Subelement F: Maritime Safety Information (M.S.I.)— Topic :
Question 37F2
Element 7R (GMDSS-RO)When do NAVTEX broadcasts typically achieve maximum transmitting range?
Explanation
NAVTEX broadcasts operate on medium frequencies (MF), primarily 518 kHz and 490 kHz. The range of MF signals is significantly affected by the ionosphere. During daylight hours, the D-layer of the ionosphere, which is created by solar radiation, absorbs MF signals, limiting their propagation primarily to ground waves.
At night, particularly in the middle of the night, the D-layer dissipates due to the absence of solar radiation. This allows MF signals to penetrate to the higher F-layer of the ionosphere, which then reflects them back to Earth. This phenomenon, known as skywave propagation, dramatically extends the range of MF transmissions, often allowing them to be received hundreds or even thousands of miles away. Therefore, the "middle of the night" offers the optimal conditions for maximum transmitting range.
Related Questions
36E6 Which statement is true regarding Inmarsat “hot-key” Distress Alerts?37F1 How is mutual interference on 518 kHz among NAVTEX stations avoided?37F3 What should a GMDSS Radio Operator do if a NAVTEX warning message is received but it contains too many errors to be usable?37F4 Which of these cannot happen when a paper model NAVTEX receiver runs out of paper?37F5 Which of the following is the primary frequency that is used exclusively for NAVTEX broadcasts internationally?