[time-nuts] GPSDO TC

Bruce Griffiths bruce.griffiths at xtra.co.nz
Thu Jan 8 17:09:19 EST 2009


Björn Gabrielsson wrote:
> On Fri, 2009-01-09 at 10:28 +1300, Bruce Griffiths wrote:
>   
>> Richard Moore wrote:
>>     
>>> On Jan 8, 2009, at 2:58 AM, time-nuts-request at febo.com wrote:
>>>
>>>   
>>>       
>>>> Message: 6
>>>> Date: Thu, 08 Jan 2009 11:51:50 +0100
>>>> From: Magnus Danielson <magnus at rubidium.dyndns.org>
>>>> Subject: Re: [time-nuts] GPSDO time constant
>>>> To: Tom Van Baak <tvb at leapsecond.com>, 	Discussion of precise time and
>>>> 	frequency measurement <time-nuts at febo.com>
>>>>     
>>>> For ThunderBolt owners it is pretty straightforward to adjust the  
>>>> TC and
>>>> damping, which is very nice. Use this oppertunity!
>>>>     
>>>>         
>>> So, Magnus (and Tom), what damping factor do you suggest for a TBolt?  
>>> I'm running a verrry long TC now. If 1.2 is not actually critically  
>>> damped, what value would be? Any guesses? BTW, I really like that  
>>> plot of Tom's that tracks the oven and then gets better from the GPS...
>>>
>>> Dick Moore
>>>
>>>   
>>>       
>> Richard
>>
>> As always, the problem is how do you know that the time constant you are
>> using is anywhere near optimum?
>>
>>
>> Bruce
>>     
>
> So what is optimum... from control theory we learn, that with an even
> better model of your system, you can push performance to the edge! But
> you always loose robustness in doing that. 
>
> So what is the implication of a to large TC here? Nothing going instable
> in the control loop? We are just following the "freerunning" OCXO curve
> past the point where GPS goes downhill?
>
> --
>
>    Björn
>
>
>   

Björn


My point was that measurements are required to establish the optimum for
each individual OCXO not just for a given OCXO model.

Bruce




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