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The correct ANSWER is (d) 36000km

The explanation is: Satellite BROADCASTING takes place between directional parabolic antennae, where the signal is sent via cable to antennae which beams it to the satellite and then the satellite sends BACK a signal to ANOTHER location on Earth. A communication satellite amplifies radio telecommunications signals with the help of a transponder. The distance between it and earth’s SURFACE is approximately 36000km.

Correct answer is (c) ULTRA High Frequency

Explanation: Ultra High Frequency (UHF) are frequencies at ultra high LEVELS, THUS consisting of radio frequencies in the range of 300 MHz and 3 GHz. Rest of the options don’t have any EXISTENCE.

The correct option is (c) 30 to 300 Megahertz

Explanation: The VHF (Very HIGH Frequency) are frequencies in the range of 30 MHz to 300 MHz. Frequencies in the range 30 to 300 Kilohertz BELONG to LF (Low Frequency) range, WHEREAS frequencies in the range 300 to 3000 Kilohertz belong to MF (MEDIUM Frequency) range. Frequencies in the range 3 to 30 Megahertz belong to HF (High Frequency) range.

Correct choice is (c) transit-time noise

To explain: Transit-time noise is alike to shot noise, and RESULTS if the time taken by ELECTRONS to reach from emitter to collector is comparable to the period of signals being amplified. Thus, transit-time noise occurs at HIGH frequencies, whereas FLICKER noise occurs below a few kilohertz and Johnson noise, also known as THERMAL noise, occurs at all frequencies.

The CORRECT option is (a) very high frequency

The BEST explanation: The VHF (Very High Frequency) are frequencies in the range of 30 MHz to 300 MHz. Rest OPTIONS don’t have any existence.

Correct choice is (c) AM

To elaborate: Only AM (AMPLITUDE Modulation) is Analog CONTINUOUS Modulation technique while rest are DIGITAL Modulation techniques. In AM, the amplitude of a carrier WAVE is varied with respect to the instantaneous amplitude of the MESSAGE signal. This is how amplitude modulation takes place.

Right choice is (d) INTERNATIONAL TELECOMMUNICATION Union

Explanation: The International Telecommunication Union (ITU) is an United Nations agency serving to correlate all operations REGARDING telecommunication and provide SERVICES all over the world. Rest options are all invalid.

Right answer is (b) poor efficiency

The best I can explain: In low-level modulation, the generated amplitude modulated signal UTILIZES less POWER, followed by the AM signal being amplified by a chain of linear amplifiers. However, in high power applications, the amplifiers that FOLLOW the modulator stage will be linear amplifiers which will render the whole modulation as INEFFICIENT.

The CORRECT choice is (b) an ac resistance

Explanation: Radiation resistance is that PART of an antenna that is caused by the radiation of electromagnetic waves from the antenna. It is considered to be an equivalent resistance DISSIPATING the same amount of power as an ACTUAL antenna would have radiated. Radiation resistance of an antenna is usually an ac resistance.

Right ANSWER is (a) MAGNITUDE spectrum

Easy explanation: White noise is a random signal having equal intensities of different frequencies. IMPULSE noise is a type of noise CONSISTING of sudden sounds, which includes unwanted and instantaneous signals. THUS, they have only their magnitude in common.

The correct option is (a) it radiates its power uniformly in all directions

The BEST EXPLANATION: An isotropic antenna is considered to be an ideal antenna that radiates power uniformly in all directions. GENERALLY, this TYPE of antenna does not exist. HOWEVER, it is often used to determine certain antenna characteristics like antenna gain.

The correct CHOICE is (a) Single Sideband Modulation

Best explanation: In SSBSC, the carrier is suppressed and only either of the two SIDEBANDS is TRANSMITTED. This reduces the power consumption and ALSO lessens the bandwidth. While in DSBSC, the carrier is suppressed but both the sidebands are transmitted, whereas in AM, the carrier as WELL as both the sidebands are transmitted.

Correct choice is (b) very large carrier power

To elaborate: In Communication Systems, a transmitter produces radio WAVES, which are the modulated message signals, and are transmitted VIA the antennae. These message signals carry INFORMATION which are modulated using a carrier wave, having frequency higher than the message signal frequency. Thus, for TRANSMITTING information to a large distance, it is necessary that a very large carrier wave is USED for modulation.

Correct answer is (c) will INCREASE, if the modulating voltage amplitude remains CONSTANT

The explanation is: In frequency modulation, the modulation index is the ratio of frequency deviation to modulating frequency. Therefore, modulation index can be made INVERSELY PROPORTIONAL to the modulating frequency by keeping amplitude constant. THUS, if we decrease modulating frequency then the modulation index will increase, with amplitude remaining constant.

