[time-nuts] Cavity frequency air filled vs vacuum?

[cdelect at juno.com]

Hi everyone!

I'm trying to figure out what change if any to a cavities resonant
frequency would be when measured with ambient air pressure and then with
a vacuum inside. There will not be any pressure on the cavity when under
vacuum as the outside of the cavity will also be at vacuum. The cavity
frequency under vacuum will be 1420Mhz + (Maser frequency). 

Thanks,  Corby