RST Engineering wrote:
Except for the fact that the antenna ships with a thin rubber gasket to keep
water out of the airframe (and insulates the antenna from the airframe
mechaincally).

The antenna "grounds" to the airframe mechanically through the three bolts
holding it to the airframe. Make sure that they are cutting through to the
metal of the antenna base/airframe. Electrically, the antenna is connecting
to the airframe through the capacitor formed by the base of the antenna to
the airframe with the rubber gasket as the dielectric.

Jim

Effectively, the capacitor Jim mentions is shorted by the three/four
mounting bolts, so the mounting bolts must make a good electrical
contact with the aluminum skin on the inside of the aircraft. I like the
NoAlOx, too.

Dont forget a doubler plate. Mounting the antenna directly only to the
aircraft skin is a no-no.

On the off chance you are using just a stainless whip mounted on the
porcelin feed-thru bushing, then the coax cable shield needs to be
grounded to the aircraft skin within an inch or two from the antenna
base, and the coax center conductor connects to the whip.