Engineering Specification
ES-3U5T-1B257-AA
EMC Design Guide for Printed Circuit Boards
Frame 19 of 78
Rev. A
10/01/2002
Printed copies are uncontrolled
3.4. Wavelength and Frequency
All electrical signals travel as waves with a finite velocity. Figure 36 shows the
amplitude plot of a wave as a function of time. Its wavelength is the distance between
any two equivalent points on the waveform.
Figure 36. Wavelength of an Electrical Signal
The propagation medium determines the wave's velocity. In space a wave travels at the
speed of light c (c = 3x10
8
meters/second). However, the wave travels more slowly
through wires or printed circuit board tracks (approx. 0.6 the speed of light).
Equation 31 relates wavelength () to frequency in free space or in air. Table 32 shows
that the wavelength and frequency are inversely proportional. Consequently, as the
frequency increases, the wavelength will decrease.
(MHz)
f
300
=
[meters]
Equation 31. Wavelength
The atmosphere contains many electromagnetic fields generated by transmitters, which
operate in a range from a few kilohertz to many gigahertz. Table 33 shows some of the
frequency spectrum allocations in the United States (US), Europe (E), and Japan (J). All
undesignated sources are in the United States.
Time
Amplitude
Wavelength
Summary :
Wavelength and Frequency All electrical signals travel as waves with a finite velocity. Equation 31 relates wavelength () to frequency in free space or in air. Table 32 shows that the wavelength and frequency are inversely proportional.
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