How to test *your* microwave oven distribution pattern.

[Jim Choate <ravage@EINSTEIN.ssz.com>]

Here's a simple way to test the bounce-pattern of your micro-wave oven:

 -	Go to your local hobby store and buy some small balsa or pine
        sheeting, stringers (4x), and glue (non-water based). You'll
        also need several small open top containers (like a shot glass
        but smaller for best effect) and a marker.

 -	Cut the stringers to the vertical height of your oven cavity.

 -	Cut the sheeting into 1in. sq. pieces.

 -	Mark the stringers evenly such that there is enough room to glue
        the sheeting between the stringers, forming a multi-leveled tower.

 -	On each level place your container with a suitable amount of
	water (fill it almost to the brim).

 -	Place the tower w/ it's containers in one of the corners. Mark
        a line around the base so you know where you been.

 -      Start your microwave up (adjust time as needed, say start with
        30s) and note the temperature of each container after the time.
	Note that putting your thermometer in there will cool it slightly
        and you'll also need to have the same number of runs and levels so
        so each level can be measured immediately after opening the door.
 	If you have access to an optical pyrometer you could potentialy
        measure them all.

 -	Once you've measured it here, move it over to be adjacent to the
	lines you drew above, outline the base again and repeat as needed.

 -	Run your regression and your done, tadah.

Some glasses will be hot, others won't. Trace the path of the beam out of
the magnetron and you'll get a good idea of what your oven is really doing.

Whether the cavity is stricly a corner reflector (ie corners are square) or
is trapezoidal (slightly off square to help disperse the bounce pattern not
the beam) is irrelevant to the actual holes in the pattern, they will be
there.

I'll mention but not go into the shadowing effect of objects placed in the
cavity and the requirement for even cooking means that they have to be
rotated for even dispersal of the cooking effect. Another indication that
the beam doesn't disperse as widely or quickly as some claim.

On another topic about holes and escaping microwaves, if the holes are the
right size (which the screen in the glass in the front of your oven is)
they will preferentialy absorb the microwave, if it's correctly grounded
very little of the radiation will escape (as you can measure with a standard
microwave oven leak detector).

Now, let's talk about ways to build a laptop that will reduce the emissed
radiation to a minimum.

First, put all the computing guts into a small box that is well grounded
(running on a battery will pretty much screw you here since it ain't
grounded unless you drive a stake into the ground). Then make sure that any
openings or gaps are in the front edge or on the bottem pointed down. There
should be no breaks in the sides, rear, or top. Make sure the floppy, CD,
hard drive are placed in the front of the laptop container adjacent to the
metal box above and make sure any openings in them point out. The reason you
want the openings in the front edge is that  your body will make a
very good sheild to that hi-energy rf that folks want to tap. The openings on
the bottem will direct it to the ground where where they are absorbed (why they
call it a ground-plane). Make sure that all cabling from the peripherals to
the computing box are shielded (remember, ground the shield at one end
only). The seam or hinge between the display and the case should be shielded
with standard copper fingers. The cabling should also be well shielded. Make
sure there is a grounded screen covering the front of the LCD (and for gods
sake don't ever use a plasma display). The exterior case should be metal
(why I love my Tadpole 3XP and IBM N40). All openings for batteries and such
should be screwed down and not simply retained by a latch of some sort. The
*ONLY* way to power the laptop should be by battery. There should be no
provision to power it off the ac mains (this is going to be inconvenient
since you'll need to carry extra batteries, an external charger for them,
and the screw drivers and such to change them - no simply and easy pop-outs
here).

As to the display, the ideal display would be a dual-display HMD that was
also sheilded. This is based on the assumption that if your data is so
sensitive that you don't want people snarking it out of the air you probably
don't want them reading it over your shoulder (up close or through a
tele-photo).

If you do decide to stake your laptop as refered above there are a few
things to know....

 -	Make sure the stake is in suitable ground without lots of quartz
        and other similar peizo-electric materials.

 -	The stake should extend at least 3ft. into the ground.

 -	When the stake is driven in, the ground should be thoroughly wetted
        which usualy means quite a bit of water (30 gals or so should do
        it), if possible wet it over a 24 hour period prior to staking.

 -	Make sure the stake and the cable leading to the laptop are copper
        (or silver if you're rich)

 -	You don't want to be close to phone, power, and other sorts of
        underground utilities.


    ____________________________________________________________________
 
       To know what is right and not to do it is the worst cowardice.

                                                     Confucius

       The Armadillo Group       ,::////;::-.          James Choate
       Austin, Tx               /:'///// ``::>/|/      ravage@ssz.com
       www.ssz.com            .',  ||||    `/( e\      512-451-7087
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