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G9C12

ANTENNAS AND FEED LINES · - Directional antennas

G9C12G9C →

Which of the following is a characteristic of using a gamma match with a Yagi antenna?

  1. AIt does not require the driven element to be insulated from the boom
  2. BIt does not require any inductors or capacitors
  3. CIt is useful for matching multiband antennas
  4. DAll these choices are correct
Why A gamma match feeds the driven element off-center: the coax shield connects to the middle of the element (the zero-voltage point) and the center conductor goes through a series capacitor to a gamma rod tapped out along the element. Because the element's center is at RF ground potential, the element can be a single unbroken tube bolted straight to the boom, with no insulating center section or split needed. That mechanical simplicity and ruggedness is the main reason gamma matches are popular on Yagis.
Watch out The claim about needing no inductors or capacitors is wrong because a gamma match normally includes a series capacitor, with the gamma rod itself supplying inductive reactance; the gamma match is also a narrowband, single-band matching device, not a multiband solution.
Gamma = Grounded element: no split, no insulator, but yes a series capacitor.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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The rest of G9C

  1. G9C01 Which of the following would increase the bandwidth of a Yagi antenna?
  2. G9C02 What is the approximate length of the driven element of a Yagi antenna?
  3. G9C03 How do the lengths of a three-element Yagi reflector and director compare to that of the driven element?
  4. G9C04 How does antenna gain in dBi compare to gain stated in dBd for the same antenna?
  5. G9C05 What is the primary effect of increasing boom length and adding directors to a Yagi antenna?
  6. G9C07 What does "front-to-back ratio" mean in reference to a Yagi antenna?
  7. G9C08 What is meant by the "main lobe" of a directive antenna?
  8. G9C09 In free space, how does the gain of two three-element, horizontally polarized Yagi antennas spaced vertically…
  9. G9C10 Which of the following can be adjusted to optimize forward gain, front-to-back ratio, or SWR bandwidth of a Y…
  10. G9C11 What is a beta or hairpin match?
  11. G9C12 Which of the following is a characteristic of using a gamma match with a Yagi antenna?
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