Explore topic-wise InterviewSolutions in .

This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.

1.

Distance between direct broadcasting satellite and earth’s surface is ________(a) 4500km(b) 33000km(c) 5200km(d) 36000kmI got this question in a national level competition.Origin of the question is Time Domain Description in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

2.

UHF stands for ________(a) Ultra High Electric Field(b) Ultraviolet High Frequency(c) Ultra High Frequency(d) Ultra High Magnetic FieldI had been asked this question in my homework.This is a very interesting question from Time Domain Description topic in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

3.

What is the ITU designation range for VHF?(a) 30 to 300 Kilohertz(b) 300 to 3000 Kilohertz(c) 30 to 300 Megahertz(d) 3 to 30 MegahertzI got this question in an interview for internship.Question is from Time Domain Description topic in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

4.

Effective noise at high frequencies is ________(a) Johnson noise(b) Flicker noise(c) transit-time noise(d) Partition noiseThe question was posed to me during an interview.I need to ask this question from Time Domain Description topic in section Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

5.

VHF stands for ________(a) very high frequency(b) very high electric field(c) very high magnetic field(d) very high electromagnetic fieldI got this question in an internship interview.I need to ask this question from Time Domain Description topic in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

6.

Which among the following is the Analog Continuous Modulation technique?(a) PAM(b) PCM(c) AM(d) PMI had been asked this question during an interview.Origin of the question is Time Domain Description topic in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

7.

ITU stands for ________(a) Indian Telecommunication Union(b) Indian Telephonic Union(c) International Telephonic Union(d) International Telecommunication UnionThe question was posed to me by my school principal while I was bunking the class.This interesting question is from Time Domain Description in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

8.

If AM transmitter has low level modulation then it has ________(a) high efficiency(b) poor efficiency(c) high modulating power(d) high resistance towards noiseThe question was asked in an online interview.This question is from Time Domain Description in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

9.

Radiation resistance of an antenna is ________(a) a dc resistance(b) an ac resistance(c) a constant value(d) neither ac nor dc resistanceI had been asked this question during an online interview.Question is from Time Domain Description in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

10.

The spectrum of white noise and impulse noise is similar in terms of ________(a) magnitude spectrum(b) phase spectrum(c) both magnitude spectrum and phase spectrum(d) amplitude spectrumI have been asked this question at a job interview.The question is from Frequency Domain Representation in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

11.

What do you understand by isotropic antenna?(a) it radiates its power uniformly in all directions(b) it radiates its power non-uniformly in all directions(c) it radiates its power specifically in one direction only(d) it does not radiate any powerThis question was posed to me in homework.Enquiry is from Time Domain Description topic in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

12.

The amount of power and bandwidth necessary to be transmitted for a given amount of information are reduced in _________(a) Single Sideband Modulation(b) Double Sideband Modulation(c) Vestigial Sideband Modulation(d) Amplitude ModulationThis question was addressed to me by my college professor while I was bunking the class.This interesting question is from Frequency Domain Representation in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

13.

A long wave AM broadcast transmitter needs _________(a) very small carrier power(b) very large carrier power(c) small carrier power(d) large carrier powerI got this question during an internship interview.I'm obligated to ask this question of Frequency Domain Representation topic in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

14.

In FM, if we decreases modulating frequency then the modulation index ________(a) will increase, if the modulating voltage amplitude increases(b) will decrease, if the modulating voltage amplitude increases(c) will increase, if the modulating voltage amplitude remains constant(d) will decrease, if the modulating voltage amplitude remains constantThis question was addressed to me during an interview.Question is taken from Frequency Domain Representation in section Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

15.

LCD uses ________(a) sematic crystals(b) twisted nematic crystals(c) nematic crystals(d) cholesteric crystalsThis question was addressed to me in a national level competition.This is a very interesting question from Generation of DSBSC Waves topic in section Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

16.

Which of the following modulation system is used for video-modulation?(a) DSB-SC(b) SSB-SC(c) VSB(d) FMI got this question in examination.The question is from Frequency Domain Representation topic in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

17.

In SSB modulation, only a single sideband is transmitted leaving the other sideband and the carrier.(a) True(b) FalseThe question was asked in an internship interview.The doubt is from Frequency Domain Representation in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer» CORRECT choice is (a) True

To explain: In SSBSC, the carrier is suppressed and only either of the two sidebands is transmitted. This REDUCES POWER consumption and also lessens the BANDWIDTH.
18.

For demodulation of PCM, it is first converted into __________(a) PDM(b) PWM(c) PPM(d) PAMThe question was asked in unit test.Asked question is from Frequency Domain Representation topic in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

19.

