C.15)A digital system is required to amplify a binary encoded audio signal.The user should be able to control the gain of the amplifier from a minimum to a maximum in 100 increments.The minimum number of bits required to encode, in straight binary is
(a)9
(b)6
(c)7
(d)none of these
Answer is ( )
C.16)The sinc (¶) function which is used widely in communication, becomes zero when
(a)π¶ = infinity
(b)sin(π¶)=zero
(c))both (a) & (b)
(d)cannot determine
Answer is (c)
C.17)Suppose that the modulating signal is m(t)=2 cos(2*pi*fm*t) and the carrier signal is c(t)=Ac cos(2*pi*fc*t), which one of the following is a conventional AM signal without over-modulation?
(a) x(t)=Ac m(t) cos(2*pi*fc*t)
(b) x(t)=Ac [1+m(t)] cos(2*pi*fc*t)
(c) x(t)=Ac cos(2*pi*fc*t) + (Ac/4) m(t) cos(2*pi*fc*t)
(d) x(t)=Ac cos(2*pi*fm*t) cos(2*pi*fc*t) + Ac sin(2*pi*fm*t) sin(2*pi*fc*t)
Answer is ()
C.18)Assertion: LPF are used to eliminate the higher (greater than 3rd)side lobes of an energy signal whose Fourier Transform spans an infinite duration Reason:For a finite duration signal, the Fourier transform of the energy is concentrated in it's main lobe (upto 95%) & upto 99% till it's 3rd lobe, the remaining higher order side lobes are insignificant
(a) Both the first and second statements are true
(b) Both the first and second statements are true and the second is the correct reason of the first
(c) either of them are true
(d) both are false
Answer is (b)
C.19) VSB modulation is preferred in TV because
(a) it reduces the bandwidth requirement to half
(b) it avoids phase distortion at low frequencies
(c) it results in better reception
(d) none of the above
Answer is ()
C.20) For an AM signal s(t) given by 20(1+0.9cos2π10^4t)cos (2π10^6t), find the modulation efficiency ?
(a) 25%
(b) 24.4%
(c) 28.8%
(d) none of the above
Answer is (c)
C.21) The colour subcarrier and sidebands produced by its modulation with the chrominance signals are accommodated in the standard channel width by the process of
(a)frequency adjustment
(b)frequency interleaving
(c)frequency changing
(d)frequency amalgamation
Answer is ()
C.22)The signal s(t) given by 4cos1800πt + 2cos 2000πt+ 2cos2200πt, find the bandwidth,options:
(a) 2000Hz
(b) 2200Hz
(c) 2300Hz
(d) 1900Hz
Answer is ()
C.23)The minimum sampling frequency (in samples/sec) required to construct the following signal from its samples without distortion should be x(t) = 5(sin 2*pi*1000*t/pi*t)^3 + 7(sin 2*pi*1000*t/pi*t)^2
(a) 2x10^3
(b) 4x10^3
(c) 6x10^3
(d) 8x10^3
Answer is ()
C.24)The amplitude of AM wave varies from 5V to 15V,the modulation index and power of carrier respectively are:
(a)0.5 , 10 W
(b)0.1, 10 W
(c)insufficient data
(d)none of above
Answer is ()
C.25) In FM signal with a modulation index m_f is passed through a frequency tripler. The wave in the output of the tripler will have a modulation index of
(a)m_f
(b)3m_f
(c) m_f/3
(d) m_f/9
Answer is ()
C.26) What are the characteristics of a receiver?
(a) Selectivity.
(b) Sensitivity
(c) Fidelity
(d) all of above
Answer is ()
C.27) A carrier signal= 20 cos 2π ×10^6t is modulated by a message signal having three frequencies 5kHz,10kHz,20kHz. The corresponding modulation indices are 0.4,0.5 & 0.6.The modulation efficiency is:
(a) 28%
(b) 27.79%.
