Interview Questions.

Top 100+ Amplitude Modulation (am) Interview Questions And Answers - May 26, 2020


Top 100+ Amplitude Modulation (am) Interview Questions And Answers

Question 1. What Is Modulation And Demodulation ?

Answer :

Modulation is the technique of changing the traits of the amplitude, frequency, or section perspective of the high-frequency signal in accordance with the immediate price of the modulating wave.

Demodulation is the manner of extracting the authentic data signal from a modulated service sign.

Question 2. Explain The Need Of Modulation And Demodulation ?

Answer :

Modulation is needed to send the information over lengthy distances as low frequency signals are not able to cowl massive vicinity.

While demodulation is required to get lower back the facts despatched at the receiving aspect.

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Question three. What Is Analog Modulation And State Various Techniques?

Answer :

In it, the modulating method is implemented to the analog facts signal. Its numerous techniques are:

Amplitude modulation(AM)
Frequency modulation(FM)
Phase modulation(PM)
Question four. Why Frequency Modulation Is Better Than Amplitude Modulation?

Answer :

Modulation is better as it offer extra resistance to noise as compared to demodulation.

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Question 5. What Is Digital Modulation And State Various Techniques?

Answer :

We can keep in mind it as conversion of analog to digital signal. Its numerous techniques are:

PSK- Phase shift keying
ASK- Amplitude shift keying
FSK- Frequency shift keying
QAM- Quadrature amplitude modulation
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Question 6. State The Techniques Of Demodulation?

Answer :

There are numerous methods of demodulation relying on how parameters of the provider signal, along with amplitude, frequency or section.

For a sign modulated with a linear modulation, like AM, we can use a synchronous detector.
For a signal modulated with an angular modulation, we need to use an FM demodulator or a PM demodulator.
Question 7. Which Type Of Modulation Is Used In Tv Transmission?

Answer :

Vegestial aspect band modulation (VSBM).

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Question eight. What Is The Difference Between Detector And Demodulator?

Answer :

A detector is a device that recovers statistics of hobby contained in a modulated wave.

Demodulation is updated shape of detector which extracts the authentic information from a modulated service wave.

Question 9. What Is Depth Of Modulation?

Answer :

It refers back to the ratio of the unmodulated service amplitude to the amplitude deviation for which the modulated provider wave reaches its minimal fee.

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Question 10. What Is The Difference Between Coherent And Non-coherent Demodulation?

Answer :

In case of coherent, provider used for demodulation cause is in phase and frequency synchronism with service used for modulation purpose whilst for non-coherent, it is not in synchronism.

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Question 11. Calculate The Power In One Of The Side Band In Ssbsc Modulation When The Carrier Power Is 124w And There Is 80% Modulation Depth In The Amplitude Modulated Signal?

Answer :

Modulation Index = zero.8
Pc = 124W
Power in sidebands may be calculated as = m2 Pc/four
= (zero.8)2 * 124/four
= seventy nine.36 W

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Question 12. Advantages Of Analog Communication Over Digital Communication Are?

Answer :

Due to analog to virtual conversion, the information price will become excessive in virtual conversation. So the transmission bandwidth is likewise accelerated. Digital transmission also wishes synchronization in positive programs which isn't always wanted in case of analog communication systems.

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Question thirteen. What Is The Carrier Frequency In An Am Wave When Its Highest Frequency Component Is 850hz And The Bandwidth Of The Signal Is 50hz?

Answer :

Upper frequency = 850Hz
Bandwidth = 50Hz
Therefore decrease Frequency = 850 - 50= 800 Hz
Carrier Frequency = (850-800)/2
= 825 Hz

Question 14. In Terms Of Signal Frequency (fs) And Intermediate Frequency (fi), The Image Frequency Is Given By?

Answer :

The photograph frequency is described because the signal frequency delivered to twice the price of intermediate frequency. It is the unwanted frequency generated on the receiver which also gets amplified with the message signal. The photograph frequency causes interference and therefore  or greater stations or sources may be received concurrently on the receiver output.

