On Sun, 30 Oct 2016 20:38:49 +0000 "Dr. David Kirkby (Kirkby Microwave Ltd)" <drkir...@kirkbymicrowave.co.uk> wrote:
> I was just reading the Keysight forum on VNAs. Someone was having issues > measuring a bit of waveguide 80 m long. Dr. Joel Dunsmore pointed out that > humidity has an effect in waveguide. > > I'm guessing this is due to the change in permittivity in the air, which > would be most noticeable near the cutoff frequency of the waveguide. That > should change the magnitude of the reflection, not just the phase, so it > might be a relatively cheap way to measure humidity. > > Just thinking aloud. I'm probably talking rubbish. This has been used for quite some time. Though cheap is relative :-) A non-representative selection of papers that I have lying around here: "A Reference Standard for Measuring Humidity of Air Using a Re-entrant Radio Frequency Resonator", by Huang, Ripple, Moldover, Scace, 2006 http://www.nist.gov/customcf/get_pdf.cfm?pub_id=902995 "Automatic digital microwave hygrometer", by Hasegawa, Stokesberry, 1975 http://dx.doi.org/10.1063/1.1134331 "ELECTRICAL PROPERTIES OF ATMOSPHERIC MOIST AIR: A SYSTEMATIC, EXPERIMENTAL STUDY", by Carlon, 1988 http://www.dtic.mil/dtic/tr/fulltext/u2/a199599.pdf "The Refractive Indices and Dielectric Constants of Air and its Principal Constituents at 24,000Mc/s", by Essen, Froome, 1951 http://dx.doi.org/10.1088/0370-1301/64/10/303 Don't ask why i have these papers.... Attila Kinali -- Malek's Law: Any simple idea will be worded in the most complicated way. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.