Subelement D: Other Equipment— Topic 24: NAVTEX
Question 1-24D5
Element 1 (MROP)When do NAVTEX broadcasts typically achieve maximum transmitting range?
Explanation
NAVTEX broadcasts operate on Medium Frequencies (MF), primarily 518 kHz and 490 kHz. During the day, the sun's radiation creates the D-layer in the ionosphere, which strongly absorbs MF signals. This limits daytime propagation primarily to ground waves, resulting in shorter ranges.
At night, particularly in the middle of the night, the D-layer dissipates due to the absence of solar radiation. Without the D-layer to absorb them, MF signals can travel higher into the ionosphere (to the E and F layers), reflect, and return to Earth. This phenomenon, known as skywave propagation, allows signals to travel much greater distances, significantly increasing the transmitting and receiving range of NAVTEX broadcasts. Therefore, the middle of the night provides the optimal conditions for maximum range.
Related Questions
1-24D3 Which of the following is the primary frequency that is used exclusively for NAVTEX broadcasts internationally?1-24D4 What means are used to prevent the reception of unwanted broadcasts by vessels utilizing the NAVTEX system?1-24D6 What is the transmitting range of most NAVTEX stations?1-2A1 Which commercial radio operator license is required to operate a fixed-tuned ship RADAR station with external controls?1-2A2 When is a Marine Radio Operator Permit or higher license required for aircraft communications?