[time-nuts] Re: Long term ADEV of 5071

[Magnus Danielson]

Hi,

On 2021-03-25 19:21, Poul-Henning Kamp wrote:
> --------
> Attila Kinali writes:
>
>> Does someone of those who own a 5071 have long-term ADEV data?
>> I'm looking for multi-year data. While there are plenty of ADEV
>> plots online, most of them stop at 1Ms or even at 100ks.
> As I understand it, cesium beams are considered "primary" standards
> because once the ADEV hits the floor, it stays down there ?

"primary" standard means different things in different context.

In telecom, it means it adheres to ITU-T G.811 specifications, which
effectively puts within 1E-11 in maximum frequency error, which is what
analog cesiums can deliver. Most of the cesiums we attain as hobbyists
was designed to meet this spec. The underlying specification driving it
was to keep data-slip rate between two operators down to once in 70
days. It was reasonably achieveable with the technology at hand and for
the total cost so I think it was fair.

In metrology "primary standard" has a complete different meaning, and in
practice all clocks we hobbyists gets to have would not fit, they would
all be more or less good "secondary standards".

The sales people for vendors will be happy to underblow the
understanding of you being able to buy and have your own "primary
standard". If it where, you would not be needing traceability to
anything else, but you end up needing to have that anyway, and in
reality the "primary" reference is actually one of the few that
contributes to the international realization. I've seen a few of those,
but not in my basement.

The "primary reference" is not about ADEV hitting the floor, all devices
do that (for a strict definition of what should be measured in ADEV).
It's about the context one consider it "primary".

It would be cool to say one has a "primary standard", and depending on
context I have several working or none. Coolness aside, when talking to
metrology folks and national metrology labs, I might have some clocks,
but I do not call them "primary reference", because most of them does
not have that either.

So, I think we should be careful with the term, it's get thrown around
too lightly.

Cheers,
Magnus