Stefan wrote:
shield side of the coax goes to ground through a 0.1uF cap.
For optimum results with respect to high RF frequencies, I'd expect
that you would need this cap to be annular, so that the cable can
pass through the middle, and the outside connects to the chassis
hole all around.
The coax itself remains coaxial through the connector -- it is just
the point on the shield that is bypassed to chassis that is not
annular. The low impedance of the shield makes this non-critical up
to frequencies where you should be using a waveguide anyway. It is a
well-known and proven technique for bypassing shields to chassis with
no galvanic connection. (In some cases, the capacitor is paralleled
with a resistor of 10 ohms to 1k ohms -- this provides some DC/LF
continuity while limiting the possible ground loop current to levels
that [hopefully] don't cause noise problems.)
Rarely is the cap as large as 0.1uF -- 0.01uF is most common, and 1nF
is also quite common. You want the cap to have low inductance (high
first self-resonant frequency), and you need to keep the leads very short.
Best regards,
Charles
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