Mark Keith wrote:
"For DX transmitting on the lower bands, vertical polarization is the
best way to go."

In some cases. If that were always the case, why do commercial shortwave
stations all use horizontal polarization for both point-to-point service
and broadcasting?

During my years in shortwave broadcasting, I never saw a single
vertically polarized antenna used for HF transmitting.

My experience is not unique. E.A. Laport was Chief Engineer, RCA
International Division of Radio Corporation of America (RCA). For many
years RCA was the largest short-wave communications organization in the
world. In his book, "Radio Antenna Engineering", Ed Laport says:

"The earliest high-frequency beam antennas used vertical polarization,
but subsequent evolution has caused the almost universal use of
horizontal polarization. There may be a reversion to vertical
polarization in the future for certain applications."

It was natural to try vertical polarization first for directional arrays
as low and medium frequencies were first exploited for radio and these
had to use vertical antennas. It was uneconomical to elevate horizontal
antennas to heights necessary for sky wave performance and there is no
ground wave propagation of horizontally polarized waves. The directional
vertical antenna had been developed early in broadcasting by Brown,
Lewis, and Epstein who did their RCA development work at HF for economy
and convenience. Work was already in place for the earliest vertical HF
beam antennas. These only evolved into the universal horizontal
polarization at HF due to real advantages.

Huge investments are made in HF transmitting antenna farms. I worked in
a station that had a farm of over 400 acres of HF antennas, all
horizontally polarized. This was no flip of a coin decision. The
decision was based on the preponderance of experience at the time. Our
paths were so long that we had to consider 2-hops in addition to a
single hop on most.

There surely must be instances where vertical polarization proves better
than horizontal, but these are exceptions, not the rule.

An example might be an antenna closely surrounded by the sea. A vertical
array should be ideal.

Best regards, Richard Harrison, KB5WZI