Question 15. Cross Talk Is ?

Answer :

Cross talk is the disturbance precipitated within the close by channel or circuit due to transmitted sign. Cross speak is normally as a result of undesired coupling of capacitors or inductors from one channel to every other. Electromagnetic interference (EMI) causes go talk inside the circuits or the channels. In crosstalk, the indicators journeying towards each other intrude with every different and cause disturbance inside the signal.

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Question sixteen. The Costas Receiver Is Used For ?

Answer :

Costas receiver is a synchronous receiver machine used for demodulating DSB-SC waves. The incoming modulated carrier is implemented at  inputs of the coherent detectors of the receiver. The domestically generated provider carried out to the two inputs is but in phase quadrature with each different. The frequencies of the nearby providers are adjusted as identical because the carrier frequency of the acquired sign.

Question 17. The Advantages Of Using An Rf Amplifier Are?

Answer :

The RF amplifiers are used in exceptional heterodyne receivers. The advantages of using RF receivers are 

They have better sensitivity i.E. They've progressed advantage to the sign
They have higher sign to noise ration than other amplifiers
The selectivity is higher as they have higher rejection to the adjacent undesired signals.
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Question 18. Function Of Frequency Mixer In Super Heterodyne Receiver Is?

Answer :

The feature of a frequency mixer in a exquisite heterodyne receiver is that it mixes or multiplies the incoming modulated service with the domestically generated carrier. It then produces some of frequencies. The produced frequencies are either the sum or the differences of the frequencies of the acquired signals. The output of the mixer is used to detect the modulating or records sign from the acquired modulated carrier.

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Question 19. The Functions Of Radio Receiver Are?

Answer :

The radio receivers obtain the incoming modulated service by the receiving antennas. Then they choose the wanted sign from the service and reject the undesirable signals and noise. The received signal is then amplified by way of the RF amplifiers. Detection of the records signal is accomplished from the acquired carrier and the facts or the modulating signal is then filtered and amplified.

Question 20. The Standard Value For Intermediate Frequency (if) In Am Receivers Is?

Answer :

Intermediate frequency (IF) is a frequency at which the received service frequency is shifted for detection of message signal. The IF is generated by blending the obtained carrier with the regionally generated signal. The IF is generated and is shifted to in addition amplifiers and detectors for amplification and detection of message sign respectively. In extraordinary heterodyne AM receivers, an intermediate frequency of 455 KHz is used.

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Question 21. Intermediate Frequency (if) Should Be Carefully Chosen As?

Answer :

Intermediate frequency (IF) need to be carefully selected as

High IF outcomes in poor selectivity and therefore negative rejection of adjacent channels.
High IF consequences in troubles in monitoring of alerts inside the receivers.
Image frequency rejection becomes terrible at low IF or if very excessive.
Question 22. Advantages Of Using An Rf Amplifier Are?

Answer :

The RF amplifiers have more advantage this is they have got better sensitivity. They have better capacity to expand weak alerts acquired by the receiver. The RF amplifiers have higher selectivity i.E., better ability to select the desired signals a number of the various incoming signals. The incoming vulnerable signals are raised to a higher stage via the RF amplifiers and consequently they enhance sign to noise ratio.

Question 23. Selectivity Of A Receiver?

Answer :

The ability of the receiver to pick the desired indicators the various diverse incoming indicators is termed as Selectivity. It rejects the alternative alerts at intently mendacity frequencies. Selectivity is determines overall performance of a radio receiver that how a whole lot it responds only to the radio signal this is required to get hold of. Selectivity of a receiver changes with incoming signal frequency and is poorer at high frequencies.

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Question 24. The Factors That Determine The Sensitivity Of Super Heterodyne Receiver Are?

Answer :

Sensitivity of a receiver is defined as the ability of the receiver to make bigger weak indicators acquired via the receiver. It is the voltage that must be applied at the enter terminals of the receiver to reap a minimal popular output at the output of the receiver. The factors that determine the sensitivity of exceptional heterodyne receiver are?

