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Frequency Modulation

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1. What type of signal is represented by the code 15A3?
2. Briefly explain the difference between phase and frequency modulation.
3. A 15 mV sinusoid with input frequency 450 Hz is applied to an FM generator with k = 1000 Hz/20 mV. Find the positive frequency deviation.
4. An FM signal is given by e = 40 sin (2Æ'Ã? ~106t + 10 sin 600 Æ'Ã?t). What is the carrier frequency? What is the modulation index?
5. An FM signal 400 sin (2Æ'Ã? ~108t + 8 sin 200 Æ'Ã?t) is applied to a 100 Æ'¶ antenna. What is the transmitted power?
6. The maximum deviation in broadcast FM is 75 kHz. Suppose that a commercial FM system has modulating frequencies 40 Hz to 20 kHz. What is the permissible range for the modulation index?
7. What is the sensitivity of an FM receiver with a 100 mV quieting voltage and a voltage gain of 50,000?
8. Consider phase locked-loop FM demodulation. What is the meaning of the term hold-in range?
9. Name the 3 possible states of operation for a phase locked-loop.
10. An FM station transmits at 96.5 MHz. Find the local oscillator frequency and image frequency if the receiver has a 10.7 MHz IF.

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Frequency Modulation

Double sideband suppressed carrier AM (DSB-SC AM) is used in the transmission of stereo signals in sound broadcasting using frequency modulation. The transmitted stereo signal is a voltage proportional to L-R, where L and R are the left and right audio signals.
a. A DSB-SC AM waveform is generated by modulating a 38 kHz carrier with a 10 kHz audio sine wave signal. What are the frequencies of the sidebands of the DSB-SC AM signal?
b. Is the 38 kHz carrier present in the DSB-SC AM signal in part (a) above?
c. How is the DSB-SC AM signal demodulated in the radio receiver to recover the L-R signal?
d. How are the left (L) and right (R) signals obtained separately in the radio receiver to drive the dual channel audio amplifier and speakers?

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