[time-nuts] u-blox "naked" chips - anyone brave enough to try them?
attila at kinali.ch
Wed Jun 15 19:44:40 EDT 2016
On Wed, 15 Jun 2016 18:43:38 -0400
Bob Camp <kb8tq at n1k.org> wrote:
> > Same as above.
> > If you lock the VCXO to an OCXO, this will be much better.
> Each time you steer the OCXO to lock things up, you will degrade both it’s ADEV and it’s
> phase noise. If the GPS drops out when you do this …. the GPSDO never locks up.
Yes, sure. The ADEV of an OCXO will turn upwards again at taus somehwere
around 10 to 1000 seconds. The loop bandwidth of the PLL that locks the OCXO
to GPS should be in the same range in order not to degrade the short term
stability of the OCXO. Also the PLL should have a rather damped behaviour
in order to average out the "phase jumps" resulting from the jitter of
the GPS PPS.
If these two points are not taken care of, then yes, the ADEV, resp the
phase stability will degrate and thus can cause the GPS receiver to lose
track of the satellites.
Any simple idea will be worded in the most complicated way.
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