In accordance with the applicable rules, amateur radio operators are permitted to use frequencies within the ranges that have been authorised for amateur radio operators. The International Telecommunication Union (ITU) oversees how much of the radio spectrum is set aside for amateur radio transmissions, but it is then up to each national telecommunication authority to carry out the amateur radio frequency allocation.
Low frequency (LF) is the ITU designation for radio frequencies (RF) in the range of 30–300 kHz. The wavelengths are within the 10 to 1 km range, which has given rise to the name kilometre band.
LF radio waves are characterised by low signal attenuation (the signal´s gradual loss of flux intensity as it moved through the medium) and are therefore highly suitable for long-distance communication.
In the western hemisphere, the low-frequency spectrum is mainly used for aircraft beacons, navigation information (LORAN), and weather systems. In Europe and parts of Africa and Asia, part of the LF spectrum is used for AM broadcasting and is known as the longwave band.
A number of time signal broadcasts use the LF spectrum.
Medium frequency (MF) is the ITU designation for radio frequencies in the 300 kilohertz (kHz) to 3 megahertz (MHz) range. It is known as the hectometre band, as the wavelengths range from 10 to 1 hectometre (i.e. 1,000 to 100 metres).
Part of the hectometre band is the medium wave (MW) AM broadcast band.
In addition to being used for AM radio broadcasting, the MF is important for maritime ship-to-shore communication, navigational radio beacons, and transoceanic air traffic control.
High frequency (HF) is the ITU designation for radio frequencies in the 3 to 30 megahertz (MHz) range. This band is also known as the decametre band, since the wavelength range from 1 to 10 decametres (10 to 100 metres).
The high-frequency band is a major part of the short-wave band of frequencies, i.e. “shortwave radio”. Among other things, it is used by international short-wave broadcasting stations (3.95-25.82 MHz), weather stations, government time stations, and for aviation communication.
The high frequencies are suitable for very long-distance communication, as the radio waves in this band can reflect back to our planet by the ionosphere layer in the atmosphere. This is known as “skip” or “skywave” propagation. In addition to very long-distance communication, skywave propagation is also important for radio operators located in mountainous terrains.
High frequency is not the highest possible band; radio frequencies higher than 30 MHz exist and comprise the very high frequency (VHF) band and the ultra-high frequency (UHF) band. The UHF band consists of frequencies above 300 MHz.
Works significantly better in winter than in summer.
Only amateurs in the Americas and a few other countries have access to all of this band. In the rest of the world, amateurs are limited to the bottom 300 kHz or even less.
In the United States, five channels are available, centred on 5.332, 5.348, 5.368, 5.373, and 5.405 MHz.
In many countries, only the bottom 100 kHz or 200 kHz of the 40 metres band are designated for amateurs. Historically, the 40 metres band have been used by a lot of commercial short-wave broadcasters, which is why the amateurs have been relegated to the bottom rung. Today, the number of short-wave commercial broadcasting stations is much lower than in the past, so we might see changes in the nearby future where amateurs are allowed to take over more of the 40 metres band.
Many QRP operators have 14.060 MHz as their primary calling frequency in this band.
For long-distance communication, including cross-oceanic communication, this band is best during solar maximum.
FM operations are commonly found at the high end of this band. In many countries, repeaters are in the 29.5-29.7 MHz range.
Very high frequency: Above 30 MHz and up to and including 300 MHz
Ultra high frequency: Above 300 MHz
At the VHF and UHF levels, the bands allocated for amateurs are many megahertz wide and allow for high-fidelity audio transmission modes (FM). Very fast data transmission modes are possible here; modes that would not be feasible for the kilohertz-wide allocations of the high frequency bands.
A radio signal transmitted on VHF from a standard hand-held portable will normally travel 5-10 km, depending on the terrain. If the operator instead has access to a low power home station and a simple antenna, that range can be extended to around 50 km. Reaching up towards 1,000 km with CW or SSB modes is possible, but considerably more expensive equipment is necessary, e.g. a long yagi antenna and 100 Watts of power.