The Geneva Frequency Plan of 1975 goes into effect, realigning many of Europe's longwave and mediumwave broadcasting frequencies.
The Geneva Frequency Plan of 1975 (Aka "The Final Acts of the Regional Administrative LF/MF Broadcasting Conference (Regions 1 and 3) Geneva, 1975" or simply "GE75") is the internationally agreed frequency plan which was drawn up to implement the provisions of the Final Acts of the Regional Administrative LF/MF Broadcasting Conference (Regions 1 and 3) held in Geneva, Switzerland, in 1975. It covers radio broadcasting in the long and medium wave bands outside the Americas (separate agreements being in place for North and South America).
The plan was drawn up under the auspices of the World Administrative Radio Conference (WARC) of the International Telecommunication Union (ITU) with the assistance of the European Broadcasting Union (EBU/UER).
The Geneva plan replaced the 1948 Copenhagen plan. It became necessary because of the large number of broadcasting stations in these frequency ranges leading to ever more mutual interference (Many countries had refused to ratify the Copenhagen plan and compliance was patchy even among those which had). The Geneva plan entered into force on 23 November 1978 and although its intended lifespan was only until 1989, it is still valid (with small modification by mutual coordination between countries) today, and compliance has been far more widespread.
Most existing European radio stations were required to change their broadcasting frequencies following implementation of the plan. In most cases the changes were slight (less than five kilohertz) but were more drastic in some cases, particularly in the United Kingdom, where all BBC national stations moved to a new wavelength or band. However the increased number of radio services and reduction (in most cases) of interference to radio signals (particularly at nighttime) was considered by most broadcasters to be worth the initial inconvenience.
As a result of the plan most medium wave (and later longwave) stations outside North and South America operate on exact multiples of 9 kHz; the sum of all digits of the frequency will be 9 or a multiple of 9 (see 9#Mathematics).