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Learn / Amateur Extra course

Lesson 8: Antennas and Transmission Lines

Lesson 8 of 10, syllabus topic E9. The exam asks 8 questions from this topic, one from each of its 8 groups.

Antennas and transmission lines at this level add patterns, matching, line behavior and the Smith chart.

What you will learn

  • E9A Basic antenna parameters: radiation resistance, gain, beamwidth, efficiency; effective radiated power (ERP) and effective isotropic radiated power (EIRP)
  • E9B Antenna patterns and designs: azimuth and elevation patterns; gain as a function of pattern; antenna modeling
  • E9C Practical wire antennas; folded dipoles; phased arrays; effects of ground near antennas
  • E9D Yagi antennas; parabolic reflectors; feed point impedance and loading of electrically short antennas; antenna Q; RF grounding
  • E9E Impedance matching: matching antennas to feed lines; phasing lines; power dividers
  • E9F Transmission lines: characteristics of open and shorted feed lines; coax versus open wire; velocity factor; electrical length; coaxial cable dielectrics; microstrip
  • E9G The Smith chart
  • E9H Receiving antennas: radio direction finding (RDF) techniques; Beverage antennas; single- and multiple-turn loops

1. Read

  1. Antennas and feed lines: Gain and directivityHelps with E9A, E9B
  2. Antennas and feed lines: The half-wave dipoleHelps with E9C
  3. Antennas and feed lines: Yagis and other beamsHelps with E9D
  4. Antennas and feed lines: Loading and shortened antennasHelps with E9D
  5. Antennas and feed lines: Antenna tunersHelps with E9E
  6. Antennas and feed lines: SWR: what it does and does not tell youHelps with E9E
  7. Antennas and feed lines: Coax and other feed linesHelps with E9F
  8. All 93 E9 questions with their answers and explanationsEvery group, with the rule or source behind each answer

2. Explore

  • Decibels

    Work out the ERP for 150 watts with 4.2 dB of losses and 7 dBd of gain. The net gain is 2.8 dB, a factor of about 1.9, so the ERP is about 286 watts.

    This is exam question E9A02.

  • SWR and feed line loss

    Plot a load on the Smith chart and follow the circle of constant SWR around the 50 ohm center.

  • Matching network

    Match an antenna feed point to 50 ohm coax with an L network.

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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