wrote:
There seems to be a number of commercial antennas
described as H-field antennas intended for LORAN
application. Most claim improved immunity to
precipitation static. Is there a theoretical basis
for such claims?


Yes. It increases sales just like zoom zoom zoom in car advertisements.

Seriously, precipitation static is caused by corna discharge from an
antenna or object someplace near the antenna. The radiated field from
that leakage current can be almost any field impedance and will always
be a mixture of time-varying electric and magnetic fields.

What a small loop actually buys you is a compact antenna that has no
sharp protruding edges, and that decreases the chances of having corona
right from the antenna. A whip would have a sharp protruding point, and
that would encourge corona discharge and the resulting noise we call
"precipitation static".

Other than that, there is no advantage.

73 Tom


I think the precipitation static talked about is
caused by the accumulation on the antenna of
charges carried by precipitation particles (e.g.,
snow). Apparently this is a common problem on
aircraft antennas, and hence the interest in LORAN
antennas with better immunity to the accumulation
of precipitation charges.

Doesn't sound like a simple antenna geometry issue
and it doesn't sound like a corona issue.

Which is not to say it isn't all hype, but
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?

Chuck

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