141. Pre-emphasis is used to amplify
A. low frequency
B. high frequency
C. both (a) and (b) above
D. none of the above
142. In the stablized reactance modulator AFC system
A. the discriminator must have a fast time constant to prevent demodulation
B. the higher the discriminator frequency, the better the oscillator frequency stability
C. the discriminator frequency must not be too low, or the system will fail
D. phase modulation is converted into FM by the equalizer circuit
143. An FM signal has a frequency deviation of 20 kHz produced by 2 V audio signal of 4000 Hz. What will be the modulation index?
A.2.5
B.4
C.5
D.10
144. De-emphasis circuit is used
A. prior to modulation
B. after modulation
C. for de-emphasising high frequency component
D. for de-emphasising low frequency component
145. Foster Seelay discriminator uses a
A. single tuned circuit
B. double tuned circuit with primary and secondary tuned to the same frequency
C. couble tuned circuit with primary and secondary tuned to the different frequency
D. none of the above
146. The commercial FM radio broadcast band is
A. 535 to 1600 kHz
B. 20 to 80 kHz
C. 88 to 180 MHz
D. 300 to 3000 MHz
147. The difference between PM and FM
A. lies in the poorer audio response of phase modulation
B. is too great to make the two systems compatible
C. is purely theorctical because practically both are identical
D. lies in the different definitions of the modulation index
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