4-31
COMPOSITION OF NONSINUSOIDAL WAVES
Pure sine waves are basic wave shapes from which other wave shapes can be constructed. Any
waveform that is not a pure sine wave consists of two or more sine waves. Adding the correct frequencies
at the proper phase and amplitude will form square waves, sawtooth waves, and other nonsinusoidal
waveforms.
A waveform other than a sine wave is called a COMPLEX WAVE. You will see that a complex
wave consists of a fundamental frequency plus one or more HARMONIC frequencies. The shape of a
nonsinusoidal waveform is dependent upon the type of harmonics present as part of the waveform, their
relative amplitudes, and their relative phase relationships. In general, the steeper the sides of a waveform,
that is, the more rapid its rise and fall, the more harmonics it contains.
The sine wave which has the lowest frequency in the complex periodic wave is referred to as the
FUNDAMENTAL FREQUENCY. The type and number of harmonics included in the waveform are
dependent upon the shape of the waveform. Harmonics have two classifications — EVEN numbered and
ODD numbered. Harmonics are always a whole number of times higher than the fundamental frequency
and are designated by an integer (whole number). For example, the frequency twice as high as the
fundamental frequency is the SECOND HARMONIC (or the first even harmonic).
View (A) of figure 4-25 compares a square wave with sine waves. Sine wave K is the same
frequency as the square wave (its fundamental frequency). If another sine wave (L) of smaller amplitude
but three times the frequency (referred to as the third harmonic) is added to sine wave K, curve M is
produced. The addition of these two waveforms is accomplished by adding the instantaneous values of
both sine waves algebraically. Curve M is called the resultant. Notice that curve M begins to assume the
shape of a square wave. Curve M is shown again in view (B).