A noise can be represented as superposition of spectral components.(a) True(b) FalseI had been asked this question in examination.The question is from Frequency Domain Representation topic in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer» RIGHT choice is (a) True

Explanation: Noise is any undesirable electrical ENERGY that falls under the passband of the signal. It is a general term for the unwanted signals that GETS added to our original signal. It is usually REPRESENTED as the superposition of spectral components.
20.

Which of the following stage is present in FM receiver but not in AM receiver?(a) Amplitude limiter(b) Demodulator(c) AM amplifier(d) MixerI got this question during an online interview.This intriguing question comes from Generation of DSBSC Waves in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer» CORRECT ANSWER is (a) Amplitude limiter

Explanation: Amplitude Limiter circuit is used in FM receiver to remove the noise or any variation in amplitude PRESENT in the received signal. Thus, the output of the amplitude limiter has a constant amplitude. So it is only used in frequency MODULATION and not in amplitude modulation.
21.

Function of duplexer in a RADAR is to permit the use of same antenna for transmission and reception.(a) True(b) FalseI got this question in an internship interview.My question is taken from Generation of DSBSC Waves topic in section Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

22.

Single Sideband Modulation (SSB) is generally reserved for point-to-point communication.(a) True(b) FalseI got this question in final exam.The doubt is from Generation of DSBSC Waves in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

23.

For an AM transmitter, class C amplifier can be used after the modulation stage.(a) True(b) FalseI have been asked this question in an online quiz.I need to ask this question from Generation of DSBSC Waves in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

24.

For which of the modulated system, the linear amplified modulated stage is used?(a) low level amplitude modulated system(b) high level amplitude modulated system(c) high level frequency modulated system(d) low level frequency modulated systemThis question was posed to me in an interview.My doubt stems from Generation of DSBSC Waves in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

25.

When noise is passed through a narrow band filter, the output of filter should be?(a) triangular(b) square(c) parabolic(d) sinusoidalThe question was asked in an online quiz.This intriguing question comes from Generation of DSBSC Waves in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

26.

Phase array radar can track many targets together.(a) True(b) FalseThis question was addressed to me in an online interview.My enquiry is from Generation of DSBSC Waves topic in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

27.

A narrow band noise can exist in _________(a) AM only(b) PCM only(c) FM only(d) AM and FM bothThe question was posed to me during an interview.Enquiry is from Generation of DSBSC Waves topic in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

28.

The upper and lower sideband frequencies for 5KHz amplitude modulation with a 30KHz carrier frequency will be?(a) 35KHz and 25KHz(b) 34KHz and 24KHz(c) 25KHz and 35KHz(d) 0.35KHz and 0.25KHzI have been asked this question in final exam.The query is from Generation of DSBSC Waves in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

29.

Which among the following is the drawback of Pulse Position Modulation (PPM)?(a) Synchronization is required between receiver and transmitter(b) Synchronization is not required between receiver and transmitter(c) Amplitude is constant(d) Instantaneous power of PPM modulated signals is constantI had been asked this question by my college director while I was bunking the class.This question is from Coherent Detection of DSBSC Waves topic in section Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

30.

Calculate the Nyquist rate for the signal x(t) = 12cos50πt + 7 cos75π t – 13 cos100πt.(a) 300 Hz(b) 600 Hz(c) 100 Hz(d) 150 HzThe question was posed to me during an online interview.This question is from Coherent Detection of DSBSC Waves topic in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

31.

Carson’s rule is used to calculate________(a) Bandwidth of FM signal(b) SNR(c) Modulation index of FM signal(d) Figure of meritThis question was posed to me during an online interview.My doubt is from Coherent Detection of DSBSC Waves topic in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

32.

What is the need of doing Pre emphasis?(a) For boosting of modulating signal voltage(b) For boosting of modulating signal frequency(c) For removing amplitude variations due to noise(d) For removing frequency variationsThe question was posed to me in homework.I would like to ask this question from Coherent Detection of DSBSC Waves topic in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

33.

Consider an AM broadcast station that transmits modulating frequencies up to 10kHz. If it transmits a frequency of 1000 kHz. Find its maximum and minimum upper and lower sidebands frequencies and also the total bandwidth?(a) 900 KHz, 820 KHz, 1000 Hz(b) 720 KHz, 650 KHz, 1020 Hz(c) 1010 KHz, 880 KHz, 15000 Hz(d) 1010 KHz, 990 KHz, 20000 HzI had been asked this question in exam.My enquiry is from Coherent Detection of DSBSC Waves topic in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer» RIGHT CHOICE is (d) 1010 KHz, 990 KHz, 20000 Hz

For explanation: Maximum Frequency, fm = (1000 + 10) KHz = 1010 KHz.

