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Subelement C

Receiving Systems

Section 20

Mixers

The diagram in Fig. 8C9 shows a simplified RADAR mixer circuit using a crystal diode as the first detector. What is the output of the circuit when no echoes are being received?

  • 60 MHz CW.
  • 4095 MHz CW.
  • 4155 MHz CW.
  • Correct Answer
    No output is developed.

"(Radar) Echoes" is a synonym for "radar signals".

If no radar signals are being recieved, the mixer is only receiving the signal from the LO - Local Oscillator, therefore the mixer is generating no output signal.

No signal in, no signal out, so Answer D. is the right answer.

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In the receive mode, frequency conversion is generally accomplished by a:

  • Tunable wave-guide section.
  • Pentagrid converter.
  • Correct Answer
    Crystal diode.
  • Ferrite device.
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An RF mixer has what purpose in a RADAR system?

  • Mixes the CW transmitter output to form pulsed waves.
  • Correct Answer
    Converts a low-level signal to a different frequency.
  • Prevents microwave oscillations from reaching the antenna.
  • Combines audio tones with RF to produce the RADAR signal.
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In a RADAR unit, the mixer uses a:

  • Pentagrid converter tube.
  • Field-effect transistor.
  • Correct Answer
    Silicon crystal or PIN diode.
  • Microwave transistor.
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What component of a RADAR receiver is represented by block 49 in Fig. 8A1?

  • Discriminator.
  • IF amplifier.
  • Klystron.
  • Correct Answer
    Crystal detector (the mixer).
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In a RADAR unit, the mixer uses:

  • Correct Answer
    PIN diodes and silicon crystals.
  • PIN diodes.
  • Boettcher crystals.
  • Silicon crystals.
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