Shortwave bands are frequency allocations for use within the shortwave radio spectrum (the upper MF band and all of the HF band). They are the primary medium for applications such as maritime communications, 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, measured in metres. Propagation behavior on the shortwave bands depends on the time of day, the season and the level of solar activity.
International broadcast bands
The bands and frequencies below are derived from multiple sources, and different radios may have different frequency numbers. Most international broadcasters use amplitude modulation with 5 kHz steps between channels; a few use single sideband modulation. The World Radiocommunication Conference (WRC), organized under the auspices of the International Telecommunication Union, allocates bands for various services in periodic conferences. The most recent WRC took place in 2012. At WRC-97 in 1997, the following bands were allocated for international broadcasting:
|120 m||2300 – 2495 kHz||Mostly used locally in tropical regions, with time stations at 2500 kHz. Although this is regarded as shortwave, it is a MF band.|
|90 m||3200–3400 kHz||Mostly used locally in tropical regions, with limited long-distance reception at night.|
|75 m||3900–4000 kHz||Mostly used in the Eastern Hemisphere; not widely received in North and South America. Shared with the North American amateur radio 80 m band.|
|60 m||4750–5060 kHz||Mostly used locally in tropical regions, although widely usable at night. Time stations use 5000 kHz.|
|49 m||5900–6200 kHz||Good year-round night band; daytime reception poor.|
|41 m||7200–7450 kHz||Reception varies by region – reasonably good night reception, but few transmitters in this band target North America. According to the WRC-03 Decisions on HF broadcasting, in International Telecommunication Union regions 1 and 3, the segment 7100–7200 kHz is reserved for amateur radio use and there are no new broadcasting allocations in this portion of the band. 7350–7400 kHz is newly allocated; in Regions 1 and 3, 7400–7450 kHz was also allocated effective March 29, 2009. In Region 2, 7200–7300 kHz is part of the amateur radio 40 m band.|
|31 m||9400–9900 kHz||Most heavily used band. Good year-round night band; seasonal during the day, with best reception in winter. Time stations are clustered around 10 MHz.|
|25 m||11,600–12,100 kHz||Generally best during summer and the period before and after sunset year-round|
|22 m||13,570–13,870 kHz||Substantially used in Eurasia. Similar to the 19 m band; best in summer.|
|19 m||15,100–15,800 kHz||Day reception good, night reception variable; best during summer. Time stations such as WWV use 15 MHz.|
|16 m||17,480–17,900 kHz||Day reception good; night reception varies seasonally, with summer best.|
|15 m||18,900–19,020 kHz||Lightly utilized; may become DRM band in future|
|13 m||21,450–21,850 kHz||Erratic daytime reception, with very little night reception. Similar to 11 metres, but long-distance daytime broadcasting keeps this band active in the Asia-Pacific region.|
|11 m||25,600–26,100 kHz||Seldom used. Daytime reception poor low in the solar cycle, but potentially excellent when the solar cycle (generally indicated by the number of sunspots) is high. Nighttime reception nonexistent, except for local groundwave propagation. Digital Radio Mondiale has proposed that this band be used for local digital shortwave broadcasts, testing the concept in Mexico City in 2005. Citizens' Band allocation in most countries, is slightly higher in frequency than the broadcasting 11 m band. There are reports of CB radio users operating equipment on frequencies as low as 25.615 MHz. This band is also shared with Studio-to-Transmitter Links (STLs), from 25.87 to 26.03 MHz in FM mode.|
Amateur HF bands
Amateur radio operators in many countries are allocated specific shortwave bands for private, non-commercial use. Amateur radio is an educational hobby and can be useful for emergency communications, especially in remote regions or disaster areas.
Marine, air, land mobile and fixed allocations
Designated bands in the shortwave spectrum are used for ships, aircraft, and land vehicles. Shortwave (HF radio) is used by transoceanic aircraft for communications with air-traffic control centers out of VHF radio range. Most countries with HF citizens'-band allocations use 40 or 80 channels between approximately 26.6 MHz and 27.5 MHz, in 10 kHz steps. Illegal "freeband" CB activity can be heard from 25 to 28 MHz, with operators generally using AM below 26.965 (CB channel 1) and SSB above 27.405 (CB channel 40). CB radio in the UK can be heard from 27.60125 to 27.99125 MHz in 10 kHz steps as well as the lower 26.965 to 27.405 MHz allocation. The UK and Ireland both operate Community Audio Distribution (CADS) in the UK or Wireless Public Address System (WPAS) in Ireland services in the 27.600 to 27.995 MHz portion, AM and FM mode, with two overlapping sets of 40 channels (27.60125 to 27.99125 MHz in 10 kHz steps, and 27.605 to 27.995 MHz in 10 kHz steps). These transmissions are usually rebroadcasts of church services and can sometimes be heard hundreds or even thousands of km (miles). Part of the 11 m/27 MHz band was also allocated in many countries for early-model cordless phones. Due to antenna-length requirements and the band's long-distance propagation characteristics (undesirable in these cases), much land-mobile radio activity has moved to VHF or UHF and most cordless-phone use is at UHF or higher. Some segments of the HF spectrum are allocated for fixed services, providing point-to-point communication between sites with no access to wired communications.
Military HF use
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 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 under-use of the HF bands. The military in the Americas and 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 27.12 MHz to heat bulk materials or adhesives for the purpose of drying or improving curing. The industrial use of the frequency suggested the use of the 11 m band for CB radio. About a dozen narrow ("sliver") allocations for ISM exist throughout the radio spectrum. These allocations are among the smallest in the HF band, with respect to national HF allocations.
- High frequency
- Medium frequency (for the unique case of the 120 m band)
- International broadcasting
- World Radiocommunication Conference
- World Administrative Radio Conference
- http://www.monitoringtimes.com/html/swb.html Short wave broadcast bands, retrieved 2010 Nov 19
- Introduction on digital technology in the HFBC bands Accessed 2011-10-20. (Archived by WebCite® at http://www.webcitation.org/62aCbliW6
- American Radio Relay League—the United States lobbying body for amateur radio and the body responsible for the ARRL Handbook
- Radio Amateurs of Canada—Canada's National Amateur Radio Society
- World Radio and Television Handbook
- EiBi & DX - Complete list of International Broadcasting Stations worldwide, frequently updated.
- UnwantedEmissions.com - Radio spectrum allocations reference.
- short-wave.info - Easy to interrogate frequency schedules of short wave broadcasters.