On Tue, 06 Jun 2006 20:49:54 -0400, chuck wrote:
I think the precipitation static talked about is
caused by the accumulation on the antenna of
charges carried by precipitation particles (e.g.,
snow).

Hi Chuck,

Snow, rain, dust, soot, anything airborne which in fact is the
principle carrier of current from earth to air in the current cycle
that feeds the electrostatic potential of lightning clouds (which
amounts to about 600 V/m).

wouldn't the charge on the antenna simply
redistribute itself over the body of the aircraft
(assuming it is metal) and not accumulate on the
antenna as it would were the antenna insulated
from the aircraft body?

Charge moves to the smallest radius surface, and once there, if there
is sufficient flux will break down insulators (air being one) and
arc-over (corona discharge). One solution is to reduce the number of
small radius surfaces (pin-points) and loops qualify (vastly larger
radius than a monopole tip). However, and at altitude, if the loop is
in fact a square, then the corners are prone to discharge. HCJB
antenna design tested this at altitude in Quito, Ecuador and they
solved it by moving the feed point so that the high potential fell in
mid-span, instead of at the corners. Auto manufacturers also had to
contend with the problem, they put small round caps on the ends of
their car antennas.

73's
Richard Clark, KB7QHC