↑ What is Greyline propagation?

Edited by Doron Tal, 4X4XM

Greyline propagation is a term used in radio communication to describe a specific type of propagation that occurs at the junction between day and night on the Earth's surface. The "grey line" is the boundary between the illuminated and dark portions of the Earth, which moves as the Earth rotates.

Greyline illustration
The height of the F and D layers
is exaggerated in comparison to Earth dimensions.		   An example of a greyline mapref.

Greyline map

During greyline propagation, radio waves are refracted by the ionosphere in such a way that they can travel further than during other times of the day. This is because the ionosphere is in a state of transition, with some areas still reflecting radio waves, while others have started to absorb them. This can create a "sweet spot" for HF radio communication that allows signals to travel longer distances with less attenuation than during other times of the day.

Greyline propagation can be particularly advantageous for long-distance communication, as it allows radio waves to travel further than they might otherwise. However, it is a relatively short-lived phenomenon, lasting only a few hours each day as the Earth rotates and the grey line moves. In addition, the specific conditions of the ionosphere can affect the behavior of radio waves during greyline propagation, and not all frequencies may work equally well during this time.

Amateur radio operators often take advantage of greyline propagation to make long-distance contacts with other operators around the world. Some operators use specialized software or tools to help identify when the grey line is passing over their location, and to determine the best frequencies and modes of propagation to use during this time. Overall, greyline propagation is an interesting and useful phenomenon that can provide unique opportunities for long-distance radio communication.

Back to the main page: why is radio propagation better along the greyline, as well as in-depth tutorial about the propagation of sky waves. See also an index for HF Radio Propagarion.