Fellow time-nuts,
I spent last week at the European Frequency and Time Seminars 2015 in
Besancon, France. It was a week full of seminars and also labsessions.
It was a nice mixture of phase-noise, stability measures, GNSS,
fibre-based time and frequency transfer, atomic clocks, laser cooling,
crystal oscillators etc. from a distinguished set of lectures.
This was the third run, with the assistance of Prof. Enrico Rubiola.
Sharing lunch and sometimes breakfast or dinner with these lectures sure
helped to spread the knowledge. Enrico was eager to share knowledge and
answer questions, turning the paper table tablet upside down to draw and
explain over lunch.
Some of the labs stood out as good labs, and that includes Francois
Vernottes data-analysis lab which illustrated the ADEV and MDEV uses, so
that you needed MDEV to separate noises. It illustrated the linear drift
limitations and how you can use either HDEV or drift-removal to recover
the actual noise below that limit. All this using his Sigma THETA tool:
https://theta.obs-besancon.fr/spip.php?article103&lang=fr
As a side-note, the question came up about delta-counters and the claim
of using MDEV to process it "correctly". Francois and I teamed up to
explain why it does not work, and how the hockey-puck/droop response
shapes. Later in the week I saw a diagram that had that response as
measured for an optical clock, so I turned to Attila, waved my finger
and said "Bad science! Bad science!".
The analysis of Omega-counters (those using linear regression for
frequency estimation) triggered the discovery of the PDEV measure.
However, there you use m-altering weighing rather than the typical fixed
width filtering of delta and omega counters.
The GNSS time transfer lecture of Pascale Defraigne from the Royal
Observatory of Belgium was also interesting, showing her CGGTTS methods
for comparing clocks between labs and also for the PPP stuff.
The WhiteRabbit lecture was interesting, and the lab-session was really
impressive in all its simplicity. CERN has certainly been thinking about
how things should work. Thomasz was also a great guy to hang out with.
Learning about pulsars and the efforts to measure those was also
interesting.
Also get to learn about DROs, CPT etc. through the combination of labs
and lab-visits was interesting. We also got a tour of their
crystal/resonator lab, which is where they did the research of the BVA.
A particular nice exercise was to visit their observatory and then later
on see Jupiter and three moons as well as Venus in the same view.
Sharing this experience with fellow time-nut Attila Kinali was nice, and
we picked up additional friends on the way, such as Guilermo who does
MEMS design in his PhD and William that does Ca+ ion clocks in his PhD.
As we could not stop talking we ended up in Enricos office and as we
where migrating out of that we joined forces with another professor for
a nice evening dinner on Friday, which included integration of flicker
noise from an estimate of universes total age to the frequency so high
it creates a black hole and ending up with just above 22 dB over the
white noise floor. Epic moment! We also had a very good time and good
food.
The heat was considerable, so for a northerner like me it was a bit of a
challenge, but I managed to cope with it better over the week.
For people wanting to learn more about this, do consider going to the
EFTS next year.
Oh, before going to Besancon I came first to Geneva so I could do a
presentation at CERN and meet up with the White Rabbit team. They where
generous and showed me around! As I was going to Paris I was also setup
with a contact at SYRTE as part of Observatoir de Paris, so I got a nice
visit of SYRTE too. Did some other visits there, including some form of
temporary tower that Gustaf Eiffel seems to have left behind, it's a
L-beam marvel.
Cheers,
Magnus
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