Gain of the IF amplifier
Noise parent of the receiver
Gain of RF amplifier
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Question 25. In Automatic Gain Control Of The Am Receiver?

Answer :

The computerized advantage manipulate (AGC) circuit is used to adjust the advantage of the receiver relying upon the power of the obtained sign on the receiver. The AGC gives a DC voltage as an output that is proportional to the amplitude of the acquired signal. In AGC, the output is a linear feature of the enter.

Question 26. Squelch Circuit Is?

Answer :

Squelch circuit suppresses the output audio while there's inadequate preferred enter signal at the receiver. The circuit is used to suppress the undesirable channel noise while there may be no reception with the aid of the receiver. Squelch circuits can be used in wi-fi microphones live faraway from replicating the noise while sufficient signal isn't acquired. Regulating squelch is supplied in a few structures for the receiver.

Question 27. Frequency Components Of An Am Wave (m = Modulation Index) Are?

Answer :

Frequency additives of an AM wave having m modulation index are 

service frequency (ωc ) with amplitude A
top aspect band (ωc + ωm) having amplitude mA/2
lower facet band (ωc - ωm) having amplitude mA/2
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Question 28. Examples Of Low Level Modulation Are?

Answer :

In a Low stage Amplitude Modulation system, modulation is achieved at lower strength of carrier and modulating sign. Therefore the output power of modulation is low. So energy amplifiers are required to boost the sign up to the favored electricity degree. Examples of low level modulation are

Square regulation diode modulation
Switching modulation
Question 29. If Modulation Index Is Greater Than 1?

Answer :

Modulation index is the measure of quantity to which the parameter of the provider is various in accordance with the modulating signal. If modulation index is more than 1, or the modulation percent is extra than 100%, it is known as over modulation. 

The baseband signal isn't always preserved inside the envelope of the AM signal and consequently, the recovered sign is distorted on the output of the receiver.

Question 30. In An Amplitude Modulation?

Answer :

In an Amplitude Modulation, the amplitude of the service varies consistent with the instant values of the baseband sign. The frequency and the phase of the service remain regular. 

The envelope of the AM wave has the equal shape because the message of the base band signal.

Question 31. Automatic Gain Control Is?

Answer :

Automatic gain manage affords controlled sign amplitude on the output even if there are amplitude variations at the input. This managed output adjusts the input to output gain to a suitable price in order that the device may fit properly even for wide range of versions on the enter. 

The AGC is utilized in AM radio receivers for controlling the vulnerable and sturdy sound indicators.

Question 32. Vestigial Side Band Signals Are Detected By?

Answer :

Vestigial facet band signals are detected by way of Synchronous detection or coherent detection technique. The distortions in a VSB signal can be decreased by decreasing the modulation index and increasing the width of VSB.

Question 33. Phase Shift Method Is?

Answer :

Phase shift approach is one of the methods used for the generation of SSB-SC alerts. This approach includes  balanced modulators and two section transferring networks and avoids the use of filters. Both the balanced modulators produce side band as an output. 

The SSB-SC alerts are generated the usage of a couple of tone modulating signals as if performed with single tone modulating sign, they do now not carry any beneficial statistics.

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Question 34. Limitations Of Frequency Discrimination Method Are?

Answer :

Limitations of Frequency discrimination technique are that as the base band sign must be accurately associated with the carrier signal frequency, the designing of band pass clear out is hard if the carrier frequency is pretty better than the bandwidth of the baseband signal. The machine isn't beneficial for video communication reason.

Question 35. Generation Of Ssb Sc Signal Is Done By?

Answer :

SSB-SC indicators are the alerts in which simplest one of the sidebands is transmitted in an AM wave. The carrier is also suppressed at the same time as transmitting the AM sign. SSBSC signal can be generated through two strategies:

Frequency discrimination approach or filter out technique
Phase discrimination method or section shift method
Question 36. Pilot Carrier Is?

