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What causes tropospheric ducting?

Temperature inversions in the atmosphere.

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  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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References

Answer: Temperature inversions in the atmosphere. 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.

  1. HamStudy 2026-2030 Technician pool, section T3C hamstudy.org/browse/E2_2026/T3C
    commonly out to a few hundred miles (around 300 miles) on a regular basis
    Checked 2026-10-09.

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