> I wonder if the forced convection is to strong. You don't want to
> hit the limits of the oven control-range. Wonder if this is a
> long-term effect and if even small adjustment to the setup can
> remove the bursts of noise you are seeing.
Now, some hours after switching off the fan, I'm discovering such noise
bursts even without ventilation :-( That means, I can't be sure, that
the change in deviation for small tau is caused by the ventilation. May
be it's just within the natural variation.
I have to state, that this experiment can't proof the assumtion that a
constant air flow affects the deviation curves of an HP 10811
significantly. Except for the humps in the greater tau ranges - what
averages out. In fact, if there is any effect, the effect is small.
What could be worked on further: Not comparing the OCXO with the
internal GPS signal (which is quite noisy in short term) but with an
external oscillator. I've got an HP 10544 (similar to the 10811), which
could be the reference for external time interval measurement.
I'll need some more days...
Volker
Am 22.12.2012 19:14, schrieb Magnus Danielson:
On 12/22/2012 06:44 PM, Volker Esper wrote:
Thank you for your statement, I have to think about it.
It seems to be clear, that ADEV/MDEV aren't the convenient tools for
characterizing such an event. My goal was to answere the question asked
in the beginning of this thread: Does a constant ventilation of the OCXO
affect the deviation curves and if so in what manner? More precisely: do
I have worse deviation due to ventilation?
Well, the deviation curves was only meant to separate various
phase-noise forms, not systematic effects, even if they may be
illustrated to some degree using the tool. However, since noise(s) and
systematic effects have completely different properties in how
confidence intervals builds, so they are better measured and treated
separately before being put back together again. For longer taus the
systematic effects dominates, so drift, temperature, supply voltage and
pressure kicks in.
> ... phase/frequency/drift plots and FT of them might be more
> useful.
So let's have a look at the time domain. The picture shows the PPS-TI of
the Z3805 (blue: time difference between OCXO and GPS; red: EFC).
In the middle of the diagram we recognize the reaction to the
ventilation. Before that happens, the curve has a somewhat stable "high"
frequency noise. After starting the ventilation this noise is extremely
varying in amplitude. IMHO that might mean, that Allan deviation will be
affected at the short term values of tau. This seems to coincide with
the MDEV vs time curves of my diagrams.
Agree?
Agree. I wonder if the forced convection is to strong. You don't want to
hit the limits of the oven control-range. Wonder if this is a long-term
effect and if even small adjustment to the setup can remove the bursts
of noise you are seeing.
Cheers,
Magnus
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