Answer :

Pilot carrier is a small service transmitted with modulated signal from the transmitter. It is separated on the receiver and used to section lock the domestically generated carrier signal generated on the receiver. It gives synchronization at the receiver. 

As a vulnerable service is transmitted with the DSB sign, it is also called partly suppressed provider gadget, as the provider is not totally suppressed. So it's miles a case of over modulation.

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Question 37. Quadrature Amplitude Modulation (qam) Is?

Answer :

The modulation scheme Quadrature Amplitude Modulation (QAM) permits identical bandwidth used for transmission of  DSB-SC indicators. It is also known as Bandwidth Conservation scheme. However it wishes synchronous detection so it needs a further device for era of carrier. Also called Quadrature Carrier Multiplexing, the scheme is utilized in color tv.

Question 38. Disadvantages Of Using Synchronous Detection Of Am Signal Are?

Answer :

Disadvantages of using synchronous detection of AM signal are that it desires an extra system for technology of provider. The frequency of the locally generated carrier need to be equal to that of transmitted provider. And the phase of the regionally generated carrier need to be synchronized to that of transmitted service in any other case the detected signal could get distorted so it desires an additional system for synchronization of provider. This makes the receiver complex and dearer.

Question 39. Requirements Of Synchronous Detection Of Am Signal Are?

Answer :

Synchronous detection of AM sign requires nearby generation of the carrier signal on the receiver. The frequency of the locally generated provider must be identical to that of transmitted provider. And the segment of the locally generated service have to be synchronized to that of transmitted provider otherwise the detected sign might get distorted.

Question forty. In Synchronous Detection Of Am Signal?

Answer :

In synchronous detection of AM signal, the provider sign is regionally generated after which handed via a low bypass filter out. At the output of the low pass clear out, the authentic modulating sign is recovered. The synchronous detection calls for the technology of provider on the receiver additionally. So extra circuitry is needed at the receiver.

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Question forty one. What Is The Maximum Transmission Efficiency Of An Am Signal?

Answer :

The transmission performance (η) of AM wave is described as the percentage of total power contributed by facet bands of the AM sign. The most transmission performance of an AM sign is 33.33%, i.E., handiest one 1/3 of the full transmitted energy is carried through the aspect bands in an AM wave. The final two 0.33 of the full transmitted strength receives wasted.

Question forty two. Ring Modulator Is

Answer :

Ring modulator is a product modulator used for DSB SC era. It consists of four diodes linked in the shape of ring. In AM , the hoop modulator acts as a product modulator for a square wave carrier and modulating sign and generated a Double Side Band-Suppressed Carrier signal.

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Question forty three. The Process Of Recovering Information Signal From Received Carrier Is Known As?

Answer :

Detection or demodulation of the acquired signal is the recovery of records or the unique message that became transmitted by the transmitter after modulation. The manner is likewise referred to as demodulation it recovers the original signal from the modulated sign acquired.

Question forty four. Am Demodulation Techniques Are?

Answer :

AM signals are detected or demodulated the use of Square law demodulator or envelope detector. The demodulators extract the facts from the received AM sign. 

Square regulation demodulators are distinctly nonlinear in low voltage place so they may be used for low stage modulated alerts. Envelope detectors extract the envelope of the AM wave.

Question 45. In High Level Amplitude Modulation?

Answer :

In High stage Amplitude Modulation device, Modulation is accomplished at high strength of carrier and modulating indicators so Power amplifiers are used to enhance the provider and modulating signals earlier than modulation. Collector modulation technique is the instance of High stage Amplitude Modulation.

Question 46. In Low Level Amplitude Modulation?

Answer :

In a Low level Amplitude Modulation device, modulation is done at decrease electricity of provider and modulating sign. Therefore the output power of modulation is low. So strength amplifiers are required to boost the sign as much as the preferred electricity stage.

