Pulse Analog Modulation - Electronic Engineering (MCQ) questions & answers

ANSWER: 400 Hz

Explanation:
In the given signal, the highest frequency is given by f = 400 π/ 2π
= 200 Hz

The minimum sampling rate required to avoid aliasing is given by Nyquist rate. The nyquist rate is = 2 * f
= 2 * 200
= 400 Hz.

ANSWER: All of the above

Explanation:
The techniques used for sampling are:

a) Instantaneous sampling
b) Natural sampling
c) Flat top sampling

The natural sampling and the flat top sampling techniques are used practically to sample a signal.

ANSWER: f_s < 2f_m

Explanation:
If the signal of frequency f_m is sampled at the rate f_s ≥ 2f_m only then the spectrum of the sampled signal is obtained without overlapping. For f_s < 2f_m the sampled signal spectrum overlap each other, and therefore the signal cannot be recovered easily. For reconstruction of signal to be free from distortion, the important condition is
f_s ≥ 2f_m

ANSWER: Both a and b

Explanation:
In Pulse Position Modulation, the position of the pulse of the carrier is varied with reference to the position of a reference pulse. The position is varied in accordance with the sampled modulating signal. In PPM, synchronization is required between the transmitter and the receiver. Large bandwidth is required in Pulse position Modulation as compared to the Pulse amplitude modulation.

ANSWER: To remove noise

Explanation:
In pulse width modulation, the width of the carrier varies with the amplitude of the modulating signal at the time of sampling. In PWM signal reception, the received PWM signal is applied to the Schmitt trigger circuit. The Schmitt trigger circuit is used to remove noise in the PWM waveform. This output is the supplied further for detection of the original information.

ANSWER: Synchronization is not required between transmitter and receiver

Explanation:
In pulse width modulation, the width of the carrier varies with the amplitude of the modulating signal at the time of sampling. Pulse width modulation is a type of Pulse Time Modulation. As there is no variation in the amplitude of the carrier, the noise may be easily removed at the receiver. It does not require synchronization between the transmitter and the receiver.

ANSWER: All of the above

Explanation:
There are types of Pulse Width Modulation. In one of the variations, leading edge of the pulse is kept constant and pulse width is measured with respect to leading edge. In second type, tail edge of the pulse is kept constant and pulse width is measured with respect to it. And the third type has a constant centre of the pulse and the pulse width changes on both the sides of the centre of the pulse.

ANSWER: All of the above

Explanation:
In Pulse time modulation (PTM), amplitude of the carrier is kept constant and the Position or width of the carrier varies with the amplitude of the modulating signal at the time of sampling. Pulse width modulation and pulse position modulation are the types of Pulse Time Modulation.
As there is no variation in the amplitude of the carrier, the noise may be easily removed at the receiver.

ANSWER: All of the above

Explanation:
In PAM, Bandwidth is very large as compared to modulating signal frequency. In PAM, the amplitude of the rectangular pulse train is varied according to the instantaneous value of the modulating signal. Due to this, the required power for transmission is also varied. Due to varying amplitude of carrier, the interference of noise is very high in PAM. So it is difficult to remove noise at receiver.

ANSWER: Both a and b

Explanation:
In pulse modulation systems, the carrier is a train of pulses rather than a continuous signal. The parameters of the pulses are varied according to the instantaneous value of the modulating signal. The carrier is a train of pulses rather than a continuous signal. In PTM, the timing of the pulses of the carrier is varied in accordance with modulating signal. PTM includes:
- Pulse width modulation
- Pulse position modulation