 confidence, by ernments of neighbouring countries. Some specific management calculation, to ensure that spectrum is used efficiently. The national functions are co-ordinated through recognised international organi- register of frequency assignments may be inaccurate, leading to sations with specialised responsibilities; for example, national use sub-optimal new assignments or interference when new assign- of some frequency bands allocated for civil aviation purposes is CO- ments are taken into operation. Or there may not be a suitable ordinated through the International Civil Aviation Organisation frequency available in a heavily loaded frequency band without the (ICAO). However, the International Telecommunication Union re-arrangement of frequencies already assigned to other stations. (ITU) is the primary world forum for radio spectrum management. Even without such complications, it is a labour intensive process Governments set up bureaux to manage the spectrum. Usually demanding a lot of expertise. Furthermore, being a random process, such a bureau is part of a government department but some func- it may not provide optimum use of the spectrum. tions may be devolved to a body responsible to, but outside, govern- There are various ways of making this process more systematic, ment. The national authority, however it is constituted, is known as easier to apply and, in favourable circumstances, more efficient in the administration. using spectrum. Thus: 26/4 Radio spectrum management SUB - BAND B SUB - BAND A 2 MHz B18 B20 B2 B4 CHANNEL NUMBERS CHANNEL A17A19 NUMBERS A2 A4 A18 A20 Figure 26.1 Radio channelling plan, providing channels 2MHz wide hexagonal cells, each allotted an equal number of channels. admin- 1. A national radio channelling plan is sometimes drawn up. For of Alternatively, an irregular plan based, for example, on local example, when planning for hi-directional links, a frequency and istrative areas and channel allotments proportionate to the and band would be split into two equal sub-bands, A and