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

A half-wave dipole in free space has a radiation resistance of approximately 73 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

A Yagi provides directional gain and improved front-to-back ratio compared to an isotropic or dipole antenna.

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

A line terminated in its characteristic impedance is a matched line, presenting that same impedance at every point along it.

Question 4

What type of antenna produces a circularly polarized signal?

Accepted Answer

Helical antenna in axial mode

Answer

A helical antenna operating in axial mode produces a circularly polarized wave, useful for satellite communications.

Question 5

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

Accepted Answer

0.66

Answer

Solid polyethylene dielectric coaxial cable has a velocity factor of approximately 0.66, meaning signals travel at 66% of the speed of light.

HAM - Radio Extra Class Test Practice Test