Advance Physics MCQs – Communication Systems ( Advance Physics ) MCQs
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Advance Physics MCQs – Communication Systems ( Advance Physics ) MCQs
The most occurred mcqs of Communication Systems ( ) in past papers. Past papers of Communication Systems ( Advance Physics ) Mcqs. Past papers of Communication Systems ( Advance Physics ) Mcqs . Mcqs are the necessary part of any competitive / job related exams. The Mcqs having specific numbers in any written test. It is therefore everyone have to learn / remember the related Communication Systems ( Advance Physics ) Mcqs. The Important series of Communication Systems ( Advance Physics ) Mcqs are given below:
Elements of a Communication System
1. How many elements are essential for any communication system?
a) 3
b) 2
c) 4
d) 7
Answer: a
Explanation: Communication is the very act of transmission of information. Irrespective of its nature, every communication system has three essential elements, namely a transmitter, a medium or channel, and a receiver.
2. Which of the following is the purpose of the transmitter?
a) Converts signals to electric form
b) Operating the received signal
c) Converting the signal into a suitable form
d) Reduces noise from signals
Answer: c
Explanation: The purpose of a transmitter is to convert the message signal produced by the source of information into a suitable form that can be transmitted through the channel that connects the transmitter and the receiver.
3. Which among the following can be an input to a transmitter?
a) Voice signal
b) Electric signal
c) Light signal
d) Wave signal
Answer: b
Explanation: If the output of the information source is a non-electrical signal such as a voice signal, then that’s where the transducer comes into play. The transducer converts this voice signal into an electric form before giving it as an input to the transmitter.
4. A channel can be either in the form of wires or wireless.
a) True
b) False
Answer: a
Explanation: Yes, this is a true statement. Depending upon the type of the communication system, a channel can be in the form of wires or cables connecting the transmitter and the receiver or it can also be wireless.
5. Which of the following is the reason for signal distortion?
a) Speed of the signal
b) Wearing down of the essential elements
c) Absence of a channel
d) Channel imperfection
Answer: d
Explanation: Channel imperfection is that the reason for distortion when a transmitted signal propagates along the channel. Moreover, the receiver receives a corrupted version of the transmitted signal thanks to the addition of noise to the transmitted signal.
6. What is the function of the receiver?
a) Converts signal into electric form
b) Reducing noise during transmission
c) Operating on the received signal
d) Converting the signal into a useful form
Answer: c
Explanation: The receiver does the function of operating on the received signal. The receiver reconstructs a recognizable form of the original message signal in order to deliver the signal to the user of information.
7. Find the odd one out.
a) Radio
b) Telephone
c) Television
d) Computer networking
Answer: b
Explanation: The telephone is the odd one out. Telephones belong to the category of point-to-point communication, whereas all the others belong to the broadcast mode of communication. In point-to-point communication mode, communication takes place over a link between a single transmitter and a receiver. In broadcast mode, there are a large number of receivers corresponding to a single transmitter.
Basic Terminology Used in Electronic Communication Systems
1. What is the electrical analogue of the information produced by the source?
a) Attenuation
b) Amplification
c) Signal
d) Modulation
Answer: c
Explanation: Signal is the electrical analogue of the information produced by the source. It may be defined as a single-valued function of time (that conveys the information) and which, at every instant of time, takes a unique value.
2. What is defined as the largest distance between the source and the destination upto which a signal can be received with sufficient strength?
a) Modem
b) Range
c) Attenuation
d) Amplification
Answer: b
Explanation: Range is defined as the largest distance between the source and the destination upto which a signal can be received with sufficient strength. Generally, it is the difference between the highest and the lowest values.
3. Identify the device which is a combination of a transmitter, an amplifier and a receiver which picks up a signal and retransmits it.
a) Multi-tandem transmitter
b) Repeater
c) Amplifier
d) Modem
Answer: b
Explanation: A repeater is a combination of a transmitter, an amplifier and a receiver which picks up a signal from the transmitter, amplifies and retransmits it to the receiver sometimes with a change of carrier frequency.
4. What refers to the band of frequencies of the original signal?
a) Range
b) Broadband
c) Bandwidth
d) Baseband
Answer: d
Explanation: The term baseband refers to the band of frequencies of the original signal, i.e. a signal that is not changed by the modulation, as is produced by the source of information. For example, an audio signal may have a baseband range from 20 to 20,000 hertz.
