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

[Magnus Danielson]

You can do the ADEV just fine using Circular T. Long-term 5071 does not
dominate the TAI phase/frequency, but they do dominate for stability.

This is the difference between EAL and TAI, the 5071's go into EAL, but
EAL is then frequency corrected with a handful of primary references
(cesium fointains) into TAI. EAL just try to be as stable as possible,
without careing too much about phase and frequency.

Cheers,
Magnus

On 2021-03-26 11:00, Azelio Boriani wrote:
> 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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