[time-nuts] using Fury GPSDO with Rb

[SAIDJACK at aol.com]

Hi Scott,
 
a good setting is when the unit recovers in minimal time and with  only minor 
overshoot from a manual coarsedac change.
 
Try dacgain 1000 - 2000.
 
TI of 1.2ns / SD 2.2ns is not bad. The M12 errors can be expected to be  
larger than this over 8 hours.
 
bye,
Said
 
 
In a message dated 4/9/2008 07:06:45 Pacific Daylight Time, smace at intt.net  
writes:

I've  been running with dacgain 4000, efcscale 1.2, efcdamping 25, 
phaseco  15.  It has been locked for about 8 hours (since I started the  
test).  average TI 1.2ns sd 2.2ns.

I tried bumping the  coarsedac by 2 increments to see what happens.
It tries to recover, but  will oscillate wildly after about 45min or so.
I wonder what will happen  after an extended holdover period.

It looks like the EFC on this this  FRS-A is more than twice as sensitive 
as the LPRO.

Scott



SAIDJACK at aol.com wrote:
> Hello  Scott,
>  
> forgot to mention: also try setting the  serv:efcdamping lower. It's an IIR 
 
> low pass filter, and will  introduce phase-shift that can cause instability 
if 
> it  is set  too high.
>  
> bye,
> Said
>   
>  
> In a message dated 4/8/2008 22:59:22 Pacific Daylight  Time,  
SAIDJACK at aol.com 
> writes:
> 
> Hello   Scott,
> 
> this means the gain is set too high so that there is  not enough  phase  
> margin.
> 
> You can try to  set the serv:dacgain lower, and  serv:efcs / serv:phaseco  
>  lower.
> 
> Contrary to OCXO's, Rb's are  quite stable so  they don't need strong  
> control, 
> they just need a   gentle nudge, so you can try starting with low  numbers.
> 
>  Let me  know if that works,
> bye,
> Said
> 
>  
> 
> 
> In a message dated  4/8/2008 21:31:50 Pacific  Daylight Time, 
smace at intt.net   
> writes:
> 
>  I've  found that once the units gets into an  overshoot/oscillation  cycle
> it never  recovers and I have to manually  adjust the  dac to break the 
cycle.
> Is the  notion that you use   conservative enough settings so that this
> never    happens?
> 
> Scott
> 
> SAIDJACK at aol.com  wrote:
>> Hi   Scott,
>>  
>> let me  reply on this list since other users  are  also using  Rb's.
>>  
>> Here is a quick   pointer:
>>   
>> 1) determine EFC slope of Rb  (pos =  frequency goes higher with  higher  
> EFC  
>> voltage). Set the  slope with serv:efc:slop   [positive/negative]
>>  
>> 2)  Determine maximum  frequency  deviation at EFC = 0V (serv:coarsedac  
0)   
>> using a frequency  counter
>>   
>>   
>> 3) Determine maximum frequency   deviation at EFC = 5V  (serv:coarsedac   
255)
>>
>>   
>> 4) Set  Dacgain  according to table in user manual depending on the   
>  frequency  
>> difference between 2) and  3)
>>   
>>  5) Set Integral part of loop to  zero: serv:phaseco 0.0, this  helps for  
 
>  now
>>  
>> 6) Set Proportional part  of loop to a  number that  makes the unit lock 
as  
>> quickly  as  desired without oscillation  and overshoot (for example:    
> serv:efcs 1.0 
>> to serv:efcs  6.0
>>   
>> 7)  Set the integral part of the loop so that the   phase is driven to 0ns 
 
> UTC  
>> offset as quickly  as desired without   overshoot/oscillation, for 
example:   
>> serv:phaseco   20.
>>  
>>  Repeat 6) and 7) after some  hours.
>>   
>>  Hope that helps,
>> bye,
>>  Said
>>   
>>>  -----Original Message-----
>>>  From:  Scott Mace
>>>  Sent:  Saturday, April 05, 2008   17:51
>>> To: Said  Jackson
>>> Subject:  Re:   Fury   GPSDO
>>>
>>>
>>> Said,  I finally  got  my fury up  and  running, I'm using a efratom  
>>> FRS-A and  also a  LPRO-101.
>>> Do  you  have any recommending starting  points for  tuning the  servo 
>>> for a  rubidium    unit?
>>>
>>>  Scott
>>>   
>>  
>>  
>>
>>
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