The electromagnetic spectrum (Fig. 1-1) is broken into bands for the sake of
convenience and identification. The spectrum extends from the very lowest ac fre-
quencies and continues well past visible light frequencies into the X-ray and gamma-
ray region. The extremely low frequency (ELF) range includes ac power-line
frequencies as well as other low frequencies in the 25- to 100-hertz (Hz) region. The
U.S. Navy uses these frequencies for submarine communications.
The very low frequency (VLF) region extends from just above the ELF region,
although most authorities peg it to frequencies of 10 to 100 kilohertz (kHz). The low-
frequency (LF) region runs from 100 to 1000 kHz—or 1 megahertz (MHz). The
medium-wave (MW) or medium-frequency (MF) region runs from 1 to 3 MHz. The
amplitude-modulated (AM) broadcast band (540 to 1630 kHz) spans portions of the
LF and MF bands.
The high-frequency (HF) region, also called the shortwave bands (SW), runs
from 3 to 30 MHz. The VHF band starts at 30 MHz and runs to 300 MHz. This region
includes the frequency-modulated (FM) broadcast band, public utilities, some tele-
vision stations, aviation, and amateur radio bands. The ultrahigh frequencies (UHF)
run from 300 to 900 MHz and include many of the same services as VHF. The mi-
crowave region begins above the UHF region, at 900 or 1000 MHz, depending on
source authority.
You might well ask how microwaves differ from other electromagnetic waves.
Microwaves almost become a separate topic in the study of RF circuits because at
these frequencies the wavelength approximates the physical size of ordinary elec-
tronic components. Thus, components behave differently at microwave frequencies
than they do at lower frequencies. At microwave frequencies, a 0.5-W metal film re-
sistor, for example, looks like a complex RLC network with distributed L and C val-
ues—and a surprisingly different R value. These tiniest of distributed components
have immense significance at microwave frequencies, even though they can be ig-
nored as negligible at lower RFs.
Before examining RF theory, first review some background and fundamentals.
Units and physical constants
In accordance with standard engineering and scientific practice, all units in
this book will be in either the CGS (centimeter-gram-second) or MKS (meter-
kilogram-second) system unless otherwise specified. Because the metric system de-
2 Introduction to RF electronics
1-1 The electromagnetic spectrum from VLF to X-ray. The RF region covers from less than
100 kHz to 300 GHz.
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Introduction to RF electronics