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Chameleon Knowledge Base · The Complete Online HF Antenna Handbook

What Is Knife-Edge Diffraction?

Learn what knife-edge diffraction is and how radio signals can bend around obstacles to reach receivers beyond line of sight.

Getting Started HF Fundamentals Reviewed 2026-07-14
Short Answer: Learn what knife-edge diffraction is and how radio signals can bend around obstacles to reach receivers beyond line of sight.

Explanation

Overview Knife-edge diffraction occurs when a radio wave encounters a sharp obstacle such as a mountain ridge, hill, or building edge and bends around it. This allows communication to continue even when there is no direct line of sight between the transmitting and receiving stations. Common Obstacles Mountain ridges. Buildings. Cliffs. Large terrain features. Signal Loss Although diffraction allows signals to reach areas behind an obstruction, some signal strength is always lost during the bending process. Factors Affecting Diffraction Frequency. Obstacle shape. Obstacle height. Distance. Applied to Chameleon Products Portable Chameleon antennas used in mountainous terrain may still achieve successful communication through diffraction, even when direct line of sight is blocked. Related Articles What Is Diffraction Loss? What Is Line-of-Sight Propagation? What Are Fresnel Zones? What Is Ground Wave Propagation? Related Products All Chameleon Portable Antennas

The exact result depends on the complete station: frequency, geometry, feed line, matching network, return-current path, environment, operating power, and the reference plane of any measurement. A low SWR establishes an impedance relationship at that point; it does not by itself prove efficiency, radiation pattern, compatibility, or safety.

What to Verify

  • Use the newest official product guide or primary service documentation.
  • Confirm the exact model, revision, components, configuration, and operating conditions.
  • Begin tests at low power and change one variable at a time.
  • Do not infer compatibility from connector or thread fit.

Learn Next

  • Antenna Selection: A Mission-First Decision Guide
  • Engineering Design Tradeoffs in Portable HF Antennas
  • Antenna Measurement Reference Planes
  • Understanding Common-Mode Current

Source note: Independently synthesized with reference to The ARRL Handbook for Radio Communications, 99th edition (2022), and The ARRL Antenna Book for Radio Communications, 24th edition (2019). Verify changing regulations, services, software, specifications, availability, and safety requirements against current primary sources.