This set of Digital Communications Multiple Choice Questions & Answers (MCQs) focuses on “Signals”.
1. In the digital communication system, signals in different frequency bands are
a) Orthogonal
b) Non orthogonal
c) Orthogonal & Non orthogonal
d) None of the mentioned
View Answer
Explanation: In digital communication system, signals from different frequency bands are orthogonal thus interference won’t occur.
2. Properties of impulse function are
a) Symmetry
b) Time scaling
c) Shifting
d) All of the mentioned
View Answer
Explanation: Some of the properties of impulse function are symmetry, time scaling and shifting.
3. Properties of Fourier transform are
a) Duality property
b) Time shifting property
c) Modulation property
d) All of the mentioned
View Answer
Explanation: Some of the properties of Fourier transform are duality property, time scaling property, time shifting property, modulation property and many more.
4. A base-band signal can be up-converted using
a) Sine wave
b) Cosine wave
c) Filtering
d) None of the mentioned
View Answer
Explanation: A base-band signal can be up-converted to band-pass filter by applying cosine wave.
5. A band-pass signal can be down-converted using
a) Sine wave
b) Cosine wave
c) Time delayed wave
d) None of the mentioned
View Answer
Explanation: For down-conversion of a band-pass signal also cosine signal is used and multiplied with it.
6. In down-conversion multiplication with cosine wave is followed by
a) Low pass filter
b) High pass filter
c) Bandpass filter
d) Bandstop filter
View Answer
Explanation: Downconversion of bandpass signal includes multiplication with sine wave followed by low pass filtering.
7. ADSL has _____ information channels.
a) One
b) Three
c) Four
d) None of the mentioned
View Answer
Explanation: Asymmetric digital subscriber line has three information channels – a high speed downstream channel, ISDN channel and medium speed duplex channel.
8. Fourier transform of a signal gives the
a) Frequency content
b) Bandwidth
c) Frequency content & Bandwidth
d) None of the mentioned
View Answer
Explanation: Fourier transform of a signal give the frequency content and also determines the bandwidth of the signal.
9. Random things in a communication system are
a) Timing offset
b) Device frequency
c) Attenuation
d) All of the mentioned
View Answer
Explanation: Some of the random things in the communication system are noise in the channel, attenuation, fading, channel filtering, device frequency, phase and timing offset.
10. Which can be used for periodic and non periodic?
a) Fourier series
b) Fourier transforms
c) Fourier series & transforms
d) None of the mentioned
View Answer
Explanation: Fourier series is limited to only periodic signals where as Fourier transforms and laplace transforms can be used for both periodic and non periodic signals.
11. A band-pass signal has a Fourier transform equal to
a) One
b) Zero
c) Infinity
d) Cannot be determined
View Answer
Explanation: A band-pass signal has a Fourier transform equal to zero for all value in both frequency and time domain.
12. A band-pass signal has
a) DC component
b) No DC component
c) No side lobes
d) Cannot be determined
View Answer
Explanation: A band-pass signal has no DC components and has Fourier transform equal to zero. Outside the band it will not be exactly zero. Thus this results in presence of side lobes.
13. Which are orthonormal signal representation?
a) Sine and cosine at same frequency
b) Wavelets
c) Complex sinusoids at a different frequency
d) All of the mentioned
View Answer
Explanation: Some of the common orthonormal signal representations are sine and cosine at the same frequency, Fourier serier, sinc functions centered at sampling times, wavelets etc.
14. Constellation diagram is plotted in
a) Constellation space
b) Signal space
c) Orthogonal space
d) Boundary space
View Answer
Explanation: The constellation diagram is plotted in a space called as signal space.
15. Cumulative distributive function is
a) Non negative
b) Non decreasing
c) Non negative & decreasing
d) None of the mentioned
View Answer
Explanation: Cumulative distribution function is non negative and non decreasing function.
16. Which are non negative functions?
a) PDF
b) PMF
c) PDF & PMF
d) None of the mentioned
View Answer
Explanation: PDF, PMF and CDF are non negative functions.
Sanfoundry Global Education & Learning Series – Digital Communications.
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