Amateur radio frequency allocation is done by national telecommunication authorities. Globally, the International Telecommunication Union (ITU) oversees how much radio spectrum is set aside for amateur radio transmissions. Individual amateur stations are free to use any frequency within authorized frequency ranges; authorized bands may vary by the class of the station license.
Radio amateurs use a variety of transmission modes, including Morse code, radioteletype, data, and voice. Specific frequency allocations vary from country to country and between ITU regions as specified in the current ITU HF frequency allocations for amateur radio. The list of frequency ranges is called a band allocation, which may be set by international agreements, and national regulations. The modes and types of allocations within each frequency band is called a bandplan; it may be determined by regulation, but most typically is set by agreements between amateur radio operators.
National authorities regulate amateur usage of radio bands. Some bands may not be available or may have restrictions on usage in certain countries or regions. International agreements assign amateur radio bands which differ by region.Larry D. Wolfgang et al., (ed), The ARRL Handbook for Radio Amateurs, Sixty-Eighth Edition, (1991), ARRL, Newington CT USA Chapter 37
Band characteristics
Low frequency
2200 metres – 135.7–137.8 kHz Just below the Asian and European longwave broadcast band and far below the commercial AM broadcast band.
Medium frequency
630 metres – 472–479 kHz Just below the commercial AM broadcast band and the maritime radio band.
160 metres – (1.800–2.000 MHz) Just above the commercial AM broadcast band. Allocations in this band vary widely from country to country; it was formerly shared with the largely defunct Loran-A radionavigation system. This band is often taken up as a technical challenge, since long distance (DX) propagation tends to be more difficult due to higher D layer ionospheric absorption. Long-distance propagation tends to occur only at night, and the band can be notoriously noisy particularly in the summer months. 160 metres is also known as the "top band". For many years it was the longest-wavelength amateur band; although often included among the shortwaves, it is actually located near the top end of the medium frequency band.
High frequency
Most of the customary band names given below are only nominal wavelengths, not actual wavelengths. For example: In the western hemisphere the nominal 80 m band actually ranges between about 85.7–74.9 m, and the international portion from 85.7–83.3 m. The nominal "17 m" band actually covers 16.6–16.5 m. The nominal "15 m" band actually ranges from 14.28–13.98 m. By common sense, the "15 m" band ought to be called "14 m", but that name has been in longtime use for a shortwave broadcast band.
80 metres or – – 85.65–74.95 m actual Best at night, with significant daytime signal absorption. Works best in winter, due to atmospheric noise from hemispheric thunder storms during summer. Only countries in the Americas and few others have access to all of this band; in other parts of the world amateurs are limited to the bottom 300 kHz (or less) (85.65–83.28 m).
In the US and Canada the portion of the band from 3.600–4.000 MHz, regulation permits use of single-sideband voice as well as AM voice; this sub-band is often referred to as "the 75 metre band", in part to distinguish it from the internationally available frequencies below it.
60 metres – 5 MHz region – around 56 m A relatively new allocation and originally only available in a small number of countries such as the United States, United Kingdom, Ireland, Norway, Denmark, and Iceland, but now continuing to expand. In most (but not all) countries, the allocation is broken into channels and may require a special licensing request. Five 2.8 kHz-wide channels are available in the U.S., centered on 5.332, 5.348, 5.368, 5.373, and 5.405 MHz. Since most radios in SSB mode display the (suppressed) carrier frequency, in USB mode the dial frequencies would all need to be set 1.5 kHz lower. Voice operation is generally in upper sideband mode, which is mandatory in the U.S. The U.S. and Canada allow 100 Watts in the currently available channels.
The 2015 ITU World Radiocommunication Conference (WRC-15) approved a new worldwide frequency allocation of 5.351.5–5.366.5 MHz to the amateurs on a secondary basis. The allocation limits amateur stations to 15 watts effective isotropic radiated power (EIRP); however some locations will be permit up to 25 W EIRP.
40 metres – 7.000–7.300 MHz – 42.83–41.51 m actual Considered the most reliable all-season long distance (DX) band. Popular for DX at night, 40 metres is also reliable for medium distance (1,500 km / 1,000 miles) contacts during the day. Much of this band was shared with broadcasters, and in most countries the bottom 100 kHz or 200 kHz are available to amateurs. However, due to the high cost of running high-power commercial broadcasting facilities, decreased listenership, and increasing competition from Internet-based international broadcast services, many shortwave broadcasting services are being shut down, leaving the 40 metre band free of other users for amateur radio use.
30 metres – 10.100–10.150 MHz – 29.68–29.54 m actual A very narrow band, which is shared with non-amateur services. It is recommended that only Morse code and data transmissions be used here, and in some countries amateur voice transmission is actually prohibited.
For example, in the US, data, RTTY, and CW are the only modes allowed at a maximum 200 W peak envelope power (PEP) output. Not released for amateur use in a small number of countries.
Due to its location in the centre of the shortwave spectrum, this band provides significant opportunities for long-distance communication at all points of the solar cycle. 30 metres is a WARC band. "WARC" bands are so called due to the 1979 special World Administrative Radio Conference allocation of these newer bands to amateur radio use. Amateur radio contests are not run on the WARC bands.
