[time-nuts] time-nuts Digest, Vol 101, Issue 152
lists at rtty.us
Mon Dec 31 03:14:16 UTC 2012
…. sorry for the previous blank message….
A lot depends on what kind of inductors they are. If it's a static field, then you have to saturate the core. That's pretty hard unless the core is ferrite. Most powdered iron and (of course) air are fairly immune to static field.
If it's an AC field, then the frequency of the field and the location of the coil in the circuit matter a lot. In a typical OCXO, the coils are essentially part of a tuned tank of some sort. They are pretty good at rejecting off frequency signals. A field at a high enough frequency to be "inside" the tank will have a tough time with the case of a sealed OCXO.
Even with a static field, if the case is steel, it will create a magnetic path around the OCXO innards. What you see on the outside probably will not be what you see on the inside.
If you are talking about the field from a 600 to 1200 rpm fan (the question that started this) the field could be as low as 10 to 20 Hz. Even if it's a bit above that (say 160 to 320 Hz) it's still a lot closer to a static field than the AC case.
Can you find an OCXO that's susceptible to a field - sure you can. Can you buy them rated to have spurs below -180 dbc with a field of so many gauss at frequencies from 1 to 100,000 Hz - sure you can. It all depends on the design.
On Dec 30, 2012, at 9:25 PM, Said Jackson <saidjack at aol.com> wrote:
> But all those inductors surrounding the crystal will be sensitive to magnetic flux variations and could cause spurs and jitter..
> Sent From iPhone
> On Dec 30, 2012, at 18:04, Bob Camp <lists at rtty.us> wrote:
>> Precision crystals have clips made from nickel. The posts are likely Kovar. That's been true for a *long* time. Neither one is very magnetic. Both likely are hard enough to be even less magnetic than they might be.
>> On Dec 30, 2012, at 6:27 PM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
>>> On 30/12/12 23:27, Bob Camp wrote:
>>>> A quartz crystal in insensitive to magnetic field. This being
>>>> Time Nut's that's not the whole story.
>>> As I recall it, the steel clips sometimes used to hold the resonators is claimed to be one of the sources for static magnetic field sensitivity. The mounting has developed since then, so I wonder how much that is relevant to new oscillators, but could still be possible to find for older ones.
>>> time-nuts mailing list -- time-nuts at febo.com
>>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
More information about the time-nuts