VIVA QUESTION FOR ANALOG COMMUNICATION
VIVA QUESTION FOR ANALOG COMMUNICATION:1. What is amplitude modulation?2. What is modulation?3. What are the different types of analog modulation?4. What is the need for modulation?5. What are the objectives met by modulation?6. What are the advantages of PWM over PAM?7. What is pulse position modulation?8. What is the advantage of PPM over PWM and PAM?9. What are the applications of pulse position modulation?10. What are the purposes of using differential pulse position modulation?11. What are the advantages of pulse position modulation?12. What are the applications of PPM?13. Explain the principle of PPM?14. What is the purpose of PPM?15. What are the analog analogies of PAM, PPM, and PWM?16. What is frequency modulation?17. What is PWM? Or pulse length modulation? Or pulse duration modulation?18. What are the disadvantages of PWM?19. Explain the principle of PWM?20. Mention the applications of PWM.21. What is the purpose of PWM?22. What is PAM?23. What are the drawbacks of PAM?24. How is modulation done in PAM?25. Mention the applications of PAM.26. Explain briefly how PAM can vary in different systems?27. What is PAM in practical circuits?28. What is the basic principle of PAM?29. What are the advantages of PAM?30. What is a filter?31. Give the application of filter.32. What are the different types of filter?33. What are active filters?34. Why inductors are not often used in active filters?35. What is low-pass filter?36. What is an ideal low-pass filter?37. What is the difference between an ideal and a practical low pass filter?38. Why doesn't low-pass filter use DSP?39. What is high pass filter?40. What does the term "pass" mean in any low pr high pass filter?41. What does "roll off" mean?42. What are passive filters?43. What is a pass band?44. What is stop band?45. Why is butterworth filter used most often?46. What is band pass filter?47. What is an ideal band pass filter?48. What are band reject filter?49. Name the types of band rejection filter.50. What are signal filters?51. What are digital filters?52. How do EMI and RFI filters work?53. What are long pass filters?54. What are RF and microwave filters?55. What is a precision rectifier?
9.90.91.92.93.94.95.96.With only one diode, why does a precision half wave rectifier saturate?What is the solution to saturating precision rectifier?How can we obtain two output precision half wave rectifier?Why use an op-amp as a rectifier?Why an absolute value circuit is called so?What is a precision full wave rectifier?Who invented the full wave rectifier?What are the advantages of Precision rectifier?What is DAC?What are the different types of DAC techniques?What is an R-2R ladder network?Explain switch bounce or contact bounce.What are harmonics?What do you mean by timer?What is an Oscillator?What are flip-flops?What is a multivibrator?What is the purpose of a multivibrator?Why is an astable multivibrator called so?Why is an monostable multivibrator called so?What is an astable multivibrator?What is an monostable multivibrator?What is the purpose of a monostable multivibrator?Give some example of a multivibrator?Mention the applications of multivibrator?What does the term "stable" mean to you?Explain the operation of an astable multivibrator.Explain how an astable multivibrator can be recognized?What is the principle of a monostable multivibrator?Explain the principle of operation of a monostable multivibrator circuit.How does a monostable multivibrator work in terms of the astable multivibrator?What is the disadvantage of astable multivibrator?Give examples of a monostable multivibrator in use.What are the different types of multivibrator circuits?What is the principle of basic of BJT monostable multivibrator?What is a Schmitt trigger?Explain the operation of a Schmitt trigger.What are the advantages of a Schmitt trigger?Who invented Schmitt trigger?What is the purpose of Schmitt trigger?Why is a Schmitt trigger called a regenerative comparator?
ANALOG COMMUNICATION VIVA QUESTIONS WITH ANSWER SETQ1. What is amplitude modulation?Ans: The process of amplitude modulation consists of varying the peak amplitude of a sinusoidal carrierwave in proportion to the instantaneous amplitude of the modulation signal.Q2. What is modulation?Ans: Modulation may be defined as the process by which some parameters of a high frequency signaltermed as carrier, is varie in accordance with the signal to be transmitted.Q3. What are the different types of analog modulation?Ans: 1) Amplitude modulation 2) angle modulation.Q4. What si the need for modulation?Ans: Consider, for example, picture signal of a T.V camera. It has frequency spectra of DC to 5.5MHz.such awide band of frequency can’t be propagated through ionosphere. However, if this signal is modulated with acarrier in VHF and UHF range, the percentage bandwidth becomes very small and the signal becomesuitable for transmission through atmosphere.Q5. What are the objectives met by modulation?Ans: Length of antenna is shortened, signal loss is reduced, ease of radiation, adjustment of bandwidth,shifting signal frequency of the assigned value.Q6. What are the advantage of PAM and PWM?Ans: PWM system gives a greater signal to noise ratio as compared to PAM but requires a larger bandwidthto achieve this.Q7. What is Pulse position modulation?Ans: Pulse position modulation (PPM) is the process in which the position of a standard pulse is varied as afunction of the amplitude of the sampled signal.
