18. An AM transmitter has a percen percentag tage e of modula modulatio tion n of 88. The carrier power is 440 W. The power in one sideband is
19. An AM transm transmiit iiter er antenn antenna a current current is measur measured ed with with no modula modulation tion and found to be 2.6 A. With modulation, the current rises to 2.9 A. The percentage of modulation is
13. 13. A carri carrier er of 880 880 kHz is modul modulate ated d by a 3.5 kHz sine wave. The LSB and USB are, respectively,
Ans: 876.5 and 883.5 kHz
14. A disp displlay of sig signal nal ampl mplitu itude versus frequency is called the
Ans: frequency domain
17. 17. For For 100 100 perc percen entt modu modula lati tion on,, what what percent ag age of power is in eac h sideband?
Ans: 70 percent
The The opp oppos osit ite e of of mod modul ulati ation on is
16. 16. An AM signa signall has a carr carrie ierr power power of 5 W. The percentage of modulation is 80 percent. The total sideband power is
Ans: 85 W
Ans: Vm > Vc
12. The The new new sign signal als s modulation are called
Ans: 1.6 W
8. For For idea ideall AM, AM, whic which h of the the fol follo lowin wing g is true?
2. Whic Which h of the the follo followi wing ng is not not true true about AM?
15. Most of of the powe powerr in an AM AM signal signal is the
ND COMMUNICATION ELECTRONIC 2EDITION - FRENZEL
20. 20. What What is the the carr carrie ierr powe powerr in the problem above if the antenna resistance is 75 ohms?
Ans: 507 W
21. 21. In an AM sign signal al,, the the tran transm smit itte ted d information is contained within the
22. An AM signa signall without without the the carrie carrierr is called a(n) 2
Ans: DSB 23. What is the minimum AM signal needed to transmit information?
Ans: One sideband
24. The main advantage of SSB over standard AM or DSB is
Ans: Less spectrum space is used
25. In SSB, which sideband is the best to use?
Ans: neither upper or lower
26. The typical audio modulating frequency range used in radio and telephone communications is
Ans: 300 Hz to 3 kHz
27. An AM signal with a maximum modulating signal frequency of 4.5 kHz has a total bandwidth of
Ans: 9 kHz
28. Distortion of the modulating signal produces harmonics which cause an increase in the signal
29. The process of translating a signal, with or without modulation, to a higher or lower frequency for processing is called
Ans: frequency conversion
30. Frequency translation is carried out by a circuit called a
19. The equivalent circuit of a quartz crystal is a
Ans: Series resonant circuit and parallel resonant circuit
Ans: Envelope detector
17. The principal circuit in the popular 1496/1596 IC balanced modulator is a
Ans: RC networks and op-amps
10. The c irc uit t hat recovers the original modulating information from an AM signal is known as a
23. A balanced modulator used to demodulate a SSB signal is called a(n)
18. The most commonly used filter in SSB generator uses
P = VI = 24 x 0.5 = 12 W
11. The most commonly amplitude demodulator is the
Ans: phase shift
20. A crystal lattice filter has crystal frequencies of 27.5 and 27.502 MHz. The bandwidth is approximately
Ans: 2 kHz
24. Frequency translation is done with a circuit called a
Ans: mixer 25.
The inputs to a mixer are f o and f m. In down conversion, which of the following mixer output signals is selected
Ans: f o - f m
26. Mixing for frequency conversion is the same as
Ans: Liner summing
27. Which of the following can be used as a mixer
Solution: BW = f 2 – f 1 = 27.502MHz–27.5MHz = 2 kHz 21. An SSB generator has a sideband filter cent ered at 3. 0 M Hz. The modulating signal is 3 kHz. To produce both upper and lower sidebands, the following carrier frequencies must be produced:
Ans: 2997 and 3003 kHz
Ans: Balanced modulator, FET and Diode modulator 28. The desired output from a mixer is usually selected with a
Ans: Crystal filter 29.
The two main inputs to a mixer are the signal to be translated and a signal from a(n)
Ans: Local oscillator
Solution: LSB = 3.0 MHz – 3 kHz = 2997 kHz USB = 3.0 MHz + 3 kHz = 3003 kHz 22. In the phasing method of SSB generation, one sideband is canceled out due to COMMUNICATION ELECTRONIC 2EDITION - FRENZEL ND
30. An NE602 mixer IC has a difference output of 10.7 MHz. The input is 146.8 MHz. The local oscillator frequency is
Ans: 157.5 MHz
Solution: f o = 146.8 MHz + 10.7 MHz
Chapter 4: FM 1. The amount of frequency deviation from the carrier center frequency in an FM transmitter is proportional to what characteristic of the modulating signal?
8. To compensate for increases in carrier frequency deviation with an increase in modulating signal frequency, what circuit is used between the modulating signal and the phase modulator?
Ans: Low-pass filter 9.
The FM produced by PM is called
Ans: Indirect FM
2. Both FM and PM are types of kind of modulation?
3. If the amplitude of the modulating signal decreases, the carrier deviation
4. On an FM signal, maximum deviation occurs at what point on the modulating signal?
10. If the amplitude of the modulating signal applied to a phase modulator is constant, the output signal will be
Ans: The carrier frequency
11. A 100 MHz carrier is deviated 50 kHz by a 4 kHz signal. The modulation index is
Ans: 12.5 Solution:
Ans: Both positive and negative peak amplitude
5. I n P M, a frequency s hif t o cc urs while what characteristic of the modulating signal is changing?
6. Maximum frequency deviation of a PM signal occurs at