Saturday, April 08, 2017


The "grey line" is a band around the Earth that separates daylight from darkness.  Propagation along the grey line is very efficient.  One major reason for this is that the D layer, which absorbs HF signals, disappears rapidly on the sunset side of the grey line, and it has not yet built upon the sunrise side. Ham radio operators and shortwave listeners can optimize long distance communications to various areas of the world by monitoring this band as it moves around the globe.
See a grayline realtime map

Paul Harden, NA5N on Grayline
Read his full story

Earth imagery derived from the NASA Blue Marble