# Digital Communications Questions and Answers – Digital Communication System

This set of tough Digital Communication Questions & Answers focuses on “Digital Communication System”.

a) True
b) False

Explanation: The modulation channel takes an analogue signal as input and outputs a modulated signal in the form of an analogue waveform.

2. If operating frequency bands are higher ______ is available.
a) Smaller bandwidth
b) Larger bandwidth
c) Smaller & Larger bandwidth
d) Cannot be determined

Explanation: Larger bandwidth is available when operating frequency bands are higher.

3. Ground wave communication occurs in
a) Low frequency band
b) Medium frequency band
c) Low & Medium frequency band
d) None of the mentioned

Explanation: Ground wave communication can take place in both low frequency and medium frequency bands.

4. Sampling theorem is used for converting
a) Continuous time signal to discrete
b) Discrete to continuous time signal
c) Continuous time signal to discrete & vice versa
d) None of the mentioned

Explanation: For transforming continuous time signals to discrete type signals and vice versa, the sampling theorem is used.

5. A signal can be recovered from its sample by using
a) Low pass filter
b) High pass filter
c) Band pass filter
d) Band stop filter

Explanation: A signal can be recovered from its sampled version by using an ideal low pass filter.

6. Which is practically realizable?
a) A train of pulses
b) Impulse train
c) All of the mentioned
d) None of the mentioned

Explanation: A train of pulses with narrow bandwidth is realizable than the impulse train.

7. In flat top sampling scheme, ______ is kept constant after sampling.
a) Amplitude
b) Phase
c) Frequency
d) Time period

Explanation: In flat top sampling scheme, the amplitude is kept constant after sampling.

8. Loop filter is a ______ used to reduce noise.
a) Low pass filter
b) High pass filter
c) Band pass filter
d) Band reject filter

Explanation: Loop filter is a low pass filter used to reduce noise.

9. Which are the common transmission media used in digital communication system?
a) Coaxial cable
b) Twisted copper cable
d) All of the mentioned

Explanation: Twisted copper cable, high-quality coaxial cable, and radio frequency bands are some of the most regularly utilised physical transmission media.

10. The basic transmission-reception system is a ______ system.
a) Two block system
b) Three block system
c) Four block system
d) None of the mentioned

Explanation: Three blocks make up the basic transmission-reception system: transmitter, transmission medium, and receiver.

11. Modulation channel consists of
a) Amplifier
b) Signal processing units
c) Amplifier & Signal processing units
d) None of the mentioned

Explanation: When data must be transmitted over a long distance, it must be amplified. An amplifier and other signal processing devices make up a modulation channel.

12. The equivalent temperature in a receiver design must be kept
a) Low
b) High
c) Does not affect the receiver
d) None of the mentioned

Explanation: The receiver’s equivalent temperature is a result of its design, and it must constantly be kept low.

13. Which corrects the sampling time problem in a digital system?
a) Interpolator
b) Decimator
c) Equalizer
d) Filter

Explanation: Interpolator corrects the sampling time problem using discrete time processing.

14. What are the main features of a transmitter?
a) Higher clock speed
b) Linear power amplifier
c) Directional antennas
d) All of the mentioned

Explanation: More clock speeds, higher transmit power, directional antennas, and the necessity for a linear amplifier are some of the primary aspects that make the transmitter difficult.

15. Transmission media used in low frequency band are
a) Air
b) Water
c) Copper cable
d) All of the mentioned

Explanation: Air, water and copper cable can be used as transmission media in low frequency band communication.

16. Transmission media used for medium frequency band are
a) Air
b) Water
c) Copper cable
d) All of the mentioned

Explanation: Only air and copper wire can be utilised as a transmission medium for medium frequency band communication.

17. Matched filter technique is used to
a) Increase SNR
b) Decrease SNR
c) SNR is not affected
d) None of the mentioned

Explanation: Matched filter technique is a demodulation process used to increase SNR.

18. Matched filter can also be used as least squares estimator.
a) True
b) False

Explanation: A matched filter can also be used as a least squares estimator.

19. Digital communication system can handle
a) Analog signals
b) 1D signals
c) 2D signals
d) All of the mentioned

Explanation: Signals that are analogue or already digital can be handled by a digital communication system. It also works with 1D and 2D signals.

20. The information source of a digital communication system can be
a) Packetized
b) Continuous
c) Packetized & Continuous
d) None of the mentioned

Explanation: Information source comes from a higher networking layer. It can be continuous or packetized.

21. What are the main features of a receiver?
a) Synchronization
c) Synchronization & Multiple parallel receiver chain
d) None of the mentioned

Explanation: The major aspects of a receiver that increase its complexity are carrier, phase, and timing synchronisation, as well as several parallel receiver chains.

22. What conditions must be fulfilled in a good digital communication system?
a) High data rate
b) High fidelity
c) Low transmit power
d) All of the mentioned

Explanation: High data rate, high fidelity, low bandwidth, low transmit power, and minimal transmitter and receiver complexity are some of the requirements for a digital communication system.

23. Wired channels are
a) Lossy
b) Lossless
c) Lossy & Lossless
d) None of the mentioned

Explanation: Wired channels are lossy channels.

Information is conveyed as a sequence of digits in a digital communication system, which are first changed to an analogue form by modulation at the transmitter and then converted back to digits by de-modulation at the receiver. The coder input and output in convolutional coding are continuous streams of digits. Digital communication channels refer to a variety of different methods of digital communication. Email, phone conversations, video conferencing, and various types of instant messaging, such as SMS and web chats, are all examples. Blogging, podcasting, and video are all examples of digital communication.