Antenna patterns for mixed groundwave & skywave

                              Mixed Groundwave & Skywave Operation
                              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I would be pleased if someone could advise me how to use NEC to generate
antenna patterns which can be used for mixed-path propagation predicitions.

Background
~~~~~~~~~~
My original fortran program was written to predict the strength of the
groundwave and skywave reaching a given point. The groundwave signal is
predicted using look-up tables based upon ITU-REC368 and the skwave by using
ITU-REC435. These recommendations were developed by Broadcast engineers
concerned with the location of the night fading zone (NFZ). Ideal ground
was assumed, and the common element linking both calculations was the
antenna gain, defined as the CMF of the antenna compared with 300 volts.
Patterns were predicted for standard ITU monopole arrays using pattern
multiplication, and the resulting directivity gain values compressed into a
64 kb data block at 1 degree horizontal and vertical intervals. The
assumptions behind these prediction methods were made before NEC became
available to model real antennas, and Although extensive research was
carried out into effects of real ground, and the foreground terrain, very
little became recommended practice or even reached ITU publications.
 

New Requirement
~~~~~~~~~~~~~~~
The program has now been re-written afresh in ANSI C, and I need to predict
combined effects of groundwave and skywave for ship-shore radio below 4 MHz,
particularly for the distress related frequencies just below 2.2 MHz. Once
more the starting point for both calculations is antenna gain, and I need to
use NEC to generate antenna gain data for the various antennas available (T
antennas, bi-conicals, monopoles, log-periodic monopole sets, and possibly
the standard LPV)

The Problem
~~~~~~~~~~~
To define the antenna gain in such a way that

1 it can be predicted using NEC
2 it is equally valid for skywave and groundwave output
3 it results in values of skywave and groundwave level which can be used to
assess fading.

Thank you

Phil Ede

Regards

Phil Ede
Received on Mon Oct 07 1996 - 16:57:00 EDT