Category: Communications Systems

Information theory involves communication in general—on wires, fibers, or over the air—and it’s applied to widely varied applications such as information storage on optical disks, radar target identification, and the search for extraterrestrial intelligence. In general, the goal of a communication system is to pass “information” from one place to another through a medium contaminated by…

In the last few sections methods of transmitting analog information using analog signals were explained. This section will consider methods of transmitting digital data using analog signals. The most familiar use of these methods is in data communications, where modems and telephone networks are used; because integrated circuits are generally used a block diagram approach…

The most frequently used modulator in FM systems is the reactance modulator, which incorporates some method of varying the reactance across the oscillator circuit. This can be done by incorporating a device which changes either its inductive or capacitive reactance, depending on the oscillator involved. With a Colpitts oscillator some type of capacitive modulator would…

With frequency modulation the frequency (rather than the amplitude) of a constant-amplitude, constant-frequency sinusoidal carrier is made to vary in proportion to the amplitude of the applied modulating signal. This is shown in Figure 19.10, where a constant-amplitude carrier is frequency-modulated by a single tone. Note how the frequency of the carrier changes. Figure 19.10 Constant-amplitude carrier…

The function of a modulator, as has been shown, is to superimpose the baseband signals on to a carrier while the demodulator provides the reverse role by extracting a carrier, known as the intermediate frequency, and leaving the baseband. There are many modulators and demodulators commercially sold on the market as integrated chips or as part…

 Amplitude Modulation When the amplitude of a carrier signal is varied in accordance with the information signal, amplitude modulation is produced. This method is mainly used where large power outputs are required for long-distance communications. Figure 19.3 shows a constant-amplitude, constant-frequency carrier being modulated by a single tone. In practice, many modulating signals may be used.…

shows a simplified block diagram of a color television receiver. We will refer to it throughout this chapter. It shows that any receiver must be capable of extracting information from the incoming channels to which it is tuned. The shaded blocks show examples of where demodulation or detection occur for the video and audio signals.…