[time-nuts] Z3805A cooling requirements?
ailer2 at t-online.de
Sat Dec 22 20:34:09 UTC 2012
> 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...
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. 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.
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> and follow the instructions there.
More information about the time-nuts