Principles of Communication
Name: _________________________________________________ BSECE II-1
I. IDENTIFICATION. Fill in the blanks.
1. The general name given to both FM and PM is _________ modulation.
2. The amount of frequency shift during modulation is called the ________________.
3. The amount of frequency shift in PM is directly proportional to the __________ of the modulating signal.
4. In PM, the carrier ___________ is varied in proportion to the amplitude of the modulating signal.
5. A varying phase shift produces ___________________ _____.
6. A phase modulator produces a frequency deviation only when the modulating signal is _________.
7. In __________________, the frequency deviation is proportional to both the modulating signal amplitude and
frequency.
8. When the modulating signal amplitude crosses zero, the phase shift and frequency deviation in a phase modulator are
at _____________________.
9. A phase modulator may use a _______________________ to offset the effect of increasing carrier frequency
deviation for increasing modulating frequency.
10. The FM produced by a phase modulator is known as ____________________.
11. An FM signal has a modulation index of 2.5. How many significant pairs of sidebands are produced? _________
12. What is the relative amplitude of the 4th significant pair of sidebands in an FM signal with a deviation ratio of 4? ___
13. The amplitudes of the sidebands in an FM signal are dependent upon a mathematical process known as_________.
14. A PM signal has a deviation ratio of 3. The maximum modulating signal is 5 kHz. The bandwidth of the signal is
_____kHz.
15. If the maximum allowed deviation is 5 kHz but the actual deviation is 3.75 kHz, the percentage of
modulation is _____ percent.
16. A negative sign on the carrier and sideband amplitudes means a__________ _____.
17. The main advantage of FM over AM is its immunity from _____.
18. FM receivers reject noise because of built-in circuits called _________________.
19. The________________ in an FM receiver causes a stronger signal to dominate a weaker signal on the same
frequency.
20. Typically FM transmitters are more efficient than AM transmitters because they use class _____ amplifiers.
21. The biggest disadvantage of FM is its excessive use of ___________.
22. Noise interferes primarily with _____ modulating frequencies.
23. The method used to offset the effect of noise in FM transmissions by boosting high frequencies is known as _____.
24. To boost high frequencies, a _______________________ circuit is used.
25. To correct for the high-frequency boost, a ______________________ circuit is used at the receiver.
II. PROBLEM SOLVING. Show your solution/s.
1. If a 2-volt instantaneous value of modulating signal amplitude causes a 10-kHz deviation in carrier frequency,
what is the deviation sensitivity of the modulator?
2. If a 2-kHz audio tone causes a frequency deviation of 4 kHz, what is the modulation index?
3. What will be the deviation caused by a 3-kHz tone if the modulation index is 3?
4. If the deviation sensitivity of an FM modulator is 2 kHz /V, what will be the modulation index caused by a 1-volt,
1-kHz audio signal?
5. At a modulation index of 2, how much power is in the carrier of a 1000-watt FM transmitter?
6. Using Carson's rule, what is the approximate bandwidth of an FM signal with a modulation index of 2 being
modulated by a 5-kHz signal?
7. Using the Bessel chart, what is the bandwidth of an FM signal with a modulation index of 2 being modulated by
a 5-kHz signal if we ignore sidebands containing less than 1% of the total power?
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