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G3B05

RADIO WAVE PROPAGATION · - Maximum Usable Frequency; Lowest Usable Frequency; short path and long path propagation; determining propagation conditions; ionospheric refraction

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How does the ionosphere affect radio waves with frequencies below the MUF and above the LUF?

  1. AThey are refracted back to Earth
  2. BThey pass through the ionosphere
  3. CThey are amplified by interaction with the ionosphere
  4. DThey are refracted and trapped in the ionosphere to circle Earth
Why The MUF (Maximum Usable Frequency) is the highest frequency the ionosphere will bend back to Earth on a given path at a given time; the LUF (Lowest Usable Frequency) is the lowest frequency that survives D-layer absorption and still arrives with usable signal strength. Between those two limits is the usable window, where the wave is refracted enough to return to the ground and complete the hop. Above the MUF the bending is insufficient and the signal escapes into space; below the LUF the signal is absorbed before it can be heard.
Watch out Passing through the ionosphere is what happens above the MUF, not within the window, and the ionosphere is a passive medium that can only refract and attenuate, never amplify.
Between LUF and MUF is the sweet spot: too high and it escapes, too low and it is absorbed.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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The rest of G3B

  1. G3B01 What is a characteristic of skywave signals arriving at your location by both short-path and long-path propag…
  2. G3B02 What factors affect the MUF?
  3. G3B03 Which frequency will have the least attenuation for long-distance skip propagation?
  4. G3B04 Which of the following is a way to determine current propagation on a desired band from your station?
  5. G3B05 How does the ionosphere affect radio waves with frequencies below the MUF and above the LUF?
  6. G3B06 What usually happens to radio waves with frequencies below the LUF?
  7. G3B07 What does LUF stand for?
  8. G3B08 What does MUF stand for?
  9. G3B09 What is the approximate maximum distance along the Earth's surface normally covered in one hop using the F2 r…
  10. G3B10 What is the approximate maximum distance along the Earth's surface normally covered in one hop using the E re…
  11. G3B11 What happens to HF propagation when the LUF exceeds the MUF?
  12. G3B12 Which of the following is typical of the lower HF frequencies during the summer?
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