Amplitude Modulation
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The action of impressing inte intell llig igen ence ce upon upon a trans transmi miss ssio ion n medium is referred to as a. modula ulating b. demodulating c. het heterod erodyn ynin ing g d. wave wave gene genera rati ting ng Answer: A You can communicate with others using which of the following transmissions mediums? a. Light b. Wire lines c. Radio wa waves d. Each Each of the abov abovee Answer: D When hen you you use a vect vector or to indic ndicat atee for force in a diag diagrram, am, what hat do (a) (a) length length and (b) arrowhe arrowhead ad positi position on indicate? a. (a) Magnitude (b) direction b. (a) Magnitude (b) frequency c. (a) Phase (b) frequency d. (a) Phase (b) direction Answer: A Vect Vector orss are used used to show show whic which h of the following characteristics of a sine wave? a. Fidelity b. Amplitude c. Resonance d. Distortion Answer: B A rotating coil in the uniform magnetic field between two magnets produces a sine wave. It is called a sine sine wave wave beca becaus usee the vol voltage tage depends on which of the following factors? a. The The numb number er of of tur turns ns in in the the coil coil b. The speed at which the coil is rotating
c. The angula angularr posit position ion of the the coil coil in the magnetic field d. Each Each of the abov abovee Answer: D 6 . The part of a sine wave that is above the voltage reference line is referred to as the a. peak peak ampl ampliitude ude b. positive alternation c. nega negati tive ve alter alterna nati tion on d. inst instan anta taneo neous us ampl amplit itude ude Answer: B 7. The degree to which a cycle has been completed at any given instant is referred to as the a. phase b. period c. frequency d. amplitude Answer: B 8. The frequency of the sine wave is determined by which of the following sinewave factors? a. The The max maxim imum um volt voltag agee b. The rate at which the vector rotates c. The The numb number er of of degr degree eess of vec vecto tor r rotation d. Each Each of the abov abovee Answer: B 9. Which of the following waveform characteristics determines the wavelength of a sine wave? a. Phase b. Period c. Amplitude d. Phas hase An Angle Answer: B 10. The ability of a c ircuit to faithfully reproduce the input signal in the output is known by what term? a. Fidelity b. Fluctuation c. Directivity d. Disc Discri rimi mina nati tion on Answer: A
11. In RF communications, modulation impresses information on which of the following types of waves? a. Carrier wave b. Complex wave c. Modulated wave d. Modulating wave Answer: A 12. Which of the following types of modulation is a form of amplitude modulation? a. Angle b. Phase c. Frequency d. Continuous-wave Answer: D 13. What effect, if any, does a nonlinear device have on a sine wave? a. It amplifies without distortion b. It attenuates without distortion c. It generates harmonic frequencies d. None of the above Answer: C 14. For the heterodyning action to occur in a circuit, (a) what number of frequencies must be present and (b) to what type of circuit must they be applied? a. (a) Two (b) linear b. (a) Two (b) nonlinear c. (a) Three (b) nonlinear d. (a) Three (b) linear Answer: B 15. Spectrum analysis is used to view which of the following characteristics of an RF signal? a. Phase b. Bandwidth c. Modulating wave d. Modulation envelope Answer: B 16. The method of RF communication that uses either the presence or absence of a carrier in a prearranged code is what type of modulation?