Right choice is (B) twisted NEMATIC crystals

Explanation: LCD uses liquid crystal display. It uses twisted nematic crystals which are a TYPE of liquid crystal, consisting of a substance called the nematic. The nematic liquid crystal is placed between TWO plates of polarized glass.

Correct CHOICE is (c) VSB

Easiest explanation: Vestigial Sideband Modulation (VSB) is a TYPE of amplitude modulation in which the CARRIER and only one sideband is completely transmitted and the other sideband is PARTLY transmitted. THUS, video signals are transmitted using VSB modulation.

The correct choice is (d) PAM

The best I can explain: Pulse Code MODULATION DEALS with CONVERTING an analog signal to a digital signal. During it’s demodulation, the wave to be TREATED is to be parallel. The series pulse wave signal is then converted into a parallel digital signal using a SERIAL to parallel converter, after which it is further converted into the original analog signal with the help of a decoder or detector.

Correct option is (a) True

The explanation: A duplexer is being an ELECTRONIC UNIT, allows bi-directional COMMUNICATION over the same path. The TRANSMITTER and receiver can communicate SIMULTANEOUSLY. In radar, the duplexer isolates the receiver from the transmitter while allowing them to share a common antenna.

The correct CHOICE is (a) True

To EXPLAIN I would say: A point-to-point communication refers to bidirectional communication between only ONE transmitter and one receiver.In SSB-SC modulation technique, the carrier is suppressed and only one of the two side-bands are transmitted. Thus, it REDUCES power consumption and LESSENS bandwidth. Thus, it is preferred for point-to-point communication.

The CORRECT option is (b) False

Easy EXPLANATION: In an AM transmitter, the required transmission power is obtained from CLASS C amplifier, as it is a power amplifier, for low-level or high-level MODULATION. So it is not used after the modulation STAGE.

The correct answer is (a) low level amplitude MODULATED SYSTEM

Easiest EXPLANATION: In low-level modulation, the generation of amplitude modulated signal takes place at low power levels. The generated AM signal is then amplified USING a chain of linear AMPLIFIERS, which are required to avoid waveform distortion. Thus, linear amplified modulated stage is used in low level amplitude modulated system.

The CORRECT choice is (d) SINUSOIDAL

For explanation I WOULD SAY: Narrow band filter is used to isolate a narrow band of frequencies from a wider bandwidth signal. It is a combination of band pass and band reject filter. When noise gets passed through it, the output of it should be sinusoidal.

Right choice is (a) True

For explanation: A phased array radar is an array of radiating elements, with each having a phase-shifter. The phase of the signal being emitted from the radiating element is CHANGED to produce beams, thereby producing CONSTRUCTIVE or destructive interference for steering the beams in the required direction. Thus, it can TRACK MANY targets together.

Correct choice is (d) AM and FM both

To explain: Narrow band filter is used to ISOLATE a narrow band of frequencies from a WIDER bandwidth signal. It is a COMBINATION of band pass and band reject filter. So it can be used in both AM and FM to pass a band of frequencies or to attenuate a band of frequencies.

Correct option is (a) 35KHz and 25KHz

Explanation: UPPER sideband FREQUENCY will be (30 + 5) = 35 KHZ and Lower sideband frequency will be (30 – 5) = 25 KHz.

The correct option is (a) Synchronization is required between receiver and transmitter

The explanation: Pulse Position Modulation (PPM) is a type of modulation process in whichposition of the pulse of the carrier wave is varied with RESPECT to the instantaneous position values of the message SIGNAL. In PPM, there is minimum noise INTERFERENCE but the MAIN disadvantage of the PPM modulation technique is that synchronization between transmitter and receiver must be needed.

Right ANSWER is (c) 100 Hz

To EXPLAIN I WOULD say: On comparing with general Equation, Acosωt and substituting ω = 2×π× f. We have F1 = 25 Hz, f2 = 37.5Hz, F3 = 100π/2π= 50Hz.

Taking the maximum modulating frequency, fmax = 50Hz

Nyquist rate = 2 × fmax= 2 × 50 = 100 Hz.

The correct option is (a) Bandwidth of FM signal

To explain I would say: Carson’s rule states that only (β+1) (where β = modulation index) upper and lower SIDEBANDS along with the carrier, have significant MAGNITUDE and contain 99% of total power. Thus, as per Carson’s rule, required bandwidth is EQUAL to the twice of sum of the maximum frequency deviation (fd) and the maximum modulating frequency(fm), B = 2(fd + fm)Hz.

Right answer is (a) For boosting of modulating signal voltage

Explanation: Pre-emphasis is vastly applied in communication SYSTEMS to improve signal strength before TRANSMISSION. It refers to boosting the amplitudes of the weak modulating voltages for HIGH audio frequencies in the RANGE of 2 to 15KHz.

