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Modulation Question & Answers

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This article lists 100+ Modulation MCQs for engineering students. All the Modulation Questions & Answers given below include a solution and link wherever possible to the relevant topic. This is helpful for users who are preparing for their exams, interviews, or professionals who would like to brush up their fundamentals on Modulation topic which is core in Electronics Engineering.

In digital communication, information is transmitted by encoding and decoding process using various modulation techniques. Modulation is a process of converting analog data into a digital signal form with a piece of information added to the carrier signal. It mainly consists of a modulator on the transmitter side for modulation purposes and a demodulator on the receiver side for the demodulation purpose. They are classified into 4 types, namely analog-type modulation, digital type modulation, pulse type modulation, spread spectrum type modulation. Where analog modulation refers to the process of transferring a low-frequency signal over a high-frequency signal.

These analog-type modulations are classified into 3 types like Amplitude type modulation (AM), frequency type modulation (FM), Phase type modulation (PM). Digital type modulation is the process of encoding the signals information in digital form to amplitude, phase, frequency of transmitted signals. These are classified into two types namely single carrier modulation types like amplitude type shift keying ASK, frequency type shift keying FSK, Phase type shift keying PSK, Orthogonal type amplitude modulation. and multicarrier frequency division multiplexing (OFDM).

Pulse-type modulation is a process where the signal pulse is varied with respect to the amplitude or width of a signal. Spread type spectrum modulation is a process where signals are spread in the frequency domain using various spread spectrum techniques. The main advantage of using modulation techniques is that it reduces the size of the antenna in the circuit and improves the quality of signal in communication.

1). A signal is a _____ that carries data from one network to another.
HintA signal is an electrical current that carries data from one network to another.
2). A signal can be in which form?
HintA signal can be in audio, video, speech, speech, image forms.
3). Modulation is of _____ types.
HintIn electronics, modulation is of 4 types, analog type modulation, digital type modulation, Pulse type modulation, and Spread spectrum type modulation. These modulations are classified based on signal form ( analog signal or digital signal)
4). Examples of analog modulation techniques
HintExamples of analog modulation techniques are frequency type modulation and amplitude type modulation. Such modulations are used in radio broadcast applications.
Read more about Analog Modulation.
5). What is modulation?
HintIt is a process of converting data into electrical signals optimized for transmission.
Read more about Modulation
6). What are the different types of digital modulation?
HintDigital modulation is classified into two types single carrier modulation and multicarrier modulation. Single carrier modulation exploits only one signal frequency. Multicarrier modulation exploits multiple signal frequencies.
7). Which of the following is single carrier modulation?
HintSingle-carrier modulation is classified into 4 types namely Amplitude type shift keying ASK, Frequency type shift keying FSK, Phase type shift keying PSK, Orthogonal amplitude modulation QAM.
8). Which type of modulation method is used in multicarrier modulation?
HintMulticarrier modulation uses Orthogonal frequency division multiplexing OFDM methodology.
9). What is the function of a modulator?
HintA modulator modulates signal, by controlling input audio signal called carrier.
10). What is the function of demodulation?
HintA demodulator demodulates the received signal from the modulator.
11). What are the units of modulation rate?
HintModulation rate is expressed in terms of baud.
12). On which component modulation is performed?
HintModulation is performed between transmitter and receiver.
13). Which oscillator is used in the transmitter?
HintCrystal oscillator used in the transmitter.
14). Which type of modulation is used for radio transmission in India?
HintAmplitude modulation is used in India for radio transmission.
15). The useful power in amplitude modulation is carried by ________.
HintThe useful power in amplitude modulation is carried by sidebands.
Read more about Amplitude Modulation.
16). The relation between bandwidth and audio signal frequency in amplitude modulation is __________.
HintIn amplitude, modulation bandwidth is 2 times of frequency audio signal.
17). In AM, the strength of _____ is varied with respect to the strength of _____.
HintIn AM, the strength of the carrier is varied with respect to the strength of the signal.
18). At what condition over modulation occur?
HintOvermodulation occurs in telecommunication when the signal amplitude is greater than carrier amplitude. This results in spurious emission by the modulated carrier and distortion of the recovered modulated signal.
19). What should be the value of modulation index for under modulation?
HintThe value of modulation index for under modulation should be less than 1.
20). What should be the value of modulation index for perfect modulation?
HintThe value of the modulation index for perfect modulation should be 1.
21). Modulation index is also called as _________.
HintThe modulation index is also called modulation depth.
22). Modulation index is denoted as __________.
HintThe modulation index is denoted as µ.
23). Percentage modulation is denoted as __________.
HintPercentage modulation is denoted as m.
24). If the value of the modulation index is 0.8 then the modulation is called __________.
HintIf the value of the modulation index is 0.8 then the modulation is called under modulation.
25). If the value of the modulation index is 1.3 then the modulation is called ___________.
HintIf the value of the modulation index is 1.3 then the modulation is called over modulation.

