2-49Figure 2-48A.—Quantization levels. MODULATION.Figure 2-48B.—Quantization levels. TIMING.Figure 2-48C.—Quantization levels. QUANTIZED 5-LEVEL.Figure 2-48D.—Quantization levels. QUANTIZED 10-LEVEL.Although the quantization curves of figure 2-48 are based on 5- and 10-level quantization, in actualpractice the levels are usually established at some exponential value of 2, such as 4(2^{2}), 8(2^{3}), 16(2^{4}),32(2^{5}) . . . N(2^{n}). The reason for selecting levels at exponential values of 2 will become evident in thediscussion of pcm. Quantized fm is similar in every way to quantized AM. That is, the range of frequencydeviation is divided into a finite number of standard values of deviation. Each sampling pulse results in adeviation equal to the standard value nearest the actual deviation at the sampling instant. Similarly, forphase modulation, quantization establishes a set of standard values. Quantization is used mostly inamplitude- and frequency-modulated pulse systems.Figure 2-49 shows the relationship between decimal numbers, binary numbers, and a pulse-codewaveform that represents the numbers. The table is for a 16-level code; that is, 16 standard values of aquantized wave could be represented by these pulse groups. Only the presence or absence of the pulsesare important. The next step up would be a 32-level code, with each decimal number represented by aseries of five binary digits, rather than the four digits of figure 2-49. Six-digit groups would provide a64-level code, seven digits a 128-level code, and so forth. Figure 2-50 shows the application ofpulse-coded groups to the standard values of a quantized wave.

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