On Fri, 30 Aug 2002, Morgan Olsson wrote:

>Peter:
>Good idea, the microwave absorption might also be a solution.
>If we could make a cheak microwave osc and reciever.
>I have no RF experience so i have no ideas.

Obtain one of those radar door openers (not the IR kind), put a paper
napkin in front of it, see what happens when you soak it with water. You
may have to adjust the sensitivity control. Make sure you get one with an
adjustment. You may have to move the napkin to have it react (put it on
cardboard and move the cardboard). You can duplicate this with a sample of
your dirt. Small modifications to the detector will remove the requirement
to move the napkin. This kind of sensor is non-contact (can be mounted on
a pole looking down etc).

>BTW, both microwave and NMRI solutions will probably make it different
>for certification.  2,45(?) GHz is free for low power (and spread
>spectrum?) IIRC.  But precise microwave do sound expensive.

What 'precise' ? ;-)

>Also moist dust with salt might damp much too.

I think that you need to define to yourself what kind of water you need to
detect. You seem to have no clear ideas yourself. Do you mean water, as
in, 3 feet under ? 3 cm under ? Just a little wet ? Rain ? Spray ? How
slowly can it accumulate ?

>And it might conduct too much to use a capacitive method to differ it
>from water sucessfully.

Conduction and loss at RF are different things.

Peter

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