Post-war and on to 1975 (continued)

As another basis for planning and developing the network, the APO specified telephone network transmission performance standards with separate requirements for each of the subscribers' services, the junction and the trunk network. In the case of the junction network an individual transmission design, using a mixture of loaded and unloaded cable of varying conductor weights, or in some cases carrier circuits, was required for each city as follows:

1. The total attenuation between any two exchanges not to exceed 15 db, including the loss of all intermediate exchanges on a through connection, but not the loss in the terminal exchange which was part of the subscribers' service standard.


2. The total attenuation from any exchange within the junction network to the trunk exchange not to exceed 7.5 db.

The transmission design for the trunk network is illustrated in Fig. (17) and was based on:

1. trunks between main trunk centres to be zero loss equivalents;


2. the total loss from any trunk exchanges to its main trunk centre not to exceed 7.5 db.

14 Typical "E" Section transposition design showing selected pairs for 12 channel carrier operation.

While transmission performance standards were being developed, a planning basis was established for a rapid increase in main line trunk circuits. In the longer term, developments in radio were seen as holding promise but it was clear that for many years carrier circuits on open wire routes would be a major method of trunk channel provision, with carrier cables between certain large provincial cities and their capital city also playing a role, while tentative plans were developed for the first coaxial cable systems, but these did not mature for more than a decade.

Thus the APO looked to the full exploitation of the channel carrying capacity of existing open wire routes, together with the construction of new high grade routes. It was decided also that rather than develop transposition schemes for individual routes, a series of standard transposition designs would be produced. To meet the electrical requirements, consideration had to be given to:

1. Use of suitable transposition types


2. Control of third circuit effects


3. Reduction of coupling between pairs


4. Uniform construction to allowable tolerances


5. Impedance matching to specified limits between different types of construction


6. Layout of transposition sections


7. Use of suitable junction transposition schemes

17 Portion of trunk network showing allocation of line losses

Australian Academy of Technological Sciences and Engineering