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Correct OPTION is (a) Frequency Modulation

Easy 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.

Correct choice is (a) A method in which one of the properties of a CARRIER signal varies in PROPORTION to an instantaneous value of modulation signal

The best 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.

Correct choice is (b) ^ʎ⁄4

The BEST explanation: For effective transmission, HEIGHT of antenna should be one-forth of ʎ.

(H = ^ʎ⁄4 where ʎ = ^c⁄f). The reason for maintaining antenna height to ʎ/4 is for matching IMPEDANCE. It means that the antenna is atleast 1/4^th above ground LEVEL.

The correct choice is (b) Recovering INFORMATION from a modulated signal

Easy 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.

The correct CHOICE is (a) The system is linear

Best 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.

The correct OPTION is (d) CHANNEL

The 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.

Right answer is (C) Cross Modulation

The best 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.

Right option is (B) electrical signal

Easiest 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.

The correct CHOICE is (d) radio waves

To elaborate: 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.

Right CHOICE is (a) Selectivity

The 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.

Correct choice is (d) VARACTER diode

The BEST I can explain: 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.

Right answer is (d) Transmitter

The explanation is: 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.

Right choice is (b) VSB

For explanation: 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.

The CORRECT choice is (c) used for amplitude modulation

Best explanation: 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.

Right choice is (a) used for DSB-SC generation

To explain: 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.

The CORRECT choice is (d) to produce radio waves to transmit data

For explanation I would say: 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.

Right choice is (b) 33.33%

To EXPLAIN I WOULD say: 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.

Correct option is (c) Automatic Volume Control

For EXPLANATION: 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.

The correct answer is (d) DEMODULATE a signal

Explanation: 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.

Correct option is (b) Receiver

For explanation I would say: Demodulation refers to extracting the ORIGINAL message signal from a transmitted modulated wave. The extraction of the message signal is generally carried out in the receiver. Channel is the medium through which the modulated message signal is transferred and ANTENNA receives the transmitted signal. Transducer CONVERTS the electrical signal to SOUND waves and vice-versa.

Right option is (a) Equally AMPLIFIES all the signal frequencies at receiver

The EXPLANATION: Fidelity is the ability of the receiver to reproduce all modulating signals, equally, without any distortion. The ability of receiver to select wanted signal from various INCOMING signals is called Selectivity while Sensitivity is the minimum magnitude of input signal required to produce a specified output. It is the ability to AMPLIFY weak signals.

Correct ANSWER is (b) Hartley

Easiest EXPLANATION: Oscillator which is USED as a local oscillator in radio RECEIVER is generally a tuned circuit. This tuned circuit consists of inductors and capacitors to DETERMINE the resonant frequency, therefore it is an LC tuned circuit. Out of the four options, only Hartley Oscillator has an LC resonant tank circuit.

Right answer is (C) Demodulation

To explain I would say: Demodulation means extracting information or message signal from the transmitted modulated wave, while minimum magnitude of input signal required to produced a specified output is known as SENSITIVITY. The ability of RECEIVER to select wanted signal from various INCOMING SIGNALS is called Selectivity. Fidelity means reproducing all modulating frequencies equally, without any distortion.

Correct CHOICE is (a) to detect and amplify information signal from the CARRIER

The explanation: Receiver is to detect and amplify information signal from the carrier. Transmitter is used to modulate message signal and produce radio waves. TRANSDUCER is used to convert one signal form of energy into another form.

Correct answer is (d) TUNING

The 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.

Right answer is (a) Ratio of OUTPUT SIGNAL to noise ratio to INPUT signal to noise ratio

To explain: Figure of merit is a numerical QUANTITY based on the characteristic of SYSTEM that represents a measure of efficiency or effectiveness. It is defined as the ratio of output signal to noise ratio to input signal to noise ratio.

