 at the website. Access Technologies Chapter 6 Those characteristics include the amplitude, or loudness, of the wave; the frequency, or pitch, of the wave; and the phase, or angle of inflection, of the wave. By modulating these characteristics, a carrier wave can be made to transport information, whether it is a radio broadcast, a data stream, or a telephone conversation. (Please review this topic in Chapter 1 for more information.) Transmission "space" is allocated based on ranges of available fre- quency. This range is known as a spectrum, a word that means "a range of values." The radio spectrum represents a broad span of electromagnetic frequencies between one kilohertz (1,000 cycles per second) and ten quin- tillion (that's ten followed by 19 zeroes) cycles per second. Most radio- based applications operate at frequencies between 1 kHz and 300 GHz. One concern that has surfaced repeatedly over the years since the inception of radio is spectrum availability. Different services require differing amounts of spectrum for proper operation. For example, a modern FM radio channel requires 30 kHz of bandwidth, while an AM channel only requires 3 kHz. Television, on the other hand, requires 6 MHz. As you might imagine, battles between the providers of these dis- parate services over spectrum allocation became quite heated in the years that followed. Improving the Model The first FM radiotelephone systems were massively inefficient. They required 120 kHz of channel bandwidth to transport a 3 kHz voice sig- nal. As the technology advanced, though, this requirement was reduced. In the 1950s the FCC mandated that channels be halved to 60 kHz, and by the 1960s things had advanced to the point that the spectrum could be further reduced to 30 kHz, where it remains today in analog systems. Realize that this is still a 10:1 ratio. AT&T introduced the first commercial mobile telephone service in St. Louis in 1946. It relied on a single, high-power transmitter placed atop one of the city's tallest buildings and had an effective