Modulation Interview Questions

26). If the value of the modulation index is 1 then the modulation is called __________.
HintIf the value of the modulation index is 1 then the modulation is called perfect modulation.
27). Bandwidth is expressed in terms of __________.
HintThe amount of data that is transferred from one end to another end in a network within a specific time is called bandwidth. It is usually expressed in terms of bits per second.
28). What happens when overmodulation occurs?
HintOver modulation is a condition where the modulation index is greater than 1, at this point signal gets distorted.
29). Demodulation occurs in __________.
HintDemodulation occurs in a radio receiver.
30). Which medium is used in radio transmission?
HintSpace is used as a medium in radio transmission.
31). In amplitude modulation the carrier amplitude with instantaneous values changes with change in the _____ and _____ variation of modulation.
HintIn amplitude type modulation, the sine wave amplitude varies with the signal applied. the instantaneous values of carrier amplitude changes with change in the amplitude and frequency variation of the modulation.
32). Modulating signal has a reference line up to _____ limit
HintModulating signal uses the peak value of carrier, and the envelope varies above and below the peak carrier amplitude. The zero reference line of modulating signal coincides with the peak value of the unmodulated carrier.
33). Distortion causes _____ in the signal.
HintWhen the amplitude of modulating signal is greater than the amplitude of the carrier signal distortion will occur. Due to this, an error is introduced in the information of the transmitted signal. Hence in amplitude type modulation, the modulating signal peak value should be less than the carrier signal peak value.
34). Which circuit is used to produce Amplitude Modulation?
HintA modulator is used to generate amplitude modulation. Generally, it has 2 input signals namely, a carrier signal and a modulating signal, and one output signal called modulated signal, which is the product of input signals.
35). The signal is modulated at 7.5 V and carrier voltage is of 9V, calculate modulation percentage.
HintModulating signal = 7.5V, carrier voltage = 9V ; m = Vm / Vc = 7.5 / 9 * 100 = 83.33.
36). If Vmax = 5.9v and Vmin = 1.2V, calculate modulation index.
HintModulation index = m= Vmax – Vmin / Vmax + V min = 5.9 – 1.2 / 5.9 + 1.2 = 0.662
37). If carrier voltage is 10v , which voltage of Modulating signal causes over modulation?
HintWhen the voltage of Modulating signal exceeds carrier signal voltage it causes over modulation, where m>1; 12/10 = 1.2 which is greater than 1.
38). Find voltage of modulating signal, if Vmin and Vmax are 5.9 v and 1.2v.
HintVoltage of Modulating signal = V max – Vmin / 2 = 5.9 – 1.2 / 2 = 2.35v.
39). Which modulation technique is equipped in all EDM instruments?
HintIn frequency modulation, the amplitude and frequency of carrier wave vary in proportion to the amplitude of modulating wave. Hence frequency modulation is used in all EDM instruments.
40). Calculate the maximum value of wavelength, if accuracy is 10mm for 1/1000 parts
HintMax wavelength is calculated by the product of assumed wavelength and accurate wavelength; Wavelength = 10 * 1000 = 10m
41). Phase comparison cannot be done in which zone?
HintPhase comparison cannot be done in a high-frequency zone.
42). Distance transmission is not compatible for ________ frequency.
HintLow frequency is not suitable for distance transmission, due to several atmospheric conditions like interference, reflection, fading, and scattering. This decreases both frequencies and transmitted information.
43). Which phase technique is capable of resolving wavelength?
HintThe modern phase technique is capable of resolving wavelength, at 1/1000 part of a wavelength.
44). Calculate carrier frequency of amplitude modulation wave, if highest frequency component is 850 Hz and signal bandwidth is 50Hz.
HintUpper frequency = 850 Hz ; bandwidth = 50 Hz ; low frequency = 850 - 50 = 800 Hz; Carrier frequency = 850 -800 / 2 = 825 Hz
45). What is the advantage of an RF amplifier?
HintRF amplifier has a high gain property which provides good sensitivity, also they amplify a weak signal. They have better-required signal selectivity ability from a group of signals. RF amplifier improves SNR ratio by raising incoming weak signal to a higher level.
Read more about Amplifiers.
46). What is the value of standard intermediate frequency used in AM receiver?
Hint455 kHz is the value of standard intermediate frequency used in AM receiver.
47). What is the advantage of analog communication over digital communication?
HintThe advantage of analog communication over digital communication is that it has a low data rate, low bandwidth of transmission, no synchronization required.
48). What is the formula of image frequency?
HintImage frequency f image = f s + 2 fi.
49). What is cross-talk?
HintThe disturbance caused in a nearby channel or circuit in a transmitter signal is a cross-talk. It usually occurs due to an electromagnetic interface.
50). What is the need for costas receiver?
HintCostas receiver is used in Double sideband – SC signal, it is a synchronous receiver system.

