The radio frequency spectrum extends from approximately 10 kHz to 300,000 GHz (see
Table 2-6).
Frequency range
Name of the Range
Symbol
30 300 kHz
LF
300 3,000 kHz
Medium frequency
MF
3 30 MHz
High frequency
HF
30 300 MHz
Very high frequency
VHF
300 3,000 MHz
Ultrahigh frequency
UHF
Table 2-6 -- Radio frequency spectrum
A Hertzian wave is an oscillating electromagnetic field. A continuous series of such
waves of like characteristics is called a continuous wave (CW) (see Figure 2-10 View
A). Such a wave can be used in Morse code transmissions, the code being keyed so
that the signal is interrupted when desired (see Figure 2-10 View B). A continuous wave
may be modified with some characteristics of an audio frequency signal, such as that
produced by the human voice. When used in this way, it is called a carrier wave. The
process of modifying the carrier wave in this manner is called modulation. After
modulation, the carrier wave may be called a modulated carrier wave (see Figure 2-10
View C). When this form of radio transmission is used, the transmitting station
generates the carrier wave and modulates it by the message to be conveyed. The
receiver demodulates the incoming signal by removing the modulating signal and
converting it to its original form.
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