HAM Antenna Theory and Design 2

Question 1

What is the radiation resistance of a half-wave dipole antenna 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 effect of adding a ground plane to a quarter-wave vertical antenna?

Accepted Answer

It provides a low-impedance return path and creates an electrical image of the antenna

Answer

A ground plane provides a low-impedance return path and acts as a mirror, creating an electrical image that completes the half-wave dipole equivalent.

Question 3

What is the input impedance of a folded dipole antenna compared to a standard dipole?

Accepted Answer

Four times the impedance (about 292 ohms)

Answer

A folded dipole has approximately 4 times the impedance of a standard dipole, or about 292 ohms, due to the transformer action of the folded element.

Question 4

Which antenna type uses a driven element, a reflector, and one or more directors?

Accepted Answer

Yagi-Uda antenna

Answer

The Yagi-Uda antenna uses a driven element, a slightly longer reflector behind it, and one or more shorter directors in front.

Question 5

What is the typical front-to-back ratio of a well-designed 3-element Yagi antenna?

Accepted Answer

10 to 15 dB

Answer

A well-designed 3-element Yagi typically achieves a front-to-back ratio of 10 to 15 dB.

HAM - Radio Extra Class Test Practice Test

HAM - Radio Extra Class Test Practice Test

HAM Antenna Theory and Design 2