1. Modulation is used to [ ]A. Allow the use of practicable antennasB. Separate different transmissionsC. Ensure that intelligence may be transmitted over long distances.D. All2. In a low-level AM system, amplifiers following the modulated stage must be [ ]A. linear devicesB. Harmonic devicesC. Class C amplifiersD. Nonlinear devices.3. Amplitude modulation is the process of [ ] A. Superimposing a low frequency on a high frequency B. Superimposing a high frequency on a low frequencyC. Shifting phaseD. Shifting frequency.4. If the carrier of 100percent modulated AM wave is suppressed, the percentage power saving will be A.50 B. 150 C. 100 D. 66.665. For AM with fc=100KHz, fm =5KHz,theupper and lower sidebands extends from carrier are [ ]A. 105, 95 B. 110, 90 C. 120, 80 D. 115,1056. The modulation index of an AM wave is changed from 0 to 1.The transmitted power is [ ]A. Unchanged B. Halved C. Doubled D. increased by 50 percent7. The modulation index of AM when fm=10KHz , fc=500KHz,Am=7.5p-p,Ac=20p-p [ ]A. 37.5 B. 3.75 C. 0.375 D. None8. If the modulation index is decreased the carrier power in the AM [ ]A. Increases B. Decreases C. Remains the same D. None.9. What is the ratio of modulating power to total power at 100 percent modulation? [ ]A. 1:3 B. 1:2 C. 2:3 D. None of the above.10. A carrier is simultaneously modulated by two sine waves with modulation indices of 0.3 and 0.4; the total modulation index [ ]A. is 1 B. Cannot be calculated unless the phase relations are known C. is 0.5 D. is 0.711. If the modulation index is decreased the sideband power in the AM [ ]A. Increases B. Decreases C. Remains the same D. none.12. The maximum modulating signal frequency that can be used with amplitude modulator system of 20KHz bandwidth is _________13. For a maximum positive envelope of 12V and a minimum positive envelope of 4V,the modulation index is___________14. Write the expression for AM waveform with the following parameters. Ac=20, m=0.4, fm=5KHz, fc=200KHz.15. AM spectrum is symmetrical about carrier frequency. [True/False]16. In AM the sum and difference frequencies are displaced from the carrier frequency by twice the modulating signal frequency [True/False]