On 28/03/14 12:33, Bob Camp wrote:
Hi
Crystals are susceptible to vibration. That’s pretty well documented. They have
resonances in the mount structure. They have a 2G tip sensitivity.
Audio when it “impacts” an oscillator induces vibration. If your noise source
is a rocket engine, then the vibration is “non trivial”. You do indeed see
phase noise on the oscillator from audio …
The effect is well known and different approaches to reduce impairment
of vibration have been presented. One approach have been to mount two
crystals as a pair such that they will first-degree cancel each other.
Those have been electrically operated in parallel.
Another approach have been in mounting, both the direct mounting of the
crystal but also mounting of the assembly. For instance, the Ashtech
Z-12 has it's 20 MHz OCXO mounted in a vibration-reduced setup, which
makes sense since it is a box intended to be carried around in the field
and as one intends to collect carrier-phase measurements you want to
avoid carrier phase cycle-slips.
For other uses such as helicopters, vibration is a big deal, and well,
guess what makers of vibration-improved oscillators address as a market.
Then we have those that want their oscillators to not be too much
affected as it is shot out of a canon. The acceleration kick is 12000 g.
Cheers,
Magnus
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