ed string. The nominal impedance is 75 ohms, and special cable is available with a 50-ohm impedance. Attenuation (dB) Bandwidth Frequency (Hz) Figure 2.11 The concept of the 3-dB power bandwidth. Figure 2.12 A pictorial representation of a coaxial cable section. 2.5 INTRODUCTION TO TRANSPORTING ELECTRICAL SIGNALS Impedance can be defined as the combined effect of a circuit's resistance, inductance, and capacitance taken as a single property and is expressed in ohms for any given sine wave frequency. Further explanation of impedance will be found in Appendix A. From about 1953 to 1986, coaxial cable was widely deployed for long-distance, mul- tichannel transmission. Its frequency response was exponential. In other words, its loss increased drastically as frequency was increased. For example, for 0.375-inch coaxial cable, the loss at 100 kHz was about 1 dB and the loss at 10 MHz was about 12 dB. Thus, equalization was required. Equalization tends to level out the frequency response. With the advent of fiber-optic cable with its much greater bandwidth and comparatively flat frequency response, the use of coaxial cable on long-distance circuits fell out of favor. It is still widely used as a (radio-frequency) (RF) transmission line connecting a radio to its antenna. It is also extensively employed in cable television plant, especially in the "last mile" or "last 100 ft" of connectivity to a subscriber's television set. 2.5.3 Fiber-Optic Cable Fiber-optic cable is the favored transmission medium for very wideband terrestrial links, including undersea applications. It is also used for cable television "super trunks." The bandwidth of fiber-optic strand can be measured in terahertz (THz). In fact, the whole usable RF spectrum can be accommodated on just one such strand. Such a strand is about the diameter of a human hair. It can carry one serial bit stream at 10 Gbps (gigabits per second) transmission rate, or by wave division multiplexing methods (WDM), an aggregate of 100 Gbps or more. Fiber-optic transmission will be