1-8
Figure 1-7.—Comparison of waves with different amplitudes.
Cycle
Refer to wave 1 in figure 1-7. Notice how similar it is to the sine wave you have already studied. All
transverse waves appear as sine waves when viewed from the side. In figure 1-7, wave 1 has four
complete cycles. Points ABCDE comprise one complete cycle having a maximum value above and a
maximum value below the reference line. The portion above the reference line (between points A and C)
is called a POSITIVE ALTERNATION and the portion below the reference line (between points C and
E) is known as a NEGATIVE ALTERNATION. The combination of one complete positive and one
complete negative alternation represents one cycle of the wave. At point E, the wave begins to repeat
itself with a second cycle completed at point I, a third at point M, etc. The peak of the positive alternation
(maximum value above the line) is sometimes referred to as the TOP or CREST, and the peak of the
negative alternation (maximum value below the line) is sometimes called the BOTTOM or TROUGH, as
depicted in the figure. Therefore, one cycle has one crest and one trough.
Wavelength
A WAVELENGTH is the distance in space occupied by one cycle of a radio wave at any given
instant. If the wave could be frozen in place and measured, the wavelength would be the distance from the
leading edge of one cycle to the corresponding point on the next cycle. Wavelengths vary from a few
hundredths of an inch at extremely high frequencies to many miles at extremely low frequencies;
however, common practice is to express wavelengths in meters. Therefore, in figure 1-7 (wave 1), the
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signify wavelength. Why lambda and not "l" or "L"? This is because "L" is used conventionally as the
