Shortwave bands

Shortwave bands are frequency allocations for use within the high frequency radio spectrum. They are the primary medium for applications such as marine communication, international broadcasting, and worldwide amateur radio activity because they take advantage of ionospheric skip propagation to send data around the world. The bands are conventionally stated in wavelength as measured by meters. Many bands, most notably the VHF 6 meters band, are notable for their behavior that depends on the season and the level of solar activity.

The "11-meter" (27 MHz) band is the most significant location allocated by most countries for Citizen's Band service (as well as some early cordless phones), though due to the band's propagation characteristics, which allow long-distance interference with local signals, most land mobile radio activity has moved to VHF or UHF, and most cordless phone activity is also in UHF or higher.

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International broadcasting bands

The band frequencies below are derived from multiple sources, and different radios can have different numbers. Most international broadcasters use amplitude modulation with a stepping of 5 kHz between channels; a few use single sideband modulation. Different radios may define the bands differently.

• 11 meters – 25.67–26.10 MHz – Very little broadcasting activity in this band. Day reception tends to be poor, night reception nonexistent. This band could be used for daytime 'single hop' regional coverage, but very few broadcast transmitters and antennas function in this band. Digital Radio Mondiale has proposed that this band be used for local digital shortwave broadcasts and conducted an extensive test of the concept in Mexico City in 2005. [1] Not to be confused with the Citizen's Band 11-meter allocation, which in most countries runs from 26.965 MHz to 27.405 MHz.
• 13 meters – 21.45–21.85 MHz – Somewhat shaky day reception, very little night. Similar case to 11 metres, but long distance daytime broadcasting keeps this band humming in the Asia-Pacific region.
• 15 meters – 18.90–19.02 MHz – Seldom used.
• 16 meters – 17.48–17.90 MHz – Day reception good, night reception varies seasonally, with summer being the best.
• 19 meters –15.00–15.825 MHz – Day reception good, night reception variable, best during summer. Time stations such as WWV are clustered around 15 MHz.
• 22 meters – 13.57–13.87 MHz – Similar to 19 meters; best in summer.
• 25 meters – 11.50–12.16 MHz – Generally best during summer; said to be ideal during the period before and after sunset.
• 31 meters – 9250–9995 kHz – Good year-round night band; seasonal during the day, with best reception in winter. Time stations are clustered around 10 MHz.
• 41 meters – 7100–7600 kHz – Reception varies by region – reasonably good night reception, but few transmitters in this band are targeted to North America.
• 49 meters – 5800–6300 kHz – Good year-round night band; daytime reception is lacking.
• 60 meters – 4400–5100 kHz – Mostly used locally in tropical regions, though usable at night. Time stations are clustered around 5000 kHz.
• 75 meters – 3900–4050 kHz – Mostly used in Eastern Hemisphere, not widely received in the Americas.
• 90 meters – 3200–3400 kHz – Mostly used locally in tropical regions, with limited long-distance reception at night.
• 120 meters – 2300–2495 kHz – Mostly used locally in tropical regions, with time stations clustered around 2500 kHz. Not technically a shortwave band; resides in the upper reaches of the mediumwave band.

Amateur HF bands

Main article: Amateur radio bands

Marine and land mobile allocations

The international maritime distress frequency is 2182 kHz; formerly 500 kHz was reserved for Morse Code distress signals, but this frequency allocation has been discarded in favor of systems such as GMDSS and Inmarsat. As mentioned above, most countries that have HF Citizen's Band allocations allocate 40 channels between 26.965 MHz to 27.405 MHz, in 10 kHz steps.

Military HF allocation

In the US and Canada, as well as the Americas (ITU Region 2) as a whole, there are no pre-designated HF allocations for military use.

Similar rules exist in Western and Eastern Europe, where it has become necessary for European amateurs to police the bands due to overcrowding. Most military HF band incursions into the HF Ham bands occur in Europe or Africa.

Since the end of the Cold War, specific military HF allocations have gradually disappeared from the HF bands -- except for Africa and some parts of Asia.

In Australia, the military shares the HF bands with civilian users -- this is mainly due to low population density and relative underuse of the HF bands.

The military in the Americas (as well as in Australia) has tended to use the civilian fixed, maritime mobile, and aeronautical mobile allocations on an ad-hoc (non-interference) basis.

Industrial/Scientific/Medical (ISM) and other HF allocations

Above 10 MHz there are numerous frequencies set aside for Radio Astronomy, Space Research (FCC terminology), and standard frequency and time services.

RF diathermy equipment uses 27.12MHz to effect heating of bulk materials or adhesives for the purpose of drying or increasing the cure rate. The industrial use of the frequency was one of the motivations to permit widespread use by the citizenry of the 11m band for CB Radio.

About a dozen narrow or "sliver" allocations for ISM exist throughout the radio spectrum. See ISM band for more information.

These allocations are perhaps the smallest in the HF band, with respect to national HF allocations.

See also

• Shortwave and high frequency (HF)
• International broadcasting