bb wrote:
"Would vertical phasing be an improvement?

Vertical antennas launch waves along the surface of the earth. Vertical
antennas tend to have a null directly overhead.

According to B. Whitfield Griffith, Jr. in "Radio-Electronic
Transmission Fundamentals", the field intensity at 10 miles from an
antenna will be 1000X stronger at 0.5 MHz than at 5.0 MHz if the soil
conductivity is 10 mmhos/m (sort of ordinary) and if the same power is
being radiated on both frequencies.

High attenuation of the groundwave at high frequencies was the reason
frequencies above 1500 KHz were thought no good in the early days of
radio.

Sea water has a conductivity of about 5000 mmhos/m, or about 500X better
than ordinary earth. So, the lower HF spectrum is good for some maritime
and tropical broadcasting services in island areas. Antennas need to be
located near the water`s edge to avoid excessive loss in traversing land
to get to the water.

Salt air is not the best environment for a shortwave broadcast station.
Shortwaves traveling along the earth`s surface are severely attenuated.
Though I worked for years in shortwave broadcasting, I never saw a
shortwave broadcast station that used vertical polarization. Shortwave
stations are usually sited away from the sea coast for protection and
equipped with horizontal antennas to launch sky waves, not ground waves.

The broadcaster wants to concentrate energy both horizontally and
vertically to useful azimuths and elevation angles. These ideally are
tailored to the broadcast target. The broadcaster gratefully accepts any
useful reflection from the earth but does not tend to rely much upon it.

There is no inviolable rule of one type or even of one polarization of
antenna being best for all situations. There are many types. Kraus lists
24 types "as a preview to more detailed treatments." If you would really
make your own discriminating choices instead of relying upon the advice
of others, you would need to carefully study some book like Kraus`
"Antennas".

Best regards, Richard Harrison, KB5WZI