DATA TRANSMISSION

Modem Definition

Modem Definition: The term Modem Definition is an acronym for modulator-demodulator. The primary modem function is to convert digital data into an analog form which is suitable for transmission on common carrier circuits (example telephone lines). Modulation is the D/A conversion in which the digital data is placed on the transmission line by modulation of […]

Pulse Wave Code Format

Pulse Wave Code Format: There are many different code formats of pulse wave. The classification is based on three criteria, namely, form of information transmission, relation to zero level, and direction. Based on the form of information transmission, the format used can be any one of the following Full binary transmission, where both 0 and […]

Delta Modulation

Delta Modulation(DM): Delta modulation(DM) is process of modulation in which train of fixed width pulses is transmitted. Their polarity indicates whether the demodulator output should rise or fall at each pulse. The input is caused to rise or fall by a fixed step height at each pulse. Figure 18.20 shows the block diagram of a […]

Pulse Code Modulation

Pulse Code Modulation(PCM): Pulse Code Modulation(PCM) is different from the other forms of pulse modulation studied so far, PCM also uses sampling techniques, but it differs from the others in that it is a digital process. Instead of sending a pulse train capable of continuously varying one of the parameters, the PCM generator produces a […]

Pulse Position Modulation

Pulse Position Modulation(PPM): In this Pulse Position Modulation system, the amplitude and width of pulses is kept constant, while the position of each pulse, in relation to the position of a recurrent reference pulse, is varied by each instantaneous sampled value of the modulating wave. PPM may be obtained very simply from PWM, as shown […]

Pulse Width Modulation

Pulse Width Modulation(PWM): Pulse width modulation of PTM is also often called Pulse Duration Modulation (PDM). In this system, shown in Fig. 18.8, we have a fixed amplitude and starting time of each pulse, but the width of each pulse is made proportional to the amplitude of the signal at that instant. In Fig. 18.8, […]

Pulse Time Modulation

Pulse Time Modulation(PTM): In Pulse Time Modulation the signal is sampled in the same way as in PAM, but the pulses indicating instantaneous sample amplitudes have a constant amplitude themselves. However, one of their timing characteristics is varied, being directly proportional to the sampled signal amplitude at that instant. The variable characteristics may be width, […]

Pulse Amplitude Modulation

Pulse Amplitude Modulation(PAM): Pulse Amplitude Modulation(PAM) is the simplest form of Pulse Modulation. It is shown in Fig. 18.7. PAM is a pulse modulation system in which the signal is sampled at regular intervals, with each sample proportional to the amplitude of the signal at the instant of sampling. The pulses are then sent either […]

Pulse Modulation

Pulse Modulation: Pulse modulation may be used to transmit analog information, such as continuous speech or data. It is a system in which continuous waveforms are sampled at regular intervals. Information regarding the signal is transmitted only at the sampling times, together with any synchronising pulses that may be required. At the receiving end, the […]

Time Division Multiplexing

Time Division Multiplexing(TDM): Time Division Multiplexing – Any pulse modulation scheme involves translating the audio, or modulating signal into a series of encoded pulses, sending these pulses over a transmission medium and reverting the pulses back to an analog signal. Regardless of the encoding used, a PAM signal is always obtained initially. The audio signal […]

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