AW: Grounding / Shielding Question

[Haible Juergen]

	>Question - can shielding work like an antenna rather than a
shield? 

Definetly yes. A slit in the shield has approximately the same 
effect as a wire antenna of the same dimensions, for example.
A shielding foil that doesn't go all around the electronics, but
is just there at one side of the enclosure, makes a good patch 
antenna.

	>What if
	>you're using a dual supply and the ground for the power supply
isn't
	>connected to earth ground (like the power cable has a ground
lifter on it).

The best way I have found so far is this:

Use a full metal enclosure.
Connect earth gnd dirctly to the enclosure.
Insulate all input and output jacks from the enclosure.
Connect the signal gnd and the enclosure with a ceramic
capacitor (47nF is a good value). This will make a good connection
at HF (for shielding), but has a high enough impedance at low
frequencies to avoid ground loops.
Put two large diodes (1n4007 or similar) in parallel to the
capacitor.

	>Does the thickness of the material used for the shielding make
a
	>difference?

Yes. (Not for the electric field, but for the magnetic field.)

	JH.