Minimum Frequency, FL = (1000 – 10) KHz = 990 KHz and,

Bandwidth = 2 * Modulating frequency = Maximum Frequency–Minimum Frequency

= (1010 – 990) KHz = 20000 Hz.
34.

Amount of data transmitted for a given time is called _________(a) Noise(b) Frequency(c) Bandwidth(d) PowerI had been asked this question in an interview for internship.Question is from Coherent Detection of DSBSC Waves topic in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

35.

What is the bandwidth of a FM wave when maximum allowed deviation is 50KHz and the modulating signal has a frequency of 15KHz?(a) 130 KHz(b) 260 KHz(c) 65 KHz(d) 50 KHzThe question was asked in final exam.The doubt is from Coherent Detection of DSBSC Waves in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

Correct answer is (a) 130 KHz

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

36.

For signal, m(t) = 50cos(10 × 90t + 30 sin100t), the power dissipated by the 20Ω resistor is ________(a) 100W(b) 65W(c) 74.7W(d) 62.5WThe question was asked in a job interview.I'd like to ask this question from Coherent Detection of DSBSC Waves in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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,

37.

Signal and its Hilbert transform have________(a) same energy density spectrum(b) same power(c) a phase difference of 60°(d) a phase difference of 120°I got this question in an internship interview.The query is from Coherent Detection of DSBSC Waves topic in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

38.

For a large amount of power, a push pull amplifier is designed for operation as ________(a) class C(b) class B(c) class AB(d) class AThe question was asked in unit test.Origin of the question is Hilbert Transform topic in division Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

39.

If a receiver has poor selectivity then it also have poor ________(a) sensitivity(b) blocking of unwanted signals(c) double spotting(d) receptionThis question was posed to me in examination.The query is from Hilbert Transform in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

40.

In frequency modulation, there is a large increase in noise and hence decrease in the signal to noise ratio.(a) True(b) FalseThis question was posed to me in semester exam.This interesting question is from Hilbert Transform topic in section Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

41.

In a Vidicon camera tube, the side of target plate facing the light has a coating of antimony trisulphide and the side facing electron gun has a coating of tin oxide.(a) True(b) FalseThe question was asked in an internship interview.The query is from Hilbert Transform in section Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

42.

Autocorrelation function of which noise is a constant?(a) white noise(b) shot noise(c) transit time noise(d) extraterrestrial noiseThe question was posed to me in an online quiz.This interesting question is from Hilbert Transform topic in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer» RIGHT OPTION is (a) white noise

The explanation is: White noise is a RANDOM signal having equal intensities at different FREQUENCIES. The autocorrelation of white noise signal has a straight vertical LINE at origin and is zero for rest points. Thus the Autocorrelation function of white noise is constant.
43.

The output of a battery eliminator is closed to ________(a) 70V DC(b) 70V AC(c) 6V AC(d) 6V DCThis question was addressed to me in exam.Question is taken from Hilbert Transform in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

44.

In India, the subcarrier frequency for transmission of color difference signals in television is approximately ________(a) 10.47 MHZ(b) 5.4 MHZ(c) 7.67 MHZ(d) 1.3 MHZThis question was posed to me by my college director while I was bunking the class.My question is based upon Hilbert Transform topic in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

45.

The advantage of using mechanical filter in filter system of sideband suppression is good attenuation characteristics.(a) True(b) FalseI got this question in final exam.The above asked question is from Hilbert Transform in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

46.

Costa’s receiver is used for ________(a) coherent detection of AM-SC signal(b) asynchronous detection of AM-SC signal(c) amplification of signal(d) frequency mixing of signalThe question was posed to me in an international level competition.I need to ask this question from Costas Loop in section Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

47.

Helical antenna is mainly used for ________(a) bandwidth calculation(b) production of video signals(c) radio transmission(d) satellite trackingThis question was posed to me in an interview for job.I'm obligated to ask this question of Costas Loop in portion Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

48.

Sampling frequency of a compact disk is about ________(a) 30 KHz(b) 50 KHz(c) 10 KHz(d) 70 KHzI had been asked this question by my college professor while I was bunking the class.This is a very interesting question from Costas Loop topic in section Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

49.

Image frequency is given by ________(a) fs + fi(b) fs ± fi(c) fs + 2fi(d) fs ± 2fiThe question was asked in an interview.My question is from Costas Loop topic in section Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.

50.

In frequency modulation, there is a large increase in noise and hence increase in the signal to noise ratio.(a) True(b) FalseThis question was addressed to me in semester exam.Enquiry is from Costas Loop topic in chapter Double Sideband Suppressed Carrier Modulation of Analog Communications

Answer»

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.