Gray Line
The gray line (or grayline) is the twilight zone that separates day from night on Earth. This zone offers unique propagation conditions, particularly on low bands.
Why Gray Line is Special
In the terminator zone (the sunrise/sunset line):
- D layer is absent or weak: less absorption on low bands
- F layer is still ionized: allows reflection
- Unusual paths: waves that would normally be absorbed can propagate
The result is a "window" of a few minutes where difficult contacts become possible.
Favorite Bands
Gray line is particularly useful on:
- 160m (1.8 MHz): the "gentleman's band" depends almost entirely on gray line for intercontinental DX
- 80m (3.5 MHz): excellent for DX toward difficult directions
- 40m (7 MHz): extends range beyond normal
On higher bands the effect is less pronounced but can still help.
How to Exploit Gray Line
To maximize opportunities:
- Calculate times: use a gray line map to see which areas share the terminator with you
- Be punctual: the window may last only 15-30 minutes
- Point the antenna: orient toward the terminator direction
- Listen first: you'll often hear stations you normally can't
Short and Long Path Gray Line
There are two types of gray line propagation:
- Short path: signal follows the terminator for the shortest route
- Long path: signal goes the long way, always staying in the twilight zone
Long path gray line can enable contacts impossible via the normal path!