Operation Manual

OM-E 2072-09287-00
B-2
B-3.1 Horizontal Dipole
A dipole antenna consists of two conducting elements with a center junction connected by a coaxial to the
antenna dipole connector on the radio.
The most common configuration is the horizontal dipole, shown in Figure B-1. The radiation pattern for
this antenna is broadside to the antenna elements (that is, perpendicular to the running direction of the
wire). The vertical radiation angle of a horizontal dipole is a function of its height above ground. In general,
mounting closer to the ground increases the near-vertical incident skywave (NVIS), which is best for
short-distance communications.
Mounting the horizontal dipole higher up causes the vertical radiation angle to tilt down, towards the
horizon. This will favor long-distance communications. In any case, the recommended height range is
from
10
1
λ (minimum) to ¼ λ (maximum), where λ is the wavelength.
E
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e
v
a
t
i
o
n
:
5
t
o
1
0
m
Coaxial
Cable
Support
Rope
Radio Set
Figure B-1. Horizontal Dipole Configuration
NOTE
When using trees as end supports, wrap end of support rope around tree
three or four times. Make sure to leave slack in support rope, so that the
center of the antenna sags down.
B-3.2 Inverted V Dipole
At low frequencies, the required antenna element length is very long. To minimize physical stress and
sag at the center point, an inverted V configuration (Figure B-2) should be used, instead of a standard
horizontal dipole. This configuration will result in better RF performance, since the feedpoint (the
point of maximum radiation) is placed high above ground. In addition, the use of a halyard support
may be helpful; as it will relieve the antenna wire from excessive stresses and increase its life span.
This alternative to the horizontal dipole has an added advantage: to install the inverted V, only one
support is needed (at the center), instead of the two needed for the horizontal dipole.