2-29
removed by filtering before transmission or further modulation. This filtering action limits the bandwidth
of the output signal frequencies. The resulting wave is shown in view (D).
The exact waveform of figure 2-25, view (D), can be obtained by logic operations of timing and
data. This is illustrated in figure 2-26, where a timing signal [view (A)] is used rather than a carrier
frequency. The data (intelligence) is shown in view (B) and is combined with the timing signal to produce
a combination digital modulation signal, as shown in view (C). The square-wave pattern of the digital
modulation is filtered to limit the bandwidth of the signal frequencies, as shown in view (D). This system
has been used in some high-speed data equipment, but it offers no particular advantage over other systems
of modulation, particularly the pulse-modulated systems for high-speed data transmission.
Q-11.
What type of modulation depends on the carrier-wave phase shift?
Q-12.
What components may be used to build a basic phase modulator?
Q-13.
Phase-shift keying is similar to what other two types of modulation?
Figure 2-26A.—Simulated phase-shift keying. TIMING.
Figure 2-26B.—Simulated phase-shift keying. DATA.
Figure 2-26C.—Simulated phase-shift keying. DIGITAL MODULATION.
Figure 2-26D.—Simulated phase-shift keying. DIGITAL MODULATION AFTER FILTERING.
