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3D156 - Volume 2 check answers > Unit 1. Localizer and Glide Slope > Flashcards

Unit 1. Localizer and Glide Slope Flashcards

Localizer and Glide Slope

1
Q
  1. Functional description

What does the localizer shelter contain?

A

The shelter houses power switching, lighting, environmental controls, and two equipment cabinets
containing the ILS electronic equipment and a workbench with electrical outlets.

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2
Q

How is primary power fed from the external junction box to the inside of the shelter?

A

Via conduit.

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3
Q

What are the primary power requirements for the localizer?

A

115/225 VAC ±10 percent, 50 ±3 Hz or 60 ±3 Hz, and 3 phase at 100 amperes.

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4
Q

How many log-periodic dipole antennas are used in the antenna array?

A

14.

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5
Q

How are transmitting and monitoring signals routed to and from the antenna?

A

Via the antenna distribution box.

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6
Q
  1. Capabilities and limitations

Where can you find a detailed discussion of the AN/GRN-30 technical characteristics?

A

Chapter 1 of TO 31R4-2GRN30-2.

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7
Q

Within what frequency range is the localizer capable of operating?

A

108 to 112 MHz.

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8
Q

What signals modulate the carrier of the localizer, and at what depth of modulation?

A

The carrier is modulated with 90 Hz, 150 Hz, and 1,020 Hz AM with a depth of modulation of 20 percent,
20 percent, and 5 percent respectively.

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9
Q

What output status tones does the control indicator produce?

A

705 Hz, 1,410 Hz, 2,820 Hz, and 2,256 Hz.

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10
Q

If an alarm occurs in the localizer, what is the actual time delay from main transmitter shutdown to standby transmitter on?

A

20.3 seconds.

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11
Q
  1. Block diagram theory of operation

What are the three basic operations of the localizer station?

A

(1) Radiate the pattern, (2) monitor the pattern, and (3) control the transmitter.

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12
Q

How are the station DC power supplies connected and why?

A

In parallel, so that one power supply can power the entire station if necessary.

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13
Q

How many kHz below the SAF is the CLR carrier transmitted?

A

4.75.

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14
Q

What are the functions of the changeover unit?

A

Measure the output signals power and switch which transmitter is routed to the distribution unit.

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15
Q

Why won’t the course and clearance signals combine in space?

A

Because they are at different frequencies.

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16
Q

Describe integral monitoring.

A

The signals that will be radiated by the localizer are monitored before they are radiated.

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17
Q

Which localizer unit is responsible for automatic transfer of the transmitters?

A

The control unit.

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18
Q

Which localizer unit is responsible for control of the CLR transmitters?

A

The CRS transmitters.

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19
Q

Where is the detected signal in the antenna distribution unit sent?

A

To the CRS and CLR monitors.

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20
Q

What is the only localizer unit not tied into the control unit?

A

The distribution unit.

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21
Q

What is the purpose of the dual power supply?

A

To provide all regulated DC power for the electronic components of the localizer station and keep the backup batteries charged.

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22
Q

What are the normal CSB and SBO powers for the localizer?

A

CSB = 15 watts, SBO = 360 milliwatts.

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23
Q

What is the 1,020 Hz signal used for in the course transmitter?

A

To modulate the CSB signal for station identification.

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24
Q

What produces the RF frequency for the CRS transmitter?

A

SFS.

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25
Q

Where is the output of the SFS sent?

A

Diode switching network.

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26
Q

What is the crystal-controlled oscillator frequency in the 90 and 150 Hz generator assembly?

A

460.8 kHz.

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27
Q

What happens in the 90- and 150-Hz generator assembly if there is a phase difference in the 15-Hz signals?

A

An output occurs to reset the divider chain, thus the proper phase relationship between the 90 and 150 Hz signals is assured.

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28
Q

What is the purpose of the absolute value circuit in the modulator assembly?

A

To change the input waveform such that all negative swings are changed to positive.

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29
Q

What are the two functions of the diode switching network?

A

Routing and switching.

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30
Q

What is the output of the 4A5 RF amplifier?

A

Sideband only.

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31
Q

What is the nominal power setting of the clearance CSB and SBO?

A

CSB = 10 watts, SBO = 300 milliwatts.

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32
Q

Where is the CLR transmitter ID signal generated?

A

In the course transmitter.

