InterviewSolution

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51.	The average noise power of white noise is(a) 0(b) Infinity(c) 1(d) None of the mentionedThe question was asked in an interview for internship.Enquiry is from Signals and Noises topic in chapter Baseband Demodulation and Detection of Digital Communications
Answer» Correct answer is (B) Infinity For explanation I would say: White noise is a idealized process with two SIDED spectral density EQUAL to constant N0/2 and frequencies varying from minus infinity to plus infinity. THUS the average noise power is infinity.

52.	The composite equalizing filter is the combination of(a) Receiving and equalizing filter(b) Transmitting and equalizing filter(c) Amplifier and equalizing filter(d) None of the mentionedI have been asked this question in a job interview.This key question is from Signals and Noises in section Baseband Demodulation and Detection of Digital Communications
Answer» Right choice is (a) RECEIVING and equalizing filter Explanation: The functions of both receiving and equalizing filter can be performed by only the equalizing filter ALONE. Thus equalizing filter is the combination of equalizing and receiving filter.

53.	The filter which is used to recover the pulse with less ISI is called as(a) Matched filter(b) Correlator(c) Matched filter & Correlator(d) None of the mentionedThe question was posed to me in a job interview.Question is from Signals and Noises in chapter Baseband Demodulation and Detection of Digital Communications
Answer» The correct answer is (b) Correlator To explain I would SAY: The optimum filter used to recover the pulse with best possible signal to NOISE ratio and LESS or no ISI is called as correlator or matched filter.

54.	Which are called as hard decisions?(a) Estimates of message symbol with error correcting codes(b) Estimates of message symbol without error correcting codes(c) All of the mentioned(d) None of the mentionedThe question was asked in examination.This question is from Signals and Noises topic in portion Baseband Demodulation and Detection of Digital Communications
Answer» Right option is (b) ESTIMATES of message symbol WITHOUT ERROR correcting codes The best I can explain: If error correcting codes are not present, the DETECTOR output consists of estimates of the message symbol which is also called as hard decisions.

55.	White noise has _______ power spectral density.(a) Constant(b) Variable(c) Constant & Variable(d) None of the mentionedThis question was addressed to me in an interview for internship.Question is from Signals and Noises topic in section Baseband Demodulation and Detection of Digital Communications
Answer» The CORRECT choice is (a) CONSTANT Easy EXPLANATION: The AWGN has constant POWER spectral DENSITY.

56.	The causes for error performance degradation in communication systems are(a) Interference(b) Electrical noise(c) Effect of filtering(d) All of the mentionedI got this question in quiz.Enquiry is from Signals and Noises topic in chapter Baseband Demodulation and Detection of Digital Communications
Answer» RIGHT answer is (d) All of the mentioned The explanation is: The MAIN CAUSES of error performance DEGRADATION are interference electrical noise effect of filtering and also DUE to the surroundings.

57.	Thermal noise in the communication system due to thermal electrons(a) Can be eliminated(b) Cannot be eliminated(c) Can be avoided upto some extent(d) None of the mentionedI had been asked this question during an internship interview.I would like to ask this question from Signals and Noises in portion Baseband Demodulation and Detection of Digital Communications
Answer» RIGHT answer is (b) Cannot be eliminated Explanation: THERMAL noise which cannot be eliminated is caused by the MOTION of thermal electrons causes degradation in SYSTEM.

58.	The term heterodyning refers to(a) Frequency conversion(b) Frequency mixing(c) Frequency conversion & mixing(d) None of the mentionedThe question was posed to me by my school principal while I was bunking the class.Question is taken from Signals and Noises topic in division Baseband Demodulation and Detection of Digital Communications
Answer» Correct answer is (C) FREQUENCY conversion & mixing Explanation: The method heterodyning means frequency conversion and mixing and this RESULTS in a SPECTRAL shift.