The Federal Communications Commission (FCC) assigns segments of the radio spectrum to categories of users, and specific frequencies within each segment to individual users. Since demand for channel space exceeds supply, the process is complex. The radio spectrum can be compared to a long ruler: the portion from 10-540 kiloHertz has been set aside for long-range radiotelegraph; from 535-1605 kiloHertz is for AM broadcasts; from 1605 kiloHertz to 25 magaHertz is for long-distance and international communications, ships at sea and aircraft in flight; from 25-890 megaHertz is for AM radio and TV; 890 megaHertz to 40 gigaHertz is for other specialized services, and above 40 gigaHertz is used for experimental work. Not all broadcasters require the same amount of radio spectrum. An FM station requires 20 times the channel space of an AM station. A TV signal uses 600 times more space than an AM station. Some increased use of channels is obtained by fequency sharing or "pooling". Some new users could be squeezed into the radio spectrum with more efficiency and cooperative effort by current users. (MG)