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The correct option is (B) Class A

To elaborate: We called a MODULATION as LOW level when the modulation takes place prior to the output element of the final stage of the amplifier at low power. Class A AMPLIFIERS are used for this PURPOSE.

Correct choice is (c) 1

The best I can EXPLAIN: Figure of merit is the ratio of output signal to NOISE ratio to INPUT signal to noise ratio of a receiver system, oftenly used to describe the performance of a system. Figure of merit for SSB modulation is ALWAYS 1.

Right answer is (d) Both higher bandwidth than SSB and less power REQUIRED as COMPARED to DSB-SC

To explain I would say: Vestigial SIDE BAND is similar to single sideband (SSB) transmission, in which the second sideband is not completely removed, but is filtered to remove the range of frequencies that are not required. It has higher bandwidth than SSB-SC and less power consumption than DSB-SC.

Right choice is (a) Poor SELECTIVITY

The explanation is: Selectivity is USED to SEPARATE out closely lying COMPONENTS in TERMS of frequency. If the receiver has poor selectivity then it also has a poor capacity of blocking adjacent channel interference.

Right ANSWER is (c) m > 1

To elaborate: When the modulation index m is GREATER than 1 i.e. m > 1 it is called OVERMODULATION. It generates modulation with DISTORTIONS and overlapping in the envelope of the modulated signal which makes it difficult to recover the information.

Right option is (d) Both detection of MODULATING signal and REMOVAL of UNWANTED signal

To explain I would say: TRF receivers are used for detection of modulating signal and removal of unwanted signal. The receiver RECEIVE the modulated signal and detect the information signal from received modulating signal.

The correct answer is (a) 33.33%

The best I can explain: The PERCENTAGE of total power CONTRIBUTED by sidebands of the AM SIGNAL is known as transmission efficiency of an amplitude modulated system. The maximum transmission efficiency of an AM signal is 33.33%, thus SUPPRESSING the carrier which contains no USEFUL information.

Right answer is (B) 108W

For explanation: The total power for DSB is PC (^m^2⁄2) = 600X(^0.6^2⁄2) = 108W.

The total power for DSB-SC = PC (^u^2⁄2). (where Pc = Power of Carrier, u = Modulation INDEX)= 600 X ((0.6)^2/2) = 108W.

Correct option is (a) True

The best I can EXPLAIN: Due to ANALOG to digital CONVERSION, data rate becomes high in digital COMMUNICATION which increases the bandwidth in digital communication. Thus, REQUIREMENT of bandwidth is more in digital communication than in analog communication.

Right option is (a) PHASE discrimination METHOD and Frequency discrimination method

The explanation: SSB-SC SIGNALS are the signals where only ONE of the side band is transmitted in an AM wave. SSB-SC signal is generated by two METHODS, frequency discriminator method or filter method and phase discriminator method or phase shift method.

Correct answer is (a) GAIN of the receiver is adjusted

To explain I would say: Automatic Gain Control provides controlled signal amplitude at the output EVEN if there are amplitude VARIATIONS at the INPUT. This controlled output ADJUSTS the input to output gain to a suitable value.

Correct choice is (c) AM

To EXPLAIN I would say: ANALOG COMMUNICATION is a type in which the message to be transmitted is analog in nature. Here the message signal modulates a high FREQUENCY CARRIER signal. In AM, amplitude of the carrier is varied with respect to the instantaneous amplitude of the wave which is to be propagated. It is also an example of continuous wave analog modulation.

Correct answer is (C) Sampling

Explanation: Conversion of an analog signal into DIGITAL signal converts a continuous TIME signal in the FORM of digits, by discretizing it. Thus, the conversion is done with the help of sampling technique.

Correct option is (d) Electromagnetic WAVES

To explain: Radio COMMUNICATION or WIRELESS communication takes place through electromagnetic waves. The message is TRANSMITTED through OPEN space via electromagnetic waves or radio waves.

The correct CHOICE is (c) INCLUDES the CARRIER frequency in AM spectrum

The best explanation: Upper Side Band is the band of FREQUENCIES above the carrier frequency that lies in AM spectrum. It is a part of the shifted spectrum obtained after amplitude MODULATION.

Right CHOICE is (a) Square LAW demodulator and Envelope DETECTOR

The best I can explain: AM signals are detected or demodulated using Square law demodulator and Envelope detector. The demodulator extracts the information from the RECEIVED AM signal.

Correct answer is (d) Synchronous Detection

The best I can explain: Vestigial side BAND SIGNALS are detected by Synchronous detection or coherent detection TECHNIQUE. The distortion in a VSB signal may be reduced by REDUCING the MODULATION index and increasing the width of VSB.

Right answer is (c) Amplitude of the modulating signal

Easy explanation: The amount of FREQUENCY deviation in the FM signal depends on amplitude of the modulating signal. So for any audio signal, as the loudness increases frequency deviation in CARRIER signal ALSO increases. Frequency deviation helps in determining the bandwidth of FM signal.

Correct choice is (a) Multiplication of incoming signal and the locally generated CARRIER

The best I can explain: The function of a frequency mixer in a SUPER heterodyne RECEIVER is that it MIXES or multiplies the incoming modulated signal with the locally generated carrier in order to bring the incoming RF signal to a band of FREQUENCIES which can be processed easily.