Line Drivers 1979

Line Drivers 1979

The University of Queensland developed these short distant voltage-differential line drivers for use on campus in response to the fierce monopolisation of data communications by the Post Master General’s Department (now Telstra).

As computers became increasingly affordable during the 1970s there was growing demand for domestic and international data exchange.  In Australia, the PMG, which controlled all postal, telegraph and telephone services in Australia since federation in 1901, launched their Datel service in 1969.  Services from 200 bps to 48 Kbps were available over switched and dedicated voice grade lines.  The number of Datel services increased from around 800 in 1970 to nearly 5,000 in 1975 when there was estimated to be over 2,000 mainframe computers installed in Australia.  By 1975 the typical cost of a low speed service up to 1,200 bps was AU$150 pa for the modems and AU$50 pa per 1.6 Km of line length within a local call area.  A 48 Kbps service < 1,000 Km would cost in excess of AU$30,000 pa.

The PMG would not even permit non-PMG cables to be installed in the same ducts or building risers with telephone cables.  For many organisations, this meant having to use PMG modems within their own buildings or campus.  In response, the University installed a considerable amount of its own copper cable and line drivers and as well took the PMG to task over the ownership of all of its cabling on campus.  In time, the PMG also approved the University line drivers for use on cables that were used for telephone services.  This effectively broke the PMG monopoly on campus.  By the late 1980s the University had installed over 1,500 services using these line drivers.

These devices used an integrated circuit type 488 Voltage-Differential Line Drivers that complied with the EIA RS-422 transmission standards and optically isolated the terminal equipment. A rack mounted version was produced as well as the 'modem' like boxes shown below.