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Lesson 8: Antennas and Feed Lines

Lesson 8 of 10, syllabus topic G9. The exam asks 4 questions from this topic, one from each of its 4 groups.

Antennas and feed lines use the reactance and decibel ideas from the earlier lessons.

What you will learn

  • G9A Feed lines: characteristic impedance and attenuation; standing wave ratio (SWR) calculation, measurement, and effects; antenna feed point matching
  • G9B Basic dipole and monopole antennas
  • G9C Directional antennas
  • G9D Specialized antenna types and applications

1. Read

  1. Antennas and feed lines: Coax and other feed linesHelps with G9A
  2. Antennas and feed lines: SWR: what it does and does not tell youHelps with G9A
  3. Antennas and feed lines: Antenna tunersHelps with G9A
  4. Antennas and feed lines: The half-wave dipoleHelps with G9B
  5. Antennas and feed lines: Quarter-wave verticalsHelps with G9B
  6. Antennas and feed lines: Gain and directivityHelps with G9C
  7. Antennas and feed lines: Yagis and other beamsHelps with G9C
  8. Antennas and feed lines: Loading and shortened antennasHelps with G9D
  9. How radio signals travel: Day and night by bandHelps with G9D
  10. All 46 G9 questions with their answers and explanationsEvery group, with the rule or source behind each answer

2. Explore

  • SWR and feed line loss

    Enter a 200 ohm resistive load on 50 ohm line. The SWR is 4 to 1, the larger impedance divided by the smaller.

    This is exam question G9A09.

  • Antenna length

    Compare the half-wave dipole and the quarter-wave vertical for the same frequency: the vertical element is half as long.

  • Decibels

    Convert a gain of 7 dBd to dBi by adding 2.15 dB: 9.15 dBi.

    This is exam question G9C04.

  • Matching network

    Match a load that is not 50 ohms with an L network and see the two component values it needs.

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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