[time-nuts] using Fury GPSDO with Rb
Scott Mace
smace at intt.net
Fri Apr 11 14:19:08 EDT 2008
The output of the Rb was TTL also. What are the side effects
of using that with the Fury (other than not getting a sine output)?
This FRS-A looks like a regular FRS with an additional connector board that makes
it pin-compatible with the LPRO and a slightly larger enclosure. In
reading the manual, it's possible to change it from TTL to sine output, but
probably not worth the effort. I opened up the unit and found
that the range is set from the factory with a small resistor piggybacked on
R13 on the power supply board. It states that this might need to be
adjusted over time.
Scott
SAIDJACK at aol.com wrote:
> 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
>>> Guides.
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>>>>
>>>
>>
> (http://travel.aol.com/travel-guide/united-states?ncid=aoltrv00030000000016)
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