FREE HAM Radio Extra Class Test Antenna Design & Theory Questions and Answers

Question 1

Which of the following describes the primary advantage of a log-periodic dipole array (LPDA) antenna over a Yagi-Uda antenna for multi-band HF operation?

Accepted Answer

LPDAs provide consistent gain and SWR across a wide frequency range without retuning.

Answer

LPDAs offer a significantly smaller footprint for the same gain across multiple bands.

Answer

LPDAs inherently have a lower take-off angle suitable for DX on all bands.

Answer

LPDAs are simpler to construct and tune for a single band compared to Yagis.

Question 2

An amateur operator observes that their vertically polarized mobile antenna exhibits significant signal nulls and peaks when driving through a city with many tall buildings. This phenomenon is primarily caused by:

Accepted Answer

Multipath propagation and reflections off various structures.

Answer

Atmospheric ducting effects specific to urban environments.

Answer

Faraday rotation due to the Earth's magnetic field interacting with the signal.

Answer

Overload of the receiver's front end from strong local signals.

Question 3

What is the primary purpose of a balun when connecting a balanced antenna (like a dipole) to an unbalanced transmission line (like coaxial cable)?

Accepted Answer

To prevent common-mode currents on the outer shield of the coaxial cable.

Answer

To provide impedance matching between the antenna and the transmission line.

Answer

To convert direct current (DC) to radio frequency (RF) current.

Answer

To increase the bandwidth of the antenna system.

Question 4

When designing an antenna for optimal long-distance (DX) communication on HF, which of the following characteristics is generally most desirable for the radiation pattern?

Accepted Answer

A low take-off angle to enhance skywave propagation over long distances.

Answer

An omnidirectional pattern to maximize coverage in all directions.

Answer

A high take-off angle to facilitate NVIS propagation.

Answer

A broadside pattern with equal gain in all horizontal directions.

Question 5

Which type of antenna typically exhibits circular polarization and is often used for satellite communications to mitigate the effects of Faraday rotation?

Accepted Answer

Helical antenna

Answer

Yagi-Uda antenna

Answer

Quad antenna

Answer

Discone antenna

Question 6

What is the primary effect of increasing the boom length of a multi-element Yagi-Uda antenna (assuming proper element spacing and tuning)?

Accepted Answer

Increased gain and improved front-to-back ratio.

Answer

Increased bandwidth and reduced Q.

Answer

Reduced front-to-back ratio and higher SWR.

Answer

Lower radiation resistance and narrower beamwidth.