Greyline

Grey line or gray line propagation is a form of radio signal propagation that provides surprisingly long distance radio communications at dawn and dusk sometimes when other forms of ionospheric propagation may not be expected to provide signal paths of these distances (electronics notes).

Greyline is used on HF, not VHF and above. The greyline time for a specific location is when the center of the sun is at the horizon.

Display the greyline on one of two ways:

1. The area in shadow is shaded, or
2. The night lights map is alpha-blended onto the main map.