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 Modulation Angle Modulation Spectral Modulation None of the above HintPhase and Frequency modulation2). The man behind the invention of frequency modulation is ______________. Edwin Howard Armstrong John Chowning Reginald Fessenden None of the above Hint FM method described by Edwin Howard Armstrong3). The original signal of source in modulation is known as _________. Baseband signal Attenuated signal Deviated signal Carrier signal HintSource signals4). Conversion of analog or digital data into analog form is known as ___________. Encoding Modulation Decoding Attenuation HintModulation technique5). To encode the information in the carrier signal by altering the wave frequency instantaneously is known as ____________. Amplitude Modulation Frequency Modulation Phase Modulation None of the above HintVarying frequencies6). What types categorized under Analog modulation? Amplitude Modulation Frequency Modulation Phase Modulation None of the above HintAmplitude and angle modulation prefer analog signals7). What are the various Frequency modulations? Analog FM Digital FM Both a and b None of the above HintBoth variants of analog and digital8). Modulation index in frequency modulation can be determined by using _________. δf / fm Am/fm Am/Ac Ac/fm HintRatio 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? 0.555 0.667 0.778 0.889 Hintβ = δf/ fm10). NBFM bandwidth is ________. fm 2fm (β+1) 2 fm fm (β+1) HintBandwidth of amplitude modulation11). What is the basic difference between NBFM and AM signal? Bandwidth Frequency deviation Sidebands Algebraic sign reversal for the lower side frequency HintAM and NBFM differ by the reverse sign at the lower side frequency12). Bandwidth of WBFM is ________. fm 2fm (β+1) 2 fm fm (β+1) HintCarson’s rule13). 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? 100 101 102 103 HintCarson’s rule, B = 2(δf + fm)14). Based on modulation index FM is classified as __________. Multitone FM Narrow band FM (NBFM) Wide band FM (WBFM) Both b and c HintModulation index classifies the FM15). In NBFM the modulation index is ____________. Less than 1 Greater than 1 Infinity Can’t say HintNBFM utilizes a small part of the channel16). Modulation of the source signal with multiple frequency components in it is called _______________. Amplitude Modulation Frequency Modulation Phase Modulation Multitone Modulation HintSingle component of frequency known as modulated single tone signal17). Modulation index will be greater than 1 in _________________. Amplitude Modulation Phase Modulation Narrow Band Frequency Modulation Wide band Frequency Modulation HintWide range of frequencies18). The transmitted power is independent of modulation index in _________________. Amplitude Modulation Frequency Modulation Phase Modulation None of the above HintFrequency-modulated signals are more immune to noise19). Noise immunity is superior in ________________. Amplitude Modulation Frequency Modulation Phase Modulation None of the above HintFM more superior in terms of noise immunity20). Modulation index in Frequency modulation is proportional to _______________. Modulating frequency Modulating signal Both a and b None of the above HintModulating signal and frequency are proportional to its index21). In _____________ angle is in direct proportion with the integral of modulating signal. Amplitude Modulation Frequency Modulation Phase Modulation None of the above HintAmplitude will always remain constant but angle varies22). Departure of maximum instantaneous frequency from the carrier’s frequency is known as ________________. Amplitude deviation Phase deviation Frequency deviation Frequency shift keying HintTo describe the range of a modulating frequency signal23). Side bands present in frequency modulation are ____________. Finite Infinite Large Both b and c HintSidebands in the FM is large24). Total variation of frequency from its low to high point is termed as __________. Carrier swing Sideband width Frequency deviation None of the above Hint2 times of δf of FM25). In FM signals the amount of frequency deviated is dependent upon ________. Modulating frequency Carrier frequency Amplitude Phase HintModulating signal's amplitudeFrequency Modulation Multiple Choice Question & Answers26). Sidebands in FM are controlled based on selected ____________. Modulating frequency Carrier frequency Deviation Phase HintLesser deviation leads to few