[time-nuts] using Fury GPSDO with Rb
SAIDJACK at aol.com
SAIDJACK at aol.com
Wed Apr 9 02:06:23 EDT 2008
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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