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T3A04

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

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What is the effect of antenna cross-polarization over a line-of-sight VHF or UHF path?

  1. AModulation sidebands might become inverted
  2. BReceived signal strength is reduced
  3. CSignals have an echo effect
  4. DNothing significant will happen
Why Antennas transmit and receive best when their electric field orientation matches. If one station uses a horizontal antenna and the other vertical, the polarizations are 90 degrees apart and only a small fraction of the energy couples into the receiving antenna, typically costing 20 dB or more on a direct line-of-sight path. That shows up simply as a much weaker received signal, not as distortion.
Watch out Echoes and inverted sidebands come from other mechanisms: multipath reflections cause flutter or ghosting, and sideband inversion is a mixing or modulation issue, neither of which is caused by antenna orientation. Saying nothing happens is only close to true for long skywave paths where the ionosphere scrambles polarization anyway.
Mismatched polarization = big signal loss. That's why FM repeaters are vertical and SSB/CW weak-signal work is horizontal.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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The rest of T3A

  1. T3A01 Why do VHF signal strengths sometimes vary greatly when the antenna is moved only a few feet?
  2. T3A02 How does vegetation affect UHF and microwave signals?
  3. T3A03 What antenna polarization is normally used for long-distance CW and SSB contacts on the VHF and UHF bands?
  4. T3A04 What is the effect of antenna cross-polarization over a line-of-sight VHF or UHF path?
  5. T3A05 When using a directional antenna, how might your station be able to communicate with a distant repeater if bu…
  6. T3A06 What is the meaning of the term "picket fencing"?
  7. T3A07 What weather condition might decrease range at microwave frequencies?
  8. T3A08 What is a likely cause of irregular fading of signals propagated by the ionosphere?
  9. T3A09 Which of the following results from the fact that signals propagated by the ionosphere are elliptically polar…
  10. T3A10 What effect does multi-path propagation have on data transmissions?
  11. T3A11 Which region of the atmosphere can reflect HF radio waves?
  12. T3A12 What effect does fog or rain have on 10-meter and 6-meter band signals?
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