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Correct answer is (d) to PRODUCE 100% MODULATION

Explanation: For achieving 100% modulation, balanced modulator is mainly USED in CIRCUITS.

Right answer is (b) False

Best EXPLANATION: Varacter diode modulator is not an indirect WAY of GENERATING FM. It is a Armstrong modulator which is an indirect way of generating FM.

The CORRECT answer is (d) By ARMSTRONG modulator

Explanation: Armstrong modulator which is the only way for indirect generating of FREQUENCY modulation.

The correct answer is (B) False

The explanation is: Convex lens has POSITIVE focal power and CONCAVE lens have NEGATIVE focal power.

Correct choice is (b) False

For explanation: CONVEX LENS has NEGATIVE focal POWER and CONCAVE lens have positive focal power.

Correct choice is (a) True

Easiest explanation: In angle modulation, PHASE or frequency of the carrier wave is varied with respect to the instantaneous AMPLITUDE of the message SIGNAL. The general expression for FM and PM are as follows:

FM (t) = Ac sin (2πfct + βsin(2πfmt)),

PM (t) = Ac sin (2πfct + βcos(2πfmt)), where symbols have their usual meaning.

Correct answer is (b) PWM

The explanation: Frequency transmitting and RECEIVING equipment are generally costly when compared to amplitude MODULATED equipment, as the power required in FM TRANSMISSION is LESS and bandwidth is high. Also, the noise interference is also less in case of FM.

Right choice is (b) False

Explanation: Pulse density MODULATION (PDM) is used to REPRESENT an ANALOG signal using a DIGITAL signal. For generating PDM, a monostable multi-vibrator is used, which is externally triggered and has only ONE stable state.

Right option is (b) False

Explanation: FSK (Frequency SHIFT Keying) is a method used to transmit binary data in form of digital SIGNALS. It is MAINLY used for telegraphy. In telegraphy, a modem is used to convert binary data to FSK and vice-versa, for the communication between computers and over TELEPHONE LINES.

Right option is (a) Monostable multi-vibrator

For explanation: PULSE DENSITY MODULATION (PDM) is used to represent an analog signal USING a digital signal. For generating PDM, a monostable multi-vibrator is used, which is externally triggered and has only one STABLE state.

Right answer is (B) False

Easiest explanation: If the modulating frequency in FM lowered and the modulating voltage remains CONSTANT then the AMPLITUDE of DISTANT SIDEBANDS increases, as the modulating frequency has no role to play in determining the amplitude of the sidebands.

Right option is (a) True

To elaborate: A skip distance is a distance between the point, where the radio waves from a TRANSMITTER are transmitted and the point where the waves are received, after having been refracted by different layers of the IONOSPHERE. It basically depends on time of DAY as well as on ANGLE of INCIDENCE.

Correct choice is (b) False

Explanation: LEAK bias is a type of bias in which the input signal draws GRID CURRENT from a circuit made of resistors and capacitors. Thus, Leak bias is mainly used to PREVENT excessive grid current in plate modulated amplifiers.

Correct OPTION is (b) False

The best explanation: PULSE density modulation (PDM) is used to represent an analog signal USING a digital signal. For generating PDM, MONOSTABLE multi-vibrator is used, which is externally triggered and has only one stable state.

Correct CHOICE is (b) False

Best EXPLANATION: If the modulating frequency in FM lowered and the modulating voltage remains constant then the amplitude of DISTANT sidebands increases, as the modulating frequency has no ROLE to play in DETERMINING the amplitude of the sidebands.

The correct option is (b) False

Explanation: A skip distance is a distance between the point, where the radio WAVES from a transmitter are transmitted and the point where the waves are received, after having been REFRACTED by different LAYERS of the ionosphere. It BASICALLY depends on time of day as WELL as on angle of incidence.

The CORRECT option is (b) False

To EXPLAIN I would say: Full duplex OPERATIONS allow simultaneous communication between two POINTS whereas HALF Duplex operation allows transmission between two points one at a time.

The correct option is (a) ʎ

To EXPLAIN I would say: For GETTING ZERO radiation at right angles, length of antenna should be EQUAL to the whole WAVELENGTH.

The correct CHOICE is (B) low pass filter

To explain I would say: A woofer is connected from the input through a low pass filter to restrict the HIGH FREQUENCIES and only allows the low frequencies to pass through it.

Correct choice is (B) False

To EXPLAIN I WOULD say: If the length of antenna is equal to WHOLE wavelength only the radiations which is at right angles is zero.

Right option is (d) shunt capacitance

Explanation: Shunt capacitance is used to improve the power factor in the network. It ALSO improves voltage stability. It SERVES as a low pass filter and THUS is used in the communication system for attenuating HIGH frequencies.

Right choice is (B) 75 KHz

Easiest explanation: FREQUENCY DEVIATION is the difference between the maximum instantaneous modulated frequency and carrier frequency. Frequencies lying NEARLY about 75KHZ is considered as commercial frequency deviation for frequency modulation.

Correct option is (c) by CHANGING the orientation of antenna

Explanation: CHANGE in antenna orientation helps in IMPROVING the reception of signals which further REMOVES ghosts in the picture.

The correct choice is (b) False

Explanation: PCM stands for PULSE code modulation. In PCM, the amplitude of the analog signal is discritised and converted into DIGITAL form for transmission of binary data. PCM USUALLY requires a large BANDWIDTH.

Right choice is (a) 1

Easy explanation: The possible MAXIMUM VALUE of MODULATION can be one. It signifies 100% modulation and THUS at this value we have maximum undistorted transmitted power.

