Reg, G4FGQ wrote:
"Richard, why don`t you just say that the angle of elevation of the
radio path has nothing whatsoever to do with the type of transmitting
and receiving antennas or the directions in which they may be pointing
or elevated, or even the operating frequency."

Confuse the readers?

Geometry and trigonometry are involved. What`s more, the signal may take
more than one path between only two points, or multiple hops, or
multiple azimuths. This causes fading and distortion.

Transmitted energy in directions other than to a receiver is wasted.
That`s one of several reasons to use antenna directivity in azimuth and
elevation.

Maybe Cecil`s IEEE Dictionary defines TOA. The references I`ve found are
to "elevation angle" above the horizon.

In general, an antenna`s angle of maximum response is lowered by raising
the antenna height. If you have stacked horizontal elements you can
adjust their phasing to skew the elevation angle up or down some.

An ideal HF antenna may be a giant array of dishes that might be aimed
for one-hop, if possible, in a multiple diversity system.

Something almost as good is a triple diversity system which uses
rhombics. 3 receiving rhombics are plavced with about 10-wavelengths of
lateral spacing at the lowest frequency received. Multicouplers on each
rhombic feed various receivers , often at various frequencies. Diversity
combiners select the best received signal of three carrying the same
program. The results are spectacular. We used such TDR systems for
broadcast program relay. Often the quality was as if the program arrived
by cable.

Best regards, Richard Harrison, KB5WZI