Frequency Modulation Question & AnswersJuly 5, 2021 By WatElectronics This article lists 100+ Frequency Modulation MCQs for engineering students. All the Frequency Modulation Questions & Answers given below include a hint and wherever possible link to the relevant topic. This is helpful for the users who are preparing for their exams, interviews, or professionals who would like to brush up their fundamentals on the Frequency Modulation topic.Digital signals are preferred for transmission, but it is not always feasible as it needs high bandwidth with low pass characteristics. To overcome such issues analog transmission is considered, as it possesses low bandwidth and bandpass characteristics. Information about the source gets imposed on the carrier signal by modifying certain characteristics of it. This process in the analog transmission is termed modulation.Move the signal spectrum to a frequency that is less susceptible to attenuation in a medium is necessary. Further, the modulations are classified into two types. They are Amplitude modulation and angle modulation. Frequency modulation is part of an Angle modulation. 1). Modulation in which the carrier wave angle varies in accordance with the baseband signal is termed as ___________.Amplitude ModulationAngle ModulationSpectral ModulationNone of the aboveHintPhase and Frequency modulation 2). The man behind the invention of frequency modulation is ______________.Edwin Howard ArmstrongJohn ChowningReginald FessendenNone of the aboveHint FM method described by Edwin Howard Armstrong 3). The original signal of source in modulation is known as _________.Baseband signalAttenuated signalDeviated signalCarrier signalHintSource signals 4). Conversion of analog or digital data into analog form is known as ___________.EncodingModulationDecodingAttenuationHintModulation technique 5). To encode the information in the carrier signal by altering the wave frequency instantaneously is known as ____________.Amplitude ModulationFrequency ModulationPhase ModulationNone of the aboveHintVarying frequencies 6). What types categorized under Analog modulation?Amplitude ModulationFrequency ModulationPhase ModulationNone of the aboveHintAmplitude and angle modulation prefer analog signals 7). What are the various Frequency modulations?Analog FMDigital FMBoth a and bNone of the aboveHintBoth variants of analog and digital 8). Modulation index in frequency modulation can be determined by using _________.δf / fmAm/fmAm/AcAc/fmHintRatio of frequency deviation (δf) to the modulating frequency (fm) 9). A carrier signal of 100 MHz modulated using a sine wave whose frequency is 75 kHz with a deviation frequency of 50 kHz. What will be the modulation index?0.5550.6670.7780.889Hintβ = δf/ fm 10). NBFM bandwidth is ________.fm2fm (β+1)2 fmfm (β+1)HintBandwidth of amplitude modulation 11). What is the basic difference between NBFM and AM signal?BandwidthFrequency deviationSidebandsAlgebraic sign reversal for the lower side frequencyHintAM and NBFM differ by the reverse sign at the lower side frequency 12). Bandwidth of WBFM is ________.fm2fm (β+1)2 fmfm (β+1)HintCarson’s rule 13). A 12 MHz carrier gets modulated by a sine signal with a frequency of 500 Hz bearing the frequency deviation of about 50 kHz. Find the bandwidth?100101102103HintCarson’s rule, B = 2(δf + fm) 14). Based on modulation index FM is classified as __________.Multitone FMNarrow band FM (NBFM)Wide band FM (WBFM)Both b and cHintModulation index classifies the FM 15). In NBFM the modulation index is ____________.Less than 1Greater than 1InfinityCan’t sayHintNBFM utilizes a small part of the channel 16). Modulation of the source signal with multiple frequency components in it is called _______________.Amplitude ModulationFrequency ModulationPhase ModulationMultitone ModulationHintSingle component of frequency known as modulated single tone signal 17). Modulation index will be greater than 1 in _________________.Amplitude ModulationPhase ModulationNarrow Band Frequency ModulationWide band Frequency ModulationHintWide range of frequencies 18). The transmitted power is independent of modulation index in _________________.Amplitude ModulationFrequency ModulationPhase ModulationNone of the aboveHintFrequency-modulated signals are more immune to noise 19). Noise immunity is superior in ________________.Amplitude ModulationFrequency ModulationPhase ModulationNone of the aboveHintFM more superior in terms of noise immunity 20). Modulation index in Frequency modulation is proportional to _______________.Modulating frequencyModulating signalBoth a and bNone of the aboveHintModulating signal and frequency are proportional to its index 21). In _____________ angle is in direct proportion with the integral of modulating