[time-nuts] Another "atomic" clock question

Bob Camp lists at rtty.us
Sun Mar 2 13:02:34 EST 2014


These days, you can get some *very* low cost crystals. They sell by the pound rather than by the piece. The tolerance as delivered may be 0.1% for temperature plus calibration. Aging is likely to be “who knows”. The temperature characteristic could be a third order curve. More likely it’s a straight line in one direction or the other. Cost is the driver, and not much else matters. They make millions of them a week.


On Mar 2, 2014, at 12:56 PM, Hal Murray <hmurray at megapathdsl.net> wrote:

> bob91343 at yahoo.com said:
>> But I thought conventional wisdom is that most crystals are AT cut and an
>> attempt at zero average coefficient is made, causing a nonlinear
>> characteristic.  But perhaps over a limited range it's linear.  The problem
>> of course is calibration.
> Most crystals are low cost.  They will have a temperature characteristic 
> similar to the graph about half way down this URL:
>  http://www.4timing.com/techcrystal.htm
> The specs on the standard oscillator packages vary from 100ppm to 20ppm.  
> That covers temperature and voltage and initial manufacturing and some amount 
> of aging.  (I haven't looked at the spec sheets recently.  I don't remember 
> seeing anything about aging.)  The point is that they are low cost and the 
> specs are reasonably clear, something a digital designer can understand and 
> use.
>> Again, how does one calibrate those 3 MHz ovenized units?
> I plug mine into a HP 5334B which is clocked by a TBolt.
> -- 
> These are my opinions.  I hate spam.
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