This set of Analog Communications online test focuses on “Demodulation of VSB Modulated Wave”.
1. What is the reason of “envelope” in an amplitude modulated signal?
a) amplitude signal
b) carrier signal
c) nematic signal
d) baseband signal
Explanation: Envelope is basically a smooth curve that outlines the extremes of any baseband signal. So basically it is message or baseband signal that determines the envelope.
2. AM stands for ________
a) Amplitude Modulation
b) Audio Modulation
c) Antenna Modulation
d) Amplified Modulation
Explanation: AM stands for amplitude modulation. Amplitude modulation is the change in amplitude of carrier wave in proportion to the waveform being transmitted.
3. What is the equation for full-carrier AM?
a) V(t) = (Ec+Em) ×(sin ωc t)
b) V(t) = (Ec+Em) ×(sin ωm t) + (sin ωc t)
c) V(t) = (Ec ×Em) ×(sin ωm t) × (sin ωc t)
d) V(t) = (Ec+Em sin ωm t) × (sin ωc t)
Explanation: Amplitude modulation is the change in amplitude of carrier wave in proportion to the waveform being transmitted. A carrier can be seen as a waveform that is modulated with input signal for the purpose of transmitting information. The equation for full-carrier AM is V(t) = (Ec +Em sinωm t) × (sin ωc t).
4. What is the cause of Overmodulation?
c) both distortion and splatter
d) half reception of signals
Explanation: Overmodulation is observed when the value of modulation index exceeds the value which is necessary to produce 100% modulation. So overmodulation is observed for modulation index greater than 1. It results in both distortion and splatter of waveform.
5. If AM radio station increases its modulation index then the audio gets louder at the receiver.
Explanation: Modulation index describes the variation of carrier signal modulation around its unmodulated level. If we increase the modulation index then audio signal gets louder.
6. For which of the modulated system, the linear amplified modulated stage is used?
a) low level amplitude modulated system
b) high level amplitude modulated system
c) high level frequency modulated system
d) low level frequency modulated system
Explanation: Linear amplified modulation is used to amplify the amplitude. Thus it is used for low level modulated system.
7. The modulation index can be derived from ________
a) frequency-domain signal
b) time-domain signal
c) both frequency and time domain signal
d) a highly modulated carrier wave
Explanation: Modulation index describes the variation of carrier signal modulation around its unmodulated level. It can be derived for frequency-domain signals as well as for time-domain signals.
8. A single sideband modulation system is more efficient than a plain amplitude modulated system?
Explanation: Single side band uses only one of its sideband among two sidebands. The two sidebands carries exactly the same information and thus removing a sideband does not have any effect on our signal. Due to the removal of one sideband total bandwidth required also decreases which makes it more efficient than others.
9. At peak modulation an SSB transmitter radiate 1000W, what will it radiate with no modulation?
a) 1000 watts
b) 500 watts
c) 250 watts
d) 0 watts
Explanation: If there is no modulation in any SSB transmitter than it will not radiate. So it will radiate 0 watts when there is no modulation.
10. Why AM stations has “low-fidelity”?
a) AM is susceptible to noise
b) Commercial AM stations use low power
c) Commercial AM stations have a narrow bandwidth
d) High quantization to noise ratio
Explanation: Low fidelity can be seen as sound recording that contain technical flaws to make sound better compared with the sound that is recorded live. High fidelity refers to the equipment that very accurately produces without any harmonic or resonance. AM stations have low fidelity to have narrow bandwidth.
Sanfoundry Global Education & Learning Series – Analog Communications.
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