This set of Analog Communications Multiple Choice Questions & Answers (MCQs) focuses on “Phase Shift Method”.
1. Which of the following is an indirect way of generating frequency modulated signals?
a) Armstrong modulator
b) Varacter diode modulator
c) Reactance FET modulator
d) Reactance modulator
Explanation: Varacter diode modulator is not an indirect way of generating FM. Instead it’s a direct way of producing FM with the help of voltage controlled oscillator mechanism. It is Armstrong modulator which is an indirect way of generating FM.
2. Which of the following determines carrier deviation in frequency modulation?
a) modulating voltage
b) modulating frequency
c) frequency deviation
d) modulating phase
Explanation: In frequency modulation, frequency of carrier varies with the modulating voltage. In frequency modulation, it is modulating voltage that is responsible for deviation of the carrier.
3. Balance modulator is used to produce __________
Explanation: A balance modulator mixes audio signal and radio frequency carrier wave, thereby producing a DSBSC wave, by suppressing the carrier. In DSB_SC, only the two sidebands are present. Thus, it has less power consumption.
4. Full AM signal is preferred over SSB in broadcasting purpose because ________
a) generation of full AM is easier
b) detection of full AM is simpler
c) requires large bandwidth
d) for both detection and generation of full AM
Explanation: SSB is preferred because of its low bandwidth and lesser power consumption. It reduces its bandwidth by suppressing the carrier and removing one of the two sidebands since both sidebands are exactly same. But full amplitude modulation is sometimes preferred over it because in its detection of full AM is simpler due to it’s simpler demodulation circuit.
5. Which among the following is not necessarily the advantage of SSB over AM?
a) required bandwidth for SSB is low
b) less power handled
c) complex circuit
d) simple circuit
Explanation: SSB is preferred because of its low bandwidth and lesser power consumption. It reduces its bandwidth by suppressing the carrier and removing one of the two sidebands since both sidebands are exactly same. But full amplitude modulation is sometimes preferred over it because in it detection of full AM is simpler due to it’s simpler demodulation circuit. SSBSC has a complex circuit anyway.
6. Which filter is used to get back the original signal from sampled signal?
a) low pass filter
b) high pass filter
c) band pass filter
d) band reject filter
Explanation: Sampling is the conversion of continuous-time signal to discrete-time signal by sampling the continuous signal with respect to specific time intervals, thereby discritising it. Now to get back the original signal we have to use low pass filter, which attenuates high frequencies and allows only low frequencies to pass.
7. Carson’s rule is used to ________
a) calculate Bandwidth of FM signal
b) calculate SNR of FM signal
c) determine the carrier frequency
d) calculate Figure of merit of FM signal
Explanation: According to Carson’s rule, the required bandwidth is twice the sum of the maximum frequency deviation and the maximum modulating signal frequency or B = 2(fd + fm)Hz.
8. FM signals can be generated by using ________
a) Varacter diode
b) Laser diode
c) Backward diode
d) Gunn diode
Explanation: Varactor diode is a diode working in the reverse-bias because of which no current flows through it. It has variable capacitance which varies with applied voltage. Varactor diodes are mainly used in generation of FM signals using Voltage Controlled Oscillator.
9. Granular noise occurs in Delta Modulation, when ____________
a) pulse rate decreases
b) pulse amplitude decreases
c) modulating signal increases
d) modulating signal remains constant
Explanation: Delta modulation is used for transmission of voice information where quality is not the primarily importance. Its drawback is it has two noises namely slope overload and granular noise. Granular noise is produced due to constant modulating input signal resulting into oscillatory output. So for getting rid from these noises we use ADM (Adaptive Delta Modulation).
10. DM stands for ________
a) Density Modulation
b) Delta Modulation
c) Double Side Band Modulation
d) Direct Modulation
Explanation: DM stands for Delta Modulation. Delta modulation is used for transmission of voice information where quality is not the primarily importance.
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