Modulation Quiz Questions and Answers

51). What is the job of frequency mixer in a superheterodyne receiver?
HintFrequency mixer in superheterodyne receiver multiplies incoming signal and locally generated carrier.
52). Which of the following is a continuous wave in analog modulation?
HintAmplitude modulation is a continuous wave in analog modulation.
53). At what conditions intermediate frequency is selected?
HintIntermediate frequency should be considered at - The high intermediate frequency that leads to weak selectivity and cause problems in the tracking of signals and at low-frequency images, frequency rejection becomes poor.
54). Which of the parameters does selectivity of a receiver has?
HintThe selectivity of a receiver varies with incoming signal frequency and At high frequency, it has a poor ratio value.
55). What kind of modulation is used in television for sound signal?
HintFrequency modulation is used in television to transmit an audio signal.
56). At what frequency RF and detection stages are tuned in a TRF radio receiver?
HintIn the TRF radio receiver, the RF and detection stages are tuned to radiofrequency.
57). After how many stages of amplification the diode detector in an AM radio receiver is found?
HintAfter several stages of amplification, the diode detector in an AM radio receiver is found.
58). Why is difference frequency chosen as the IF in a superheterodyne receiver, rather than sum frequency?
HintSince it’s easy to amplify lower frequencies difference frequency chosen as the IF in a superheterodyne receiver, rather than sum-frequency.
59). What does ferrite antenna does?
HintFerrite antenna, Increases Q of the tuned circuit.
60). Which modulation signal controls the frequency of the carrier?
HintIn Frequency modulation, the modulation signal controls the frequency of the carrier.
61). What is the advantage of FM over AM?
HintThe main advantage of FM over AM it produces less noise.
62). What is the input used at the mixer stage at the superheterodyne receiver?
HintThe input used at the mixer stage at the superheterodyne receiver is RF and local oscillator signal.
63). At what stage of superheterodyne we can observe selectivity?
HintAt the Intermediate Frequency stage of superheterodyne, we can observe selectivity.
64). AVC stands for __________.
HintAVC stands for Automatic volume control.
65). If all the signal frequencies in a radio receiver are amplified equally, then it has a high _______.
HintIf all the signal frequencies in a radio receiver are amplified equally, then it has high fidelity.
66). Which of the following statement is related to the superheterodyne principle?
HintSuperheterodyne principle obtains low fixed intermediate frequency.
67). At what order does signal voltage is induced in the aerial of a radio receiver?
HintAt µV order, the signal voltage is induced in aerial of a radio receiver.
68). Which type of modulation is a man made called?
HintThe modulation made by man is called amplitude modulation.
69). Which type of modulation is used in TV for picture signals?
HintThe type of modulation is used in TV for picture signals is amplitude modulation.
70). What happens if the modulation level is increased?
HintIf the modulation level is increased, sideband power is also increased.
71). What is the advantage of using modulation techniques?
HintThe advantage of using modulation techniques are - Antenna size is reduced, No signal mixing, Improves signal quality.
72). What is a carrier signal?
HintA carrier signal is a high-frequency signal which has phase, frequency, and amplitude but no information. The main functionality of a carrier signal is to carry the signal to the receiver after modulation.
73). What is the functionality of the carrier signal?
HintThe main functionality of a carrier signal is to carry the signal to the receiver after modulation.
74). What is modulated signal?
HintThe product of modulating signal and carrier signal is a modulated signal.
75). What is angle modulation?
HintThe carrier wave varies with respect to instantaneous modulating signal value is called angle modulation.

