HAM Antennas and Feed Lines 2

Question 1

What is the radiation resistance of a half-wave dipole in free space?

Accepted Answer

73 ohms

Answer

50 ohms

Answer

300 ohms

Answer

450 ohms

Question 2

What is the primary advantage of a Yagi antenna over a dipole for HF communication?

Accepted Answer

Directional gain and front-to-back ratio

Answer

Lower feed point impedance

Answer

Broader bandwidth

Answer

Easier construction

Question 3

What happens to the impedance of a transmission line when it is terminated in a purely resistive load equal to its characteristic impedance?

Accepted Answer

It equals the characteristic impedance at all points

Answer

It becomes purely reactive

Answer

It doubles at the source

Answer

It drops to zero

Question 4

What type of antenna produces a circularly polarized signal?

Accepted Answer

Helical antenna in axial mode

Answer

Half-wave dipole

Answer

Yagi-Uda array

Answer

Beverage antenna

Question 5

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

Accepted Answer

0.66

Answer

1.00

Answer

0.95

Answer

0.50

Question 6

What is the function of a balun at a dipole feed point when coaxial cable is used?

Accepted Answer

To prevent common-mode current on the coax shield

Answer

To increase antenna gain

Answer

To match impedance to 300 ohms

Answer

To reduce SWR on the transmission line

Question 7

How does antenna height above ground affect the elevation angle of maximum radiation for a horizontal dipole?

Accepted Answer

Greater height lowers the main lobe angle

Answer

Greater height raises the main lobe angle

Answer

Height has no effect on elevation angle

Answer

Greater height eliminates all low-angle radiation