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Subel. F
6 questions
Subelement F

Installation, Maintenance & Repair

Section 47

Equipment Faults-4

If the magnetron is allowed to operate without the magnetic field in place:

  • Its output will be somewhat distorted.
  • Correct Answer
    It will quickly destroy itself from excessive current flow.
  • Its frequency will change slightly.
  • Nothing serious will happen.

A strong magnetic field is required to keep the electron beam inside a Magnetron focused.

Without the magnetic field current runs away and destroys the Magnetron.

Answer B. is the right one.

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Targets displayed on the RADAR display are not on the same bearing as their visual bearing. What should you first suspect?

  • A bad reed relay in the antenna pedestal.
  • A sweep length misadjustment.
  • One phase of the yoke assembly is open.
  • Correct Answer
    Incorrect antenna position information.

The RADAR Display is receiving wrong position information from the antenna's Resolver so Answer D. is the right answer.

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Loss of distant targets during and immediately after wet weather indicates:

  • Correct Answer
    A leak in waveguide or rotary joint.
  • High atmospheric absorption.
  • Dirt or soot on the rotary joint.
  • High humidity in the transmitter causing power supply loading.

Water from rain in the waveguide severly increases the waveguide's losses thus decreasing the transmitter power reaching the antenna and also decreases the strength of the signals sent by the antenna to the receiver.

Answer A. is the right one because it mentions leaks in the wave guide (the rotary joint is the portion of the waveguide that bridges the fixed waveguide to the rotating waveguide leading up to the antenna).

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In a marine RADAR set, a high VSWR is indicated at the magnetron output. The waveguide and rotary joint appear to be functioning properly. What component may be malfunctioning?

  • The magnetron
  • The waveform generator
  • The STC circuit
  • Correct Answer
    The waveguide array termination

Note: Waveguide Array Termination is a synonym for Antenna.

If a high VSWR (Voltage Standing Wave Ratio) is indicated at the magnetron output in a marine RADAR set, and the waveguide and rotary joint are functioning properly, the component that may be malfunctioning is the waveguide array termination.

The waveguide array termination is a crucial component that terminates the waveguide transmission line and ensures proper impedance matching. It is responsible for absorbing and dissipating any excess energy that may cause reflections or standing waves within the waveguide.

When the waveguide array termination malfunctions, it fails to properly terminate the waveguide, leading to an impedance mismatch. This mismatch causes a significant portion of the energy to be reflected back towards the source, resulting in a high VSWR at the magnetron output.

The high VSWR indicates that the energy is not efficiently transferred from the magnetron to the waveguide and antenna system. This can lead to decreased radar performance, reduced power transfer, and potential damage to the magnetron or other components due to excessive reflected energy.

Mnemonic: "Termination Trouble"

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On a vessel with two RADARs, one has a different range indication on a specific target than the other. How would you determine which RADAR is incorrect?

  • Correct Answer
    Check the sweep and timing circuits of both indicators for correct readings.
  • Triangulate target using the GPS and visual bearings.
  • Check antenna parallax.
  • Use the average of the two indications and adjust both for that amount.

In a RADAR System the sweep and timing circuits are responsible for displaying target range correctly so Answer A. is the right answer.

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An increase in the deflection on the magnetron current meter could likely be caused by:

  • Insufficient pulse amplitude from the modulator.
  • Too high a B1 level on the magnetron.
  • Correct Answer
    A decrease of the magnetic field strength.
  • A lower duty cycle, as from 0.0003 to 0.0002.

Hint: magnet appears in both the question and answer.

A strong magnetic field is required to keep the electron beam inside a Magnetron focused.

Without the magnetic field current runs away and destroys the Magnetron.

"An increase in the deflection on the magnetron current meter" is a long-winded way to say "an increase in the Magnetron current".

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