[time-nuts] Another "atomic" clock question

Chris Albertson albertson.chris at gmail.com
Sun Mar 2 00:14:06 EST 2014


On Sat, Mar 1, 2014 at 8:05 PM, Bob Albert <bob91343 at yahoo.com> wrote:
> 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.
>
>
>
> --
> These are my opinions.  I hate spam.
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-- 

Chris Albertson
Redondo Beach, California


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