signal.Amplitude ModulationFrequency ModulationPhase ModulationNone of the aboveHintAmplitude will always remain constant but angle varies 22). Departure of maximum instantaneous frequency from the carrier’s frequency is known as ________________.Amplitude deviationPhase deviationFrequency deviationFrequency shift keyingHintTo describe the range of a modulating frequency signal 23). Side bands present in frequency modulation are ____________.FiniteInfiniteLargeBoth b and cHintSidebands in the FM is large 24). Total variation of frequency from its low to high point is termed as __________.Carrier swingSideband widthFrequency deviationNone of the aboveHint2 times of δf of FM 25). In FM signals the amount of frequency deviated is dependent upon ________.Modulating frequencyCarrier frequencyAmplitudePhaseHintModulating signal's amplitudeFrequency Modulation Multiple Choice Question & Answers 26). Sidebands in FM are controlled based on selected ____________.Modulating frequencyCarrier frequencyDeviationPhaseHintLesser deviation leads to few sidebands 27). Maximum deviation is due to __________.Transmitter DesignTransmitter ConfigurationBoth a and bNone of the aboveHintTransmitter configuration and design 28). Good audio quality needs ________.High deviationLow deviationLesser deviationNone of the aboveHintHigh deviation is preferred for better audio quality 29). Human speech prefers _______.Higher deviationLower deviationLarger deviationNone of the aboveHintLower maximum frequency of modulation is present in human speech. Hence low deviation is preferred. 30). WBFM possess ________.High deviationLow deviationLesser deviationNone of the aboveHintHigher ratio of deviation possessed by WBFM 31). If the deviation is +20 KHz indicates _________.Baseband is 20 KHz above foBaseband is 20 KHz below foCarrier is 20 KHz above foCarrier is 20 KHz below foHint+ and – indicates the carrier present above or below 32). What are the methods used to produce FM waves?Direct methodIndirect methodBoth a and bNone of the aboveHintTwo methods are used in producing FM waves 33). The wave originated from the transmitter and its frequency varies concerning modulation source is possible in __________ of FM.Direct methodIndirect methodBoth a and bNone of the aboveHintHigh-power FM signals 34). Phase of the originated wave is a function of modulation in ______________ of FM.Direct methodIndirect methodBoth a and bNone of the aboveHintWBFM waves are generated 35). Armstrong method is categorized as ____________.Direct methodIndirect methodBoth a and bNone of the aboveHintAlternative of a direct method 36). _______________ is used to estimate the bandwidth of FM signal.Barkhausen criteriaNyquist rateCarson’s ruleNone of the aboveHintCarson's rule can be used to estimate the bandwidth 37). Spectrum of NBFM is similar to the spectrum of _____________.Amplitude ModulationFrequency ModulationPhase ModulationNone of the aboveHintBandwidth of AM wave is similar to the NBFM 38). Carson’s rule formula for bandwidth calculation is _____________.fm2fm (β+1)2 fm2(Δf+fm)HintComponents present in communications 39). The Δf in the Carson’s rule stands for _________.Peak deviation in frequencyRequired bandwidthHighest frequencyModulating frequencyHintMaximum deviation in the frequency 40). _____________ device is used to convert the received FM signal converted to voltage.PLLFrequency discriminatorEnvelope detectorOscillatorHintThe converted FM signal into voltage 41). Other than frequency discriminator ________ can be used for FM demodulation.PLLFrequency discriminatorEnvelope detectorOscillatorHintFor noisy environments 42). FM is normally used above _____________ MHz.20304050HintAbove 30 MHz 43). What are the two common applications of frequency modulation?Two-way communicationsFM radioBoth a and bNone of the aboveHintFM radio and two-way 44). An FM receiver consisting of Amplitude limiters serves the purpose of _________.AmplificationFilterationDemodulationRemoval of amplitude variationsHint Noise results in the amplitude variations 45). Circuit consisting of differentiator that allows to pass _______.High frequenciesLow frequenciesHigh voltagesLow voltagesHintPre-emphasis is a circuit that possesses a high-pass filter 46). __________ circuits are used in FM.Pre-emphasisDe-emphasisFilterationBoth a and bHintPre-emphasis and de-emphasis 47). Boosting the high-level audio frequencies artificially according to the prearranged curve of response is known as ___________.Pre-emphasisDe-emphasisFilterationAmplificationHintPassage of high-frequency components 48). ________ circuit used at the transmitter of FM.Pre-emphasisDe-emphasisFilterationAmplificationHintHigh pass filter present at the transmitter 49). _______ circuit present at the receiver of