From decades of looking at optimum take-off-angles (TOA) at HF for long
paths, I have found that TOAs are rarely above 12 degrees and only
occasionally below 2 degrees. This leads to the conclusion that if cost
were not an issue and one could only put up one horizontally polarized gain
antenna (Yagi, LPDA, or such), the antenna should be 2 to 2.5 WL high. At
least one edition of the ARRL Antenna Book has the same conclusion.

A higher antenna starts to have nulls in the useful range of TOAs.

As usual, Ian has the right idea.

73 Mac N8TT


--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Ian White, G3SEK"

That is true in principle, but the problem with a ground-mounted
vertical antenna is that the angle of maximum radiation is fixed in
relation to the ground. That means the angle of the slope has to be just
right, and in general it also needs to be very steep.

With a horizontal antenna, you can vary the angle of maximum radiation
by adjusting the height above ground. That makes it easy to apply the
technique over a wide range of quite moderate slope angles, using quite
modest antenna heights.

Changing the subject slightly, hams have become over-conditioned into
wanting a "low" angle of radiation. It's true that we generally do need
more radiation at lower angles than we can easily achieve; but until
recently, we haven't had the information to understand what angles of
radiation we actually *do* need.

Modern HF propagation programs give us that information. Not
surprisingly, the optimum angle varies according to the path, the number
of hops involved, the heights of the respective layers and the
ionization levels... and hence the optimum angle also depends on the
time of day, the season, and the year in the sunspot cycle. Recent
editions of the ARRL Antenna Handbook analyse this problem in some
detail, and show that "lowest possible angle" is not always the best
objective if you're aiming to cover all possible cases.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek