sizes are as follows: Dimension (in.) Dimension (mm) 0.047/0.174 1.2/4.4 (small diameter) 0.104/0.375 2.6/9.5 The fractions express the outside diameter of the inner conductor over the inside diameter of the outer conductor. For instance, for the large bore cable, the outside diameter of the inner conductor is 0.104 in. and the inside diameter of the outer conductor is 0.375 in. This is illustrated in Figure 9.35. As can be seen from Eq. (9.27) in Figure 9.35, the ratio of the diameters of the inner and outer conductors has an important bearing on attenuation (loss). If we can achieve a ratio of b/a = 3.6, a minimum attenuation per unit length results. The characteristic impedance of coaxial cable is Z = 138 log(b/a) for an air dielectric. If b/a = 3.6, then Z = 77 S. Using dielectric other than air reduces the characteristic impedance. If we use the disks previously mentioned to support the center conductor, the impedance lowers to 75 S. Figure 9.36 illustrates the attenuation - frequency characteristics of the coaxial cable discussed in the text. Attenuation increases rapidly as frequency is increased. It is a func- tion of the square root of frequency, as shown in Figure 9.35. The telecommunication system designer is basically interested in how much bandwidth there is available to trans- mit a signal. For instance, the 0.375-in. cable has an attenuation of about 5.8 dB/mi at 2.5 MHz, and the 0.174-in. cable has an attenuation of about 12.8 dB/mi. At 5 MHz the 0.174-in. cable has about 19 dB/mi, and the 0.375-in. cable has an attenuation of about 10 dB/mi. Attenuation is specified for the highest frequency of interest. Equalization (i.e., the use of equalizers) will tend to flatten the response curves in the figure at the expense of some added loss per unit length. Equalization is defined by the IEEE (Ref. 6) as "a technique used to modify the frequency response of an amplifier or network to compensate for variations in the frequency response across the network bandwidth." The ideal result is a flat overall res