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Subel. T3
12 questions
Subelement T3

RADIO WAVE PROPAGATION

Section T3A

Radio wave characteristics: how a radio signal travels, fading, multipath, polarization, wavelength vs absorption; Antenna orientation

Why do VHF signal strengths sometimes vary greatly when the antenna is moved only a few feet?

  • The signal path encounters different concentrations of water vapor
  • VHF ionospheric propagation is very sensitive to path length
  • Correct Answer
    Multipath propagation cancels or reinforces signals
  • The Doppler effect causes slight frequency shifts which result in changes in signal strength
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How does vegetation affect UHF and microwave signals?

  • Causes knife-edge diffraction, distorting voice peaks
  • Correct Answer
    Absorbs signals, leading to poor reception of weak signals
  • Amplifies signals, improving reception of weak signals
  • Has no effect
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What antenna polarization is normally used for long-distance CW and SSB contacts on the VHF and UHF bands?

  • Right-hand circular
  • Left-hand circular
  • Correct Answer
    Horizontal
  • Vertical
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What is the effect of antenna cross-polarization over a line-of-sight VHF or UHF path?

  • Modulation sidebands might become inverted
  • Correct Answer
    Received signal strength is reduced
  • Signals have an echo effect
  • Nothing significant will happen
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When using a directional antenna, how might your station be able to communicate with a distant repeater if buildings or obstructions are blocking the direct line of sight path?

  • Change from vertical to horizontal polarization
  • Correct Answer
    Try to find a path that reflects signals to the repeater
  • Try the long path
  • Increase the antenna SWR
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What is the meaning of the term “picket fencing”?

  • Alternating transmissions during a net operation
  • Correct Answer
    Rapid flutter on mobile signals due to multipath propagation
  • A type of ground system used with vertical antennas
  • Interference from cable TV in the form of carriers at fixed intervals across the band
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What weather condition might decrease range at microwave frequencies?

  • High winds
  • Low barometric pressure
  • Correct Answer
    Precipitation
  • Colder temperatures
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What is a likely cause of irregular fading of signals propagated by the ionosphere?

  • Frequency shift due to Faraday rotation
  • Interference from thunderstorms
  • Intermodulation distortion
  • Correct Answer
    Random combining of signals arriving via different paths
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Which of the following results from the fact that signals propagated by the ionosphere are elliptically polarized?

  • Digital modes are unusable
  • Correct Answer
    Either vertically or horizontally polarized antennas may be used for transmission or reception
  • FM voice is unusable
  • Both the transmitting and receiving antennas must be of the same polarization
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What effect does multi-path propagation have on data transmissions?

  • Transmission rates must be increased by a factor equal to the number of separate paths observed
  • Transmission rates must be decreased by a factor equal to the number of separate paths observed
  • No significant changes will occur if the signals are transmitted using FM
  • Correct Answer
    Error rates are likely to increase
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Which region of the atmosphere can reflect HF radio waves?

  • The stratosphere
  • The troposphere
  • Correct Answer
    The ionosphere
  • The electrosphere
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What effect does fog or rain have on 10-meter and 6-meter band signals?

  • Absorption
  • Correct Answer
    Little effect
  • Deflection
  • Increased range
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