Grounded Chassis

[Martin Czech]

If some circuit is housed in a unearthed metall chassis, what does this
mean for interference?

I think the rf H-field will be weakened by eddy currents.  This may be
also true for the E-field component.

The coupling of E and H field should be lower for lower frequencys, in
this case the antenna/chassis is one capacitor, the chassis/ground plane
(earth) is another, i.e. a series capacitor circuit.

Will the E-field be weaker inside the chassis?

If the chassis is grounded there should be no E-field inside.
OTOH grounding means power cords, this will give some inductance.
You can't really hard ground anything for higher frequencys.

The power cord may also have common mode dirt, how can we get rid of
that without ground?

And: can we hope to get rid of that even with ground (and ground line
inductance)?

However, it seems to me that a ungrounded metal chassis is pretty useless in terms
of interference. But that's what the industry seems to sell most.


Any rf people here ?

m.c.