20 metres – 14.000–14.350 MHz – 21.41–20.89 m actual Considered the most popular DX band; usually most popular during daytime. QRP operators recognize 14.060 MHz as their primary calling frequency within the band. Users of the PSK31 data mode tend to congregate around 14.070 MHz. Analog SSTV activity centers on 14.230 MHz.
17 metres – 18.068–18.168 MHz – 16.6–16.5 m actual Similar to 20 metres, but more sensitive to solar propagation minima and maxima. 17 metres is a WARC band.
15 metres – 21.000–21.450 MHz – 14.28–13.98 m actual Most useful during solar maximum, and generally a daytime band. Daytime sporadic E propagation (1,500 km / 1,000 miles) occasionally occurs on this band.
12 metres – 24.890–24.990 MHz – 12.04–12.00 m actual Mostly useful during daytime, but opens up for DX activity at night, during solar maximum. 12 metres is one of the WARC bands. Propagates via sporadic E and by F2 propagation.
10 metres – 28.000–29.700 MHz – 10.71–10.08 m actual Best long distance (e.g., across oceans) activity is during solar maximum; during periods of moderate solar activity the best activity is found at low latitudes. The band offers useful short to medium range groundwave propagation, day or night.
Due to Sporadic E propagation during the late spring and most of the summer, regardless of sunspot numbers, afternoon short band openings into small geographic areas of up to 1,500 km (1,000 miles) occur. Sporadic E is caused by areas of intense ionization in the E layer of the ionosphere. The causes of sporadic E are not fully understood, but these "clouds" of ionization can provide short-term propagation from 17 metres all the way up to occasional 2 metre openings. FM operations are normally found at the high end of the band (Also repeaters are in the 29.500–29.700 MHz segment in many countries).
Very-high frequencies and ultra-high frequencies Frequencies between 30 and 300 MHz are referred to as Very High Frequency (VHF) region and those between 300 MHz and 3 GHz are referred to as Ultra High Frequency (UHF). The allocated bands for amateurs are many megahertz wide, allowing for high-fidelity audio transmission modes (FM) and very fast data transmission modes that are unfeasible for the kilohertz-wide allocations in the HF bands.
{| style="text-align:right;" class="infobox" |- !colspan=3; style="text-align:left;"| VHF |- |8 metres |40–45 MHz |in parts of ITU Region 1 |- | 6 metres || 50–54 MHz ||
|50–52 MHz |In parts of ITU Region 1 |- | 5 metres || 58.0–60.1 MHz || in parts of ITU Region 1 |- | 4 metres || 70–70.5 MHz || in parts of ITU Region 1 |- | 2 metres || 144–148 MHz ||
|144–146 MHz |ITU Region 1 |- | 1.25 metres || 219–220 MHz || Fixed digital message forwarding systems |- | || 222–225 MHz || US & Canada
!colspan=3; style="text-align:left;"| UHF |- | 70 centimetres || 420–450 MHz ||
|430–440 MHz |in ITU Region 1 |- | 33 centimetres || 902–928 MHz || in ITU Region 2 |- | 23 centimetres || 1 240–1 300 MHz || |- | || 1 240–1 325 MHz || in UK |- | 13 centimetres || 2 300–2 310 MHz || lower segment |- | ||2 390–2 450 MHz || upper segment
While "line of sight" propagation is a primary factor for range calculation, much of the interest in the bands above HF comes from use of other propagation modes. A signal transmitted on VHF from a hand-held portable will typically travel about 5–10 km (3–6 miles) depending on terrain. With a low power home station and a simple antenna, range would be around 50 km (30 miles).
With a large antenna system like a long yagi, and higher power (typically 100 watts or more) contacts of around 1 000 km (600 miles) using the Morse code (CW) and single-sideband (SSB) modes are common. Ham operators seek to exploit the limits of the frequencies usual characteristics looking to learn, understand, and experiment with the possibilities of these enhanced propagation modes.
Sporadic band openings Occasionally, several different ionospheric conditions allow signals to travel beyond the ordinary line-of-sight limits. Some amateurs on VHF seek to take advantage of "band openings" where natural occurrences in the atmosphere and ionosphere extend radio transmission distances well over their normal range. Many hams listen for hours hoping to take advantage of these occasional extended propagation "openings".
The ionospheric conditions are called sporadic E and anomalous enhancement. Less frequently used anomalous modes are tropospheric scatter and Aurora Borealis (Northern Lights). Moon bounce and satellite relay are also possible.
Sporadic E Some openings are caused by islands of intense ionization of the upper atmosphere, known as the E Layer ionosphere. These islands of intense ionization are called "sporadic E" and result in erratic but often strong propagation characteristics on the "low[er] band" VHF radio frequencies.
The 6 metre amateur band falls into this category, often called "the magic band", will often "open up" from one small area into another small geographic area away during the spring and early summer months. This phenomenon occurs during the fall months, although not as often.
Tropospheric refraction Band openings are sometimes caused by a weather phenomenon known as a tropospheric "inversion", where a stagnant high pressure area causes alternating stratified layers of warm and cold air generally trapping the colder air beneath. This may make for smoggy or foggy days, but it also causes VHF and UHF radio transmissions to travel or duct along the boundaries of these warm/cold atmospheric layers. Radio signals have been known to travel hundreds, even thousands of kilometres (miles) due to these unique weather conditions.