78. Indicate which of the following frequencies cannot ordinarily by used for beyond-the-horizon terrestrial communication :
A. 600 kHz
B. 15 MHz
C. 12 GHz
D.both A and C

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79. In the visible spectrum of electromagnetic waves, the following has longest wavelength
A. green
B. red
C. blue
D. white

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80. A super-heterodyne receiver with an IF of 450 kHz is tuned to a signal of 1200 kHz, the image frequency is ____ kHz.
A.750
B.1650
C.2100
D.2200

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81. D-layer in the ionosphere is largely present
A. all the 24 hours
B. during night only
C. during day only
D. during cloudy only

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82. The modulator stage in a radio transmitter is normally
A. class-C
B. class-B push-pull
C. class-A
D. class-D

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83. If the carrier of a 100% modulated AM wave is suppressed, the percentage saving of power will be
A.50
B.150
C.66.6
D.0.353

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84. Which of the following frequencies will be most suitable for satellite communication?
A. 30 MHz
B. 300 MHz
C. 2500 MHz
D. 3000 MHz

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