Where does the radio spectrum end?

The focus of this journal is ¿wireless communications¿ which is presumed to use radio spectrum. But for the purpose of regulation, what are the upper and lower limits of that spectrum? An International Telecommunications Union publication addresses part of this question as follows From a technical viewpoint, the radio spectrum is the portion of the electromagnetic spectrum that carries radio waves. The boundaries of the radio spectrum are defined by the frequencies of the transmitted signals, and are usually considered to range from 9 kHz (kilohertz; thousand cycles per second) to 3000 GHz (gigahertz; billion cycles per second). The key characteristics of the spectrum are the propagation features and the amount of information which signals can carry. In general, signals sent using higher frequencies reach shorter distances but have a higher information-carrying capacity. These physical characteristics of the spectrum limit the currently identified range of applications for which any particular frequency band is suitable.