I too am reluctant to enter this as much resembles a freshman poli-sci
student debating a third year law student.

However .... please see indented comments below

--
J. Mc Laughlin; Michigan U.S.A.
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"Reg Edwards" wrote in message
...
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.

When communication has been established between A and B, the angle of
elevation depends only on the locations of A and B on the Earth's
surface, on the number of hops, on the height of the ionospheric
layers, and on the slope of the layers.

OK as far as the statement goes.


The elevation angle is determined purely by trigonometry.

Geometry might have been a better term, but the idea is right.


It tends to be the same at both A and B. There may be simultaneously
more than one path and therefore more than one angle. In which case
multi-path distortion and fading occurs.

Here I must inject my experience. As part of a topic sentence, "tends to be
the same" is OK. However, it is common on real HF paths of over 4 or 5 Mm
for the elevation angle at which the strongest signal arrives to be
significantly different at the two ends of the path. It is easy on longer
paths for the major mode at one end to be using a high virtual-height F2
mode and for the other end to be using a low virtual-height E mode.

Allow me to put to rest the notion that optimum elevation angles are
necessarily the same at both ends of a longer (multiple hop) HF path! [Reg
did not say that optimum elevation angle are necessarily the same.]

As other have said, but not all have heard, the idea is to maximize gain
(at both ends of a path) at the elevation angle being used. Even in the
20s, antenna systems were in regular use that attempted to do just this.


Received signal strength depends on the two antenna gains in the
direction of the path.

Agreed. Such an azimuth is not always along a great-circle.

The take-off angle predicted by Eznec-type
programs is an altogether different thing. It depends on reflections
from the ground in the vicinity of the two antennas. It does however
have an effect on received signal strength but is of use only when the
locations of A and B and all other geographic and ionospheric
variables are known. They seldom are! As are ground conditions.

What does exist is a stochastic model of the ionosphere that allows one to
make useful estimates of what is going to happen along a path. As has been
said many times here, all estimates and measurements comprise at least two
numbers: the best estimate and an estimate of the estimate's uncertainty.
Even if it were possible to do so, one would not use an antenna that had all
of its gain at the predicted optimum elevation angle. One would try to
design an antenna (money enters here) that has most of its gain in the
expected band of elevation angles expected to be best for a path.

----
Reg, G4FGQ.



73 Mac N8TT