# Engineering Specification

Document source : www.fordemc.com

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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

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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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