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33
Q

What is the output frequency of the SFS assembly?

A

4.75 kHz below the station assigned frequency.

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34
Q

Name the two services the localizer changeover unit provides.

A

RF transfer and RF measurement.

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35
Q

What can be monitored by the selection of the RF signals by S1 in the changeover unit?

A

Power measurement by meter M1, or waveform observation at waveform jack J2.

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36
Q

What is the purpose of the localizer antenna distribution unit?

A

To distribute the course and clearance transmitter outputs to the antenna array in the proper phase and amplitude.

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37
Q

What is the phase relationship of the course SBO to CSB at the input to the antennas?

A

90°.

38
Q

Where are the outputs of the clearance distribution unit connected?

A

To antenna pairs 1–5.

39
Q

What is the gain of the localizer antenna array?

A

About 10 dB.

40
Q

What is the advantage of a broad bandwidth LPD?

A

It allows for minimal environmental effects.

41
Q

What is the primary purpose of the clearance transmitter?

A

Mask nulls formed by additional lobes of the course transmitter.

42
Q

What determines if a simpler antenna system is sufficient to meet the minimum standards for safe approach of an aircraft?

A

If the forward terrain in the coverage area of the localizer is free of major structures and terrain problems.

43
Q

What ensures the nulls are eliminated within the area of coverage for a single frequency localizer?

A

The antenna a-spacing.

44
Q

In the Dual Frequency RF Detector unit (RDU), where are the samples of CSB from the course and clearance transmitter taken?

A

Sampling points in the interlock assembly.

45
Q

What principle is used to down-convert the carrier frequencies before they are combined and adjusted to become monitor input signals?

A

Heterodyning.

46
Q

What is the primary difference between the dual-frequency RDU and the single frequency RDU?

A

There is no clearance transmitter to assist in producing the intermediate frequency.

47
Q

Name the two separate monitor units that make up the localizer monitor system.

A

Course monitor and clearance monitor.

48
Q

Which monitor activates an alarm if there is a short in an antenna feedline?

A

Course monitor.

49
Q

What is the frequency of the clock pulse used by the course monitor timing assembly?

A

460.8 kHz.

50
Q

Where is the master oscillator that is used in the measurement assembly located?

A

In the timing assembly.

51
Q

When is the program counter of the measurement assembly reset?

A

After the completion of the last measurement routine of the program.

52
Q

Which lines do you use to determine decimal placement in the digital readout display?

A

DP2 and DP4 lines from the display selector switch.

53
Q

How is a DC signal used by the antenna cable fault assembly to signal a short in an antenna feedline?

A

The DC signal stops the 600-Hz signal which in turn activates the alarm system.

54
Q

What is the difference between the course monitor and clearance monitor?

A

Clearance monitor checks clearance frequency; course monitor does not.

55
Q

Which assembly processes the signal from the localizer clearance detector?

A

Clearance assembly.

56
Q

Convert a 20 percent modulation difference into DDM.

A

.200.

57
Q

What causes the resultant 90 and 150 Hz localizer output signals to be unequal, yielding a DDM value that is not .000 DDM?

A

When the SBO signal is added to the CSB signal (space modulation), the 90 and 150 in the SBO will imbalance the CSB due to the 90 and 150 in the SBO being 180o out of phase.

58
Q

Name the types of localizer ground checks.

A

The near field, the far field, and the ground phasing.

59
Q

Describe the location of the two ground check measurement areas.

A

The near field arc is located approximately 1000 feet from the antenna array and consists of check points from 35o on one side of centerline to 35o on the other side. The far field arc is located around the area of the runway threshold and consists of check points from 5o to 5o penetrating the centerline.

60
Q

Why are the localizer course and clearance transmitter’s output frequencies separated by 9.5 kilohertz (kHz)?

A

To prevent the two signals from combining.

61
Q

What degree range would the clearance signal capture the aircraft receiver in a properly aligned capture effect localizer?

A

From 8 to 35o.

62
Q
  1. Functional description

1. What is the purpose of the glide slope station?

A

To provide final approach glide path information to landing aircraft.

63
Q
  1. What are the two RF signals generated by the null-reference glide slope?
A

An RF carrier signal modulated at 90 and 150 Hz and a sideband only signal modulated by 90 and 150 Hz.

