Figure 66. Vertical ground-plane antenna.
b. When maximum radiation is wanted in a horizontal direction,
the spokes are tilted down to an angle of about 50 degrees.
The
input impedance of a ground plane is 20 to 25 ohms. When the spokes
are bent downward, the impedance rises to about 50 ohms.
c. Whip antenna. The worst antenna to use is the whip antenna.
The term whip in our case means an antenna that is 15 feet in length.
The only good thing that can be said of a whip is that it is
convenient for mobile or mobile at a halt situations. We can improve
our whip (in the AN/GRC-142) by adding sections to its normal 15-foot
length.
We should add three more sections (for 2 -12 MHz use) or
until our whip approaches a quarter wave (234/f) in length. Because
the mast base loses some of its rigidity, you may have to guy the
whip. The reason the whip is so poor is
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