[time-nuts] u-blox "naked" chips - anyone brave enough to try them?

Bob Camp kb8tq at n1k.org
Wed Jun 15 20:08:48 EDT 2016


> On Jun 15, 2016, at 7:44 PM, Attila Kinali <attila at kinali.ch> wrote:
> 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.

If you take data on the ADEV and phase noise of the OCXO during the initial lock / aggressive
steering phase of the process … it’s a lot worse than a minor tip up at 100 seconds.


> 				Attila Kinali
> -- 
> Malek's Law:
>        Any simple idea will be worded in the most complicated way.
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