5. ‘X’ refers to the frequency range over which equipment operates or the range over which the frequencies in a signal vary. Identify ‘X’.
a) Range
b) Repeater
c) Bandwidth
d) Baseband
Answer: c
Explanation: Bandwidth refers to the frequency range over which equipment operates or the range over which the frequencies in a signal vary. It is the particular range of frequencies for transmitting a signal. Therefore, X is bandwidth.
6. A transmitter is a device which recovers the original message signal from the signal received at the output of the communication channel.
a) True
b) False
Answer: b
Explanation: No, this statement is false. The receiver is a device which recovers the original message signal from the signal received at the output of the communication channel. Whereas, a transmitter transmits it to the receiving end through a transmission medium.
7. What is the loss of strength of a signal during its propagation called?
a) Attenuation
b) Amplification
c) Bandwidth
d) Noise
Answer: a
Explanation: The loss of strength of a signal when travelling through the transmission medium is called attenuation. This makes the signal to become distorted. Attenuation also refers to the reduction in the amplitude of a signal.
8. What is meant by the term communication?
a) Transfer of information
b) Transfer of bytes
c) Transfer of knowledge
d) Transfer of funds
Answer: a
Explanation: The word communication refers to the faithful transfer of information or message from one point to another point in an intelligible form. The information is first converted into electrical signals and then sent electronically.
9. Name the device which converts energy from one form to another.
a) Transformer
b) Modem
c) Transducer
d) Repeater
Answer: c
Explanation: Any device that converts energy from one form to another is called a transducer. Transducers convert the corresponding variations in the electrical signal at its output.
10. Name the process of recovering the original information signal from the modulated wave at the receiver end.
a) Attenuation
b) Demodulation
c) Modulation
d) Bandwidth
Answer: b
Explanation: The process of recovering the original information signal from the modulated wave at the receiver end is called demodulation or detection. It is the reverse process of the modulation process that occurs at the transmitting end.
Bandwidth of Signals
1. The communication system needed for a given signal depends on which of the following?
a) Band of frequencies
b) Length of the channel
c) Size of the transmitter
d) Size of the collector
Answer: a
Explanation: Each of the message signals has different ranges of frequencies. The type of communication system needed for a given signal depends on the bad of frequencies which are considered essential for the communication process.
2. What is the frequency range for a speech signal?
a) 20 Hz to 20 kHz
b) 20 kHz to 20 MHz
c) 300 Hz to 3100 Hz
d) 30 Hz to 310 Hz
Answer: c
Explanation: For speech signals, the frequency range of 300 Hz to 3100 Hz is considered adequate. Therefore, speech signals require a bandwidth of 2800 Hz (3100 Hz – 300 Hz) for commercial telephonic communication.
3. The frequencies for transmitting music is which of the following?
a) Low
b) High
c) Moderate
d) Very high
Answer: b
Explanation: To transmit music, an approximate bandwidth of 20 kHz is required because of the high frequencies produced by the musical instruments. The audible range of frequencies extends from 20 Hz to 20 kHz.
4. A TV signal is allocated with a bandwidth of 6 MHz.
a) True
b) False
Answer: a
Explanation: Yes, this is a true statement. Video signals for transmission of pictures require about 4.2 MHz of bandwidth. A TV signal contains both voice and picture and is usually allocated 6MHz of bandwidth for transmission.
5. Find the true statement.
a) The value of the harmonic is equal to its contribution to the waveform
b) The value of the harmonic is directly proportional to its contribution to the waveform
c) The value of the harmonic is independent of its contribution to the waveform
d) The value of the harmonic is inversely proportional to its contribution to the waveform
Answer: d
Explanation: When the bandwidth is large enough to accommodate a few harmonics, the information is not lost and the rectangular signal is more or less recovered. This is so because the higher the harmonic, the less is its contribution to the waveform. Therefore, the value of the harmonic is inversely proportional to its contribution to the waveform.
Bandwidth of Transmission Medium
1. Which of the following is not a medium of transmission?
a) Microwave system
b) Wire
c) Free space
d) Fiber optic cable
Answer: a
Explanation: Microwave System is not a transmission medium. Instead, it is used for the transmission of data over a cable as well as lines. All the others are commonly used transmission media. Coaxial cable is a widely used wire medium, which offers a bandwidth of approximately 750 MHz.