a. Pulse modulation b. Amplitude modulation c. Continuous-wave modulation d. Pulse-time modulation Answer: C 17. What is the purpose of the key in a CW transmitter? a. It generates the RF oscillations b. It heterodynes the RF oscillations c. It controls the RF output d. It amplifies the RF signal Answer: C 18. To ensure frequency stability in a CW transmitter, you should NOT key what circuit? a. The mixer b. The detector c. The oscillator d. The RF amplifier Answer: C 19. When keying a high-power transmitter, what component should you use to reduce the shock hazard? a. A coil b. A relay c. A resistor d. A capacitor Answer: B 20. Interference detected by a receiver is often caused by the application and removal of power in nearby transmitters. This interference can be prevented by using what type of circuit in such transmitters? a. Power filter b. On-off filter c. Key-click filter d. RF detector filter Answer: C 21. Transmitter machine keying was developed for which of the following purposes? a. To increase the speed of communications b. To make communications more intelligible c. To reduce interference
d. Each of the above Answer: D 22. Which of the following advantages is a benefit of CW communications? a. Wide bandwidth b. Fast transmission c. Long-range operation d. Each of the above Answer: D 23. To prevent a transmitter from being loaded unnecessarily, where should you connect the antenna? a. At the oscillator input b. At the oscillator output c. At the power-amplifier input d. At the power-amplifier output Answer: D 24. Amplifier tubes are added to the output of a transmitter for which of the following reasons? a. To increase power b. To increase frequency c. To increase stability d. To increase selectivity Answer: A 25. Which of the following combinations of frequency multiplier stages will produce a total multiplication factor of 72? a. 36, 36 b. 4, 3, 3, 2 c. 4, 4, 3, 2 d. 18, 18, 18, 18 Answer: B 26. To change sound energy into electrical energy, which of the following devices should you use? a. A speaker b. A microphone c. An amplifier d. An oscillator Answer: B 27. What component in a carbon microphone converts a dc voltage into a varying current? a. Button
b. Diaphragm c. Transformer d. Carbon granules Answer: D 28. The action of the double-button carbon microphone is similar to which of the following electronic circuits? a. A limiter b. An oscillator c. A voltage doubler d. A push-pull amplifier Answer: D 29. A carbon microphone has which of the following advantages over other types of microphones? a. Ruggedness b. Sensitivity c. Low output voltage d. Frequency response Answer: A 30. The voltage produced by mechanical stress placed on certain crystals is a result of which of the following effects? a. Hall b. Acoustic c. Electrostatic d. Piezoelectric Answer: D 31. If you require a microphone that is lightweight, has high sensitivity, is rugged, requires no external voltage, can withstand temperature, vibration, and moisture extremes, and has a uniform frequency response of 40 to 15,000 hertz, which of the following types of microphones should you select? a. Carbon b. Crystal c. Dynamic d. Electrostatic Answer: C 32. What component in a magnetic microphone causes the lines of flux to alternate? a. The coil b. The magnet
c. The diaphragm d. The armature Answer: C 33. What are the two major sections of an AM transmitter? a. Audio frequency unit and radio frequency unit b. Audio frequency unit and master oscillator c. Audio frequency unit and final power amplifier d. Audio frequency unit and intermediate power amplifier Amplifier: A 34. The intermediate power amplifier serves what function in a transmitter? a. It generates the carrier b. It modulates the carrier c. It increases the frequency of the signal d. It increases the power level of the signal Answer: It amplifies the carrier 35. The final audio stage in an AM transmitter is the a. mixer b. modulator c. multiplier d. multiplexer Answer: B 36. The vertical axis on a frequency spectrum graph represents which of the following waveform characteristics? a. Phase b. Duration c. Frequency d. Amplitude Answer: D 37. When a 500-Hz signal modulates a MHz carrier, the MHz carrier and what two other frequencies are transmitted? a. 500 and 999,500 Hz b. 500 and 1,000,500 Hz c. 999,500 and 1,500,000 Hz d. 999,500 and 1,000,500 Hz Answer: D
38. If 750 Hz modulates a 100-kHz carrier, what would the upper-sideband frequency be? a. 99,250 Hz b. 100,000 Hz c. 100,500 Hz d. 100,750 Hz Answer: D 39. In an AM wave, where is the audio intelligence located? a. In the carrier frequency b. In the spacing between the sideband frequencies c. In the spacing between the carrier and sideband frequencies d. In the sideband frequencies Answer: C 40. What determines the bandwidth of an AM wave? a. The carrier frequency b. The number of sideband frequencies c. The lowest modulating frequency d. The highest modulating frequency Answer: D 41. If an 860-kHz AM signal is modulated by frequencies of 5 and 10 kHz, what is the bandwidth? a. 5 kHz b. 10 kHz c. 15 kHz d. 20 kHz Answer: D 42. If a MHz signal is modulated by frequencies of 50 and 75 kHz, what is the resulting maximum frequency range? a. 925,000 to 1,000,000 Hz b. 925,000 to 1,075,000 Hz c. 975,000 to 1,025,000 Hz d. 1,000,000 to 1,075,000 Hz Answer: B 43. In an AM signal that is 100 percent modulated, what maximum voltage value is present in each sideband? a. 1/4 the carrier voltage
1/2 the carrier voltage 3/4 the carrier voltage d. Same as the carrier voltage Answer: B 44. Overmodulation of an AM signal will have which, if any, of the following effects on the bandwidth? a. It will increase b. It will decrease c. It will remain the same d. None of the above Answer: A Produces SPLATTERs 45. In a carrier wave with a peak amplitude of 400 volts and a peak modulating voltage of 100 volts, what is the modulation factor? a. 0.15 b. 0.25 c. 0.45 d. 0.55 Answer: B 46. Modulation produced in the plate circuit of the last radio stage of a system is known by what term? a. Low-level modulation b. High-level modulation c. Final-amplifier modulation d. Radio frequency modulation Answer: B 47. Which, if any, of the following advantages is a primary benefit of plate modulation? a. It operates at low efficiency b. It operates at low power levels c. It operates with high efficiency d. None of the above Answer: C 48. A final RF power amplifier biased for plate modulation operates in what class of operation? a. A b. B c. AB b. c.
