[time-nuts] Phase microstepper designs?

Bob Camp kb8tq at n1k.org
Wed Dec 9 17:53:07 EST 2015


> On Dec 9, 2015, at 12:34 PM, Tom Van Baak <tvb at LeapSecond.com> wrote:
>> Are you aware of some redeeming value that phase microsteppers
>> have that would make us want to investigate them?   Am I
>> being too harsh on them?  Maybe you can champion them and they
>> will make a come back :-)
>> Rick Karlquist N6RK
> A phase microstepper is useful with many older Rb and Cs standards (e.g., 5061A and 5065A) so that you don't have to touch the C-field. It is also useful with a 5071A to improve the time sync/step/steer resolution.
> Note that you can also implement a GPSDO with a phase microstepper and this allows you to avoid Vref, DAC and EFC. Not all LO have EFC, and even if they do, it may be more stable not to use EFC. Plus with a DDS you avoid EFC-out-of-range problems.
> See also http://leapsecond.com/pages/fe405/ and the links near the bottom. This (patented) FEI design avoids the spur issues several of you have been talking about: the RF output comes from a low-noise VCXO not the low-drift OCXO+DDS itself.

It avoids the far removed spurs. If you have a close in spur, it passes right through the PLL loop and messes up your ADEV. 
Yes, this really does happen on real gear in the real world …..


> And finally, another very interesting use of a DDS as a sort of microstepper phase comparator is:
> http://www.ptfinc.com/dsheets/App_35_picoPak.pdf
> /tvb
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