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

[Jim Lux]

On 12/30/12 11:35 AM, Attila Kinali 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?
>
>

the oscillator itself probably has low sensitivity, but stuff around it 
doesn't: if you're measuring Allan dev..There are the usual concerns 
about residual magnetism in the crystal holder causing it to move 
slightly as the field changes.

When designing the system to do coherent two way ranging to the Juno 
spacecraft orbiting Jupiter, we found that the rotating magnetic field 
(because the spacecraft spins at 2RPM in Jupiter's magnetic field) was 
enough to modulate the circuits that track the received signal and 
generate the transmitted signal ( basically a PLL)...

This is if you're trying to get ADEV < few parts in 1E16 at 1000 sec, etc.