Post-war and on to 1975 (continued)

Quirk[28] gives an account of the construction of one of the relatively few routes erected to transposition CL260, the scheme adopted when 12 channel systems were required on all pairs. Taylor, Huston and Sayer{29] discuss the planning, design and operational features of a major APO project involving the reconstruction of over 1000 miles of aerial trunk route between Port Augusta and Kalgoorlie. The project employed a number of constructional techniques not previously used in Australia and these are described and illustrated, as are the electrical and mechanical design aspects.

The application of open wire carrier systems in Australia encountered special problems as a result of the very long distances which could be involved in particular calls, Perth to Cairns is an extreme example, requiring close attention to the design of repeaters, and the APO and manufacturing companies worked closely to achieve satisfactory performance. Testing, maintenance practices, unattended repeaters, power supplies, were other areas in which important Australian contributions were made to the technology. Although by 1960 the APO had commenced a major programme of broadband coaxial cable and microwave systems, in the short term it was necessary to improve the performance and carrying capacity of open wire routes to meet demand for circuits. Some development work had been undertaken in South Africa and in USA in open wire routes to this end, either moving to higher frequencies or by substantially modifying wire and pair spacing. Using this as a base, N. Watson in Queensland undertook extensive studies of crosstalk on open wire routes and on attenuation versus frequency curves of the various transposition patterns in common use, assisted by access to the electronic computer then recently installed at the University of Queensland. The outcome was an important contribution to increasing capacity by use in some cases of higher frequency systems, a better understanding of the effect on performance at carrier frequencies of irregularities in construction and leading to minor changes in wire and pair spacing.

From the mid-fifties on trunk cables were increasingly used for short haul trunk circuits, initially mainly providing voice frequency circuits, often with amplifiers, but the use of carrier systems grew during the nineteen sixties as more compact systems became available. The APO at that time had specifications for three types of cables, local, trunk and carrier, all of quad construction. The simplest and cheapest was local type, while trunk type was of similar design but manufactured to finer tolerances. Carrier cable specifications were more stringent again, with each quad being of different twist length. To obtain suitable performance from all these cables, extensive measurements were taken and jointing schedules developed to bring imbalances within accepted standards. Watson, assisted first by the Sydney Silliac, and later the Queensland University computer, studied the make-up of the cables in terms of twist lengths of the various quads and found that a substantial number of carrier systems could be routed over local type cable by allocating specified pairs as carrier bearers. This work led also to the elimination of trunk type cable and to simplification of jointing and balancing methods.

Australian Academy of Technological Sciences and Engineering