Re: NEC-LIST: Horizontally polarised MF antennas

Phil:

The thing that counts regarding launching the lower-loss O-mode is the
angle of the wave normal at incidence on the ionosphere with the
earth's magnetic field. If you are just under the magnetic dip
equator, you want a north-south (magnetic) aligned dipole (or array of
such dipoles) to launch the Ordinary (O) mode. For shorter ranges, you
get nearly omni coverage in azimuth for elevation angles down to about
35 or 40 degrees, measured from the horizon. So this is optimum for
Near Vertical Incidence Skywave (NVIS).

At MF, the operating frequency is going to be below the MUF for all
paths of interest.

You didn't define long range, and clearly the above applies to short
range out to some limit imposed by the pattern of the MF array.

The use of MF in Africa was considered about 40 years ago by Al
Barghausen or the Institute for Telecommunication Sciences, Boulder,
CO. I would imagine that the NTIA/ITS library there still has a file
copy of Al's report, which I believe was done for the Voice of America
(VOA).

Also, the VOA has installed horizontal dipole arrays for MF broadcast
into Central/South America some years back, and I believe they had
success with it as an alternative to groundwave. More recently, when
they had to replace the MF and HF sites lost to the rrevolution in
Liberia, they put some arrays on Sao Tome, an island in the armpit of
West Africa. You might inquire of the VOA what they have found to work
best. But you will need to specify what you mean by long range. The
VOA Sao tome arrays are possibly the closest match to your situation,
as they wanted to reach back from the shore of the Atlantic Ocean into
Africa.

Hope this helps.

Regards,

George Hagn
Received on Thu May 11 2000 - 03:54:43 EDT