When do NAVTEX broadcasts typically achieve maximum transmitting range?

When do NAVTEX broadcasts typically achieve maximum transmitting range?

• A. Middle of the night
• B. Early afternoon
• C. Sunrise
• D. Mid-morning

Answer: (A)

NavTEX on MF (518 kHz) relies on how radio waves propagate through and around the ionosphere. At night, the ionospheric D-layer is much less ionized, so absorption of medium-frequency signals drops and the ionosphere can reflect MF waves more effectively. That combination lets the signal reach farther before fading, increasing the usable range. During daylight, solar radiation enhances D-layer absorption, shortening the range, with sunrise and morning hours transitioning from the longer-night propagation to the shorter-day propagation. So the maximum transmitting range for NAVTEX is typically during the middle of the night.

NavTEX on MF (518 kHz) relies on how radio waves propagate through and around the ionosphere. At night, the ionospheric D-layer is much less ionized, so absorption of medium-frequency signals drops and the ionosphere can reflect MF waves more effectively. That combination lets the signal reach farther before fading, increasing the usable range. During daylight, solar radiation enhances D-layer absorption, shortening the range, with sunrise and morning hours transitioning from the longer-night propagation to the shorter-day propagation. So the maximum transmitting range for NAVTEX is typically during the middle of the night.