Q8. What is the advantage of PPM over PWM and PAM?Ans: The phase deviation are usually small. The noise produces a smaller disturbing effect on the timeposition of the modulating pulse train and as a result, PPM waves have a better performance with respect tosignal to noise ratio in comparison to PAM and PWM systems.Q9. What are the applications of pulse position modulation?Ans: It is primarily useful for optical communication systems, where there tends to be little or no multipathinterference. Narrowband RF (Radio frequency) channels with low power and long wavelength (i.e., lowfrequency) are affected primarily by flat fading, and PPM is better suited.Q10. What is the purpose of using differential pulse position modulation?Ans: It is possible to limit the propagation of errors to adjacent symbols, so that an error in measuring thedifferential delay of one pulse will affect only two symbols, instead of effecting all successive measurements.Q11. What are the advantage of PPM?Ans: One of the principle advantages of pulse position modulation is that it is an M-ary modulationtechnique that can be implemented non-coherently, such that the receiver does not need to use a phaselocked loop (PLL) to track the phase of the carrier. This makes it a suitable candidate for opticalcommunications systems, where coherent phase modulation and detecting are difficult and extremelyexpensive. The only other common M-ary non-coherent modulation technique is M-ary frequency shiftkeying, which is the frequency domain dual to PPM.The other advantages of pulse position modulation are: The amplitude is held constant thus less noise interference. Signal and noise separation is very easy. Due to constant pulse widths and amplitudes, transmission power for each pulse is same.Q12. What are the application of PPM?Ans: PPM is employed in narrowband RF channel systems, with the position of each pulse representing theangular position of an analogue control on the transmitter, or possible states of binary switch. The numberof pulse per frame gives the number of controllable channels available. The advantage of using PPM for thistype of application is that the electronics required to decode the signal are extremely simple, which leads tosmall, light-weight receiver/decoder units. (Model aircraft require parts that are as lightweight as possible).Q13. Explain the principle of PPM?Ans: The amplitude and the width of the pulse is kept constant in this system, while the position of eachpulse, in relation to the position of a recurrent reference pulse is varied by each instantaneous sampledvalue of the modulating wave. This means that the transmitter must send synchronizing pulses to operatetiming circuits in the receiver. The PPM has the advantage of requiring constant transmitter power output,but the disadvantage of depending on transmitter-receiver synchronization.Q14. What is the puprpose of PPM?
Ans: PPM may be used to transmit analog information, such as continuous speech or data.Q15. What are the analog analogies of PAM, PPM & PWM?Ans: PAM is similar to AM; PPM and PWM is similar to angle modulation.Q16. What is Frequency modulation (FM)?Ans: Frequency modulation is the process of varying the frequency of a carrier wave in proportion to theinstantaneous amplitude of the modulating signal without any variation in the amplitude of the carrierwave.Q17. What is PWM or Pulse length modulation or pilse duration modulation?Ans: In PWM, the pulse amplitude is kept constant but the leading edge, trailing edge or both may be variedas a function of the amplitude of the sampled signal and care must be taken to ensure that the pulse don’toverlap in a TDM system.Q18. What are the disadvantages of PWM?Ans: PWM, in general, requires a greater average power than PAM systems. Also, the PWM system requiresa greater bandwidth than PAMQ19. Explain the principle of PWM?Ans: Pulse-width modulation (PWM) of a signal or power source involves the modulation of its duty cycle,to either convey information over a communication channel or control the amount of power sent to a load.PWM uses a square wave whose pulse width is modulated resulting in the variation of the average value ofthe waveform is directly dependent on the duty cycle D.Q20. Mention the applications of PWM.Ans: PWM can be used to reduce the total amount of power delivered to a load without losses normallyincurred when a power source is limited by resistive means. This is because the average power delivered isproportional to the modulation duty cycle. With a sufficiently high modulation rate, passive electronicfilters can be used to smooth the pulse train and recover an average analog waveform.
