[time-nuts] Another "atomic" clock question

[Bob Camp]

Hi

When you say “adjust crystals close” do you mean:

1) Grinding / plating crystal blanks? (as in fabricating crystals from scratch)
2) Setting uncompensated crystal oscillators on frequency? (as in some radios)
3) Calibrating the OCXO that is the master reference for an instrument? 

That all covers a lot of ground. 

Cost wise, there isn’t much price difference between an Rb and a GPSDO. Both are overkill for numbers 1 and 2, but they are what is commonly used in industry.  For number 3 it’s a “that depends”. Some instruments have much better OCXO’s in them than others. The GPSDO with it’s self calibrating capability is often the device chosen for 3. 

Bob

On Mar 1, 2014, at 11:05 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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