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Subel. C
6 questions
Subelement C

Receiving Systems

Section 28

Miscellaneous

The purpose of the discriminator circuit in a RADAR set is to:

  • Discriminate against nearby objects.
  • Discriminate against two objects with very similar bearings.
  • Correct Answer
    Generate a corrective voltage for controlling the frequency of the klystron local oscillator.
  • Demodulate or remove the intelligence from the FM signal.

The corrective voltage is known as the AFC - Automatic Frequency Control.

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The MTI circuit:

  • Acts as a mixer in a RADAR receiver.
  • Correct Answer
    Is a filter, which blocks out stationary targets, allowing only moving targets to be detected.
  • Is used to monitor transmitter interference.
  • Will pick up targets, which are not in motion.

The MTI - Moving Traget Indicator is used to block-out stationary targets so only moving targets are rendered on-screen.

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Where is a RF attenuator used in a RADAR unit?

  • Between the antenna and the receiver.
  • Between the magnetron and the antenna.
  • Correct Answer
    Between the magnetron and the AFC section of the receiver.
  • Between the AFC section and the klystron.

The RF Attenuator (Block 47 in Fig. 8A1) is needed to keep the transmitter from saturating the receiver's AFC - Automatic Frequency Control circuit, so it is placed between the Transmitter and the AFC IF Amplifier and Answer C. is the right answer.

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The condition known as "glint" refers to a shifting of clutter with each RADAR pulse and can be caused by a:

  • Correct Answer
    Improperly functioning MTI filter.
  • Memory failure.
  • Low AFC voltage.
  • Interference from electrical equipment.

The MTI - Moving-Target Indicator is the circuit tasked with decluttering the display by keeping fixed targets off the screen. If clutter can't be removed then the MTI circuit is at fault, thus Answer A. is the right answer.

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An ion discharge (TR) cell is used to:

  • Protect the transmitter from high SWRs.
  • Lower the noise figure of the receiver.
  • Tune the local oscillator of the RADAR receiver.
  • Correct Answer
    Protect the receiver mixer during the transmit pulse.

The TR Tube, TR Box or TR Cell is used to disconnect the receiver during the transmit pulse, thus Answer D. is the right answer.

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When the receiver employs an MTI circuit:

  • The receiver gain increases with time.
  • Correct Answer
    Only moving targets will be displayed.
  • The receiver AGC circuits are disabled.
  • Ground clutter will be free of "rabbits."

The MTI - Moving-Target Indicator is the circuit tasked with decluttering the display by keeping fixed targets off the screen. If the MTI is engaged, only moving targests will be displayed, thus Answer B. is the right answer.

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