What is chordal-hop propagation?

Chordal-hop propagation occurs when a radio wave is refracted by the ionosphere but, instead of returning to the Earth's surface to bounce back up, it gets caught within the ionosphere itself. The wave travels along the ionosphere through successive refractions before finally escaping back to Earth. Because the wave doesn't suffer the severe absorption losses associated with bouncing off the ground or passing multiple times through the lower D-region, chordal-hop signals can travel extremely long distances with surprisingly strong signal strengths. Other options describe different phenomena: propagation across the geomagnetic equator is transequatorial propagation (TEP), and signals reflected back toward the transmitter represent backscatter.