reflections of at least 54dB down on the inputted Mazda, F.F. (1989) Electronics Engineers Reference Book 6th Edi- signal, measured with a 2ns pulse. tion, Butterworth Scientific, Section 55.18. Rowland, S. et. al. (1987) The Development of a Metal-Free Self- (b) Installed cable Supporting Optical Cable for Use on Long Span, High Voltage Overhead Power Lines. In Proceedings of the International Crosstalk Wire and Cable Symposium. The far-end crosstalk ratio between two coaxial pairs shall not be Schelkunoff, S.A. The Electromagnetic Theory of Coaxial Trans- less than the values given in Table A15.1. mission Lines and Cylindrical Shields. Bell Syst. Tech. J. 13. Worthington, P. et. al. (1986) The Design and Manufacture of Dielectric Strength Submarine Optical Cables in the U.K. In Proceedings of the The pair shall measure not less than 5000Mohm-km at 500V dc, Sub-Optic Conference, Paris. after electrification for one minute at 2000V dc. (Transmission systems frequently incorporate high voltage power feeding of de- pendent repeaters). 15.12 Acknowledgements The writer wishes to thank Mr. M.M. Ramsay and Dr. John Lees of 15.14 Appendix 15.2 BNR Europe (formerly STC Technology) for their generous assist- ance, and the directors of NT Europe (formerly STC) for per- 1.2/4.4mm coaxial pair (CCITT G.622) charac- mission to publish this paper. teristics (a) Factory Length 15.13 Appendix 15.1 Impedance 2.6/9.5mm coaxial pair (CCITT G.623) charac- The characteristics Impedance is 750hm + 10hm at 1MHz. teristics Table A15.2 Far end cross talk ratios for 1.2/4.4mm coaxial pair (a) Factory Length Impedance Section lenght Frequency band FEXTRATIO Characteristic impedance is given by Equation A15.1. 0.06 to 1.3MHz 0.06 to 4.5MHz 74.4 1 + 0.0123 ( 1 ) (A15.1) 0.3 to 12.5MHz 15/18 Telecommunication cables Typically, then Z at 60kHz is 79.80hm; at 500kHz it is 75.80hm; Dielectric at 4.5MHz it is 74 ohm; at 18MHz it is 73.5 ohm. The pair shall measure not less than 5000Mohm-km at 500C, after electrification for one minute at 1000V d