GROL - General Radiotelephone Operator License Antennas and Transmission Lines Questions and Answers

Question 1

A technician measures a Standing Wave Ratio (SWR) of 1:1 at the transmitter end of a transmission line. What does this measurement indicate?

Accepted Answer

The impedance of the antenna and transmission line are perfectly matched.

Answer

An SWR of 1:1 is the ideal condition, indicating that there are no standing waves on the line. This occurs when the load (antenna) impedance is exactly equal to the characteristic impedance of the transmission line, allowing for maximum power transfer from the transmitter to the antenna with no reflected power.

Question 2

Which of the following best describes the polarization of an electromagnetic wave?

Accepted Answer

The orientation of the electric field vector with respect to the Earth's surface.

Answer

The polarization of a radio wave is conventionally defined by the orientation and movement of its electric field (E-field) vector as it travels through space. For example, a vertical antenna produces a vertically polarized wave because its electric field is perpendicular to the Earth's surface.

Question 3

What is the approximate theoretical feed-point impedance of a quarter-wavelength vertical antenna (Marconi) when installed with a perfect ground plane system?

Accepted Answer

36 ohms

Answer

A theoretical quarter-wave vertical antenna over a perfect, infinitely conductive ground plane has a feed-point impedance of approximately 36.5 ohms. This is a fundamental characteristic used in matching the antenna to a transmission line, which often requires a matching network for optimal performance with 50-ohm coaxial cable.

Question 4

A coaxial cable is specified as having a velocity factor of 0.66. What does this signify?

Accepted Answer

The signal travels through the cable at 66% of the speed of light in a vacuum.

Answer

The velocity factor (VF) of a transmission line is the ratio of the speed at which a signal propagates through the line compared to the speed of light in a vacuum. It is always less than 1 because the dielectric material in the cable slows the wave's propagation. A velocity factor of 0.66 means the signal travels at 66% of the speed of light.

Question 5

What is the primary function of a balun in an RF antenna system?

Accepted Answer

To interface between a balanced system and an unbalanced system.

Answer

The term "balun" is a portmanteau of "balanced to unbalanced." Its primary purpose is to connect a balanced system (like a dipole antenna or twin-lead feedline) to an unbalanced system (like a coaxial cable), ensuring proper current flow and preventing the feedline from radiating.

(GROL) General Radiotelephone Operator License Practice Test

(GROL) General Radiotelephone Operator License Practice Test

GROL - General Radiotelephone Operator License Antennas and Transmission Lines Questions and Answers