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Lesson 3: Radio Wave Propagation

Lesson 3 of 10, syllabus topic G3. The exam asks 3 questions from this topic, one from each of its 3 groups.

Propagation explains when and where the HF bands open, which shapes everything you do on HF.

What you will learn

  • G3A Sunspots and solar radiation; geomagnetic field and stability indices
  • G3B Maximum Usable Frequency; Lowest Usable Frequency; short path and long path propagation; determining propagation conditions; ionospheric refraction
  • G3C Ionospheric regions; critical angle and frequency; HF scatter; near vertical incidence skywave (NVIS)

1. Read

  1. How radio signals travel: The Sun drives HFHelps with G3A
  2. How radio signals travel: When the Sun misbehavesHelps with G3A
  3. How radio signals travel: Skip, the skip zone and the MUFHelps with G3B, G3C
  4. How radio signals travel: Checking conditions right nowHelps with G3B
  5. How radio signals travel: The ionosphereHelps with G3C
  6. How radio signals travel: Day and night by bandHelps with G3C
  7. All 37 G3 questions with their answers and explanationsEvery group, with the rule or source behind each answer

2. Explore

  • Propagation conditions

    Check today's planetary K index and 10.7 cm solar flux, then read what each one means for HF.

  • Grid square locator

    Find the short path and long path headings to a distant grid square. The long path points the opposite way, 180 degrees from the short path.

    This is exam question G2D06.

3. Practice

Practice one group at a time. A group is ready when you have answered every one of its questions and learned at least 80 percent of them; a question counts as learned when your last three answers to it were correct. To review quickly, go through this lesson’s questions as flashcards.

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