappointment was the  recovery time due to various 
common 
or intentional bumps or especially,  after power loss. I also had to let 
the 
"system" settle in for a week  before acceptable tracking smoothed out. Any 
long 
term slope to  the EFC trace (gpscon) caused excessive hunting and this 
didn't  
settle down until the Rb was VERY stable. My gpscon TI and stddev  was 
virtually 
the same as Scott's if I had EFCS set to 1.0 to 1.5 but  recovery was 
unacceptable (maybe 24-hours) so I usually ran at 2.0 or 3.0  with 
slight degrading of stddev to around 3.2. This EFCS setting  allowed a much 
better settling time around 3-hours.

DACG=  1000
EFCS = 2 to 3
EFCD = 50 (25 allows little better settling  time)
PHASECO = 15 (I favor 10 Mhz over  PPS)
Regards...
Don  





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