# Analog Communications Questions and Answers – Source of Information

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This set of Analog Communications Multiple Choice Questions & Answers (MCQs) focuses on “Source of Information”.

1. FM stands for ________
a) Frequency Modulation
b) Frequency Modulator
c) Frequent Frequent Multiplier
d) Frequency Mixer

Explanation: FM stands for Frequency Modulation. It is the encoding of information on a carrier wave by varying its frequency with respect to the instantaneous amplitude of the message signal. Rest other options are the components used in the process of frequency modulation.

2. Why a sinusoidal signal is considered analog?
a) It moves in both positive and negative direction
b) It is positive for one half cycle
c) It is negative for one half cycle
d) It has an infinite number of amplitudes in the range of values of the independent variable

Explanation: A sinusoidal wave is an analog signal. An analog electrical signal is a signal with infinite number of amplitudes in the range of values of independent variable. Analog signals can take on any value in the continuous interval.

3. The minimum height of antenna required for transmission in terms of ʎ is ________
a) 2
b) ʎ4
c) 2ʎ
d) ʎ

Explanation: For effective transmission, height of antenna should be one-forth of ʎ.
(H = ʎ4 where ʎ = cf). The reason for maintaining antenna height to ʎ/4 is for matching impedance. It means that the antenna is atleast 1/4th above ground level.

4. What do you understand by the term analog communication?
a) A method in which one of the properties of a carrier signal varies in proportion to an instantaneous value of modulation signal
b) A way for data and computer communication
c) A numerical coded communication
d) A suitable method for long distance communication

Explanation: Analog communication means that information is transmitted in the form of a continuous signal through the process of modulation. Rests of the options are applicable for digital communication, where coding is applied.

5. What is Demodulation?
a) Process of varying one or more properties of a periodic waveform
b) Recovering information from a modulated signal
c) Process of mixing a signal with a sinusoid to produce a new signal
d) Involvement of noise

Explanation: Demodulation is the process of recovering information from a modulated carrier wave while it is modulation in which properties of a periodic waveform is varied. A modulator is a device that performs modulation while the demodulator performs demodulation. A modem can perform both functions.
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6. Data transmitted for a given amount of time is called ________
a) Noise
b) Power
c) Frequency
d) Bandwidth

Explanation: A Demodulation is a process of recovering the information signal from a modulated carrier wave, in which properties of a periodic waveform is varied. A modulator is a device that performs modulation while the demodulator performs demodulation. The process of mixing a signal with a sinusoid to produce a new signal is done by a mixer.

7. If Output can be represented as linear combination of input then ________
a) The system is linear
b) The system is causal
c) The system is non causal
d) The system is time invariant

Explanation: The input signal is divided into sub-components, where each sub-component is processed individually and reunited. The result is tested for additivity and homogeneity and if it satisfies both, then the system is said to be linear. It also follows superposition property.

8. Amplitude Modulation suffers from ________
a) Side-band Suppression
b) IntraPulse Modulation
c) Cross Modulation
d) Carrier Suppression

Explanation: Cross modulation generally occurs in receivers receiving an AM signal in the presence of other strong AM signal. The modulation from the strong signal cross modulates and appears on the weaker signal being received.

9. Medium which sends information from source to receiver is called ________
a) Transmitter
b) Transducer
c) Loudspeaker
d) Channel

Explanation: Channel is the medium through which information is transmitted. Transmitter is used to process the electrical signal through different aspects. The transducer is used to convert a message signal to an electrical signal. Loudspeaker is a type of Transducer.

10. Telephones send information through wires in form of ________
b) electrical signal
c) electromagnetic waves
d) microwaves

Explanation: A telephone converts sound waves into electrical signals which are suitable for transmission over long distances, where it is converted to sound waves again, through a transducer. The essential components of a telephone are a microphone which acts as a transmitter and an earphone which acts as a receiver.

11. Cell phones sent information in form of ________
a) microwaves
b) electrical signals
c) infrared Waves

Explanation: Cell phones transmit information in form of radio waves to communicate with each other. Radio waves are transmitted in all directions by the cell phone, and they travel at the speed of light in air or vacuum.

12. The ability of receivers to select the wanted signals among various incoming signal is called ________
a) Selectivity
b) Fidelity
c) Sensitivity
d) Modulation

Explanation: The ability of receiver to select wanted signal from various incoming signals is called selectivity. It rejects the other signals at closely lying frequencies. Sensitivity is the ability of the receiver to amplify weak signals. Fidelity is the feature of receiver to reproduce all modulating frequencies equally. While modulation is the process of varying one or more properties of carrier signal with respect to the modulating signal.

13. Which device is used for tuning the receiver according to incoming signal (especially in TV)?
a) Low pass filter
b) High pass filter
c) Zener diode
d) Varacter 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 Voltage Controlled Oscillators (VCOs) and RF Filters for tuning the receiver to the incoming signal or different stations.

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