[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
>
>
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