Half-rhombic antenna

Antenna Systems
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c. Half-rhombic antenna. The half-rhombic antenna (Fig 42) is another

easily constructed directional antenna. To ensure satisfactory performance,

the length of each leg of the half-rhombic antenna should be a minimum of

one wavelength at the lowest frequency used.

A typical military half-

rhombic antenna consists of 100 feet of field wire erected over a single 30-

foot support with an 80-foot counterpoise (laid about one foot above the

ground). The 100 feet of wire should be erected on the support pole so that

each leg is about 50 feet long. One leg of the antenna terminates at a 500-

to 600-ohm resistor.

One end of the counterpoise also terminates at the

resistor (Fig 42). A lead-in wire is attached between the other leg of the

antenna and the radio set. The remaining end of the counterpoise is then

grounded.

The supporting pole should be wooden and should be guyed with

rope.

In operation, current flows only from the transmitter toward the

resistor. This resistor absorbs energy that is not radiated and in so doing

prevents any reflection along the antenna.

Thus, the antenna is

unidirectional--the direction of transmission is from the radio toward the

resistor end of the antenna.

NOTE:

Resistor can be obtained through prescribed load list (PLL) channels

Figure 42.

Half-rhombic (unidirectional) antenna.