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

Dielectric loss

Answer

Radiation loss

Answer

Mismatch loss

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

To increase the boom length mechanically

Answer

To allow the antenna to operate on multiple bands

Answer

To reduce wind loading on the driven element

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

A vertical antenna with a good radial system

Answer

A high-gain Yagi pointed at the horizon

Answer

A rhombic antenna oriented for long-path propagation

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

11 feet

Answer

33 feet

Answer

66 feet

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

The coil radiates out of phase with the antenna

Answer

The coil increases the antenna's radiation resistance

Answer

The coil detunes the antenna from resonance

Question 6

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

Accepted Answer

Four times higher (about 292 ohms)

Answer

Half (about 36 ohms)

Answer

The same (73 ohms)

Answer

Eight times higher (about 584 ohms)

Question 7

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

Accepted Answer

To provide impedance matching or harmonic suppression

Answer

To increase the antenna gain

Answer

To act as a mechanical support for the antenna

Answer

To equalize the signal on both conductors of a balanced line