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Analog Communications Multiple Choice Questions focuses on “Transmitter”.
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1. Modulation is done in ________
a) Receiver
b) Transducer
c) Between transmitter and radio receiver
d) Transmitter
Answer: d
Clarification: Transmitter modulates the signal to be transmitted, by varying one of the properties of a carrier signal with respect to the instantaneous amplitude of the message signal. This process is known as modulation. Receiver demodulates the modulated signal to extract the message signal. Transducer converts the electrical signal to sound wave. Between the transmitter and the radio receiver, is the channel which acts as the medium of transmission.
2. In TV transmission, picture signal is ________ modulated.
a) DSB-SC
b) VSB
c) SSB-SC
d) Pulse
Answer: b
Clarification: All analog television systems use vestigial sideband modulation, which is a form of amplitude modulation, for transmission. In VSB, one sideband is fully transmitted and another sideband is partially removed, which further reduces the bandwidth of transmitted signal. This enables narrower channels to be used.
3. In TV transmission, sound signal is ________ modulated.
a) Phase
b) Pulse
c) Frequency
d) Amplitude
Answer: c
Clarification: Amplitude Modulation is invariably used for picture transmission while frequency modulation is generally used for transmission of sound due to its inherent advantages over amplitude modulation. It is not suitable for transmitting videos due to its large bandwidth.
4. Square Law modulators are ________
a) used for frequency modulation
b) used for pulse width modulation
c) used for amplitude modulation
d) used for phase modulation
Answer: c
Clarification: Square Law modulators are generally used for the generation of amplitude modulated signals. They have nonlinear current-voltage characteristics, such that output current or voltage varies as a square of the input.
5. Ring Modulator is ________
a) used for DSB-SC generation
b) used for SSB-SC generation
c) used for VSB generation
d) used for AM generation
Answer: a
Clarification: Ring Modulator is used for generating DSB-SC modulated waves. It is a product modulator having four diodes connected in the form of a ring. It suppresses the carrier and produces the upper-sideband and lower-sideband at the output.
6. What is the role of the transmitter in the communication system?
a) to decode a signal to be transmitted
b) to convert one form of energy into other
c) to detect and amplify information signal from the carrier
d) to produce radio waves to transmit data
Answer: d
Clarification: Transmitter is used to produce radio waves which are then sent to the antennae to transmitted. It encodes or modulates the message signal before transmission. Transducer converts a signal from one form of energy to other. Receiver detects and amplifies information signal from the carrier.
7. What is the maximum transmission efficiency?
a) 67.88%
b) 33.33%
c) 73%
d) 54.03%
Answer: b
Clarification: The maximum transmission efficiency is 33.33%. It is so because 2/3rd of the total power is contained in the carrier, which conveys no useful information. Thus, only 1/3rd of total power has useful information which is transmitted. This happens in the case of SSB-SC Modulation, where the carrier is suppressed and only either of the sidebands is allowed to pass.
8. AVC stands for ________
a) Abrupt Voltage Control
b) Audio Voltage Control
c) Automatic Volume Control
d) Automatic Voltage Control
Answer: c
Clarification: AVC stands for Automatic Volume Control. It automatically adjusts the volume of an audio signal with respect to the surrounding noise, to make the signal be heard better and also to compensate noise to some extent.
9. What is the role of Amplitude limiter in the FM receiver?
a) Filteration
b) Adjust the gain of receiver
c) Amplify a weaker signal
d) Demodulate a signal
Answer: d
Clarification: Amplitude Limiter in FM receivers are used to eliminate the amplitude changes caused due to noise interference. It does so by clipping the amplitude of output signals to the desired level, irrespective of any variations in the input signal.
10. What is Carrier swing?
a) Frequency deviation
b) Width of sideband
c) Instantaneous frequency
d) Total variation in frequency
Answer: d
Clarification: Carrier swing is defined as the total variation in frequency from the lowest to the highest point. It is equal to twice the frequency deviation of FM signal. The rest of the options are parameters in FM.
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