e. Figure 1-3 illustrates wave motion to help you better understand the terms associated with
Figure 1-3. Comparison of waves with different amplitudes
(1) Waves 1 and 2 have equal frequency and wavelength, but different amplitudes. The
reference line (rest position or point zero) is the position which a particle of matter would have if it were
not disturbed by wave motion. In the case of the water wave, the reference line is the level of the water
when no wave motion is present.
(2) Looking at wave 1, you will see it has four complete cycles. Points ABCDE illustrate
one complete cycle; it has a maximum value above and a maximum value below the reference line. Any
point above the reference line (between points A and C) is called a positive alternation, and any point
below the reference line (between points C and E) is called a negative alternation. The combination of
one complete positive and one complete negative alternation represent one cycle of waves. At point E,
the wave begin to repeat itself.
f. A wavelength is the distance in space occupied by one cycle of a radio wave for a given
period. Wavelengths vary from a few hundredths of an inch at extremely high frequencies, to many
miles at extremely low frequencies. Wavelengths are, however, expressed in meters. For wave 1 in
Figure 1-3, the distance between points A and E or points B and F is one wavelength.