Gray line — The band of twilight moving around the earth.
For a short window at sunrise and sunset, the low bands can carry signals extraordinary distances. Worth setting an alarm for.
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Related words
- Ionosphere — The layer that bounces HF signals back to earth.
- APRS — Automatic Packet Reporting System.
- Simplex vs duplex — One frequency versus two.
- FT8 — A weak-signal digital mode.
- Band — A range of frequencies set aside for a purpose.
- Solar flux — A number that tracks solar activity.
- Offset — The gap between transmit and receive frequency.
- K index — How disturbed the earth's magnetic field is.