HAM FREE HAM Radio Extra Class Test Antennas and Feed Lines Questions and Answers 2

Question 1

What is the primary advantage of using open-wire (ladder line) feed line instead of coaxial cable?

Accepted Answer

Much lower loss at high SWR

Answer

Higher power handling at UHF frequencies

Answer

Better shielding from RF interference

Answer

Easier to route through walls and conduits

Question 2

What is the approximate feed point impedance of a half-wave dipole antenna in free space?

Accepted Answer

73 ohms

Answer

50 ohms

Answer

300 ohms

Answer

36 ohms

Question 3

Which antenna type produces a circularly polarized signal?

Accepted Answer

A crossed-Yagi fed 90 degrees out of phase

Answer

A collinear vertical array

Answer

A half-wave dipole mounted at an angle

Answer

A ground-plane antenna with drooping radials

Question 4

What happens to the radiation resistance of a shortened antenna compared to a full-size resonant antenna?

Accepted Answer

It decreases significantly

Answer

It increases significantly

Answer

It remains the same

Answer

It becomes purely reactive

Question 5

What is the purpose of a balun at the feed point of a dipole antenna fed with coaxial cable?

Accepted Answer

To prevent common-mode current on the coax shield

Answer

To increase the gain of the antenna by 3 dB

Answer

To match 50-ohm coax to 300-ohm feed line

Answer

To filter harmonics before they reach the antenna

Question 6

What is the velocity factor of a typical solid polyethylene dielectric coaxial cable?

Accepted Answer

Approximately 0.66

Answer

Approximately 0.95

Answer

Approximately 0.82

Answer

Approximately 0.50