FREE Ham Radio General Class Test Antennas and Feed Lines Questions and Answers

Question 1

What is the primary purpose of an antenna tuner (transmatch)?

Accepted Answer

To match the impedance of the transceiver to the impedance of the feed line and antenna system.

Answer

An antenna tuner, also known as a transmatch or impedance matcher, is used to ensure maximum power transfer from the transmitter to the antenna system. It does this by matching the output impedance of the transceiver (typically 50 ohms) to the impedance presented by the feed line and antenna. This minimizes reflected power (high SWR) and allows the transmitter to operate efficiently.

Question 2

In a Yagi antenna, what is the typical relationship in length between the driven element, the reflector, and the directors?

Accepted Answer

The reflector is the longest, the driven element is shorter, and the directors are the shortest.

Answer

In a typical Yagi-Uda antenna design, the reflector element is slightly longer than the driven element, and the director elements are progressively shorter than the driven element. This arrangement of element lengths is crucial for achieving the antenna's characteristic gain and directional pattern, with the signal being focused in the direction of the directors.

Question 3

A technician measures the SWR at the transmitter end of a long coaxial feed line and gets a reading of 1.1:1. However, the antenna itself is known to be a poor match for the operating frequency. What is the most likely reason for the low SWR reading?

Accepted Answer

The long feed line is attenuating the reflected wave, making the SWR appear lower than it is at the antenna.

Answer

A long run of coaxial cable has inherent loss (attenuation) that increases with frequency. This loss affects both the forward power going to the antenna and the reflected power coming back. The reflected wave is attenuated on its way back to the SWR meter, resulting in a reading that is artificially low and not representative of the actual SWR at the antenna feed point.

Question 4

What is the primary radiation pattern of a simple quarter-wavelength vertical antenna installed with a good ground-plane system?

Accepted Answer

Omnidirectional in the horizontal plane.

Answer

A quarter-wavelength vertical antenna, when used with an effective ground plane (like a set of radials), radiates equally well in all horizontal directions. Its radiation pattern is omnidirectional in the azimuth (horizontal) plane, making it a popular choice for general-purpose communication where you want to contact stations in any direction.

Question 5

The velocity factor of a coaxial cable is primarily determined by which of its physical properties?

Accepted Answer

The type of dielectric material used between the center conductor and shield.

Answer

The velocity factor represents the speed at which a radio wave travels through the feed line compared to the speed of light in a vacuum. This speed is determined almost entirely by the dielectric constant of the insulating material separating the center conductor and the shield. Materials like foam polyethylene have a higher velocity factor (closer to the speed of light) than solid polyethylene.

Ham Radio General Class Test Practice Test

Ham Radio General Class Test Practice Test

FREE Ham Radio General Class Test Antennas and Feed Lines Questions and Answers