GROL Antennas and Transmission Lines 2

Question 1

What does a standing wave ratio (SWR) of 1:1 indicate on a transmission line?

Accepted Answer

Perfect impedance match with maximum power transfer and no reflected power

Answer

An SWR of 1:1 means the transmission line and antenna impedances are perfectly matched, so no power is reflected and all power transfers to the antenna.

Question 2

What is the characteristic impedance of coaxial cable most commonly used in commercial radio transmitter installations?

Accepted Answer

50 ohms

Answer

50-ohm coaxial cable is the industry standard for commercial RF transmitter feedlines due to its balance of low loss and adequate power-handling capacity.

Question 3

What happens to RF power when there is an impedance mismatch between a transmission line and an antenna?

Accepted Answer

Standing waves are created and some power is reflected back toward the transmitter

Answer

Impedance mismatch causes a portion of the forward power to be reflected at the antenna feedpoint, creating standing waves and reducing radiated power.

Question 4

What is the velocity factor of a transmission line?

Accepted Answer

The ratio of signal propagation speed in the line to the speed of light in free space

Answer

Velocity factor is the ratio of signal speed inside the transmission line to the speed of light in vacuum, typically 0.66–0.95 for common coaxial cables.

Question 5

What is the primary risk of operating a transmitter into a high SWR load?

Accepted Answer

Excessive reflected power can overheat and damage the transmitter's final amplifier

Answer

High SWR returns significant reflected power to the transmitter, potentially causing excessive voltage or current that can destroy the final amplifier stage.

(GROL) General Radiotelephone Operator License Practice Test

(GROL) General Radiotelephone Operator License Practice Test

GROL Antennas and Transmission Lines 2