FM.Pre-emphasisDe-emphasisFilterationAmplificationHintTo nullify the artificially boosted signals coming from the transmitter 50). __________ filter is used in De-emphasis circuit.High passLow passBand passNotchHintLPF to nullify the signalsFrequency Modulation MCQs for Exams 51). Parameters constant in FM are _____________.AmplitudePhaseFrequencyBoth a and bHintCarrier frequency is varied 52). Pre-emphasis is performed before ____________.TransmissionModulationAmplificationCan’t sayHintModulation to boosts the voltage of the modulating signal 53). Pre-emphasis can be done __________.53). Pre-emphasis can be done __________.To boost the voltage of the modulating signalModulation of signal at high frequenciesBefore modulationAll the aboveHintPre-emphasis circuit is present in the transmitting section 54). What will be the change in bandwidth of the FM signal as the frequency of modulation tends to increase from 14 kHz to 28 kHz?40582824HintCarson’s rule B= 2(Δf+fm) 55). The characteristics of WBFM are _____________.Large KfWide Band widthBoth a and bNone of the aboveHintLarge frequency sensitivity and wide bandwidth 56). The characteristics of NBFM are _________.Small KfNarrow BandwidthBoth a and bNone of the aboveHintSmaller frequency sensitivity 57). PLL can be used as _______.AM demodulatorFM receiverFM demodulatorAM receiverHintFrequency demodulation 58). NBFM operates at a range of ________ modulating frequencies.30 Hz to 30 KHz30 Hz to 3 KHz3 KHz to 30 KHz30 Hz to 15 KHzHintNBFM operates at a narrow bandwidth 59). FM signal with 7 as modulation index applied to the ‘Frequency Tripler’. What will be the modulation index at the output obtained?714210HintN-times Frequency Multiplier 60). FM signal passed from mixer makes the deviation ____________.ReduceDoubleHalvedRemains unaffectedHintDeviation doesn’t get affected 61). Digitally encoded data transmitted with frequency-modulated signals referred to as _________.Frequency-shift keyingPhase-shift keyingAmplitude-shift keyingNone of the aboveHintFrequencies in FSK are represented using digits 62). FM broadcast requires ____________ max. Bandwidth for commercial uses.100 KHz200 KHz300 KHz400 KHzHint200 kHz is the max. Bandwidth 63). The purpose of Guard bands in FM is to _________.Prevent adjacent channel interferenceIncrease bandwidthIncrease noiseBoth b and cHintInterferences occur due to adjacent channels 64). In Armstrong method FM is obtained by using ____________.Amplitude ModulationFrequency ModulationPhase ModulationNone of the aboveHintFM can be generated from the Phase modulator 65). To generate WBFM, components present are _____.NBFM modulatorFrequency multiplierFrequency converterAll the aboveHintOutcome of the NBFM modulator 66). Frequency multiplier is a __________ device.LinearNon-linearIdealNone of the aboveHintInput signals are multiplied with a factor given making the multiplier non-linear 67). What are the direct methods of FM generation?FM varactor diode modulatorArmstrong methodPLL direct FM transmitterBoth a and cHintNBFM signals are generated 68). Parameter variation for FM generation is a ___________ method.DirectIndirectArmstrongNone of the aboveHintMaintaining carrier frequency-stable for an extended period is difficult 69). Carrier is in phase with upper sidebands where the carrier is out of phase with the lower sideband in ____________.Amplitude modulationNBFMPhase modulationNone of the aboveHintCarrier is in out phase with LSB 70). Crystal controlled oscillator used in FM generation is to provide ____________.Frequency deviationIncrease bandwidthIncrease noiseFrequency stabilityHintSource signal is integrated and the phase gets modulated with a crystal oscillator 71). NBFM signal’s frequency multiplied using frequency multiplier and produces _______.AMNBFMPMWBFMHintIndirect method 72). PLL is __________ feedback system.PositiveNegativeZeroCan’t sayHintIndirect demodulation of frequency is possible using PLL 73). PLL FM detector can be used in ___________ applications.AnalogDigitalBoth a and bNone of the aboveHintIndirect method of frequency demodulation 74). PLL FM detector consists of _________________.MixerLow pass filterVCOAll the aboveHintMixer, LPF followed by VCO 75). Phase Locked Loop compares the input signal’s phase with the output signals phase using ________.MixerLow pass filterVCOAll the aboveHintFeedback provided by VCOFrequency Modulation MCQs for Quiz 76). FM discriminator consists of ______________.DifferentiatorEnvelope detectorLimiterAll the aboveHintFM Discriminator comprises slope circuits and Envelope detectors 77). To ensure the input signal amplitude in FM discriminator maintained constant __________ is used.DifferentiatorEnvelope detectorLimiterAll the aboveHintLimiter placed to maintain the