[time-nuts] Fury - Rubidium

EWKehren at aol.com EWKehren at aol.com
Wed Jul 28 17:09:25 UTC 2010


Hi
I know I am repeating my self but reading Brian's experience with a FRS and 
 the Shera controller, here I go again. Not having any luck contacting 
Brooks  Shera, I did fool the controller with hardware changes and have very 
good  results controlling a FRK-H. Comparing it with a Cesium, it is right up 
there  limited only by my present measuring capabilities.
Rubidium's are today available for less than $ 100 so are Tbolt's. How ever 
 a Tbolt is a timing device and most of us have no ability or info to 
change it  to a frequency device. 
Again I ask is there any interest to revive the Brooks Shera design with a  
few updates? Total hardware cost would be less than $ 40 not counting the 
GPS  receiver. The result would be a world class standard for less than $ 200 
 counting all of you that already have rubidium's or high performance 
OCXO's it  would be less than $ 100. An other advantage if done right it could 
also be a  programmable digital loop to discipline a high performance 
oscillator to for  example a not so hot short term rubidium. My problem to complete 
the project is  I am an admitted ZERO when it comes to code and software.
Bert Kehren
 
 
 
In a message dated 7/27/2010 8:46:37 P.M. Eastern Daylight Time,  
kilodelta4foxmike at gmail.com writes:

I read  the article on PID on Wikipedia last night.  I do not fully  
understand it, but I see/learning some of the relationship.

I did a  test on the FRS-C rubidium.  The average frequency was 10 000  
000.0025 hertz at the rubidium 10 turn dial dial setting of 255, and the  
control voltage out of the pot was 1.7900 volts.  I recorded the  
frequency for a while and then changed frequency to see how long it took  
to get there.  I changed the dial setting to 516    (3.5800V) and it took 
8 seconds for the rubidium to change frequency and  settle on a average 
frequency of 10, 000 000.0131 hertz.

I did  another test and the rubidium dial setting was 000 for a control 
voltage  of 0.068V and the average frequency was 9 999 999.9933 hertz. 
The dial  setting was changed to 721 for a control voltage of 4.9999V and 
the  average frequency was 10 000 000.0216 hertz

The measurements were taken  with a HP5370B time interval counter 
referenced to a HP5065A rubidium  oscillator.  The data was recorded 
using a ProLogix GPIB  adapter.  The data was recorded in 10 minute 
intervals with the data  coming in at one measurement a second.  When the 
frequency was  changed, I allowed 20 minutes between the recordings.

Based on the  above measurements, Said, can you recommend some starting 
point for the  DAC Gain, EFC Scale, and the EFC Damping ?

Also from previous  measurements, I know this particular rubidium was at 
9x10E-11 at  0.1 sec, 1.8x10E-11 at 1 second, 5x10E-12 at 10 seconds, 
1.5x10E-12 at 100  seconds, 7x10E-13 for 1000 seconds, and 2.5x10E-13 for 
10000 seconds -  running on a Shera GPS controller - which the PIC was 
modified for this  rubidium (it was changed from a 30 second time 
interval measurement to 120  seconds, and Shera changed the sensitivity 
of the PIC to  1X10-9/volt).

Thanks to Don and Scott for the ops  info.

Thanks

Brian KD4FM





On 7/27/2010  2:57 PM, SAIDJACK at aol.com wrote:
> 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
>
>
>  _______________________________________________
> time-nuts mailing list  -- time-nuts at febo.com
> To unsubscribe, go to  
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the  instructions  there.
>

_______________________________________________
time-nuts  mailing list -- time-nuts at febo.com
To unsubscribe, go to  
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the  instructions there.



More information about the time-nuts mailing list