Question forty seven. An Oscillator For An Am Transmitter Has A 100μh Coil And A 10nf Capacitor. If A Modulating Frequency Of 10 Khz Modulates The Oscillator, Find The Frequency Range Of The Side Bands?

Answer :

Carrier frequency fc = 1/2Π√LC
= 1/ 2Π√100 * 10 - 6 * 10 * 10-9
= 1/2Π * 10-6
= 1.Fifty nine * a hundred and five Hz
= 159 KHz

The modulating frequency fm is 10KHz

Therefore the variety of AM spectrum is given by means of (fc fm ) to (fc + fm )

= (159 - 10) to (159 + 10)
= 149 KHz to 169 KHz

Question 48. Bandwidth (b) Of An Am Signal Is Given By?

Answer :

Bandwidth of the AM wave is the difference in the two intense frequencies of the AM sign. It is given via

B = (ωc + ωm)- (ωc - ωm)
= ωm

i.E., the bandwidth of the AM wave is twice the best frequency gift inside the modulating signal.

Question forty nine. Am Wave May Be Represented As E(t) Cos ωct Where E(t) Is

Answer :

An AM wave may be represented through

s(t) = [A+ x(t)] cos ωct
= E(t) cos ωct

Where x(t) is the modulating signal

A is the amplitude of service wave

E(t) is the Envelope of the AM wave

The envelope includes the modulating sign that may be recovered from AM sign the use of demodulation techniques.

Question 50. Radio Waves Travel Through?

Answer :

Radio conversation or wi-fi communication takes area via electromagnetic waves.

The message is transmitted thru open space thru electromagnetic waves or radio waves. The waves are transmitted within the open space via antenna after processing of sign.

Question fifty one. The Minimum Antenna Height Required For Transmission In Reference To Wavelength λ Is?

Answer :

For powerful transmission of sign through the transmitter, the antenna peak need to be at least quarter length of the sign wavelength i.E., λ/4

L= λ/four
= c/4f

Required antenna top decreases with increase in frequency of the signal so modulation is achieved. With modulation, the low frequency alerts are shifted to excessive frequency indicators.

Question fifty two. Analog Signal May Be Converted Into Digital Signal By?

Answer :

Conversion of analog sign into digital sign converts a non-stop time signal within the form of digits. The conversion is carried out with the assist of sampling technique. A pattern is a hard and fast of values at a point in time area. The common wide variety of samples obtained in one second is known as sampling frequency.

Question 53. Synchronous Detection Means?

Answer :

Synchronous detection manner demodulation of received sign and extracting facts from it. It requires a reference sign at the receivers with predetermined frequency and phase that is generated using more circuitry. Synchronous detection helps in extracting vulnerable indicators from noise.

Question 54. What Is The Effect On The Transmitted Power Of Am Signal When The Modulation Index Changes From 0.Eight To 1?

Answer :

The overall energy in an AM is given via 

Pt = Pc (1 + m2/2) 

Where Pc is the carrier electricity and m is the modulation index.


Pt1 = Pc (1 + zero.82/2) = 1.32 Pc
Pt2 = Pc ( 1 + 12/2) = 1.5 Pc
Increase in electricity = (1.Five Pc - 1.32 Pc)/ 1.32 Pc
= 0.1364

Question 55. Types Of Analog Modulation Are?

Answer :

Modulation is a system via which a few characteristics of sign such as amplitude or phase or frequency are various according with the immediate cost of the statistics sign . 

The signal whose characteristics are various is referred to as provider sign, because it consists of the information. The sign that carries the facts is known as modulating signal as according to it, the characteristics of service signal are numerous.

Methods of analog modulations are:

Amplitude modulation
Frequency modulation
Phase modulation
Question 56. Analog Communication Indicates?

Answer :

Analog communication manner that the statistics is transmitted within the shape of a non-stop signal, including a valid wave. The signal has various amplitude or phase or frequency. 

Coding isn't always carried out to the sign as in case of digital statistics. Amplitude modulated signal and frequency modulated alerts are the examples of analog conversation.