amplitude 78). Single slope discriminator has poor ____________.LinearityNon-linearityIdealNone of the aboveHintLinearity can be improved by using a balanced discriminator 79). Two signals of FM in which one signal’s amplitude is twice the other strongest signal gets captured and weaker one gets rejected known as ___________.Linear effectCapture effectCarson’s ruleNone of the aboveHintA stronger signal dominates the weaker signal 80). ______________ improves the Signal to Noise ratio (SNR).Pre-emphasisDe-emphasisFilterationAmplificationHintThe energy of the higher contents increased using pre-emphasisRead More About Frequency Modulation 81). AFC stands for _________________.Automatic Force ControlAutomatic Frequency ControlAutomatic Force CompulsionNone of the aboveHintAFC loop in Crosby Direct FM makes the frequency of modulation unaffected 82). What are the advantages of Indirect method to generate FM?Frequency stabilityFrequency deviationBoth a and bNone of the aboveHintTo attain frequency stability crystal oscillators are preferred 83). The maximum amount of deviation in frequency allowed for the broadcasting of FM commercially is __________.50 KHz75 KHz85 KHz100 KHzHintMaximum deviation in frequency of about 75 kHz 84). ____________ is an experimental technique utilized by FM systems to set the deviation of frequency with precision.FM varactor diode modulatorArmstrong methodPLL direct FM transmitterBessel null methodHint Carrier null method to set frequency deviation 85). Audio oscillators analog output connected to the input of the buffer amplifier in _________ method.FM varactor diode modulatorArmstrong methodPLL direct FM transmitterBessel null methodHint Bessel null method connects the output as the input 86). VCO is used in _______ method to generate FM.DirectIndirectBoth a and bNone of the aboveHintVCO is replaced with Crystal oscillator in indirect method 87). ____________ method used in the generation of FM because the frequency of the oscillator varies directly based on the modulating signals.FM varactor diode modulatorArmstrong methodPLL direct FM transmitterBessel null methodHintVaractor diodes offers AFC 88). What are the advantages of Varactor diode modulators of FM?ReliableStabilitySimpleAll the aboveHintVaractor diodes are accepted widely because of their simplicity, reliability, and stability 89). What is the drawback of Varactor diode modulators?StabilityLinearityComplexityFrequency deviationHintPeak deviation of frequency is limited in varactor diode-based modulators 90). FM circuit made using inductors known as ____________.FM saturable reactor modulatorArmstrong methodPLL direct FM transmitterBessel null methodHintInductors whose inductance in the LC circuit varied based on the modulating signals 91). Frequency Modulation can be achieved using _____________.PIN diodeKlystron oscillatorsMultivibratorsAll the aboveHintUsing Voltage controlled oscillators or devices 92). Varactor diode in the frequency modulation is __________.Forward biasedReverse biasedNeither forward not reverseNone of the aboveHintCapacitance in the circuit is dependent upon the reverse voltages 93). VCO’s frequency of oscillations has _________dependent on the voltage applied.LinearlyNon-linearlyInverselyCan’t sayHintLarge deviation of frequencies offered by using VCO 94). Armstrong’s modulator using ‘frequency-up’ conversion involves __________ methods.FM saturable reactor modulatorHeterodyneMultiplicationBoth b and cHintFrequency conversion involves two methods 95). The modulator made using Armstrong method consists of ______________.Balanced modulatorPhase shifterMultipliers and mixersAll the aboveHintModulate the phase of the Crystal oscillator phase shifter offering 90-degree 96). Desired deviation of frequency in Armstrong modulators can be attained using _________.Balanced modulatorPhase shifterMultipliers and mixersAll the aboveHintCombination of mixers and multipliers is used to achieve the desired frequency deviation 97). Which detector can detect either WBFM or NBFM modulated signals?PLL demodulatorFM discriminatorQuadrature FM detectorRatio detectorHintPLL demodulators can detect either WBFM or NBFM 98). Double tuned transformer for FM generation is used in ____________ detector.PLL demodulatorFM discriminatorQuadrature FM detectorRatio detectorHintA double-tuned transformer used in the ratio detector 99). Noise suppressed without limiters in _______ detectors.PLL demodulatorFM discriminatorQuadrature FM detectorRatio detectorHintRatio detectors perform demodulation on the FM signals 100). What is the disadvantage of FM in comparison to AM?Lesser prone to noise interferenceLarge Bandwidth neededLow power consumptionAll the aboveHintFM is lesser prone to the interference of noise Time is Up!