This is a late answer for Alice Campbell,
 I'm sorry, but I'm shooting down every weekend the list (with
NOMAIL) . Yesterday I have looking at pic arhive and I've read your
mail.
 The principle you've mentioned it's almost correct but the method is
dangerous and not recommended ( and will probably not work
either...)
 The smallest microwave power that can be achieved from a
standard 700...900 W oven magnetron it's (the best situation )
50...80W with serious transformer modification. This will alter your
measurement because microwave radiation will dry the soil in the
measuring time. The magnetron it's not very stable in this zone so a
better approach is to use some smallest power microwaves
generators like Gunn, Impatt diodes or even transistors oscillators.
( The oscillator from a 10GHz LND who is mounted on a dish
antenna  have near 5...10mW output power ) If the soil sample is
disposed into a small measuring cell, an input power of 100mW it's
enough for a moisture transmission measurement.
  The ugliest problem is temperature and granulation influence in
moisture result, but this may be compensated using a controller and
a calibration procedure for every type of measured soil...
  Vasile
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Surducan Vasile, engineer
mail: vasile@l30.itim-cj.ro
URL: http://www.geocities.com/vsurducan
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