sidebands27). Maximum deviation is due to __________. Transmitter Design Transmitter Configuration Both a and b None of the above HintTransmitter configuration and design28). Good audio quality needs ________. High deviation Low deviation Lesser deviation None of the above HintHigh deviation is preferred for better audio quality29). Human speech prefers _______. Higher deviation Lower deviation Larger deviation None of the above HintLower maximum frequency of modulation is present in human speech. Hence low deviation is preferred.30). WBFM possess ________. High deviation Low deviation Lesser deviation None of the above HintHigher ratio of deviation possessed by WBFM31). If the deviation is +20 KHz indicates _________. Baseband is 20 KHz above fo Baseband is 20 KHz below fo Carrier is 20 KHz above fo Carrier is 20 KHz below fo Hint+ and – indicates the carrier present above or below32). What are the methods used to produce FM waves? Direct method Indirect method Both a and b None of the above HintTwo methods are used in producing FM waves33). The wave originated from the transmitter and its frequency varies concerning modulation source is possible in __________ of FM. Direct method Indirect method Both a and b None of the above HintHigh-power FM signals34). Phase of the originated wave is a function of modulation in ______________ of FM. Direct method Indirect method Both a and b None of the above HintWBFM waves are generated35). Armstrong method is categorized as ____________. Direct method Indirect method Both a and b None of the above HintAlternative of a direct method36). _______________ is used to estimate the bandwidth of FM signal. Barkhausen criteria Nyquist rate Carson’s rule None of the above HintCarson's rule can be used to estimate the bandwidth37). Spectrum of NBFM is similar to the spectrum of _____________. Amplitude Modulation Frequency Modulation Phase Modulation None of the above HintBandwidth of AM wave is similar to the NBFM38). Carson’s rule formula for bandwidth calculation is _____________. fm 2fm (β+1) 2 fm 2(Δf+fm) HintComponents present in communications39). The Δf in the Carson’s rule stands for _________. Peak deviation in frequency Required bandwidth Highest frequency Modulating frequency HintMaximum deviation in the frequency40). _____________ device is used to convert the received FM signal converted to voltage. PLL Frequency discriminator Envelope detector Oscillator HintThe converted FM signal into voltage41). Other than frequency discriminator ________ can be used for FM demodulation. PLL Frequency discriminator Envelope detector Oscillator HintFor noisy environments42). FM is normally used above _____________ MHz. 20 30 40 50 HintAbove 30 MHz43). What are the two common applications of frequency modulation? Two-way communications FM radio Both a and b None of the above HintFM radio and two-way44). An FM receiver consisting of Amplitude limiters serves the purpose of _________. Amplification Filteration Demodulation Removal of amplitude variations Hint Noise results in the amplitude variations45). Circuit consisting of differentiator that allows to pass _______. High frequencies Low frequencies High voltages Low voltages HintPre-emphasis is a circuit that possesses a high-pass filter46). __________ circuits are used in FM. Pre-emphasis De-emphasis Filteration Both a and b HintPre-emphasis and de-emphasis47). Boosting the high-level audio frequencies artificially according to the prearranged curve of response is known as ___________. Pre-emphasis De-emphasis Filteration Amplification HintPassage of high-frequency components48). ________ circuit used at the transmitter of FM. Pre-emphasis De-emphasis Filteration Amplification HintHigh pass filter present at the transmitter49). _______ circuit present at the receiver of FM. Pre-emphasis De-emphasis Filteration Amplification HintTo nullify the artificially boosted signals coming from the transmitter50). __________ filter is used in De-emphasis circuit. High pass Low pass Band pass Notch HintLPF to nullify the signalsFrequency Modulation MCQs for Exams51). Parameters constant in FM are _____________. Amplitude Phase Frequency Both a and b HintCarrier frequency is varied52). Pre-emphasis is performed before ____________. Transmission Modulation Amplification Can’t say HintModulation to boosts the voltage of the modulating signal53). Pre-emphasis can be done __________.53). Pre-emphasis can be done __________. To boost the voltage of the modulating signal Modulation of signal at high frequencies Before modulation All the above HintPre-emphasis circuit is present in the transmitting section54). 