162. The modulation system inherently most noise resistant is
A. pulse-code modulation
B. pulse-position modulation
C. SSB, suppressed carrier
D. frequency modulation

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163. Which of the following instruments is used in an aeroplane to measure its height aboveground?
A. Radar altimeter
B. MI!
C. CW radar
D. Doppler radar

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164. The grade of service is measured in
A. logarithmic number
B. percentage
C. number
D. fractional number

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165. Which is the most common modulation system used for telegraphy?
A. Frequency-shift keying
B. Two-tone modulation
C. Pulse code modulation
D. Single tone modulation

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166. For a periodic function, the spectral density and the auto correlation functions are
A. one and the same thing
B. Pourier
C. Laplace transform pair
D. none of the above

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167. Frequencyshift keying is used mostly in
A. telephony
B. telegraphy
C. radio transmission
D. none of the above

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168. Regarding autocorrelation function which of the following statements is incorrect?
A. It is defined only for periodic signals
B. It is an average function
C. It is a measure of both time variation and statistical dependence
D. None of the above

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