(c) 25.5%
(d) none of above
Answer is ()
C.28) For the above question, find the total power of the signal:
(a)288W
(b)277W
(c)266W
(d)none of above
Answer is ()
(a)9
(b)6
(c)7
(d)none of these
Answer is ( )
C.16)The sinc (¶) function which is used widely in communication, becomes zero when
(a)π¶ = infinity
(b)sin(π¶)=zero
(c))both (a) & (b)
(d)cannot determine
Answer is (c)
C.17)Suppose that the modulating signal is m(t)=2 cos(2*pi*fm*t) and the carrier signal is c(t)=Ac cos(2*pi*fc*t), which one of the following is a conventional AM signal without over-modulation?
(a) x(t)=Ac m(t) cos(2*pi*fc*t)
(b) x(t)=Ac [1+m(t)] cos(2*pi*fc*t)
(c) x(t)=Ac cos(2*pi*fc*t) + (Ac/4) m(t) cos(2*pi*fc*t)
(d) x(t)=Ac cos(2*pi*fm*t) cos(2*pi*fc*t) + Ac sin(2*pi*fm*t) sin(2*pi*fc*t)
Answer is ()
C.18)Assertion: LPF are used to eliminate the higher (greater than 3rd)side lobes of an energy signal whose Fourier Transform spans an infinite duration Reason:For a finite duration signal, the Fourier transform of the energy is concentrated in it's main lobe (upto 95%) & upto 99% till it's 3rd lobe, the remaining higher order side lobes are insignificant
(a) Both the first and second statements are true
(b) Both the first and second statements are true and the second is the correct reason of the first
(c) either of them are true
(d) both are false
Answer is (b)
C.19) VSB modulation is preferred in TV because
(a) it reduces the bandwidth requirement to half
(b) it avoids phase distortion at low frequencies
(c) it results in better reception
(d) none of the above
Answer is ()
C.20) For an AM signal s(t) given by 20(1+0.9cos2π10^4t)cos (2π10^6t), find the modulation efficiency ?
(a) 25%
(b) 24.4%
(c) 28.8%
(d) none of the above
Answer is (c)
C.21) The colour subcarrier and sidebands produced by its modulation with the chrominance signals are accommodated in the standard channel width by the process of
(a)frequency adjustment
(b)frequency interleaving
(c)frequency changing
(d)frequency amalgamation
Answer is ()
C.22)The signal s(t) given by 4cos1800πt + 2cos 2000πt+ 2cos2200πt, find the bandwidth,options:
(a) 2000Hz
(b) 2200Hz
(c) 2300Hz
(d) 1900Hz
Answer is ()
C.23)The minimum sampling frequency (in samples/sec) required to construct the following signal from its samples without distortion should be x(t) = 5(sin 2*pi*1000*t/pi*t)^3 + 7(sin 2*pi*1000*t/pi*t)^2
(a) 2x10^3
(b) 4x10^3
(c) 6x10^3
(d) 8x10^3
Answer is ()
C.24)The amplitude of AM wave varies from 5V to 15V,the modulation index and power of carrier respectively are:
(a)0.5 , 10 W
(b)0.1, 10 W
(c)insufficient data
(d)none of above
Answer is ()
C.25) In FM signal with a modulation index m_f is passed through a frequency tripler. The wave in the output of the tripler will have a modulation index of
(a)m_f
(b)3m_f
(c) m_f/3
(d) m_f/9
Answer is ()
C.26) What are the characteristics of a receiver?
(a) Selectivity.
(b) Sensitivity
(c) Fidelity
(d) all of above
Answer is ()
C.27) A carrier signal= 20 cos 2π ×10^6t is modulated by a message signal having three frequencies 5kHz,10kHz,20kHz. The corresponding modulation indices are 0.4,0.5 & 0.6.The modulation efficiency is:
(a) 28%
(b) 27.79%.
(c) 25.5%
(d) none of above
Answer is ()
C.28) For the above question, find the total power of the signal:
(a)288W
(b)277W
(c)266W
(d)none of above
Answer is ()