Right choice is (c) BANDWIDTH

Easiest explanation: Bandwidth is the MAXIMUM amount of DATA transmitted over a PARTICULAR period of time. It is also DEFINED as the difference of high frequency and low frequency, of a given band.

Correct answer is (a) 130 KHz

Easy explanation: ACCORDING to Carson s rule, B = 2(fd +FM) = 2 (50 + 15) = 130 KHz.

The correct ANSWER is (d) 62.5W

To explain: In angle modulation, the amplitude of carrier remains CONSTANT and thus power depends on amplitude only. On Comparing with the EQUATION, m(t) = ACOS(ωct + mf sinωmt). We have A = 50, dissipated power,

Right option is (a) same ENERGY density spectrum

Best explanation: PROPERTIES of Hilbert TRANSFORM states that the signal and its Hilbert transform :

i) have same energy density spectrum

ii) are MUTUALLY orthogonal

iii) have same auto correlation function

iv) have same magnitude

v) have a PHASE difference of “-90” degree.

Correct answer is (b) class B

To explain: A push pull AMPLIFIER is an amplifier WHOSE output is a CUMULATIVE sum of the outputs of the currents produced by the TWO different stages of the load. It is generally used when a large amount of POWER is to be consumed. Of all the power amplifiers, only Class B amplifier is capable to produce such large amount of power.

The correct option is (b) blocking of unwanted signals

The explanation: Selectivity is the ability of a radio receiver to reject unwanted signals and ALLOW only the desired SIGNAL to pass. THUS, it’s the blocking of unwanted signals. Sensitivity is the ability of a receiver to amplify weak signals to the desired level, WHEREAS reception means to RECEIVE a signal.

The correct answer is (b) False

The BEST I can EXPLAIN: In communication system, Signal-To-NOISE ratio (SNR) is a measure of the amount of signal PRESENT compared to the surrounding noise. It is the ratio of signal power to noise power. Thus in frequency modulation, there is a large decrease in noise and hence increase in the signal to noise ratio.

The correct ANSWER is (B) False

The best explanation: A vidicon camera tube is a type of camera having a photoconductive surface within. In a Vidicon camera tube, the SIDE of target plate facing the light has a coating of Sno2 and the side facing electron GUN has a coating of ANTIMONY trisulphide.

Correct CHOICE is (d) 6V DC

For explanation I would say: A battery eliminator is an electronic device which is powered by an external source (EXCEPT battery) such that it converts the source to a particular DC voltage which can be used as POWER supply for other devices. Its output is approximately 6V.

The correct answer is (d) 1.3 MHZ

To elaborate: A carrier wave is a signal with a high FREQUENCY which is modulated for transmitting the INFORMATION signal. A subcarrier is a sideband of the carrier wave, which is also modulated to SEND additional information. In INDIA, the subcarrier frequency for transmission of color DIFFERENCE signals in television is approximately 1.3MHz.

Correct OPTION is (a) True

The explanation: The ADVANTAGE of using mechanical filter in filter SYSTEM of sideband suppression is SMALLER SIZE, good band pass, good attenuation characteristics.

Correct answer is (a) coherent detection of AM-SC signal

Explanation: A Costa’s loop is BASED on phase-locked loop (PLL). The circuit RECOVERS carrier frequency from the suppressed-carrier MODULATED signals like DSBSC and SSBSC and phase modulated signals like FSK and BFSK. It is GENERALLY used for coherent detection of AM-SC signal in receivers.

Right OPTION is (d) satellite tracking

To explain I would say: A HELICAL antenna is made of one or more conducting wires wound in the FORM of a helix. It is used for the COMMUNICATION (transmitting and receiving) Very High Frequency (VHF) SIGNALS through the different layers of atmosphere. Thus, it is used in satellite tracking.

The CORRECT choice is (C) 10 KHz

The best EXPLANATION: Sampling FREQUENCY is the number of samples per second which helps in extracting a discrete-time signal from a continuous-time signal. For a CD, it is about 10 KHz.

Correct option is (c) fs + 2fi

For explanation: In the superheterodyne receiver, during the frequency conversion process, the local oscillator and the mixer OFTEN allow an undesired frequency SIGNAL, in ADDITION to the incoming frequency signal. This results in the production of IMAGE frequency which is equal to the sum of signal frequency and DOUBLE intermediate frequency.

Right choice is (b) False

For explanation: In communication, Signal-To-Noise ratio (SNR) is DEFINED as MEASURE of the amount of signal present compared to the SURROUNDING noise. It is the ratio of signal power to noise power. Thus, in FREQUENCY MODULATION, if there is a large decrease in noise, then there will be increase in the signal to noise ratio.