Jim Lux wrote:
"Interference polarization is not necessarily the case. --------For
example, A horizontal antenna not too high over a ground plane has a
null right at zero elevation."

Good point. The worst noise is likely local and arrives via ground wave.
Ground waves are vertically polarized because horizontal components of
an electric field are exactly canceled at the surface of a perfect
reflector.

Examination of the radiation patterns of horizontal antennas confirms
that they invariably have zero response at zero elevation on their best
azimuths.

From researching susceptibility of antennas to noise I came across a
statement interesting to me in Terman`s 1955 opus on page 929:

"----a loop antenna responds much less to the electric induction field
than does a simple wire antenna of comparable intercept area. This is of
importance because electric induction fields predominate in the man-made
noise that causes disturbances in radio receivers, and this explains in
part the popularity of loop antennas in broadcast receivers."

Best regards, Richard Harrison, KB5WZI