b. Half-wave antenna. The standard tactical radio antenna is half-wave
length or a multiple thereof.
If it were possible to construct a perfect
half-wave antenna, its physical length (in meters) would be computed using
the formula L = 300 - 2 or L = 150.
F(MHz)
F(MHz)
c. Antenna energy losses.
Because of energy losses on the radiating
antenna, it is impossible to construct a perfect half-wave antenna.
This
loss is approximately five percent.
To compensate for this loss, the 150
(para 26b) is multiplied by 95. This figure (142.5) is rounded to 142 for
ease of computation. When using the formula
L=
142
or
L=
142
=
3 meters, the length of an
F(MHz)
47.3 MHz
expedient, half-wave antenna to be used on a frequency of 47.3 MHz would be
3 meters.
REMEMBER:
The use of this wavelength formula to compute the antenna
length makes it easy to see that the lower the operating
frequency, the longer the antenna; the higher the frequency,
the shorter the antenna.
PRACTICE EXERCISES:
25. In the blank space below, write the formula for a full wavelength.
26. In the wavelength formula, velocity (V) is a constant _______________.
27. Energy losses from a radiating antenna are considered to be ________
percent.
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