"Cecil Moore" wrote
The problem seems to be that the definition of TOA is
not standardized.

=======================

Cecil, it's worse than that. TOA is almost meaningless.

Whoever coined the phrase "Take Off Angle" in conjunction with Eznec-type
radiation patterns should be made to provide a 5000-word written explanation
before he went to bed on his wedding night. Another form of safe sex?

In the first place, your suggestion to hire a helicopter to fly around the
sky in the vicinity of an antenna to determine the TOA would provide a
completely different TOA from that provided by Eznec. Especially at low
angles, say less than 30 degrees.

That's because the angle at which radiation is strongest in the vicinity of
a vertical antenna, of height 5/8-wavelength or shorter, is ALWAYS at an
angle of ZERO degrees. ie., it is strongest along the ground surface
regardless of soil conditions. Distance from the antenna is too short for
the ground wave to be appreciably attenuated.

Somehow or other, Eznec manages to calculate relative field strength at some
great distance from the antenna. Which is, of course, an ultimate
worthwhile but unobtainable objective.

Unfortunately, Eznec ignores what that distance may be, whether the receiver
is at ground level or at aircraft height, or in the stratosphere. In the
extreme state of uncertainty it ignores the height of the ionospheric
reflecting layer and the number of hops. In other words, if the location of
the receiving antenna in space or time of day are unknown then the Eznec TOA
is meaningless.

So why is so much importance or significance attached to an Eznec TOA? It
is merely one of the infinite number of angles contained in a very broad
lobe of a radiation pattern.

The path actually taken by a particular radio wave is of far greater
importance. And knowing the location on the Earth's surface of both
transmitting and receiving antennas, the path taken, including elevation
angle, is calculable purely by geometric means. It has nothing to do with
the antenna, not even a G5RV.

If the ballpark Eznec TOA, by chance, happens to crudely coincide with the
actual radio path angle to a distant receiver then that's the best which can
be expected. If not, then there's nothing you can do about it except change
the antenna, all the soil in your back yard, or your geograhical location.

Save yourself the going-rate per hour of the fee for hiring a helicopter.
;o)

By the way, this assessment of the situation in no way demeans the value and
usefulness of Roy's Eznec - an excellent practical, educational and
free-issue program. My only criticism is that it requres a 4-week course of
self-instruction, two hours per day, to understand how to use it. But I
suppose, starting from scratch, this is inevitable. I imagine that simply
to point to Eznec in response to an elementary query on this newsgroup can
often lead to a waste of time down-loading it, disappointment and
frustration.
----
Reg, G4FGQ