InterviewSolution

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1.	Quantization noise occurs in ________(a) Frequency Division Multiplexing(b) Time Division Multiplexing(c) Delta Modulation(d) Amplitude ModulationThe question was asked by my college director while I was bunking the class.The above asked question is from Modulation of VSB Modulated Wave in portion VSB Modulation of Analog Communications
Answer» Right CHOICE is (d) Amplitude Modulation The explanation is: Quantisation is the process through which a range of continuous analog values are quantized or rounded off to a single VALUE, thereby forming SAMPLES of a discrete digital signal. Quantisation Error occurs when there is a difference between an INPUT value and it’s quantized value. Quantisation occurs when an analog signal is converted into it’s digital form, thus it occurs in Pulse Code modulation (PCM).

2.	Which is the greatest disadvantage of Pulse Code Modulation?(a) highly prone to noise(b) cannot travel long distances(c) its inability to handle analog signals(d) large bandwidth is required for itThis question was posed to me in class test.Enquiry is from Modulation of VSB Modulated Wave in section VSB Modulation of Analog Communications
Answer» Right answer is (d) large bandwidth is required for it The explanation is: PULSE code MODULATION (PCM) is a digital form of communication. For demodulation of PCM, it is necessary to convert it into PAM. Quantization noise occurs in PCM only. Its greatest DISADVANTAGE is its requirement for large bandwidth.

3.	Pulse communication system that is inherently highly immune to noise is ________(a) PCM(b) PPM(c) PAM(d) PWMI have been asked this question during an internship interview.My question is from Modulation of VSB Modulated Wave in chapter VSB Modulation of Analog Communications
Answer» Correct choice is (a) PCM The best explanation: Pulse Code MODULATION is a technique in which the amplitude of an analogue SIGNAL is converted to a binary value represented as a SERIES of pulses. It is less PRONE to noise and can travel through LONG distances without loss of data.

4.	What the main advantage of PCM?(a) can travel small distances(b) higher bandwidth(c) lower noise(d) good receptionI have been asked this question by my school teacher while I was bunking the class.Query is from Modulation of VSB Modulated Wave in division VSB Modulation of Analog Communications
Answer» The CORRECT OPTION is (c) lower noise The EXPLANATION: Pulse Code Modulation is a technique in which the amplitude of an analogue SIGNAL is converted to a binary value represented as a SERIES of pulses. It is less prone to noise and can travel through long distances without loss of data.

5.	In AM pilot carrier, transmission has ________(a) carrier and part of one side band(b) two side bands and a carrier(c) two side bands(d) carrier, one side band and part of other side bandThis question was posed to me in an interview for internship.I'd like to ask this question from Modulation of VSB Modulated Wave in chapter VSB Modulation of Analog Communications
Answer» Correct option is (b) two SIDE bands and a carrier The EXPLANATION is: In amplitude modulated WAVE, the TRANSMITTED wave has two side bands and a carrier. THUS it’s bandwidth is twice the maximum modulating frequency.

6.	Quantization noise depends upon both sampling rate and number of quantization levels.(a) True(b) FalseThe question was posed to me by my college director while I was bunking the class.My question is from Modulation of VSB Modulated Wave in chapter VSB Modulation of Analog Communications
Answer» CORRECT choice is (B) False Easiest explanation: Quantization NOISE in PULSE code modulation (PCM) DEPENDS upon only on number of quantization levels.

7.	Which of the following frequency is not transmitted in AM transmission?(a) Upper side band frequency(b) Carrier frequency(c) Lower side band frequency(d) Audio frequencyI got this question during an interview for a job.Asked question is from Modulation of VSB Modulated Wave in portion VSB Modulation of Analog Communications
Answer» Right ANSWER is (d) Audio FREQUENCY For explanation: Audio frequency is the frequency that is not TRANSMITTED in AM transmission.

8.	Companding is used in PCM transmitters to allow amplitude limiting in the receivers.(a) True(b) FalseThe question was posed to me in homework.The query is from Modulation of VSB Modulated Wave in chapter VSB Modulation of Analog Communications
Answer» Correct option is (b) False To explain I would SAY: COMPANDING is the process through which the signal to noise ratio of a wave is reduced by compressing and expanding the signal. It decreases the number of bits required to RECORD the STRONGEST signal. Companding also IMPROVES signal to noise ratio.

9.	What is the use of Companding?(a) in PCM transmitters to allow amplitude limiting in the receivers(b) in PCM receiver to overcome impulse noise(c) to overcome quantizing noise in PCM(d) to protect small signals in PCM from quantizing distortionI got this question during an online interview.The query is from Modulation of VSB Modulated Wave topic in division VSB Modulation of Analog Communications
Answer» Right option is (d) to protect small signals in PCM from QUANTIZING distortion The EXPLANATION is: Companding is the process through which the SIGNAL to noise ratio of a WAVE is reduced by compressing and expanding the signal. It decreases the number of bits required to record the strongest signal. Companding also improves signal to noise ratio. It is mainly USED to protect small signals in PCM from quantizing distortion.

10.	What is the reason of “envelope” in an amplitude modulated signal?(a) noise signal(b) carrier signal(c) nematic signal(d) baseband signalI got this question in examination.I need to ask this question from Demodulation of VSB Modulated Wave in chapter VSB Modulation of Analog Communications
Answer» RIGHT choice is (d) baseband signal Explanation: Envelope is basically a SMOOTH CURVE that outlines the EXTREMES of any baseband signal. So basically it is message or baseband signal that DETERMINES the envelope.

