No subject

crystal as well as my wrist watch can be a primary standard in a 1e-3 spec 
or whatever  they can repeat without Calibration.
BUT I have not hear anyone argue that any of the above are primary 
standards, even at some reduced spec. (maybe just because not cost 
effective?)

The existing Cs oscillators can not be primary standard at the new 1e-16 + 
accurate word, but they would be useful just the same in that word as a 
secondary standard.

There is always progress and change in the time world
ws

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ws

Sorry but you have completely misunderstood the concept.
It is admittedly a difficult concept to grasp; I know it took
me a long time.

A hydrogen maser with the wall shift servo'ed out will run rings
around a compact Cs beam clock like the HP5062, used on submarines.
(An interesting trivia item is that I don't believe the 5061 can
fit through a submarine hatch).  The 5062 is still a primary
frequency standard and the hydrogen maser is still a secondary
frequency standard.

Regarding "drift" of primary cesium beam standards:  the 5071A has
unmeasurable drift, aging and tempco, down to a measurement limit
of at least 1E-15.  It has a typical *random* error of a few parts
in 1E-13.  The systematic error (average error of all 5071A's built)
has been established to be below 1E-14.  It will always be a
primary standard even in the presence of longer reversible optically pumped
laboratory Cs beam standards of higher accuracy and better short term
stability, or cesium fountains, etc.  Even the 5061A/B is considered
a primary standard, albeit with reduced accuracy, even though it
has a measurable tempco.  We were very proud of the E1938A crystal
oscillator when it was able to meet the 5061 tempco spec.  It
is in no way a primary frequency standard regardless of that
or any other accomplishment.

Primary means that the clock will meet its spec without being
"calibrated" against a better clock.  Secondary means that
calibration against a primary standard is necessary.

Rick Karlquist N6RK


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WarrenS wrote:
> All very informative and useful information for sure and good to know,
> But I'm thinking the real difference between a primary and secondary
> standard,
> Has More to do with if there is anything else more accurate and repeatable
> available.
> I'd guess a Rb would of made a great cave man Primary standard.
> And sounds like it will NOT be long before the Freq and drift of a CS
> Primary will be consider just another secondary standard that will have to
> be calibrated.
> (to get the 1e-16 + or whatever accuracy/repeatability  it is they are now
> working on.)
>