2. The range of radio frequencies for communication through free space is which of the following?
a) Few hundreds of Hz to a few kHz
b) Few hundreds of MHz to a few GHz
c) Few hundreds of kHz to a few GHz
d) Few hundreds of Hz to a few thousands kHz
Answer: c
Explanation: Communication through free space using radio waves takes place over a very wide range of frequencies, i.e. from a few hundreds of Hz to a few kHz. This range of frequencies is further subdivided and allocated for various services.
3. Identify the range of optical communication from the following.
a) Visible to ultraviolet
b) Microwaves to ultraviolet
c) Microwaves to x rays
d) X rays to gamma rays
Answer: b
Explanation: Optical communication which is also called optical telecommunication is referring to a type of communication at a distance using light to carry information. Optical communication using fibers is performed in the frequency range of 1 THz to 1000 THz, i.e. microwaves to ultraviolet.
4. The bandwidth of optic fiber is high.
a) True
b) False
Answer: a
Explanation: Yes, this is a true statement. The bandwidth of optic fiber is high due to the speed with which data can be transmitted and also the range of frequencies over which the data can travel without any attenuation. An optical fiber can offer a transmission bandwidth in excess of 100 GHz.
5. Pick out the expansion of ITU.
a) Internal Telecommunication Union
b) International Telephone Union
c) International Telecommunication University
d) International Telecommunication Union
Answer: d
Explanation: The expansion of ITU is the International Telecommunication Union. It is a specialized agency of the United Nations that is responsible for all the matters related to information and communication technologies. The ITU administers the present system of frequency allocations
Propagation of Electromagnetic Waves
1. The maximum distance upto which TV transmission from a TV tower of height h can be received is proportional to which of the following?
a) h1/2
b) h
c) h3/2
d) h2
Answer: a
Explanation: The maximum distance upto which TV transmission from a TV tower of height h can be received is proportional to h1/2.
d = √2Rh.
d ∝ h1/2.
2. In communication with help of antenna if the height is doubled, then the range covered which was initially r would become what?
a) √2r
b) 3r
c) 4r
d) 5r
Answer: a
Explanation: Initial range, r = √2Rh.
When the height of the antenna is doubled,
r’ = √2R × 2h = √2r.
Semiconductor Electronics MCQs
3. Identify the layer where ozone is present.
a) Troposphere
b) Stratosphere
c) Ionosphere
d) Mesosphere
Answer: b
Explanation: The ozone layer is present in the stratosphere. The ozone layer blocks the harmful ultraviolet radiation from reaching us. For this ultraviolet radiation, the wavelength is considered to be 3 × 10-7 m.
4. Which of the following statements is wrong?
a) Ground wave propagation can be sustained at frequencies 500 kHz to 1500kHz
b) Satellite communication is useful for the frequencies above 30 MHz
c) Space wave propagation takes place through tropospheric space
d) Skywave propagation is useful in the range of 30 to 40 MHz
Answer: d
Explanation: Skywave propagation is useful for radio-waves of frequencies ranging from 2 MHz to 30 MHz. Higher frequencies than this value cannot be reflected by the ionosphere. All the other statements are correct.
5. What is the refractive index of the ionosphere?
a) Zero
b) More than one
c) Less than one
d) One
Answer: c
Explanation: Ionosphere is the uppermost layer of the earth’s atmosphere. The ionosphere has a very low density. The refractive index of the ionosphere is less than one.
6. The biological importance of the ozone layer is to stop the greenhouse effect.
a) True
b) False
Answer: b
Explanation: No, this statement is false. The ozone layer stops the harmful ultraviolet radiation. It acts as a filter for harmful Ultraviolet radiation from the sun, thereby protecting the life on earth. It is a greenhouse gas.
7. Identify a suitable frequency for skywave propagation.
a) Upto 2 MHz
b) From 2 MHz to 30 MHz
c) From 2 MHz to 50 MHz
d) From 2 MHz to 80 MHz
Answer: b
Explanation: Skywave propagation is useful for radiowaves of frequency from 2 MHz to 30 MHz. Frequencies that are higher than 30 MHz cannot be reflected by the ionosphere.