Modulation Questions and Answers

76). Angle modulation is __________.
HintAngle modulation is classified into frequency and phase modulation.
77). Which sequence of rectangular pulses is used as a carrier wave?
HintPeriodic sequence of rectangular pulses is used as a carrier wave.
78). Noise is a _________ signal.
HintNoise is an unwanted signal.
79). Which of the following are noise examples?
HintNoise can be of hiss, buzz, flicker types.
80). Hiss sound is observed in.
HintHiss sound is observed in radio receivers.
81). Buzz sound is observed in.
HintBuzz sound is observed in the Telephone receiver.
82). Flicker sound is observed in.
HintFlicker sound is observed in Television receivers.
83). Noise affects _________.
HintNoise affects system performance.
84). Noise ________ the operating range of the system.
HintNoise limits the operating range of the system.
85). Noise classification is done based on ________.
HintNoise is classified based on types of source used, transmitter-receiver used.
86). Noise is produced by ________.
HintNoise is produced by internal and external sources of a system.
87). Examples of external source noise.
HintExternal noise is produced by external sources, some of the examples are Atmospheric noise, Extra-terrestrial noise, Industrial noise.
88). Examples of internal source noise.
HintInternal source noise is produced by receiver components while functioning, some of the examples are Thermal agitation, Shot noise, Transit time.
89). SNR stands for?
HintSNR stands for the signal-to-noise ratio.
90). Figure of merit is given as?
HintFigure of merit is the ratio between output SNR and input SNR.
91). Signal is represented in _________ domains.
HintA signal is represented in both frequency and time domains.
92). Time domain in graphical representation has _______ on the x-axis and _______ on the y axis.
HintTime-domain in graphical form has time on the x-axis and amplitude on the y-axis.
93). Frequency domain in graphical representation has _______ on the x-axis and _______ on the y axis.
HintThe frequency-domain in graphical form has frequency on the x-axis and amplitude on the y-axis.
94). Frequency is expressed in terms of ________.
HintFrequency is expressed in terms of Hertz.
95). Double sideband full carrier has _________.
HintThe double sideband full carrier has a carrier and two sidebands.
96). DSBSC stands for?
HintDSBSC stands for Double sideband suppressed carrier.
97). What is double sideband suppressed carrier?
HintA double sideband suppressed carrier is a carrier that is suppressed and saved power is distributed to two sidebands.
98). SSBSC stands for?
HintSSBSC stands for Single sideband suppressed carrier.
99). The process of suppressing one of the sidebands with carrier and transmitting signal is called?
HintThe process of suppressing one of the sidebands with carrier and transmitting signal is called Single sideband suppressed carrier.
100). Which of the following are the advantages of sideband modulation?
HintThe advantages of sideband modulation are high signal power and less noise.
101). Modulation index gives the ratio of ________.
HintModulation index gives the ratio of the voltage of Modulating signal and carrier voltage. It is denoted by “ m “. where m = Vm / Vc.
102). At what condition we can obtain max power output at the transmitter in absence of noise?
HintWe can obtain max power output at transmitter without distortion at the voltage of Modulating signal = carrier voltage condition.

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