11.	AM stands for ________(a) Amplitude Modulation(b) Audio Modulation(c) Antenna Modulation(d) Amplified ModulationI have been asked this question during an internship interview.I need to ask this question from Demodulation of VSB Modulated Wave topic in section VSB Modulation of Analog Communications
Answer» Correct OPTION is (a) AMPLITUDE Modulation Best explanation: AM stands for amplitude modulation. Amplitude modulation is the change in the amplitude of carrier wave in PROPORTION to the INSTANTANEOUS amplitude of the message SIGNAL.

12.	What is the equation for full-carrier AM?(a) V(t) = (Ec + Em) × (sin⁡ ωc t)(b) V(t) = (Ec + Em) × (sin⁡ ωmt) + (sin⁡ ωc t)(c) V(t) = (Ec × Em) × (sin ⁡ωmt) × (sin⁡ ωc t)(d) V(t) = (Ec + Em sin⁡ ωmt) × (sin ⁡ωc t)This question was posed to me during a job interview.My question is taken from Demodulation of VSB Modulated Wave in chapter VSB Modulation of Analog Communications
Answer» Correct choice is (d) V(t) = (Ec + Em sin⁡ ωmt) × (sin ⁡ωc t) Easiest explanation: Amplitude MODULATION is the change in the amplitude of carrier wave in PROPORTION to the instantaneous amplitude of the MESSAGE signal. A carrier can be seen as a waveform with frequency higher than the message signal frequency,that is modulated with respect to INPUT signal for the purpose of transmitting information.The equation for full-carrier AM is V(t) = (Ec + Emsin⁡ωmt) × (sin ⁡ωct).

13.	What is the cause of Overmodulation?(a) distortion(b) splatter(c) both distortion and splatter(d) half reception of signalsI had been asked this question during an online interview.Question is from Demodulation of VSB Modulated Wave in portion VSB Modulation of Analog Communications
Answer» The correct choice is (c) both distortion and SPLATTER To explain I WOULD say: Overmodulation is the process in which the modulation index is greater than 1 such that the modulating signal voltage exceeds the required voltage to produce 100% modulation. It RESULTS out of both distortion and splatter of waveform and causes distortion and overlapping.

14.	If AM radio station increases its modulation index then the audio gets louder at the receiver.(a) True(b) FalseThis question was addressed to me in an online interview.I need to ask this question from Demodulation of VSB Modulated Wave in chapter VSB Modulation of Analog Communications
Answer» Correct choice is (a) True For EXPLANATION: MODULATION INDEX tells us the amount by which the carrier wave is varied with respect to the message signal. If we increase the modulation index then audio signal GETS LOUDER.

15.	The modulation index can be derived from ________(a) frequency-domain signal(b) time-domain signal(c) both frequency and time domain signal(d) a highly modulated carrier waveThis question was posed to me in my homework.My enquiry is from Demodulation of VSB Modulated Wave topic in chapter VSB Modulation of Analog Communications
Answer» Correct option is (C) both frequency and TIME domain signal Easiest explanation: Modulation INDEX tells us the amount by which the CARRIER wave is varied with respect to the message signal. It can be derived for frequency-domain signals as well as for time-domain signals.

16.	A single sideband modulation system is more efficient than a plain amplitude modulated system.(a) True(b) FalseThe question was asked during an online exam.The origin of the question is Demodulation of VSB Modulated Wave in chapter VSB Modulation of Analog Communications
Answer» RIGHT answer is (a) True Explanation: In SINGLE Sideband transmission, the carrier is suppressed and only either of the two SIDEBANDS is transmitted. Thus, it reduces the total POWER consumption and also reduces the bandwidth required. Whereas, in AM, the carrier being transmitted along with both the sidebands entails more power and larger bandwidth.

17.	At peak modulation an SSB transmitter radiate 1000W, what will it radiate with no modulation?(a) 1000 watts(b) 500 watts(c) 250 watts(d) 0 wattsI have been asked this question during an interview.I need to ask this question from Demodulation of VSB Modulated Wave in chapter VSB Modulation of Analog Communications
Answer» Correct ANSWER is (d) 0 watts To explain: POWER of a modulated wave is directly proportional to MODULATION INDEX. Thus, if there is no modulation in any SSB transmitter than, it will not RADIATE. So it will radiate 0 watts when there is no modulation.

18.	Why AM stations has “low-fidelity”?(a) AM is susceptible to noise(b) Commercial AM stations use low power(c) Commercial AM stations have a narrow bandwidth(d) High quantization to noise ratioThe question was asked in an international level competition.This interesting question is from Demodulation of VSB Modulated Wave topic in section VSB Modulation of Analog Communications
Answer» Right option is (C) Commercial AM stations have a narrow bandwidth Easiest explanation: Fidelity is the ability of receivers to REPRODUCE all modulating signals eually. Low fidelity can be seen as sound recording that CONTAIN technical flaws to MAKE sound better compared with the sound that is recorded live. High fidelity refers to the equipment that very accurately PRODUCES without any harmonic or resonance. AM stations have low fidelity to have narrow bandwidth.