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? 40 58 28 24 HintCarson’s rule B= 2(Δf+fm)55). The characteristics of WBFM are _____________. Large Kf Wide Band width Both a and b None of the above HintLarge frequency sensitivity and wide bandwidth56). The characteristics of NBFM are _________. Small Kf Narrow Bandwidth Both a and b None of the above HintSmaller frequency sensitivity57). PLL can be used as _______. AM demodulator FM receiver FM demodulator AM receiver HintFrequency demodulation58). NBFM operates at a range of ________ modulating frequencies. 30 Hz to 30 KHz 30 Hz to 3 KHz 3 KHz to 30 KHz 30 Hz to 15 KHz HintNBFM operates at a narrow bandwidth59). FM signal with 7 as modulation index applied to the ‘Frequency Tripler’. What will be the modulation index at the output obtained? 7 14 21 0 HintN-times Frequency Multiplier60). FM signal passed from mixer makes the deviation ____________. Reduce Double Halved Remains unaffected HintDeviation doesn’t get affected61). Digitally encoded data transmitted with frequency-modulated signals referred to as _________. Frequency-shift keying Phase-shift keying Amplitude-shift keying None of the above HintFrequencies in FSK are represented using digits62). FM broadcast requires ____________ max. Bandwidth for commercial uses. 100 KHz 200 KHz 300 KHz 400 KHz Hint200 kHz is the max. Bandwidth63). The purpose of Guard bands in FM is to _________. Prevent adjacent channel interference Increase bandwidth Increase noise Both b and c HintInterferences occur due to adjacent channels64). In Armstrong method FM is obtained by using ____________. Amplitude Modulation Frequency Modulation Phase Modulation None of the above HintFM can be generated from the Phase modulator65). To generate WBFM, components present are _____. NBFM modulator Frequency multiplier Frequency converter All the above HintOutcome of the NBFM modulator66). Frequency multiplier is a __________ device. Linear Non-linear Ideal None of the above HintInput signals are multiplied with a factor given making the multiplier non-linear67). What are the direct methods of FM generation? FM varactor diode modulator Armstrong method PLL direct FM transmitter Both a and c HintNBFM signals are generated68). Parameter variation for FM generation is a ___________ method. Direct Indirect Armstrong None of the above HintMaintaining carrier frequency-stable for an extended period is difficult69). Carrier is in phase with upper sidebands where the carrier is out of phase with the lower sideband in ____________. Amplitude modulation NBFM Phase modulation None of the above HintCarrier is in out phase with LSB70). Crystal controlled oscillator used in FM generation is to provide ____________. Frequency deviation Increase bandwidth Increase noise Frequency stability HintSource signal is integrated and the phase gets modulated with a crystal oscillator71). NBFM signal’s frequency multiplied using frequency multiplier and produces _______. AM NBFM PM WBFM HintIndirect method72). PLL is __________ feedback system. Positive Negative Zero Can’t say HintIndirect demodulation of frequency is possible using PLL73). PLL FM detector can be used in ___________ applications. Analog Digital Both a and b None of the above HintIndirect method of frequency demodulation74). PLL FM detector consists of _________________. Mixer Low pass filter VCO All the above HintMixer, LPF followed by VCO75). Phase Locked Loop compares the input signal’s phase with the output signals phase using ________. Mixer Low pass filter VCO All the above HintFeedback provided by VCOFrequency Modulation MCQs for Quiz76). FM discriminator consists of ______________. Differentiator Envelope detector Limiter All the above HintFM Discriminator comprises slope circuits and Envelope detectors77). To ensure the input signal amplitude in FM discriminator maintained constant __________ is used. Differentiator Envelope detector Limiter All the above HintLimiter placed to maintain the amplitude78). Single slope discriminator has poor ____________. Linearity Non-linearity Ideal None of the above HintLinearity can be improved by using a balanced discriminator79). 