HAM Antennas and Feed Lines 4

Question 1

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

Accepted Answer

Conductor (I²R) loss

Answer

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

Question 2

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

Accepted Answer

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

Answer

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.

Question 3

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

Accepted Answer

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

Answer

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

Question 4

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

Accepted Answer

16.5 feet

Answer

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.

Question 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?

Accepted Answer

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

Answer

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

HAM - Radio Extra Class Test Practice Test

HAM - Radio Extra Class Test Practice Test

HAM Antennas and Feed Lines 4