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