Pulse Modulation

pulse modulation [′pəls ‚mäj·ə‚lā·shən]

(communications)

A system of modulation in which the amplitude, duration, position, or mere presence of discrete pulses may be so controlled as to represent the message to be communicated.

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Pulse Modulation 

modulation of oscillations, as a result of which harmonic oscillations take on the shape of short-duration radio pulses, whose properties are determined by the shape of the modulating video pulses.

Pulse modulation is used in radar, where the distance to target is determined from the time of arrival of a pulse reflected by the target, and in systems of pulse radio communications. In this case the transmitted signal (video pulse) can change various parameters of the initial sequence of radio pulses: the height (pulse amplitude modulation); displacement of the pulse in time, without affecting its duration (pulse position modulation); or duration (width) of the pulse (pulse width modulation). In the case of pulse code modulation the transmission of differently coded pulse trains is used for various types of signals.

The pulses used in pulse modulation are mainly square or bell-shaped and have a duration of 10⁻⁹ to 10⁻⁵ sec. The off-on time ratio (the ratio of the repetition period and the duration of a pulse) ranges from 10² to 10³ for radar to several units for multichannel radio communications. Pulse modulation is usually achieved by means of pulse modulators.

REFERENCES

Itskhoki, Ia. S. Impul’snye ustroistva. Moscow, 1959.
Meerovich, L. A., and L.G. Zelichenko. Impul’snaia tekhnika. Moscow, 1953.
Evtianov, S.I. Radioperedaiushchie ustroistva. Moscow, 1950.