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L M Ericsson's H. F. Line Equipment for Small-Diameter Coaxial Cable S. TRONSLI, TELEFONAKTIEBOLAGET LM ERICSSON, STOCKHOLM UDC 621.395.455/457 LME 8424 This article presents briefly the economic arguments in favour of the smalldiameter coaxial cable systems and describes LM Ericsson's repeater equipments with 1.3 and 4 Mc/s bandwidth for this type of cable. These equipments, and the methods for tlieir connection to the cable, have been developed in consultation with the Swedish Board of Telecommunications. Through the advent of the silicon-planar technique within the transistor field, the h. f. line designer of today has amplifying elements at his disposal which have opened up entirely new possibilities. The very high reliability and insignificant aging of the silicon-planar transistors, combined with low current consumption, permit burial of intermediate repeater stations and considerably simplified remote power feeding. This has resulted in a lower cost of the intermediate repeaters compared with vacuum tube repeater equipment which, for maintenance reasons, should preferably be placed indoors. To attain the minimum price per channel-kilometre, an optimal balance is required between cable cost and repeater cost. This lower cost of amplification may therefore warrant a change of the cable dimension. Economic Considerations An increase of the coaxial tube diameter results in a higher cable price and lower repeater cost per kilometre, and vice versa. Simple calculations show the minimum channel-kilometre price for a tube diameter D„ llt to be k • N"- 2T ' where k = constant N = number of channels The value of the constant k depends on which costs one is considering. Fig. 1 shows three curves for £> opt . Curve 1 relates to the first cost, curve 2 to the annual cost on the basis of 30 and 15 years depreciation period, respectively, for cable and repeater equipment at a rate of interest of 6 per cent per annum. Curve 3 relates to the annual cost, but at 30 and 10 years depreciation, respectively, at the same rate of interest. "opt mm ; i M> ^^^\^^\^ V VI) © 1 | ^!_ Fig. 1 Optimal coaxial tube diameter as function of number of channels in the system 1 i ' ' i ii.. N channels 78
The curves show that the small-diameter coaxial cable standardized by C.C.I.T.T. with the diameter ratio 1.18/4.43 mm has an optimal system size of N ~ 900 channels when the annual costs are considered. On the basis solely of first cost, the nearest optimal system size will be about 2700 channels. For purposes of conversion a 2700-channel system will under all circumstances be economically advantageous compared with the installation of new cable. The saving in per cent of the first cost for three sizes of system through the use of small-diameter coaxial cable instead of the heavier 2.6/9.5 mm cable has been calculated below. The costs of laying of the cable have not been included since they are virtually independent of the diameter of the coaxial tubes. System Saving 300 50% 960 20% 1700 0 Another factor which makes small-diameter coaxial cable attractive also on heavy-traffic routes is that the cost of standby equipment in a multitube small-diameter coaxial system is small compared with the conditions in a normal coaxial cable system with small number of tubes. Fig. 2 Structure of small-diameter type A, with balloon insulation coaxial tube, Small-Diameter Coaxial Tube Two coaxial tubes have been standardized by C.C.I.T.T., both having the dimensions 1.18/4.43 mm, which gives an impedance of 75 ohms. The difference lies mainly in the structure of the outer conductor. Type A has an outer conductor consisting of a 0.15 mm thick copper tape, formed to a tube with a longitudinal slit, surrounded by two layers of copper-plated steel strip (fig. 2). Type B has an outer conductor thickness of 0.18 mm and steel strip without copper-plating. Owing to their different designs of outer conductor, the two types have slightly differing attenuation curves below about 500 kc/s. The insulation of type A consists of a polythene tube of outside diameter equal to the inside diameter of the coaxial tube, the polythene tube being crimped on to the inner conductor at intervals of about 20 mm (fig. 2). This procedure makes for simple manufacture and the inner conductor is well centered, which ensures high homogeneity. The cable also has a high dielectric strength and a minimum of dielectric adjacent to the inner conductor. Type B is supplied with different forms of insulation and may have a slightly higher attenuation constant in the high frequency range. Fig. 3 Attenuation constant y. as function of the frequency for small-diameter coaxial tube, type A, at + 10°C 79
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Page 12 and 13: • The four-wire circuit permits a
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Page 18 and 19: Recall to operator. If an incoming
Page 20 and 21: Rack The rack has a light-grey enam
Page 22 and 23: The tones are generated by a transi
Page 24 and 25: Common night service. The operator
Page 26 and 27: Radio Alarming of Fire Brigade ANDE
Page 28 and 29: The system in its present form cons
Page 30 and 31: Aerial There is very little possibi
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Page 34 and 35: G. H. Wieneke in Memoriam After a b
Page 36: The Ericsson Group Associated and c

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