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Subel. B
6 questions
Subelement B

MF-HF-DSC-SITOR (NBDP) Equip. & Ops:

Section 15

Receiver Faults-2:

The MF/HF receiver fails to suppress the AF output in the absence of a sufficiently strong input signal. What is the most likely cause?

  • The AGC circuit has failed.
  • The BFO circuit has failed.
  • Correct Answer
    The squelch circuit has failed.
  • The AF amplifier circuit has failed.

C. The squelch circuit has failed.

The squelch circuit is specifically designed to suppress the receiver's audio frequency (AF) output (i.e., mute the speaker) when the input signal strength is below a preset threshold, or absent altogether. This prevents the user from hearing loud noise and static ("white noise") when no signal is being received.

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The MF/HF receiver fails to produce any AF output. An ohmmeter reading is near zero between speaker leads. What is the most likely cause?

  • The 3 - 30 MHz amplifier stage has failed.
  • The speaker is shorted out.
  • Excess negative feedback is reducing AF gain.
  • Correct Answer
    The audio amplifier stage has failed.
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The MF/HF transceiver produces strong AF output but no signals are heard on any frequency. What is the most likely cause?

  • Correct Answer
    The transceiver is connected to a "Dummy Load."
  • A high Standing Wave Ratio (SWR) in the antenna system.
  • A "crowbar" circuit in the power supply is activated.
  • The squelch circuit has failed.
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The MF/HF transceiver produces strong AF output but no signals are heard on any frequency. What is the most likely cause?

  • The squelch sensitivity control is set too high.
  • Correct Answer
    There is an open circuit in the transmission line to the antenna.
  • The final stage of the AF amplifier circuit has failed.
  • The power amplifier stage in the receiver has failed.
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The MF/HF transceiver fails to produce AF output but the radio is powered on and "TX" is illuminated. What is the most likely cause?

  • The speaker is shorted out.
  • Correct Answer
    A shorted Push-To-Talk circuit in the microphone.
  • A "crowbar" circuit in the power supply has engaged.
  • The final stage of the AF amplifier circuit has failed.
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A received signal on a MF/HF transceiver breaks up rapidly and repeatedly. The signal alternates between mid scale and zero on the "Signal" meter. What is the most likely cause?

  • Intermittent gain in the AF amplifier circuit.
  • The squelch sensitivity control is set too high.
  • Correct Answer
    An intermittent connection between the antenna and coupler.
  • The AGC circuit has malfunctioned.
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