# Digital Communications Questions and Answers – Modulation and Multiplexing

This set of Digital Communications Multiple Choice Questions & Answers (MCQs) focuses on “Modulation and Multiplexing”.

1. Properties used to determine stream’s fidelity
a) Sampling rate
b) Bit depth
c) Sampling rate & Bit depth
d) None of the mentioned

Explanation: Two basic properties to determine stream’s fidelity are bit depth and sampling rate, number of times per second that samples are taken.

2. In bipolar codes, pulses can be
a) Positive
b) Negative
c) Absent
d) All of the mentioned

Explanation: In bipolar codes, the pulses can be positive, negative or absent.

3. Delta modulation is ______ conversion.
a) Analog to digital
b) Digital to analog
c) Analog to digital and digital to analog
d) None of the mentioned

Explanation: Delta modulation is the process of analog to digital and digital to analog conversion technique used for transmission of voice signals.

4. To achieve high signal to noise ratio, delta modulation must use
a) Under sampling
b) Over sampling
c) Aliasing
d) None of the mentioned

Explanation: To achieve high signal to noise ratio, delta modulation must use over sampling techniques.

5. The demodulator in delta modulation technique is
a) Differentiator
b) Integrator
c) Quantizer
d) None of the mentioned

Explanation: The demodulator used in delta modulation is a simple form of integrator.
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6. Source of noise in delta modulation is
a) Granularity
d) None of the mentioned

Explanation: Sources of noise in delta modulation are granularity and slope overload.

7. When probability of receiving a symbol is 1 then how much information will be obtained?
a) Little information
b) Much information
c) No information
d) None of the mentioned

Explanation: When the probability of receiving a symbol is 1 then the information obtained is zero.

8. In channel encoding procedure
b) Errors are corrected
c) Redundancy bits are added & Errors are corrected
d) None of the mentioned

Explanation: In channel encoding includes addition of redundancy to the signal such that any bit errors can be corrected.

9. Modulation process includes
a) Analog to digital conversion
b) Digital to analog conversion
c) All of the mentioned
d) None of the mentioned

Explanation: Modulation procedure includes digital to analog conversion which produces a continuous time signal that can be sent through the channel.

10. Switching exists in
a) Point to point communication
c) Point to point & Broadcast communication
d) None of the mentioned

Explanation: Circuit connection in point to point communication is called as switching. Switching does not exist in broadcast communication or network.

11. Space division has dedicated
a) Paths
b) Time slots
c) Paths & Time slots
d) None of the mentioned

Explanation: Space division has dedicated paths and time division has dedicated time slots.

12. In time division system, the actual switch is called as
a) Speech memory
b) Cross point
c) Connecting point
d) None of the mentioned

Explanation: In time division, actual switch is called as speech memory and in space division actual switch is called as cross point.

13. In time division, connection is established using
a) Data exchange
b) Galvanic connection
c) Data exchange & Galvanic connection
d) None of the mentioned

Explanation: In time division, connection is established using data exchange and in space division it is established using galvanic connections.

14. Analogue switches provides
a) Good bandwidth
b) Low distortion
c) Low cost
d) All of the mentioned

Explanation: Some of the features of analogue switches are good bandwidth, low cost, low distortion, lower reliability.

15. Operations performed by switching system
a) Path establishment
b) Information exchange
c) Tariff computation
d) All of the mentioned

Explanation: Operations performed by switching network are path establishment, information exchange, tariff computation, maintenance, billing etc.

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