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ECE Objective Questions { Microwave Devices and Circuits }

78. If the carrier ofa 100 percent modulated AM wave is suppressed, the percentage power saving will be

79. One of the main functions of the RF amplifier in a superheterodyne receiver is to
A. provide improved tracking
B. permit better adjactent?channel rejection
C. increase the tuning range of the receiver
D. improve the rejection of the image frequency

80. One of the following is not a reason for the use of antenna coupler
A. to make the antenna look resistive
B. to provide the output amplifier with the correct load impedance
C. to discrimination against harmonics
D. to prevent re-radiation of the local oscillator

81. The difference between phase and frequency modulation
A. is purely theoretical because they are the same in practice
B. is too great to make the two systems compatible
C. line in the poorer audio response of phase modulation
D. lies in the different definitions of the modulation index

82.  Indicate which of the following circuits could not demodulate SSB
A. balanced modulator
B. product detector
D. phase discriminator

83. Show which of the following statement about the amplitude limiter is untrue?
A. the circuit is always biased in class-C by virtue of the leak type bias
B. when th input increases past the threshold of limiting, the gain decreases to keep the output constant
C. the output must be tuned
D. leak-type bias must be used

84. In a ratio detector
A. the linearity is worse than in a phase discriminator
B. stabilization against signal strength variations is provided
C. the output is twice that obtainable from a similar phase discriminstor
D. the circuit is the same as in a discriminator except that the diodes are reversed

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