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SESK: Stuff Everyone Should Know · sesk.info/ham-tropo-ducting-cause

What causes tropospheric ducting?

Temperature inversions in the atmosphere.

  1. Temperature inversions in the atmosphere ✔
  2. Sunspots and solar flares
  3. Lightning discharges

Why: A temperature inversion is warm air sitting over cooler air. It can trap VHF and UHF signals in a duct, carrying them hundreds of miles.

Huh, didn't know that: Ducting regularly allows VHF and UHF contacts of about 300 miles.

The dad joke
Why did the radio wave take the duct? It wanted to avoid traffic.
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Sources

  1. NCVEC 2026-2030 Technician Question Pool (Element 2), errata Feb 19, 2026 https://www.ncvec.org/downloads/2026-2030%20Technician%20Pool%20and%20Syllabus%20Public%20Release%20Feb%2019%202026.pdf

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