Quantcast Half-rhombic antenna

 
  
 
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
by using NSN 5905-00-407-6167.
Figure 42.
Half-rhombic (unidirectional) antenna.
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