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Electronics Engineering Objective Questions { Digital Communication System }

218. The probability density function of the envelope of narrow band noise is
A. Uniform
B. Gaussian
C. Rayleigh
D. Rician
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219. The Fourier transform of a Gaussian time pulse is
A. uniform
B. a pair of impulses
C. gaussian
D. Rayleigh
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220. The false alarm probability (Pr) in a radar is found to be 0.05 under conditions like the large prf and pulse integration. Then the detection probability
A. is independent of pfa
B. is equal to (1 - .1075)
C. is equal to (1 -0.05)
D. depends on the power received in echo
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221. Consider the following statements The total number of modes entering an optical fibre depends on 1. core radius 2. wavelength of the optical souce 3. refractive index profile Of these statements :
A. 1 and 2 are correct
B. 2 and 3 are correct
C. 1 and 3 are correct
D. 1,2 and 3 are correct
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222. In a pulse radar system, the received echo energy is inversely proportional to (R) is the range measured
B. R2
C. R3
D. R4
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223. The radio altimeter on board an aircraft is basically a
A. Doppler radar
B. MI! radar
C. continous wave radar
D. frequency modulated CW radar
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224. The characteristic impedance of an air dielectric co-axial line is 77 W. If the air is replaced by a dielectric with er = 2.28, the characteristic impedance will be
C. 116 L.2
D. 175 S.2
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