8. What is the maximum distance upto which the TV transmission can be received, if the TV tower has a height of 220 m?
a) 37.75 km
b) 20 km
c) 59.3 km
d) 40.55 km
Answer: c
Explanation: d = √2Rh.
d = √2 × 220 × 8 × 106
d = 59329.58m ≈ 59330 m
d = 59.3 km.
9. What is the physical significance of the Ozone layer in the atmosphere?
a) Stops ultraviolet radiation
b) Stops greenhouse effect
c) Stops increase in temperature of the atmosphere
d) Absorbs pollutant gases
Answer: a
Explanation: The ozone layer stops ultraviolet radiation. It acts as a filter against the harmful Ultraviolet radiation from the sun from reaching the living being on earth, thereby protecting the life on earth. This is the significance of the ozone layer.
10. The phase difference between space current and capacitive displacement current is 0 rad, when radio waves undergo the ionosphere.
a) True
b) False
Answer: a
Explanation: Yes, this is a true statement. The phase difference between space current and capacitive displacement current is zero. This current will generate a magnetic flux and if we are distant from the capacitor, it’ll be perpendicular to every other.
Modulation and its Necessity
1. What is the modulation used to?
a) Reduce the bandwidth used
b) Separate the transmissions of different users
c) Ensure that intelligence may be transmitted to long distances
d) Allow the use of practical antennas
Answer: a
Explanation: Modulation is used to reduce the bandwidth used. The use of high-frequency carrier waves reduces bandwidth. Modulation allows us to send a signal over a bandpass frequency range.
2. Identify the limitation of amplitude modification.
a) The quality of the audio signal is high
b) Amplitude modulation suffers from noise
c) The efficiency of AM transmission is high
d) It does not require a wider channel
Answer: b
Explanation: Amplitude modification suffers from noise, the quality of the audio signal is poor, and also the efficiency of the amplitude modification transmission is low. The other statements are not valid.
3. Why audio signals cannot be transmitted directly?
a) The signal has more noise
b) The signal cannot be amplified for distance communication
c) The transmitting antenna length is very small to design
d) The transmitting antenna length is very large and impracticable
Answer: d
Explanation: Audio signals require a transmitting antenna of very large and impracticable length. This is because of the high wavelength of the sound waves produced. Therefore, audio signals cannot be transmitted directly.
4. What happens in a frequency modulated wave?
a) Frequency varies with time
b) Amplitude varies with time
c) Both frequency and amplitude varies with time
d) Both frequency and amplitude are constant
Answer: a
Explanation: In a frequency modulated wave, the frequency of the carrier wave is considered to vary corresponding to the modulating signal. At the resonant frequency, the modulated wave is resistive in nature.
5. An oscillator is producing FM waves of frequency 5 kHz with a variation of 15 kHz. What is the modulation index?
a) 1.00
b) 3.00
c) 0.5
d) 5.00
Answer: b
Explanation: Modulation index = △ff
Modulation index = 15kHz5kHz
Modulation index = 3.
6. Modulation is a process of the superposing high-frequency audio signal on low-frequency radiowaves.
a) True
b) False
Answer: b
Explanation: No, this is a false statement. Modulation refers to the superposition of low-frequency audio signals on a high-frequency radiowave. The frequency of the modulated wave is considered to vary with the amplitude of the modulating wave.
7. Why is AM used for broadcasting in the communication systems?
a) Its use avoids receiver complexity
b) It is more noise immune than other modulation systems
c) It requires less transmitting power
d) No other modulation system can give the necessary bandwidth for faithful transmission
Answer: b
Explanation: In the communication systems, amplitude modification is used for broadcasting because its use avoids receiver complexity. Only a diode and a capacitor are sufficient to separate the audio signal from the amplitude modified wave.
8. If the highest modulating frequency of the wave is 10 kHz, what is the number of stations that can be accommodated in a bandwidth of 200 kHz?
a) 10
b) 20
c) 5
d) 15
Answer: a
Explanation: Number of stations = Totalbandwidth(Bandwidth×station).
Number of stations = 200(2×10)
Number of stations = 10
9. What is the maximum distance up to which a TV transmission can be received if the TV tower has a height of 50 m?
a) 28284 km
b) 20.8 km
c) 28.2 km
d) 45 km
Answer: c
Explanation: d = √2hR.
d = √(2 × 50 × 8 × 106)
d = 28284.27 m ≈ 28284 m
d = 28.2 km.
Therefore, the maximum distance up to which the TV transmission can be received is 28.2 km.
