rious transmission media operate. Along the right-hand side is the terminology that the ITU applies to the various bands: Extremely low, very low, low, medium, high, very The Electromagnetic Spectrum and Bandwidth Transmission Media ITU-Defined Frequency Gamma Rays X-rays Ultraviolet Fiber Optics Visible Light Infrared Microwave PCS Microwave TV, Cellular Radio TV, Coax Twisted Pair Medium Audio Frequencies Very Low Extremely Low 10° 1Hz Figure 1.6 The electromagnetic spectrum high (VHF), ultrahigh (UHF), superhigh (SHF), extremely high (EHF), and tremen- dously high (THF) frequencies are all various forms of radio bands. And then move into the light range, with infrared and visible light. You can see just by the placement of the various transmission media that not all are prepared to face the high-bandwidth future that demanding advanced applications (such as streaming media, e-learning, networked interactive games, interactive TV, telemedicine, meta- computing, and Web agents) require. The radio, microwave, infrared, and visible light portions of the spectrum can all be used to generate electromagnetic waves that carry information. It is possible to modulate various measurements related to electromagnetic waves (see Figure 1.7): Frequency-The number of oscillations per second of an electromagnetic wave is called its frequency. Hertz-Frequency is measured in Hertz (Hz), in honor of Heinrich Hertz, a German physicist who, in 1887, invented the oscillator (an alternating- current generator) and was credited with the discovery of radio waves. Chapter 1 Telecommunications Technology Fundamentals Wavelength (One Cycle) Amplitude Figure 1.7 An electromagnetic wave Wavelength- The wavelength is the distance between two consecutive maxima or minima of the waveform. Amplitude-Amplitude is a measure of the height of the wave, which indi- cates the strength, or power, of the signal. Phase-Phase describes the current state of something that changes cycli- cally (i.e., oscillates). The phase of a wave refers to the angle of 