NEETS 18 1,2,3,4 Flashcards Preview

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Flashcards in NEETS 18 1,2,3,4 Deck (133):
1

Q1. Radar surface-angular measurements are referenced to true north and measured in what plane?

A1. Horizontal plane.

2

The distance from a radar set to a target measured along the line of sight is identified by what term?

Range

3

Q3. What is the speed of electromagnetic energy traveling through air?

A3. Approximately the speed of light (162,000 nautical miles per second).

4

How much time is required for electromagnetic energy to travel 1 nautical mile and return to the source?

A4. 12.36 microseconds.

5

Q5. In addition to recovery time, what determines the minimum range of a radar set?

A5. Pulse width.

6

Atmospheric interference with the travel of electromagnetic energy increases with what rf energy characteristic?

Frequency

7

Q7. How is prt related to prf?

1/prt=prf

8

Q8. What type of radar transmitter power is measured over a period of time?

A8. Average power.

9

Q9. What term is used to describe the product of pulse width and pulse-repetition frequency?

A9. Duty cycle.

10

Q10. What type of target bearing is referenced to your ship?

A10. Relative bearing.

11

Q11. What type of radar detects range, bearing, and height?

A11. Three-dimensional.

12

Q12. What characteristic(s) of radiated energy is (are) altered to achieve electronic scanning?

A12. Frequency or phase.

13

What term is used to describe the ability of a radar system to distinguish between targets that are close together?

A13. Target resolution.

14

Q14. The degree of bearing resolution for a given radar system depends on what two factors?

A14. Beam width and range.

15

What happens to the speed of electromagnetic energy traveling through air as the altitude increases?

A15. Speed increases.

16

What term is used to describe a situation in which atmospheric temperature first increases with altitude and then begins to decrease?

Temperature inversion

17

What radar subsystem supplies timing signals to coordinate the operation of the complete system?

A17. Synchronizer.

18

When a transmitter uses a high-power oscillator to produce the output pulse, what switches the oscillator on and off?

A18. High-voltage pulse from the modulator.

19

Q19. What radar component permits the use of a single antenna for both transmitting and receiving?

Duplexer

20

Q20. What is the simplest type of scanning?

A20. Single lobe.

21

How does the operator of a single-lobe scanning system determine when the target moves off the lobe axis?

A21. The reflected signals decrease in strength.

22

Q22. What are the two basic methods of scanning?

A22. Mechanical and electronic.

23

Q23. Rotation of an rf-feed source to produce a conical scan pattern is identified by what term?

A23. Nutation.

24

Q24. The Doppler effect causes a change in what aspect of rf energy that strikes a moving object?

A24. Frequency.

25

Q25. The Doppler variation is directly proportional to what radar contact characteristic?

Velocity

26

Q26. The Doppler method of object detection is best for what type objects?

A26. Fast-moving targets.

27

Q27. The beat frequency in a swept-frequency transmitter provides what contact information?

Range

28

What factor determines the difference between the transmitted frequency and the received frequency in an fm transmitter?

A28. Travel time.

29

Q29. What type of objects are most easily detected by an fm system?

A29. Stationary.

30

Q30. What transmission method does NOT depend on relative frequency or target motion?

A30. Pulse modulation.

31

What transmission method uses a stable cw reference oscillator, which is locked in phase with the transmitter frequency?

A31. Pulse-Doppler.

32

Q32. What type of radar provides continuous range, bearing, and elevation data on an object?

A32. Track radar.

33

Q33. Radar altimeters use what type of transmission signal?

A33. Frequency modulated (fm).

34

Q34. A surface-search radar normally scans how many degrees of azimuth?

A34. 360 degrees.

35

Q35. What limits the maximum range of a surface-search radar?

A35. Radar horizon.

36

Q36. What is the shape of the beam of a surface-search radar?

A36. Wide vertically, narrow horizontally.

37

Q37. Air-search radar is divided into what two basic categories?

A37. 2D and 3D.

38

Q38. What position data are supplied by 2D search radar?

A38. Range and bearing.

39

Why do 2D air-search radars use relatively low carrier frequencies and low pulse-repetition rates?

A39. Increased maximum range.

40

Q40. Why is the range capability of 3D radar usually less than the range of 2D radar?

A40. Higher operating frequency.

41

Q41. Fire-control tracking radar most often radiates what type of beam?

A41. A narrow circular beam.

42

Q42. Tracking radar searches a small volume of space during which phase of operation?

Acquisition

43

Q43. What width is the pulse radiated by fire-control tracking radar?

A43. Very narrow.

44

Q44. Which beam of missile-guidance radar is very wide?

A44. Capture beam.

45

Q1. What is the purpose of the synchronizer in a radar system?

A1. Controls system operation and timing.