C Answer: D 49. Heterodyning action in a plate modulator takes place in what circuit? a. Grid b. Plate c. Screen d. Cathode Answer: B 50. A plate modulator produces a modulated RF output by controlling which of the following voltages? a. Plate voltage b. Cathode voltage c. Grid-bias voltage d. Grid-input voltage Answer: A 51. To achieve 100-percent modulation in a plate modulator, what maximum voltage must the modulator tube be capable of providing to the final power amplifier (FPA)? a. Twice the FPA plate voltage b. The same as the FPA plate voltage c. Three times the FPA plate voltage d. Half the FPA plate voltage Answer: A 52. In a plate modulator, with no modulation, how will the plate current of the final RF amplifier appear on a scope? a. A series of pulses at the carrier frequency b. A series of pulses at twice the carrier frequency c. A series of pulses at 1/4 the carrier frequency d. A series of pulses at 1/2 the carrier frequency Answer: A 53. In the collector-injection modulator, AF and RF are heterodyned by injecting the RF into (a) what circuit and the AF into (b) what circuit? a. (a) Base (b) collector d.
(a) Base (b) emitter (a) Emitter (b) collector d. (a) Emitter (b) base Answer: A 54. Plate- and collector-injection modulators are the most commonly used modulators for which of the following reasons? a. The RF amplifier stages can be operated class C for linearity b. The RF amplifier stages can be operated class C for maximum efficiency c. They require small amounts of audio power d. They require large amounts of audio power Answer: B 55. A control-grid modulator would be used in which of the following situations? a. In extremely high-power, wideband equipment where high-level modulation is difficult to achieve b. In cases where the use of a minimum of audio power is desired c. In portable and mobile equipment to reduce size and power requirements d. Each of the above Answer: D 56. Which of the following inputs is/are applied to the grid of a control-grid modulator? a. RF b. AF c. DC bias d. Each of the above Answer: D 57. Excessive modulating signal levels have which, if any, of the following effects on a control-grid modulator? a. They increase output. amplitude b. c.
b. They decrease output amplitude c. They create distortion d. None Answer: C 58. Compared to a plate modulator, the control-grid modulator has which of the following advantages? a. It is more efficient b. It has less distortion c. It requires less power from the modulator d. It requires less power from the amplifier Answer: C 59. The control-grid modulator is similar to which of the following modulator circuits? a. Plate b. Cathode c. Base-injection d. Emitter-injection Answer: C
Figure A.—Modulator circuit. IN ANSWERING QUESTIONS 60 THROUGH 62, REFER TO FIGURE A. 60. What components in the circuit establish the bias for Q1? a. R1 and R2 b. R2 and R3 c. R1 and R3 d. None of the above Answer: A 61. The RF voltage in the circuit is applied at (a) what points and the AF voltage is applied at (b) what points? a. (a) A and B (b) C and D b. (a) C and D (b) A and B c. (a) C and D (b) E and F
d. (a) E and F (b) C and D Answer: A 62. What components develop the RF modulation envelope? a. C1 and R1 b. C2 and R1 c. C3 and R3 d. C4 and L1 Answer: D 63. A cathode modulator is used in which of the following situations? a. When RF power is unlimited and distortion can be tolerated b. When RF power is limited and distortion cannot be tolerated c. When AF power is unlimited and distortion can be tolerated d. When AF power is limited and distortion cannot be tolerated Answer: D 64. In a cathode modulator, the modulating voltage is in series with which of the following voltages? a. The grid voltage only b. The plate voltage only c. Both the grid and plate voltages d. The cathode voltage only Answer: C
Figure B.—Emitter-injection modulator. IN ANSWERING QUESTION 65, REFER TO FIGURE B. 65. In the circuit, what components develop the modulation envelope? a. Q1 b. C2 and R1
c. C3 and R3 d. C4 and L1 Answer: D
Figure 1. Block diagram of AM transmitter
Figure 2. Single-button carbon microphone
Figure 3. Plate modulation circuit
Figure 4. Collector-injection plate modulator
