Shortwave radio is radio transmission using shortwave radio frequencies.
The frequencies and bands used for short-wave radio broadcasting are agreed internationally by the International Telecommunications Union (ITU).
Not all stations stick within these bands, indeed many choose to use frequencies just outside where there are fewer competing broadcast stations and thus less interference (this is known as ‘out-of-band broadcasting’), but most do remain within the agreed limits.
If you’re just tuning around shortwave and looking for stations, the official bands are definitely the place to start. Also remember, radio frequencies below around 12000 kHz work best when it’s dark (at night!) and those above around 9000 kHz work best during daylight hours. Most short-wave radio stations are on a 5 kHz raster meaning that their frequency in kHz will either end with a ‘5’ or a ‘0’ (eg 15205 or 6110 kHz).
There are fourteen discrete bands which are allocated for broadcasting over the short wave frequency range:
Radio Amateurs (fondly referred to as ‘hams’) use a different set of frequencies to broadcasters and also use a different form of modulation for a speech called single sideband (SSB) instead of amplitude modulation (AM). Receiving SSB needs specialist equipment but even relatively low-cost receivers will often do the job. Using a normal AM receiver, SSB sounds as if someone is talking with several socks stuffed in their mouth! Of course, hams use morse code (CW) and digital transmission modes as well.
Radio amateur transmissions are not listed in the short-wave.info database, but the frequencies to listen out on are listed below.
There are lots of other short-wave frequencies which are used for all manner of purposes including ship-to-shore communications (maritime), air traffic control (aeronautical), military and defence, weather information and even spy stations and radio pirates.
Broadcasters normally use AM (though some are now digital), whereas most of the other users are either digital or use SSB as with the radio hams.
It, therefore, requires specialist receivers to listen to these other services and indeed under some jurisdictions it is illegal to do so, however, there is a world of fun to be had on a shortwave if you have the time and patience.
The only other short-wave frequencies which it is usually legal to receive and which require no specialist equipment are ‘time and frequency standard stations’. These are stations which use very accurate transmitters controlled by atomic clocks and thus serve as highly accurate references. They are very useful for checking the accuracy of your receiver.
They also transmit time information, usually as a series of ‘ticks’ each second plus messages each minute. The following stations are believed to be on-air:
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