The correct answer is (b) False

For explanation I WOULD SAY: It is generally observed that a ship to ship COMMUNICATION suffers from fading. This problem can be avoided by using frequency diversity in which the components of a radio wave are received from different channels thus reducing the ERROR that occurs in the transmission of a single frequency COMPONENT.

Correct OPTION is (a) 150 KHZ

Explanation: BANDWIDTH is the band of frequencies present within a given RANGE of frequency. The standard commercial channel bandwidth for frequency modulated system is about 150 KHz.

Correct CHOICE is (c) high gain DC amplifier

To ELABORATE: Gain of an amplifier is its ability to increase the voltage at the input and PRODUCE the result at the OUTPUT. A buffer amplifier is basically a high gain DC amplifier. It is basically used for transferring voltage from a high output impedance level to a low input impedance level circuit.

Right OPTION is (b) False

To ELABORATE: CD stands for COMPACT disk. The direction of rotation of Compact Disk is anticlockwise.

The CORRECT answer is (c) more than that of dipole

Easy explanation: A dipole antenna is the one having its CONDUCTIVE wire rod equal to HALF the MAXIMUM wavelength of an antenna. The LENGTH of receiving antenna in a TV receiver must be more than that of dipole to get a better reception of signals.

The correct answer is (c) PULSE Amplitude MODULATION

Explanation: In COMMUNICATION, PAM stands for Pulse Amplitude Modulation. In PAM, the amplitude of the individual pulses of the message SIGNAL are varied in a specific TIME interval.

The correct option is (a) Stepped INDEX OPERATION

Best explanation: In Stepped index operation, refractive index within the core is UNIFORM. There is also a sharp DECREASE in refractive index at the core-cladding interface. It generally does not CAUSE any type os losses in optical fibre cables.

Right choice is (b) frequency diversity

Best explanation: It is generally observed that a SHIP to ship COMMUNICATION suffers from fading. This PROBLEM can be avoided by using frequency diversity in which the components of a radio wave are received from DIFFERENT channels thus reducing the error that occurs in the transmission of a single frequency component.

The CORRECT OPTION is (d) 300 ohm

Best explanation: Twin wire FEEDER consists of two WIRES with spacers.For a twin wire feeder the characteristic IMPEDANCE should be close to 300 ohm.

The correct OPTION is (a) horizontal blanking

To explain: The duration of an equalizing pulse is approximately 2.5 microseconds. The REPETITION frequency of equalizing pulses is TWICE the line frequency. It is NECESSARY to sent equalizing pulses during horizontal blanking in televisions.

The correct choice is (B) False

For explanation I would say: GAIN of an amplifier is it’s ability to increase the voltage at the input and produce the result at the output. A buffer amplifier is BASICALLY a HIGH gain DC amplifier. It is basically used for transferring voltage from a high output impedance level to a low input impedance level circuit.

Right option is (b) False

The best I can explain: A square wave is a periodic non-sinusoidal waveform with an uniform frequency, in which the amplitude alternates between a FIXED maximum and minimum value. According to Fourier analysis, a square wave can be REPRESENTED as an infinite SUM of sinusoidal waves. A square wave consists of only components of odd INTEGER harmonics.

The correct CHOICE is (a) anticlockwise

Best explanation: CD STANDS for COMPACT disk. The direction of rotation of Compact Disk is anticlockwise.

Right ANSWER is (a) FM

For explanation: IMPULSE noise includes unwanted, almost instantaneous SHARP SOUNDS. It is only in frequency modulated circuits that allow REDUCTION in impulse noise.

The correct option is (a) for getting higher SPEED of communication

Easy EXPLANATION: Sampling is the conversion of continuous-time signal to discrete-time signal. It SAMPLES a continuous time signal depending on a specific range and thus produces the discrete form of the signal. It is highly USED in communication for getting higher speed of communication.

The correct OPTION is (b) False

Easiest explanation: SSB can be produced by filter method ALSO KNOWN as FREQUENCY discrimination method. It can also be produced by PHASE discrimination method.

The correct answer is (c) Slope overload and granular noise

The best I can explain: Delta modulation is used for transmission of VOICE INFORMATION where quality is not the primarily importance. Its drawback is it has TWO noises namely slope overload and granular noise. Slope overload noise occurs when the input SIGNAL slope is higher than the delta MODULATOR’s capability. Granular noise is produced due to level input signal resulting into the oscillatory output. So for getting rid of these noises we use ADM (Adaptive Delta Modulation).

Correct answer is (b) FM signals only

Easiest EXPLANATION: Varacter diode or tuning diode that has a VARIABLE capacitance. It is OPERATED as reverse-biased and therefore no current flows. It is mainly USED for generation of FM signals only.

The correct answer is (d) WAVES will get distorted

Explanation: Modulation index tells us the amount by which the CARRIER WAVE is varied with respect to the message SIGNAL. If modulation index is greater than 1, then the wave gets distorted and overlap, thus CAUSING overmodulation.

Right answer is (d) channel

Explanation: Noise is the unwanted SIGNAL present in the PASSBAND of a signal. It is very much unpleasant thus CAUSING disturbance. Its adverse effect is highly SEEN on channel.

The correct CHOICE is (b) low bandwidth is required

Easiest EXPLANATION: ADVANTAGES of FM over AM are LESS prone to noise, low modulating power required and such like. HOWEVER, disadvantage of FM is that large bandwidth is required.