[time-nuts] Building a GPSDO & trouble using Jupiter-T

Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Jan 30 04:05:17 EST 2012


What about the phase jerk (details given in the datasheet) applied to 
the 10KHz burst once per second?

Bruce

Azelio Boriani wrote:
> Timing GPS receivers usually have the sawtooth correction message and I saw
> an application of a delay line to correct the PPS before using it. Of
> course if you time the PPSes difference with a time-to-digital you don't
> need to correct the incoming hardware PPS by a delay line, but to implement
> an all-analog PPS PLL then it can be done. For those of you who use a 10KHz
> reference signal there is not even the need for a long time constant in the
> low pass filter: to average 1000 PPSes you need 1000 seconds but to average
> 1000 10KHz cycles you need only 0.1 seconds.
>
> On Mon, Jan 30, 2012 at 6:15 AM, David<davidwhess at gmail.com>  wrote:
>
>    
>> The sawtooth error in the PPS output and how they were able to correct
>> it externally was interesting.  I have seen that kind of problem
>> before in DDS and other applications.
>>
>> I wonder what other GPS receivers provide either PPS outputs without
>> sawtooth noise or a correction message.
>>
>> On Sun, 29 Jan 2012 20:40:52 -0800, Hal Murray
>> <hmurray at megapathdsl.net>  wrote:
>>
>>      
>>>        
>>>> What do you mean by "average"?  Do you mean that the GPS and PLL must be
>>>> kept on for "20 minutes to hours", or did you mean that the PLL loop
>>>>          
>> filter
>>      
>>>> must have a time constant of 20 minutes to several hours?
>>>>          
>>> You have to compare the characteristics of the oscillator with the
>>> characteristics of your GPS receiver.
>>>
>>> If your local oscillator is very stable, then you want to average over
>>>        
>> long
>>      
>>> times (hours, days).  If your local oscillator is a good thermometer and
>>>        
>> you
>>      
>>> have a very good GPS receiver, then you want a shorter time constant
>>> (minutes) so you can track temperature changes.
>>>
>>> Do you know about hanging bridges?  If not, please read Timing for VLBI by
>>> Tom Clark and Rick Hambly.  It's got some wonderful graphs.  Once you
>>> understand those, this discussion will get much more interesting.
>>>   http://gpstime.com/files/tow-time2009.pdf
>>>        
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>>      
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