MFJ MFJ-9218, Инструкция по эксплуатации, Страница: 4 / 10

MFJ-9218
SWR Meter, Wattmeter, & Dummy Load
Instruction & Technical Manual
1 RADIO-FREQUENCY RADIATION
Radio-frequency (RF) radiation is one type of electromagnetic radiation. Electromagnetic waves
and associated phenomena are discussed in terms of energy, radiation, and fields. Electromagnetic
radiation is defined as waves in electric and magnetic fields moving together, or radiating, through
space (Figure 1). These waves are generated by the movement of electrical charge. For example,
the movement of charge in a radio station antenna creates electromagnetic waves that are radiated
away from the antenna. The waves then induce charge motion in the receiving antenna, which is
detected and converted into signal by the radio. The term electromagnetic field refers to the
electric and magnetic environment existing at some location due to a radiating source such as an
antenna.
Figure 1: Horizontally-polarized Electromagnetic Plane Wave
An electromagnetic wave consists of oscillating orthogonal electric (
~
E
) and magnetic (
~
B
) fields.
These fields propagate together with direction and velocity
~v
. In a vacuum this is the speed of
light,
c
. In Earth’s troposphere, |
~v
| ≈ 0
.
9999997
c
. The two defining characteristics of an
electromagnetic wave are its wavelength (
λ
) and frequency (
f
). The wavelength is the distance
between two adjacent peaks in the wave, and the frequency is the number of peaks passing a given
point in space during a second. Wavelength and frequency are reciprocal with the speed of light
(
f λ = c ), so if you know one quantity, you can easily find the other. For example, a typical radio
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