Lesson 2/Learning Event 2
Learning Event 2:
COMMON ANTENNAS.
HORIZONTAL ANTENNAS
1. Doublet. The doublet antenna is the most common HF antenna used
by the military.
The doublet usually comes in kit form.
The kit
consists of either wire on a reel or metal tape on a reel. A coax is
the feed line. Forty foot mast section kits are also used with the
kit.
As shown in figure 43, when the antenna is longer than 120
feet, a third mast section should be used to prevent sag. As shown
in figure 44, a counterpoise may be used.
The purpose of the
counterpoise is to prevent the ground reflected wave from being
absorbed.
The signal strength of the radiated signal will be
improved if a counterpoise is used.
A counterpoise (see figure 44)
is an artificial reflecting surface used to reflect the reflected
wave.
This adds to the direct wave making the transmitted signal
stronger.
A counterpoise can also make communication worse if
connected to the equipment ground.
Always try communicating first
without the counterpoise attached to the equipment ground. Then try
with it attached to the equipment ground.
Use whichever is best.
The terms doublet and dipole antennas are used interchangeably. The
maximum radiation is at right angles to the antenna.
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