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Re: magnetrons as diodes
Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>
At 09:54 PM 1/4/2007, you wrote:
Original poster: Robert Amaya <dimon20042004@xxxxxxxxx>
When microwaves hit a metal surface, they bounce off and in the
process, induce a voltage in that metal. An example of this is when
you put a small strip of aluminum foil in the microwave, it will
blow like an overloaded fuse as a result of the induced voltage.
Using that knowledge, a thicker piece (so it will not short out) of
the aluminum foil, can be placed in front of the magnetrons output
to be monitored for any voltage fluctuation across the aluminum that
would be caused from microwaves hitting it. Im not shure on how much
voltage or amperage this will induce in the aluminum foil but I hope
Except that the induced voltage will be at 2.45 GHz. You can make
perfectly good sparks at that frequency, but the run of the mill
voltmeter isn't going to detect it.
If you're worried, go find one of those microwave oven leakage
detectors. The professional calibrated ones (e.g. from Narda) are
pretty expensive, but there are very inexpensive ones for consumer
use (Radio Shack used to sell them). It's basically a small dipole,
a suitable diodes and a voltmeter. The safety level is 2 mW/cm2, so
the consumer units are quasi calibrated in that general area. (The
pro field strength meter has a lot more dynamic range AND is
calibrated to a traceable standard)
you could build your own field strength probe, but calibration is a pain.
Just to get anyone interested in the ballpark: 2.45 GHz is 12.2
cm. The effective aperture of a 6 cm long dipole is about 1/8th
square wavelength, or roughly 18 square centimeters. So a dipole
will intercept about 40 mW at the ANSI exposure limit. Into 72 ohms
(the impedance of the dipole), this works out to about 1.6-2.7 volts.
A smaller probe intercepts less power. Make it 1 cm, and you
intercept 1/36th the power (about 1 mW) and the voltage is
correspondingly smaller (a bit less than a volt).
A variety of diodes will work. What you want is a zero bias planar
schottky or an old germanium (1n34, for instance). But, almost
anything will work (1n914, 1n5711, etc.)