[time-nuts] using Fury GPSDO with Rb
SAIDJACK at aol.com
SAIDJACK at aol.com
Fri Apr 11 17:30:28 UTC 2008
Hi Scott,
interesting, that's a very small control range.
That would explain why the Fury had a hard time locking, but seemed to work
fine once locked.
It's helpful to see how the units' output frequency behaves when setting the
dac manually between 0V to 5V using the serv:coarsedac xx command.
Please let us know how you get it to work with a different Rb,
bye,
Said
In a message dated 4/11/2008 08:44:27 Pacific Daylight Time, smace at intt.net
writes:
Turns out this unit has been set so that the EFC was only useful from within
a .5v range
centered around 2.5v, also the output was TTL. Trying with a different Rb...
Scott
SAIDJACK at aol.com wrote:
> 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
>>>>
>>>
>>>
>>>
>>>
>>> **************Planning your summer road trip? Check out AOL Travel
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