Re: How to test *your* microwave oven distribution pattern. (fwd)

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

Forwarded message:

> Date: Thu, 05 Nov 1998 11:42:41 -0800
> From: Michael Motyka <mmotyka@lsil.com>
> Subject: Re: How to test *your* microwave oven distribution pattern.

> Please explain to me why it matters that the box be grounded!

Electricity runs from a high-potential point to ground. If it isn't grounded
it radiates away into space where it can be detected. If the Faraday Cage
isn't grounded it simply acts as a parasitic oscillator and re-emits the
signal from inside, though at a lower amplitude. Remember, charge rests on
the *OUTSIDE* of a object so that any charge picked up internaly gets passed
to the outside surface.

Which raises another point. Since sharp corners radiate better because they
hold larger charges one should probably avoid sharp angles or corners.
Though you might be able to use that to advantage by having a caged needle
that radiates the majority away into the grounded cage.

Probably the ideal 'laptop' would be a metal ball with a grounding wire and
a single large mil-spec connector that drives a HMD. Something like the Rock
City by Archistrat but round instead of cubical.

> Radiated energy from chips and traces is independent of your mongo
> ground strap to the mother ship.

Not if the ground plane on the pcb is built right. The amount of free-space
radiation can be minimized because the capacitive coupling between the
emitting source and the local ground is less than the capacitive coupling
to Earth through the atmosphere. Since the signal path impedence to the
local ground plain is lower it will carry, proportionaly, the majority 
of the signal.

> All the strap does is alter the DC
> potential. Shield your box well but design out the leg irons and the
> geological requirements.

Actualy it is much more complex than that, it effects the AC signal path
impedence as well - which is exactly what one wants.

As I said above, don't ground the box and it simply acts as a secondary
emitter. This is analogous to those parasitic oscillators they put in books
and such that ring an alarm if you walk between the poles at the store.

I'm at work right now so I can't get too specific but there is a book that I
have at home that is called 'Digital Black Magic' (I believe). It covers
a lot of these sorts of issues. When I'm home later I'll post a pointer
to the correct title, author, and ISBN.

The 1st rule of electrons:

They always take the shortest path to ground. 

Corollary:

If they can't get to ground they radiate their excess energy away as
photons.



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