pulse modulation


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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.

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.

pulse modulation

pulse modulationclick for a larger image
A number of methods of converting CW (carrier wave) signals into digital pulses to reduce the bandwidth required, eliminate errors, and, where possible, improve the signal-to-noise ratio.
References in periodicals archive ?
In the ICW mode, typical pulse modulation parameters are duty cycle (DC) = [t.sub.i]/[T.sub.rm] = 0.5; pulse repetition period [T.sub.rm] = 1/[F.sub.rm] and the pulse repetition frequency [F.sub.rm] = c/4 [H.sub.max] = 31 kHz.
The instrument contains internal modulators for AM, FM and pulse modulation. Each of these modulators is coupled with a generator for internal modulation.
The demodulation and detection of baseband pulse modulation signals are described along with the probability of error.
The instrument also includes built-in digital AM, FM and pulse modulation envelope generators with digital and analog sweeps of both frequency and output power.
A transmitted signal of the carrier frequency [f.sub.O] and a pulse modulation function [A.sub.TX] are assumed as
External modulation capability and internal pulse modulation are standard, while built-in amplitude and frequency sources are available options.
If the electric field zero crossings under the optical pulse modulation envelope are uniformly spaced in time, the time-bandwidth product should be approximately 0.5.
The available options include internal reference frequency source, built-in step attenuation, phase modulation and pulse modulation.
The RF source modules contain the circuitry for imposing amplitude, frequency or pulse modulation on the microwave carrier.