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 effect Capture effect Carson’s rule None of the above HintA stronger signal dominates the weaker signal80). ______________ improves the Signal to Noise ratio (SNR). Pre-emphasis De-emphasis Filteration Amplification HintThe energy of the higher contents increased using pre-emphasisRead More About Frequency Modulation81). AFC stands for _________________. Automatic Force Control Automatic Frequency Control Automatic Force Compulsion None of the above HintAFC loop in Crosby Direct FM makes the frequency of modulation unaffected82). What are the advantages of Indirect method to generate FM? Frequency stability Frequency deviation Both a and b None of the above HintTo attain frequency stability crystal oscillators are preferred83). The maximum amount of deviation in frequency allowed for the broadcasting of FM commercially is __________. 50 KHz 75 KHz 85 KHz 100 KHz HintMaximum deviation in frequency of about 75 kHz84). ____________ is an experimental technique utilized by FM systems to set the deviation of frequency with precision. FM varactor diode modulator Armstrong method PLL direct FM transmitter Bessel null method Hint Carrier null method to set frequency deviation85). Audio oscillators analog output connected to the input of the buffer amplifier in _________ method. FM varactor diode modulator Armstrong method PLL direct FM transmitter Bessel null method Hint Bessel null method connects the output as the input86). VCO is used in _______ method to generate FM. Direct Indirect Both a and b None of the above HintVCO is replaced with Crystal oscillator in indirect method87). ____________ method used in the generation of FM because the frequency of the oscillator varies directly based on the modulating signals. FM varactor diode modulator Armstrong method PLL direct FM transmitter Bessel null method HintVaractor diodes offers AFC88). What are the advantages of Varactor diode modulators of FM? Reliable Stability Simple All the above HintVaractor diodes are accepted widely because of their simplicity, reliability, and stability89). What is the drawback of Varactor diode modulators? Stability Linearity Complexity Frequency deviation HintPeak deviation of frequency is limited in varactor diode-based modulators90). FM circuit made using inductors known as ____________. FM saturable reactor modulator Armstrong method PLL direct FM transmitter Bessel null method HintInductors whose inductance in the LC circuit varied based on the modulating signals91). Frequency Modulation can be achieved using _____________. PIN diode Klystron oscillators Multivibrators All the above HintUsing Voltage controlled oscillators or devices92). Varactor diode in the frequency modulation is __________. Forward biased Reverse biased Neither forward not reverse None of the above HintCapacitance in the circuit is dependent upon the reverse voltages93). VCO’s frequency of oscillations has _________dependent on the voltage applied. Linearly Non-linearly Inversely Can’t say HintLarge deviation of frequencies offered by using VCO94). Armstrong’s modulator using ‘frequency-up’ conversion involves __________ methods. FM saturable reactor modulator Heterodyne Multiplication Both b and c HintFrequency conversion involves two methods95). The modulator made using Armstrong method consists of ______________. Balanced modulator Phase shifter Multipliers and mixers All the above HintModulate the phase of the Crystal oscillator phase shifter offering 90-degree96). Desired deviation of frequency in Armstrong modulators can be attained using _________. Balanced modulator Phase shifter Multipliers and mixers All the above HintCombination of mixers and multipliers is used to achieve the desired frequency deviation97). Which detector can detect either WBFM or NBFM modulated signals? PLL demodulator FM discriminator Quadrature FM detector Ratio detector HintPLL demodulators can detect either WBFM or NBFM98). Double tuned transformer for FM generation is used in ____________ detector. PLL demodulator FM discriminator Quadrature FM detector Ratio detector HintA double-tuned transformer used in the ratio detector99). Noise suppressed without limiters in _______ detectors. PLL demodulator FM discriminator Quadrature FM detector Ratio detector HintRatio detectors perform demodulation on the FM signals100). What is the disadvantage of FM in comparison to AM? Lesser prone to noise interference Large Bandwidth needed Low power consumption All the above HintFM is lesser prone to the interference of noise Time is Up! Time's up
