It may be necessary to adjust the antenna height and/or length to
ensure satisfactory communication.
NOTE:
All you need to construct an expedient antenna is field wire WD-
1/TT, insulators, a pair of pliers, some tape, and the wavelength
formula.
26. COMPUTING WAVELENGTH.
As previously mentioned, the length of the
antenna is critical.
Before considering the actual construction of
expedient horizontal or vertical antennas, it is best to review wavelength.
The operation and construction of all antennas is based on the principles of
the fundamental antenna. The fundamental antenna consists of a single wire
whose physical length is equal to one-half the full wavelength of the signal
being transmitted. The wavelength is the distance between waves of energy
leaving the antenna, and is computed using the following formula:
Wavelength (in meters)(L)
=
velocity (V)(in meters)
frequency (F)(in hertz)
a. Full-wave antenna.
The velocity in this formula is the speed of
radio waves (a constant 300,000,000 meters per second).
For ease of
computation, this figure is converted to 300 megahertz. (A frequency of 300
MHz is 300,000,000.) Frequency is also converted to megahertz (the standard
graduation of the radio set band switch).
The wavelength (Fig 32) at a
frequency of 24 MHz is computed as L = 300 or L = 300 = 12.5 meters.
F(MHz)
24
Therefore, a full-wave antenna broadcasting at a frequency of 24 MHz is 12.5
meters long.
Figure 32.
Wave length.
47
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