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

David davidwhess at gmail.com
Mon Jan 30 00:15:29 EST 2012


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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