HF Radio: Still Valid After 100 Years

Discovered almost one century ago, High Frequency (HF) radio has never lost its appeal thanks to its ability to move traffic across long distances, and its resilience to electronic attack.

- Thomas Withington

Confusingly, High Frequency (HF) radio is also known as shortwave radio. The same terms cover radio traffic using a waveband of three megahertz/MHz to 30MHz. The shortwave moniker comes from the length of the radio waves but this can be deceptive. Three megahertz radio transmissions have a wavelength of almost 100 metres/m (328.1 feet/ft), reducing to almost ten metres (32.8ft) for 30MHz transmissions. At first blush such wavelengths seem rather long. The reason for the name was that in the heady days of radio in the early 20th century, shortwave did indeed use transmissions much shorter than long wave and medium wave. Medium wave transmissions, in a waveband of 300 kilohertz (kHz) to three megahertz (MHz), has wavelengths of 999.3m (3,278.5ft) to 100m, with long wave communications using transmissions of 3kHz (99.8 kilometres/62 miles) and 300kHz, although exact definitions of the upper limit of long wave remain fluid.