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

Attila Kinali attila at kinali.ch
Thu Aug 20 17:30:25 EDT 2015

On Tue, 18 Aug 2015 21:49:50 -0700
<cdelect at juno.com> wrote:

> 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). 

On a similar quest, i stumbled upon [1] where Hasegawa and Stokesberry
used resonant microwave cavities to measure humidity of air. The paper
gives a couple of formulas on how to calculate the frequency shift
due to air pressure, humidity and CO2 content.


			Attila Kinali

[1] "Automatic digital microwave hygrometer", 
by Hasegawa and Stokesberry, 1975

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