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Antennas and Feed Lines Flashcards

7 cards from real HAM practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Antennas and Feed Lines flashcards as text

  1. What type of feed line loss is dominant at lower HF frequencies?

    Answer: Conductor (I²R) loss

    At lower HF frequencies, conductor or I²R (resistive) loss dominates because skin depth is larger and conductor resistance is the primary loss mechanism.

  2. What is the purpose of a gamma match on a Yagi antenna?

    Answer: To transform the low feed point impedance to 50 ohms and provide a coax connection

    A gamma match is an impedance-matching network that transforms the low impedance of a folded or standard driven element to 50 ohms for direct coax feed.

  3. What is NVIS (Near Vertical Incidence Skywave) propagation best achieved with?

    Answer: A horizontal antenna mounted at a low height (0.1 to 0.2 wavelengths)

    NVIS requires high-angle radiation nearly straight up, achieved by a horizontal antenna mounted very low (0.1–0.2λ) above ground.

  4. What is the approximate length of a quarter-wave vertical antenna for the 20-meter band (14.2 MHz) in feet?

    Answer: 16.5 feet

    A quarter-wave at 14.2 MHz is approximately 246/14.2 ≈ 16.5 feet, using the standard formula 234/f(MHz) for a quarter-wave.

  5. What is the primary reason that antenna efficiency decreases when a small loading coil is placed at the base of a short vertical antenna?

    Answer: The coil's resistance dissipates power that would otherwise be radiated

    A loading coil has series resistance that dissipates power as heat, reducing the fraction of input power that is actually radiated.

  6. What is the feed point impedance of a folded dipole antenna compared to a standard half-wave dipole?

    Answer: Four times higher (about 292 ohms)

    A folded dipole has approximately four times the impedance of a standard dipole, making it approximately 300 ohms — ideal for 300-ohm twin-lead.

  7. What is the function of a stub (shorted or open transmission line section) connected in parallel with a feed line?

    Answer: To provide impedance matching or harmonic suppression

    Transmission line stubs present a specific reactance or act as a trap to suppress harmonics or match impedances at a specific frequency.