GROL - General Radiotelephone Operator License Radio Wave Propagation Questions and Answers

Question 1

A ship is attempting to communicate with a shore station 40 nautical miles away using a VHF marine radio in the 156-162 MHz range. The signal is blocked by a large coastal mountain range between them. What is the primary propagation path for these signals, and why is communication failing?

Accepted Answer

Space wave (line-of-sight), because VHF signals are blocked by significant physical obstructions.

Answer

VHF and UHF radio waves travel primarily via space wave, which is commonly known as line-of-sight (LOS) propagation. [1, 14, 21] These signals travel in a relatively straight line and are blocked by large physical objects like mountains, buildings, or the curvature of the Earth. [1, 11] Groundwave is effective at lower frequencies (MF/LF), and skywave is used for long-distance HF communication.

Question 2

In HF skywave propagation, what is the term for the region between the farthest reach of the groundwave and the point where the first refracted skywave returns to Earth, where the signal cannot be received?

Accepted Answer

The skip zone

Answer

The skip zone, sometimes called the silent zone or dead zone, is the area where a signal is too weak to be received via groundwave and too close to be received via skywave because the skywave overshoots the location. [20, 24, 25] It is the area between the end of groundwave coverage and the first return of the skywave. [19, 24]

Question 3

Which layer of the ionosphere is the highest in altitude, the most heavily ionized, and is primarily responsible for the long-distance propagation of HF radio signals, especially during transcontinental communication?

Accepted Answer

The F2 layer

Answer

The F layer is the most important for long-haul HF communications. During the day, it splits into the F1 and F2 layers. The F2 layer is the highest and most ionized region, making it the primary refractor of HF signals for long-distance (DX) communication. [18, 22] The D layer primarily absorbs HF energy, and the E layer refracts signals over shorter distances. The troposphere is the lowest part of the atmosphere and is not part of the ionosphere.

Question 4

A radio signal is received via two or more distinct paths, causing the signals to interfere with each other at the receiver. This results in rapid fluctuations in signal strength, sometimes causing deep fades. What is this phenomenon called?

Accepted Answer

Multipath fading

Answer

Multipath fading occurs when a radio signal reaches the receiving antenna by two or more paths. [5, 6, 10] These multiple signals can arrive out of phase, causing destructive interference that leads to a significant drop in signal strength, known as a fade. [10] This is a common issue in both HF skywave and mobile VHF/UHF communications.

Question 5

Under certain weather conditions, such as a temperature inversion where a layer of warm air sits above cooler air, VHF and UHF signals can become trapped and travel far beyond their normal line-of-sight horizon. What is this propagation mode called?

Accepted Answer

Tropospheric ducting

Answer

Tropospheric ducting occurs when a temperature inversion creates a boundary between air masses of different temperatures and humidities in the troposphere. [2, 4] This boundary can act as a duct, guiding VHF and UHF radio waves for hundreds or even thousands of miles, far beyond the normal radio horizon. [3, 4, 8]

(GROL) General Radiotelephone Operator License Practice Test

(GROL) General Radiotelephone Operator License Practice Test

GROL - General Radiotelephone Operator License Radio Wave Propagation Questions and Answers