Electromagnetic waves in this frequency range, called radio waves, are extremely widely used in modern technology, particularly in telecommunication. Above 300 GHz, the absorption of electromagnetic radiation by Earth’s atmosphere is so great that the atmosphere is effectively opaque, until it becomes transparent again in the near-infrared and optical window frequency ranges. To prevent interference and allow for efficient use of the radio spectrum, similar services are allocated microwave spectrum and bands pdf bands. For example, broadcasting, mobile radio, or navigation devices, will be allocated in non-overlapping ranges of frequencies.
Each of these bands has a basic bandplan which dictates how it is to be used and shared, to avoid interference and to set protocol for the compatibility of transmitters and receivers. Each of these bands has a traditional name.
100 to 10 metres, corresponding to a frequency range of 3 MHz to 30 MHz. ITU further divides each band into subbands allocated to different uses.
The ITU radio bands are designations defined in the ITU Radio Regulations. 1 states that “the radio spectrum shall be subdivided into nine frequency bands, which shall be designated by progressive whole numbers in accordance with the following table”. The table originated with a recommendation of the IVth CCIR meeting, held in Bucharest in 1937, and was approved by the International Radio Conference held at Atlantic City in 1947.
The idea to give each band a number, in which the number is the logarithm of the approximate geometric mean of the upper and lower band limits in Hz, originated with B. Fleming-Williams, who suggested it in a letter to the editor of Wireless Engineer in 1942.
For example, the approximate geometric mean of Band 7 is 10 MHz, or 107 Hz. This column does not form part of the table in Provision No.
The designation mm is also used to refer to the range from 30 to 300 GHz. Designations for television and FM radio broadcast frequencies vary between countries, see Television channel frequencies and FM broadcast band.
Since VHF and UHF frequencies are desirable for many uses in urban areas, in North America some parts of the former television broadcasting band have been reassigned to cellular phone and various land mobile communications systems. Even within the allocation still dedicated to television, TV-band devices use channels without local broadcasters. Airband refers to VHF frequencies 118 to 137 MHz, used for navigation and voice communication with aircraft.
Trans-oceanic aircraft also carry HF radio and satellite transceivers. The greatest incentive for development of radio was the need to communicate with ships out of visual range of shore. From the very early days of radio, large oceangoing vessels carried powerful long-wave and medium-wave transmitters. Marine VHF radio is used in coastal waters and relatively short-range communication between vessels and to shore stations.