 in a repeater chain and may lead to crosstalk and distortion on the recon- structed analog signal. In digital switching systems, jitter on the incoming lines is a potential source of slips. 12 Jitter accumulation is a function of the number of regenerative repeaters in tandem. Keep in mind that switches, fiber-optic receivers, and digital radios are also regenerative repeaters. Certainly by reducing the number of regenerative repeaters in tandem, we reduce jitter accordingly. Wire-pair systems transporting PCM at the DS1 rate have repeaters every 6000 ft (1830 m). If we are to reduce jitter, wire pair is not a good candidate for long circuits. On the other hand, fiber-optic systems, depending on design and bit rate, have repeaters every 40 miles to 200 miles (64 km to 320 km). This is another reason why fiber-optic systems are favored for long-haul application. Line-of-sight microwave radio, strictly for budgeting purposes, may have repeaters every 30 miles (48 km), SO it, too, is a candidate for long-haul systems. Satellite radio systems have the potential for the least number of repeaters per unit length. 6.9.3 Distortion On metallic transmission links, such as coaxial cable and wire-pair cable, line character- istics distort and attenuate the digital signal as it traverses the medium. There are three cable characteristics that create this distortion: (1) loss, (2) amplitude distortion (ampli- tude-frequency response), and (3) delay distortion. Thus the regenerative repeater must provide amplification and equalization of the incoming digital signal before regenera- tion. There are also tradeoffs between loss and distortion on the one hand and repeater characteristics and repeater section length on the other. 6.9.4 Thermal Noise As in any electrical communication system, thermal noise, impulse noise, and crosstalk affect system design. Because of the nature of a binary digital system, these impairments need only be considered on a per-repeater-section basis because noise does not accumulate due to the regenerat