The Evolution of Shortwave Radio by by James Careless

OTTAWA, Ontario — With the advent of radio in the 20th century, the shortwave band (1710–30,000 kHz) soon became a hotbed of long-distance radio broadcasting. Used primarily by state-run international broadcasters, plus ham radio operators and ship-to-shore radio communications, the shortwave band was prized due to its astoundingly broad reach. That reach was — and is still — made possible by the tendency of ground-based shortwave radio transmissions to bounce off the ionosphere and back to earth; allowing shortwave broadcasts to “hop” repeatedly, increasing a broadcast’s range while minimizing its decay. This writer once heard BBC World Service on 6175 kHz coming to him from both directions at once; a phenomenon proven by the “echo” he heard caused by the “around the world” shortwave signal arriving at his receiver slightly later than the “direct path” signal.
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