[time-nuts] Another "atomic" clock question

[Bob Albert]

Paul, as I said I just want to know how close my crystals are and be able to adjust them as well as they can be.


I probably will never go rubidium (note that I qualified that) but still somewhere one has to decide where to set the frequency.

I did WWV at 20 MHz for a beat of somewhat slower than one per second.  I know the phase changes but probably not much in a few minutes, as the path length doesn't vary very quickly.  And I don't need phase lock to them anyway.  In the old days they had 25 MHz and even 30 MHz for a slight improvement in settability if not stability.

Bob




On Saturday, March 1, 2014 7:38 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
 

> I am trying to understand how this is done.  Should I ever get a rubidium
> standard, I'd want to check its calibration, and that's not a trivial
> exercise. 

If you assume your rubidium is stable, then it's pretty easy to check and/or 
calibrate.

The trick is that you need someplace to stand.  A PC running ntp is good long 
term.  There is a tradeoff between good and long.  Good is ambiguous, but 
both how-good is your PC clock and how good/accurate a measurement do you 
want are appropriate.

Probably the simplest way is to get one of tvb's preprogrammed PICs.
  http://www.leapsecond.com/pic/picdiv.htm
  http://www.leapsecond.com/pic/picpet.htm

One approach is to use a picDIV to make a PPS and then monitor that.

If you have Linux, you can feed the PPS to a serial port.  My hack for 
counting 60Hz will work fine at 1 Hz.
  http://www.megapathdsl.net/~hmurray/time-nuts/60Hz/60Hz.py

Another approach is to use a picPET and connect a modem control signal from 
the monitoring PC to the Event input on the picPET.  Then the data collection 
program grabs the time, flaps a modem control signal, grabs the time again, 
then grabs the text from the picPET and logs everything.



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