ttenuation 0.66dB/km 0.31dB/km 0.22dB/km @ 1kH zo-(6)" = (15.10) Cut-off 5.7kHz frequency Coaxial pair cables 15/5 Table 15.4 Performance of unloaded unit twin cable Table 15.6 Pair cables for digital transmission. (From CCITT G.613.) Parameter Conductor size Parameter Value 0.4mm 0.5mm 0.63mm 0.9mm Operational bit rate 2048 kbit/s Impedance @ Construction Unit twin 1kHz (S) Conductor diameter 0.6mm Attenuation @ Nominal impedance 1kHz (dB/km) Attenuation @ 20° 1MHz(fo) 15.5dB/km Attenuation @ f MHz 15.2.4 Pair cables for HF carrier systems 55(6)" Attenuation @ t° a20°c + 0.002 20)) High frequency symmetric pair cables have been developed for analogue carrier telephone systems providing 12, 24, 36, 48, 60 and Sinusoidal NEXT 78 dB (nominal) 120 channels on each pair, necessitating operation at up to 550kHz. Sinusoidal FEXT 64 dB These cables have polyethylene insulated pairs in star quad forma- Direct current resistance @ 63S/km tion, and conductor sizes from 0.9mm to 1.3mm. A typical cable is described in CCITT Rec. G.611 (CCITT, 1989) from which Table 15.5 is an extract. Nominal mutual capacitance 44nF/km Table 15.5 Pair cables for analogue transmission (From CCITT G.611) the cable remote from the disturbing source. NEXT (near end Parameter Value crosstalk) is measured at the same end of the cable as the disturbing Conductor diameter 1.2mm source. Higher rate digital systems, 6Mbit/s and 34Mbit/s, have Mutual capacity 26nF/km been used over the symmetric pair cables designed for HF carrier systems discussed in Section 15.2.4. Characteristic impedance @ 60kHz Characteristic impedance @ 120kHz 15.2.6 Balanced pair cables for information Characteristic impedance @ 240kHz systems Attenuation @ 10°C, 120kHz 2.0dB/km New office blocks and industrial complexes involve the use and Attenuation @ 10°C, 240kHz 2.9dB/km interconnection of many data terminal equipment and other IT products. The contending transmission technologies have been re- Attenuation @ 10°C, 552kHz 4.8dB/km viewed by (Flatman, 1988, 1989). His main po