Right choice is (b) IF stage

To explain: A superheterodyne RECEIVER uses frequency mixing to CONVERT the received HIGH frequency signal to a fixed lower intermediate frequency (IF), which can be processed more conveniently than original received frequency. Thus, the PRINCIPLE of selectivity is applied at the IF stage as it consists of very efficient filters to only select a wanted signal and pass it to the DEMODULATING Stage.

The correct choice is (a) Mixer

Easiest explanation: A mixer is a nonlinear electrical circuit that multiplies two signal frequencies applied to it, and produces a new frequency. Mixers are widely used to shift signals from one frequency RANGE to other, which is known as heterodyning PROCESS. Generally, LOCAL Oscillator generates a frequency to be applied at one of the input TERMINALS of the mixer. Demodulator decodes the MESSAGE signal from modulated signal, while modulator encodes message signal for transmission.

Right ANSWER is (c) Band stop filter

To explain I WOULD say: NOTCH filter is a band stop filter that allows most frequencies to pass through it, except frequencies in a specific range. It is just OPPOSITE of a band-pass filter. High pass filter allows higher frequencies to pass while Low pass filter allows lower frequencies to pass through it.

Right option is (b) Periodic Signal

For explanation I WOULD say: Periodic signal is that which repeats itself after a regular interval. Sin wave is a periodic FUNCTION since it’s VALUE can be determined at any point of time, as it repeats itself at a regular interval. Aperiodic Signal does not repeat itself at regular interval of time. Random signals are the signals which have UNCERTAIN values at any time. While Deterministic signals are the signals which are constant over a period of time.

The correct option is (b) False

For explanation I would say: Periodic signal is a signal which repeats itself after a REGULAR interval. While Aperiodic Signal does not REPEAT itself at regular interval of time.

For example: Let F(X) = sin(x), be a periodic function with period 2π and g(x) = −sin(x) + sin(√2x), be an aperiodic function. Now the sum of both i.e. f(x) + g(x) = sin(√2x), which is a periodic function.

Therefore, the sum of a periodic and aperiodic signal can be periodic.

Right choice is (a) acts as a medium to SEND message SIGNALS from transmitter to receiver

The explanation is: CHANNEL acts as a medium to transmit message signal from source transmitter to the destination receiver. Transducer CONVERTS a signal from one form of energy to other. Mixer allows mixing of signals while Demodulator helps to extract original message signal from INCOMING signal.

Correct answer is (a) In the channel

For explanation: Noise is an unwanted signal that gets mixed with the TRANSMITTED signal while passing through the channel. The noise interferes with the signal and PROVIDES distortion in received signal. The transmitting antenna transmits modulated message signal while the RECEIVING antenna receives the transmitted signal. REGENERATION of information refers to DEMODULATING the received signal to produce the original message signal.

The correct answer is (C) PROTOCOL

For explanation I would say: Protocol is a set of rules that looks after data COMMUNICATION, by acting as an agreement between communication devices. Channel is the transmission medium or the path through which information TRAVELS. MODEM is a device that modulates and demodulates data.

Correct OPTION is (a) HIGH selectivity and sensitivity

To explain I would SAY: The main advantage of superheterodyning is that it provides high selectivity and sensitivity. It’s BANDWIDTH remains same. It has high ADJACENT channel rejection and high fidelity.

Correct CHOICE is (a) Flicker noise

To explain: Flicker noise is a type of ELECTRONIC noise which is generated due to fluctuations in the density of CARRIER. It’s ALSO known as 1/f as it’s power spectral density increases with a decrease in FREQUENCY or increase in offset from a signal.

The correct answer is (b) f(X) = f(-x)

For explanation I WOULD say: Geometrically a function f(x) is EVEN, if plot of the function is symmetric over y-axis. ALGEBRAICALLY, for any function f(x) to be even, f(x) = f(-x).

While for a function f(x) to be ODD, f(x) = -f(-x).

Correct ANSWER is (c) Frequency-domain plot

Explanation: RELATIONSHIP between AMPLITUDE and frequency is represented by a frequency-domain plot. Also, it REPRESENTS the relation between PHASE and frequency. While a time-domain plot shows how a signal varies over time.