46

Q2. What is the purpose of the majority of circuits in a radar system?

A2. Timing and control.

47

Q3. A self-synchronized radar system obtains timing trigger pulses from what source?

Transmitter

48

Q4. What type of multivibrator can be used as a radar master oscillator?

A4. Free-running.

49

Q5. In an externally synchronized radar, what determines the prr of the transmitter?

A5. The master oscillator.

50

Q6. In figure 2-1, what causes the initial and final pulses on the receiver output signal?

A6. Leakage from the duplexer.

51

Q7. What basic circuits meet the requirements of an externally synchronized master oscillator?

A7. Sine-wave oscillator, single-swing blocking oscillator, and master-trigger (astable) multivibrator.

52

Q8. Name a disadvantage of sine-wave oscillator synchronizers.

A8. It requires additional shaping circuits.

53

Q9. Which of the basic timing circuits produces sharp trigger pulses directly?

A9. Blocking oscillators.

54

Q10. What are the two basic types of transmitters?

A10. Keyed oscillator and power-amplifier chain.

55

Q11. What controls transmitter pulse width?

A11. The modulator.

56

Q12. In addition to a flat top, what characteristics must a modulator pulse have?

A12. Steep leading and trailing edges.

57

Q13. What type of modulator is most commonly used in modern radar systems?

A13. Line-pulsed.

58

Q14. What three types of storage elements most often are used in modulators?

A14. Capacitor, artificial transmission line, or pulse-forming network.

59

What characteristic is determined by the time required for a voltage wave to travel from the input end of an artificial transmission line to the output end and back again?

A15. Pulse width.

60

Q16. What type of tube best meets the requirements of a modulator switching element?

Thyratron

61

Q17. What modulator element controls the rate at which the storage element charges?

A17. The charging impedance.

62

Q18. What is the frequency range of magnetron oscillators?

A18. 600-30,000 megahertz.

63

Q19. What two forms of instability are common in magnetrons?

A19. Mode skipping and mode shifting.

64

Q20. What is the effect on magnetron operation if the magnetic field strength is too high?

A20. The magnetron will not oscillate.

65

Q21. What is the typical frequency range about the center frequency of a tunable magnetron?

A21. 5 percent.

66

What is the primary advantage of power-amplifier transmitters over keyed-oscillator transmitters?

A22. Frequency stability.

67

In the power amplifier shown in figure 2-10, what two signals are mixed to produce the output signal?

A23. Local oscillator and coherent oscillator.

68

Q24. What type of klystron is used as the final stage of a power-amplifier transmitter?

A24. Multicavity klystron.

69

What transmitter component allows the radiation of a large number of discrete frequencies over a wide band?

A25. Frequency synthesizer.

70

Q26. What is the result of pulsing a pulsed rf amplifier when no rf is present?

A26. Oscillations at an undesired frequency.

71

Q27. What type of switches are used as duplexers?

A27. Electronic.

72

Q28. What tube in a duplexer has the primary function of disconnecting the receiver?

A28. Tr tube.

73

Q29. How may the tr tube ionization speed be increased?

A29. Apply keep-alive voltage.

74

The actions of the tr and atr circuits depend on the impedance characteristics of what length of transmission line?

A30. Quarter-wavelength section.

75

During which of the transmit or receive cycles are both the tr and atr tubes of a parallelconnected duplexer ionized (arcing)?

A31. Transmit.

76

Q32. In a series-connected duplexer, what tube (tr or atr), if any, fires during the receive cycle?

A32. Neither fires.

77

To propagate energy down an arm of a hybrid ring duplexer, the two fields at the junction of the arm and the ring must have what phase relationship?

A33. 180 degrees out of phase.

78

Q34. What is the greatest limiting factor in a receiver’s detectable range?

A34. Noise.

79

Q35. What type of receiver is most often used in radar systems?

A35. Superheterodyne.

80

Q36. What IF frequencies are normally used in radar receivers?

A36. Thirty or sixty megahertz.

81

Which component of the receiver produces the signal that is mixed with the received signal to produce the IF signal?

A37. Local oscillator.

82

Q38. What receiver circuit actually produces the IF frequency?

A38. Mixer.

83

Q39. The IF amplifiers are connected in what amplifier configuration?

A39. Cascade.

84

Q40. Which receiver component converts the IF pulses to video pulses?

A40. Detector.

85

Which of the two types of automatic gain control, agc or iagc, is most effective in radar use for the Navy?

A41. IAGC.

86

Q42. Immediately after the transmitter fires, stc reduces the receiver gain to what level?

A42. Zero.

87

Q43. How does ftc affect receiver gain, if at all?

A43. FTC has no effect on receiver gain.

88

Q44. What type of target has a fixed phase relationship from one receiving period to the next?

