Chapter 7
wave is the sum of a 100-Hz fundamental plus harmonics of 300, 500, 700 Hz
and so on up. Figure 7-2 illustrates.
A square wave containing an infinite number of harmonics has instant transi-
tions and rise and fall times of zero. In real life, the laws of physics limit the
high frequencies and result in rise and fall times greater than zero. A signal that
contains few harmonics has gradual transitions and long rise and fall times. As
the number of harmonics increases, the edges sharpen and the rise and fall times
shorten.
Serial data is more complex than a square wave, but the basic principle is the
same: the higher the frequencies that make up the signal, the sharper the transi-
tions.
Another concept related to understanding long and short lines is cable delay.
One-way delay is the time required for a signal to travel the length of the cable.
The 1-way delay equals the cable’s physical length divided by the propagation
rate, or speed of signals in the cable.Figure 7-2: A square wave is the sum of a sine wave and its odd harmonics.