ECE Interview Questions with AnswersOnAnalog Communication1. What is Sampling? What is Sampling Theorem?Ans: Sampling is defined as the process in which an analog signals are converted into digital signals. It meansthat a continuous time signal is converted into a discrete time signal.Analog Communication notesSampling Theorem is defined as : ’The continuous time signal that can be represented in its samples andrecovered back if the sampling frequency (fs) is greater than the maximum frequency of the signal (fm) that is fs 2fm’.2. Define PAM and write down its drawbacks?Ans: Pulse Amplitude Modulation is the process by which the amplitude of the regularly spaced pulses variesaccording to the the amplitude of the modulating signal.The drawbacks are:a. Since the amplitude of the pulses varies therefore the peak power of the modulating s/g is much greater.b. The bandwidth required for transmitting is greater since the amplitude varies.3. What is Modulation? What happens in over modulation?Ans: Modulation is defined as the process in which some characteristics of the signal called carrier is variedaccording to the modulating or baseband signal. For example – Amplitude Modulation, Phase Modulation,Frequency Modulation.In case of over modulation, the modulation index is greater than one and envelope distortion occurs.4. What do you mean by Nyquist rate?Ans: In case of Nyquist rate, the sampling frequency is equal to the maximum frequency of the signal andtherefore the successive cycles of the spectrum does not overlap.5. What do you mean by FM and classify FM.Ans: Frequency Modulation can be defined as the frequency of the carrier (wc) is varied acc. to the modulatingsignal about an unmodulated frequency.FM are of 2 types:a. Narrowband FMb. Wideband FM6. What is under sampling?Ans: Under sampling is also known as aliasing effect in which the the sampling frequency is less than themaximum frequency of the signal and therefore the successive cycles of the spectrum overlap.
7. State the advantages of superheterodyning.Ans: The advantages are:a. High selectivity and sensitivity.b. No change in Bandwidth that is bandwidth remains same all over the operating range.c. High adjacent channel rejection.8. What is multiplexing? Name the types of multiplexing.Ans: Multiplexing is defined as the process in which a number of message signals are combined together toform composite signals so that they can be transmitted through the common channel.The two types of multiplexing are:a. Frequency Division Multiplexing: In this technique, fixed frequency bands are allotted to every user in thecomplete channel bandwidth. Such frequency is allotted to user on a continuous basis.b. Time Division Multiplexing: When the pulse is present for the short time duration and most of the time theiris no signal present in-between them than this free space between the two pulses can occupied by the pulsesfrom other channels. This is known as Time Division Multiplexing.9. What is Amplitude Modulation?Ans: Amplitude Modulation is defined as the process in which the instantaneous value of the amplitude of thecarrier is varied according to the amplitude of the modulating or base band signal.10. How can be aliasing be avoided?Ans: Aliasing can be avoided if:a. Sampling frequency must be greater than the frequency of the modulating signal.b. The frequency should be band limited to maximum frequency of the signal(fm) Htz.c. If pre-alias filter is used.ANALOG COMMUNICATION VIVA QUESTIONS WITH ANSWER SET
Q1. What is PAM?Ans: Pulse amplitude modulation, acronym PAM, is a form of signal modulation where the amplitude of acarrier consisting of a periodic train of rectangular pulses is varied in proportion to the sample values of amessage signal. In this type of modulation, the pulse duration is held constant.ANSWERQ2. What are the drawbacks of PAM?Ans: Before sampling a signal, it must be passed through a low-pass filter, so that the higher frequencies areeliminated from the signal and the signal conforms to the requirement of the sampling circuit. Also, thePAM technique has the same signal to noise ratio as the AM. Thus, it is not employed in the practicalcircuits but may be employed to produce other forms of pulse modulation.ANSWERQ3. How is demodulation done in PAM?Ans: Demodulation is performed by detecting the amplitude level of the carrier at every period.ANSWERQ4. Mention the application of PAM.Ans: PAM is widely used in baseband transmission of digital data, with non baseband application havingbeen largely superseded by pulse-code modulation and more recently by PPM.ANSWERQ5. What is PAM in practical circuits ?Ans: PAM is “pulse shaping”. Essentially, communications engineer realize that the shape of the pulse inthe time domain can positively or negatively affect the characteristics of that pulse in frequency domain.ANSWERQ6. What is the basic principle of PAM ?Ans: In PAM, the amplitude of individual pulses in the pulse train is varied from its default value inaccordance with the instantaneous amplitude of the modulating signal at sampling intervals. The width ofthe pulse is kept constant.ANSWERQ7. What are the advantages of PAM ?Ans: Main advantages of PAM are simple transmitter and receiver design. PAM is used to carry informationas well as to generate other pulse modulations.ANSWERQ8. What is a filter ?
