The radio frequency spectrum only offers a limited number of frequencies to potential users, despite the expansion of the usable spectrum into the higher frequencies. Faced with a very rapidly rising demand, as the result of the introduction of many new radio and television devices, the spectrum has become congested and exploitation of closely related frequencies has increased interference. It is no longer possible to instal broadcasting or television equipment unless frequencies can be allocated which do not interfere with existing services. Frequency congestion increases the risk for civil aviation because the necessary ground-air communications are inadequate, or menaced by severe interference.
Prior to 1939, any country could take into use, within certain limits, any frequency it required for any particular service. After the war the situation became chaotic and the International Frequency Registration Board was established in 1947 to maintain the Master International Frequency Register which currently lists over 363,000 frequency assignments. However, jamming renders many frequencies unusable.