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
- Offset — The gap between transmit and receive frequency.
- K index — How disturbed the earth's magnetic field is.
- SSTV — Slow-Scan Television.
- Simplex vs duplex — One frequency versus two.
- CTCSS / PL tone — A sub-audible tone that opens a repeater.
- SWR — Standing Wave Ratio.
- Sporadic E — Sudden short-lived openings.
- Solar flux — A number that tracks solar activity.