Ans: A filter is a device that passes electric signal at certain frequencies of frequency range while preventingthe passage of others.ANSWERQ9. What are the different types of filters ?Ans: Low-pass, high-pass, Band-pass, Band-elimination ( also referred to as band reject or notch).ANSWERQ10. What are active filters ?Ans: Active filters are the circuits that use an operational-amplifier as the active device in combination withsome resistors and capacitors to provide an LRC-like filters performance at low frequencies.ANSWERQ11. What is a low-pass filter ?Ans: a low pass filter is a filter that passes low frequency signal but attenuates signal with frequencieshigher than the cut-off frequency.ANSWERQ12. Why inductors are not often used in active filters ?Ans: Inductors are bulky and costly and may have large internal resistive components.ANSWERQ13. What is an ideal low pass filter ?Ans: An ideal low pass filter is a network which passes all the frequency up to cut-off frequency fc, andblocks all frequencies above fc.ANSWERQ14. What is difference between an ideal and a practical low pass filter ?Ans: The transition region present in practical filters doesn’t exist in an ideal filter. An ideal low-pass filtercan be realized mathematically by multiplying a signal by the rectangular function in the frequency domainor, equivalently, Convolution with a sinc function in the time domain.ANSWERQ15. What is high-pass filter ?Ans: a high pass filter is a circuit that attenuates all signals below a specified cut-off frequency.ANSWERQ16. What does the term “pass” mean in any low-or-high pass filters ?Ans: Pass: to cause or permit to go past or through a barrier.ANSWERQ17. What does “roll-off” mean ?Ans: It means that if you set the cut-off frequency for say 450Hz, any signal coming through to the input ofthe filter is 96dB down at 900 Hz. Set it for 1KHz, signals at 2KHz are down 96dB.ANSWERQ18. What are passive filters ?Ans: Passive filters are implemented using only passive components such as resistors, capacitors and
inductors. These filters do not produce any amplification of the input signal.ANSWERQ19. What is a pass band ?Ans: The range of frequencies that is transmitted.ANSWERQ20. What is drop band ?Ans: The range of frequencies that is attenuated.ANSWERQ21. Why is butterworth filter used most often ?Ans: in many low pass filter applications, it is necessary for the closed loop gain to be as close to 1 aspossible within the baseband. Butterworth filter is best suited for this type of application.ANSWERQ22. What is Band pass filter ?Ans: It passes a band of frequencies and attenuates frequencies on both sides of the pass band. You maketake an example of series resonant circuit for the explanation.ANSWERQ23. What is sn idesl band pass filter ?Ans: The ideal band pass filter can be used to isolate the component of a time series that lies within aparticular band of frequencies.ANSWERQ24. What are band reject circuits ?Ans: Band reject filters are tuned circuits that prevent the passage of signal within a specified band offrequencies. These devices are also known as band stop or notch filters.ANSWERQ25. Name the types of band rejection filters.Ans: Twin-T & active Wein-Robinson circuit.ANSWERQ26. What are signal filters ?Ans: Signal filters block or decrease unwanted frequencies or signal wave characteristics.ANSWERQ27. What are digital filters ?Ans: Digital filters use digital signal processing (DSP) to perform numerical calculations on sampled valuesof a signal.ANSWERQ28. What is precision rectifier ?Ans: It is an op-amp voltage follower, with a diode inserted between the op-amp output terminals and thecircuit output point.ANSWER
Q29. Why use an op-amp as a rectifier ?Ans: In diode rectifiers circuit, the voltage drop that occurs with an ordinary semiconductor rectifier can beeliminated to give precision rectification.ANSWERQ30. What is a precision full wave rectifier ?Ans: a full wave precision rectifier consists of a summing circuit and a precision half wave rectifier whichhas a voltage gain of 2.ANSWERQ31. What are the advantages of precision amplifier ?Ans: Gain of upto 100 can be achieved in this configuration, which is useful for signal conditioning of lowoutput of transducers in mV range.ANSWERQ32. What is DAC ?Ans: The process of conversion of digital
Ans: Modulation is defined as the process in which some characteristics of the signal called carrier is varied according to the modulating or baseband signal. For example – Amplitude Modulation, Phase Modulation, Frequency Modulation. In case of over modulation, the modulation index is
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