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

[Azelio Boriani]

Maybe HP5071s will get their ADEV when optical clocks will officially rule...

On Fri, Mar 26, 2021 at 9:40 AM Magnus Danielson <magnus at rubidium.se> wrote:
>
> 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
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