There is an international organisation run by the United Nations that polices the worlds airwaves. Different frequencies are made available in different parts of the world in order to avoid congestion and interferance. Also radio signals can travel enormous distances by way of "propergation". VHF and UHF (50 Watt) are usually line of sight (30 miles or less) but H.F and VLF can bounce around the earth quite easily (9,000 miles possible using only 1 watt and a good aerial). It follows that radio frequencies do need to be allocated according to the area you operate from. The closest thing to an international radio frequency I know of is the 446Mhz Low Powered (PMR) radio system which is used throughout the E.U.
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Triumph Bonneville 800 (2004), Yamaha XT600E (1999), Honda XBR500 (1986).
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