[time-nuts] time-nuts Digest, Vol 101, Issue 152

Said Jackson saidjack at aol.com
Sun Dec 30 23:42:38 UTC 2012

Hi Attila,

Makes a big difference if there are AC magnetic fields in the system, they can create spurs through mutual inductance.

Our Fury GPSDO is designed completely without any switching regulators for that reason. One customer used it on helicopters for measuring magnetic field variations -read finding submarines - and said all other GPSDOs they tried such as trimble etc create false returns. We have a magnetic field emissions measurement of the Fury showing barely any increase in ambient magnetic field.

We had a switching regulator next to our docxo on our FireFly synthesizers and it created a spur in the phase noise. Switching to a shielded inductor fixed that issue.

So yes, a typical fan would likely create measurable EMI and AC magnetic fields.. And at the femtosecond, -175dBc levels, and ppt levels we are interested in here it probably makes a difference.


Sent From iPhone

On Dec 30, 2012, at 11:35, Attila Kinali <attila at kinali.ch> wrote:

> On Fri, 21 Dec 2012 09:53:51 -0800
> Said Jackson <saidjack at aol.com> wrote:
>> Volker, I wonder if you also see fan-induced spurs in the phase
>> noise from 1Hz to 100Hz. I would not be surprised if the fan
>> vibration adds significant spurs to the 10811A crystal.
> How susceptible are OCXOs on magnetic fields?
> Most fans (even "computer" fans) have a quite strong, changing field.
> Or is that insignificant compared to other sources of noise?
>            Attila Kinali
> -- 
> There is no secret ingredient
>         -- Po, Kung Fu Panda
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