# [time-nuts] using Fury GPSDO with Rb

SAIDJACK at aol.com SAIDJACK at aol.com
Wed Apr 9 01:57:48 EDT 2008

```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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