10. What happens in frequency modulation?
a) The amplitude of the modulated wave varies as the frequency of the carrier wave
b) The frequency of the modulated wave varies as the amplitude of the modulating wave
c) The amplitude of the modulated wave varies as the amplitude of the carrier wave
d) The frequency of modulated wave varies as the frequency of modulating wave
Answer: b
Explanation: The frequency of the modulated wave varies as the amplitude of the modulating wave. To generate a frequency modulated signal, the frequency of the radio carrier is changed in line with the amplitude of the incoming audio signal.
Amplitude Modulation
1. Identify the type of modulation where the frequency of the modulated wave is equal to that of the carrier wave.
a) Frequency modulation
b) Amplitude modulation
c) Carrier modulation
d) Phase modulation
Answer: b
Explanation: In Amplitude modulation, the modulating wave is superimposed on a high-frequency carrier wave such that the amplitude of the modulated wave varies as the amplitude of the modulating wave.
2. What does AGC stand for?
a) Automatic gain control
b) Automatic gear control
c) Amplitude gain control
d) Automotive gear center
Answer: a
Explanation: AGC stands for automatic gain control. Automatic gain control changes (AGC) the overall gain of a receiver automatically so that the strength of the received signal remains almost constant.
3. Why is AM used for broadcasting in the communication systems?
a) Its use avoids receiver complexity
b) It is more immune to other modulation systems
c) It requires less transmitting power
d) No noise disturbances
Answer: a
Explanation: Amplitude modulation (AM) is used for broadcasting because it avoids receiver complexity. Moreover, only a diode and a capacitor are sufficient to separate the audio signal from the amplitude-modulated wave.
4. Of the following which is the preferred modulation scheme for digital communication?
a) Pulse code modulation
b) Pulse amplitude modulation
c) Pulse position modulation
d) Pulse width modulation
Answer: a
Explanation: Pulse code modulation is the one preferred for digital communication. Pulse codes are used to convert an analog signal to a digital one. It is the standard form of digital audio in computers, compact discs, etc.
5. A carrier of peak voltage 15 V is used to transmit a message signal. If the modulation index is 70%, then what will be the peak voltage of the modulating signal?
a) 25 V
b) 11 V
c) 10.5 V
d) 30 V
Answer: c
Explanation: μ = AmAc.
Am = μ × Ac.
Am = (70100) × 15 V
Am = 10.5 V.
6. PAM stands for pulse attenuation modulation.
a) True
b) False
Answer: b
Explanation: PAM stands for pulse amplitude modulation. It is defined as the process in which amplitudes of the regularly spaced rectangular pulses vary in direct proportion to the instantaneous values of the continuous message signal.
7. ‘X’ for an AM is the ratio of change in amplitude of the carrier wave to the amplitude of the original carrier wave. Identify ‘X’.
a) Automatic gain control
b) Modulation index
c) Phase index
d) Amplitude index
Answer: b
Explanation: The modulation index for an AM wave is defined as the ratio of change in the amplitude of the carrier wave to the amplitude of the original carrier wave.
μ = (Changeintheamplitudeofthecarrierwave)(Amplitudeoftheoriginalcarrierwave).
8. How can the noise be reduced in AM signal?
a) Increasing amplitude
b) Increasing wavelength
c) Increasing bandwidth
d) Increasing frequency deviation
Answer: d
Explanation: Noise is a form of amplitude variations in the transmitted signal due to several factors such as the atmosphere, industries, etc. This noise can be reduced by increasing the deviation of the frequency of the signal.
9. Suggest a possible communication channel for the transmission of a message signal that has a bandwidth of 200kHz.
a) TV transmission
b) Optical fiber
c) AM radio
d) FM radio
Answer: d
Explanation: The communication channel for the transmission of a message signal that has a bandwidth of 200kHz is FM radio. AM radio is the channel required for a message signal having a bandwidth of 5 MHz. Other options are not valid.
10. Identify the type of modulation where the modulating wave is superimposed on a high-frequency carrier wave.
a) Phase modulation
b) Amplitude modulation
c) Frequency modulation
d) Wavelength modulation
Answer: b
Explanation: In Amplitude modulation, the modulating wave is superimposed on a high-frequency carrier wave such that the amplitude of the modulated wave varies as the amplitude of the modulating wave. The frequency of the modulated wave is equal to the frequency of the carrier wave.