Stationary

89

What signal is used to synchronize the coherent oscillator to a fixed phase relationship with the transmitted pulse?

A45. Coho lock pulse.

90

Q46. What is the phase relationship between the delayed and undelayed video?

A46. Opposite.

91

When a large signal and a small signal are applied to a lin-log amplifier at the same time, what is the effect on the small signal?

A47. Amplification is reduced.

92

Q48. What happens to the overall gain of a lin-log amplifier as each stage saturates?

A48. Decreases.

93

Q49. A monopulse receiver has how many separate channels?

A49. Three.

94

If a target is on the bearing axis of the radiated beam, what is the input to the bearing IF channel?

A50. Zero.

95

What characteristic of the bearing and elevation output signals determines the direction of antenna movement?

A51. Phase.

96

Q1. What are the three fundamental quantities involved in radar displays?

A1. Range, bearing, and elevation.

97

Q2. What are the required radar inputs for proper indicator operation?

A2. Triggers, video, and antenna information.

98

Q3. What coordinates are displayed on an rhi scope?

A3. Range and elevation.

99

Q4. What coordinates are presented on a ppi scope?

A4. Range and bearing.

100

Q5. What type of deflection is preferred for a crt electron beam?

A5. Electromagnetic.

101

Q6. Which of the two types of deflection coils (fixed or rotating) is used most often?

Fixed

102

What type of ranging circuit is most often used with a radar that requires extremely accurate range data?

A7. Range gate or range step.

103

Q8. The range sweep in a range-gate generator is started at the same time as what other pulse?

A8. Transmitter.

104

Q9. Range-marker generators produce pulses based on what radar constant?

A9. The radar mile (12.36 microseconds).

105

Q10. What radar scope uses a range step for range measurement?

A10. The A scope.

106

Q11. Which of the two general classes of antennas is most often used with radar?

A11. Directional.

107

Q12. The power gain of an antenna is directly related to what other antenna property?

A12. Directivity.

108

Q13. A parabolic reflector changes a spherical wavefront to what type of wavefront?

A13. Plane.

109

Q14. How many major lobes are produced by a paraboloid reflector?

One

110

Q15. What type of radiator normally drives a corner reflector?

A15. Half-wave.

111

Q16. The broadside array consists of a flat reflector and what other elements?

A16. Two or more half-wave dipoles.

112

Q17. Horn radiators serve what purpose other than being directional radiators?

A17. Waveguide impedance matching devices.

113

Q1. The spectrum of a radar transmitter describes what characteristic of the output pulse?

A1. Frequency distribution.

114

Q2. Where should the transmitter spectrum be located with respect to the receiver response curve?

A2. In the center.

115

Q3. The ideal radar spectrum has what relationship to the carrier frequency?

A3. Symmetrical above and below the carrier frequency.

116

The display screen of a spectrum analyzer presents a graphic plot of what two signal characteristics?

A4. Power and frequency.

117

Q5. The peak power of a radar depends on the interrelationship of what other factors?

A5. Average power, pulse width, and prt.

118

Q6. Transmitter power readings are most often referenced to what power level?

A6. 1 milliwatt.

119

Q7. A loss of receiver sensitivity has the same effect on range performance as what other loss?

A7. Transmitter power loss.

120

Q8. You determine receiver sensitivity by measuring the power level of what signal?

A8. Minimum discernible signal (mds).

121

Q9. When measuring receiver sensitivity, what quantities must you add to the dBm reading obtained on the signal generator or test set?

A9. Attenuations of the directional coupler and the connecting cable.

122

Q10. Receiver bandwidth is defined as those frequencies spread between what two points of the receiver response curve?

A10. Half-power points.

123

Q11. The end of the usefulness of a tr tube is indicated by an increase in what quantity?

A11. Recovery time.

124

Q12. Most shipboard distribution systems use ac power that has what number of phases?

Three

125

Q13. How is emergency power applied when normal power is lost?

Automatically

126

What device is used to switch power from the normal source to an alternate source for nonvital users?

A14. Manual bus transfer (MBT) unit.

127

Q15. What procedure should you use when a power input to your equipment is missing?

A15. Work backwards from the load to the source.

128

Q16. What is the normal source of dry air for a radar system?

A16. Ship's central dry-air system.

129

What is the major difference between the electronics dry-air branch and the vital service lp air main?

A17. Degree of dehydration.

130

Q18. What is the air control panel designed to control?

Pressure

131

Q19. What type of cooling is used to control ambient room temperature?

A19. Air conditioning.

132

Q20. A typical liquid-cooling system is composed of what loops?

A20. Primary and secondary.

133

Q21. What loop of a cooling system is often supplied by sea water?

A21. The primary loop.