Horizontal Antenna Mounted for Short-Range Sky Wave.
the direction off the dipole or wire ends. Due to the
The required antenna gain is computed to provide
p r o x i m i t y of the antenna to ground, this latter
a given field strength at a receiver site from the
mode radiates like a lossy transmission line and
t o t a l propagation path loss, the operating fre-
i t s efficiency is generally poorer than a whip.
loss is found to be 101 dB (NBS Report 72491).
T h e shape of the radiation pattern of the hori-
The power delivered to the antenna by the AN/
zontal dipole is essentially constant for heights
PRC-47 is assumed to be 25 watts, taking into
account coupler losses. The equation for computing
ective gain of these horizontal antennas is 7 dB
above an isotropic. Half-power beamwidths of the
T h e gain is 2 dB above an isotropic radiator.
v e r t i c a l l y radiated lobe are 80 degrees in the
plane of the dipole and 100 degrees in the plane
T h e required effective height of the antenna is
normal to the dipole axis.
found by considering the following.
For a fixed height above ground, the amount of the
W h e n a horizontal antenna is close to ground,
input power radiated proportionately in each of
e n e r g y is radiated in two modes. The desired
these modes is a function of the relative percentage
dipole mode produces radiation with a maximum
in the vertical direction. The undesirable Bever-
mode. Each of these, in turn, is a function of the
age mode creates a vertical electric field between
t h e conductor and ground, producing vertically
input resistance and that portion due to the dipole
polarized ground-wave signal with a maximum in
mode as the dipole height is varied. As the height
Haydon, G. W., Lucas, D. L., and Harrison, R. A., "Technical Considerations in the Selection of
Optimum Frequencies for High Frequency Skywave Communication Services," p. 45, NBS Report 7249,
U. S. Dept. of Commerce, Boulder, Colorado.