Production of Amplitude Modulated Wave
1. Which one of the following is a way to produce a signal?
a) Superimposition with a carrier signal
b) Superimposition with a received signal
c) Superimposition with a transmitted signal
d) No superimposition is required
Answer: a
Explanation: Any signal that is generated from a source and is required to be sent over large distances from the source to the receiver, needs to be modified. This can be achieved by superimposition with a carrier signal in order to ensure that the signal is transmitted in a suitable bandwidth.
2. Which of the following is true about carrier signal?
a) Carrier signals have low frequency
b) Carrier signals are used to increase the wavelength of the signal
c) Carrier signals have high frequency
d) Carrier signals and message signals are the same
Answer: c
Explanation: Carrier signals have high frequencies and hence are used in the transmission of radio waves. This is because since space is an insulator, for having electric current in order to magnetize it is only possible if the source contains a rate of change of voltage or a varying electric field. All the other statements are not valid.
3. Identify the one that is not required in the process of production of amplitude modulated wave?
a) Square law device
b) Rectifier
c) Bandpass filter
d) Combination of message and carrier signal
Answer: b
Explanation: Rectifier is not involved in the process of production of the amplitude-modulated wave. When the message signal is superimposed with the carrier signal to form the desired signal, that signal is in one phase only. So, to overcome this problem we use a square-law device placed in the circuit to square the waveform generated. Bandpass filters are also used in the process.
4. A bandpass filter rejects direct current.
a) True
b) False
Answer: a
Explanation: Yes, this is a true statement. A bandpass filter rejects low and high frequencies and allows a band of frequencies to pass through. So, when a signal is passed through a bandpass filter, it rejects dc and the sinusoids of frequencies ωm, 2ωm, and 2ωc and retains the frequencies ωc, ωc – ωm, and ωc + ωm.The output of the bandpass filter, therefore, is of the same form is hence an AM wave.
5. Which of the following is false?
a) Bandpass filters filter out the unwanted frequencies
b) The transmitting antenna transmits the signal over large distances
c) Attenuation should be reduced for a signal
d) The modulated signal is quite strong
Answer: d
Explanation: No, the modulated signal is quite weak and cannot sustain attenuation over a large distance. So, the modulator is followed by a power amplifier that provides the necessary power, and then the modulated signal is fed to an antenna of appropriate size for radiation.
Detection of Amplitude Modulated Waves
1. What is the full form of IF?
a) Intermediate frequency
b) Internal frequency
c) Interval frequency
d) Immediate frequency
Answer: a
Explanation: Intermediate frequency (IF) is a frequency to which a carrier wave is shifted as an intermediate step during the transmission of a signal in order to facilitate further processing. In this, the carrier frequency is usually changed to a lower frequency preceding the detection.
2. Which of the following is not part of the detector system?
a) Rectifier
b) Envelope detector
c) Amplifier
d) AM wave
Answer: c
Explanation: The amplifier is a part of the receiver system, of which, the detector is a part of. But, the detector system alone consists of the rectifier, envelope detector, and obviously the amplitude-modulated wave that passes through it.
3. Which one of the following is the process of recovering the modulated signal?
a) Amplification
b) Detection
c) Attenuation
d) Transmission
Answer: b
Explanation: Detection is the process of recovering the modulating signal from the modulated carrier wave. The transmitted message gets attenuated in propagating through the channel. The receiving antenna is, therefore, to be followed by an amplifier and a detector. The detected signal may not be strong enough to be made use of and hence is required to be amplified.
4. The rectifier produces the output required in a communication system.
a) True
b) False
Answer: a
Explanation: Yes, this is a true statement. A rectifier converts alternating current (AC), which periodically reverses its direction, to direct current, which travels only in one direction. In a communication system, the modulated signal coming from the intermediate frequency (IF) stage is passed through the rectifier, located in the detector system, and the rectifier, in turn, produces the output required.
5. Which among the following can be detected by an envelope detector?
a) Low frequency AM waves
b) Very low frequency AM waves
c) Envelope detectors cannot detect AM waves
d) High frequency AM waves
Answer: d
Explanation: An envelope detector is used to detect high-frequency amplitude modulated (AM) waves. It takes high-level AM waves as input and then provides an output that can be considered as an envelope of the original signal. An envelope detector may consist of a simple RC circuit.