64
Q
  1. What conditions cause abnormal indications on the control indicator but do not initiate equipment transfer?
A

Abnormal primary power, abnormal shelter temperature, abnormal battery charge/discharge current, power supply fault, and single monitor alarms.

65
Q
  1. What is the purpose of the alarm-monitors?
A

To continuously monitor the navigational components of the glide slope RF signal and activate an alarm circuit should these components vary outside preset limits.

66
Q
  1. What is an image-type antenna?
A

An antenna that utilizes the ground plane in front of the antennas to reflect signal, thereby forming nulls as if a mirror image antenna of opposite phase were buried below the tower.

67
Q
  1. Capabilities and limitations

1. How can the glide slope station be controlled?

A

Locally, from the site, or remotely, from the control tower or RAPCON.

68
Q
  1. What degree of glide angle can the glide slope provide?
A

The system provides an adjustable glide path between 2 and 4 depending on the individual installation.

69
Q
  1. What output status tones does the control unit use?
A

705 Hz, 1,410 Hz, 2,820 Hz, and 2,256 Hz.

70
Q
  1. To what input control frequencies does the control unit respond? What is each used for?
A

900 Hz, the interlock frequency; 1,175 Hz, the remote control frequency.

71
Q
  1. Block diagram theory of operation

1. What is the purpose of the null-reference glide slope station?

A

It provides final approach glide path information to landing aircraft.

72
Q
  1. What two RF frequencies are generated by the glide slope station?
A

RF carrier signal modulated at 90 and 150 Hz (CSB) and a double sideband, suppressed carrier signal modulated at 90 and 150 Hz (SBO).

73
Q
  1. What happens if the limits are exceeded in the monitor?
A

An alarm signal is sent to the control unit that initiates a transfer to the standby transmitter.

74
Q
  1. What function does the control unit perform?
A

Provides automatic control of the glide slope station transmitter used to select either transmitter 1 or 2 as the main transmitter, initiates transfer from main to standby if both monitors detect a radiated fault, and displays and provides a status signal to the RC/DU.

75
Q
  1. What information is derived from the integral detectors?
A

The detected path and width signals.

76
Q
  1. What is the result of an alarm indication from the standby transmitter?
A

The station being turned off.

77
Q
  1. Name the three units of glide slope equipment that are identical to those used in the localizer.
A

Control unit, changeover unit, and power supply.

78
Q
  1. What is required to interchange monitor cards (other than A3 and A8) between the localizer and glide slope?
A

Alignment.

79
Q
  1. Is the diode switching network operation identical with that in the localizer? Why or why not?
A

Yes the operation is the same, instead of 180o length of line in the localizer, it is 3 times or 540o in the glide slope.

80
Q
  1. What is the normal output power of the glide slope CSB and SBO signal?
A

CSB = 3 watts, SBO = 45 milliwatts.

81
Q
  1. Which glide slope configuration uses a clearance transmitter?
A

The capture-effect system.

82
Q
  1. What does the antenna assembly consist of?
A

Three colinear, horizontally polarized dipoles spaced 3/4 wavelength apart.

83
Q
  1. What samples the radiated signal from each antenna?
A

Loops located within the respective antenna assembly.

84
Q
  1. What components sample the SBO and CSB RF signals?
A

Probes.

85
Q
  1. What is the purpose of the phaser Z-1?
A

Adjusts the relative phase of the signal to make sure that the sideband signals are in phase with the carrier signals.

86
Q
  1. Which signal simulates the signal received by a glide slope receiver when on the glide path?
A

Path output.

87
Q
  1. When is the clearance portion of the glide slope monitor used?
A

In a capture-effect glide slope.

88
Q
  1. When the timing assembly is used in the capture-effect glide slope, what additional functions does it perform?
A

Generates a zero reference signal for the integral detectors. Also, an auto zero 1 and an auto zero 2 are generated.

89
Q
  1. What parameters are processed by the clearance assembly?
A

Clearance and glide slope carrier frequency difference, clearance modulation percentage, and clearance carrier level.

90
Q
  1. What is the range of time between which the delay of a transfer from a defective unit can be adjusted?
A

0.5 to 14.5 seconds.

91
Q
  1. Which function of the glide slope control unit allows maintenance to be performed on the standby unit without disturbing the radiating unit?
A

Station transfer bypass.

3D156 - Volume 2 check answers (3 decks)

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