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I'm proud to have been involved with Australia's growth in the Telephone Communications field, having spent the greater part of my working life in the PMG (later Telecom Australia, now Telstra), maintaining and growing the telephone communication services needed by a developing nation.
In 1959 I was persuaded by my elder brother, Bram to apply for a position in the Post Master General department (PMG), which at that time was responsible for maintaining both the telephone and the postal services in Australia. The postal
side of things didn't interest me, as I had dabbled in electronics prior to this, also with Bram's encouragement, so I applied for a position as a Technical Assistant and was accepted to work at our local Telephone Exchange.
After that time. I worked in several exchanges, both step-by-step and crossbar, and on the team responsible for the conversion of Exchange gear to allow International Subscriber Dialling (ISD), then later, in the Special Services Restoration Centre (SSRC) in Perth, which maintained voice and data services around Western Australia for corporate, business and private customers.
This page looks at the growth in Australian Telephony services from the early 'fifties to the present day, as seen by a technical worker within it.
The requirements of a telephone system are
- A transmitter/receiver set (telephone, switchboard or similar)
- Cable or other medium to connect the users' apparatus
- A means of identifying, selecting, connecting, monitoring and disconnecting users
- Electrical power for the various pieces of equipment
- Monitoring, maintenance, testing and repair of equipment
- A billing system for use of common equipment
All of these components have changed in many ways since the "Good Old Days".
Telephone transmitters and receivers have become more compact, sensitive and powerful. Early transmitters used a small chamber of carbon granules, with an embedded electrode that moved in response to sounds to create variations in resistance of the carbon, and so vary the current sent to the receiving equipment. Receivers used an electromagnet with a diaphragm close to its poles. The incoming signal varied the strength of the electromagnet's field, moving the diaphragm and creating sound. Later, a much more efficient system known as the "rocking-armature" receiver replaced the carbon granule type. Electro-static receivers later replaced these. Various configurations of the customers' equipment allowed several incoming exchange lines, internal and external extensions, loud-sounding and flashing alarms, and loud-speaking receivers to be used.
Cables were once mounted on wooden or steel poles, which meant high installation and maintenance costs and limited cable sizes. Cables have mostly been placed underground now except in some country areas, making them less susceptible to weather
conditions and other forms of damage, and allowing much larger cables to be used. They are protected by a waterproof lead or plastic cover.
These are still at risk of damage by excavators, farm machinery and other ground disturbances. Some of these risks are reduced by the use of "armoured cable" - cable with a protective shield of toughened steel wires.
To protect from water-invasion when the protective coating was damaged, cables with a large number of wires are sealed and filled with compressed air. A pump at the Exchange maintains this air pressure, and one cable pair is used to hold a contactor that warns the Exchange of any drop in pressure. When a cable is damaged, the escaping air keeps the water at bay until a repair man arrives to repair the damage.
Early exchanges were manually operated, with a team of operators who were signalled by subscribers wishing to call a number, tested that number to see if it was free and connected them by plugging two cords into jacks
.When either line was released, a light alerted the operator and they unplugged, releasing the lines. In later years the cords were replaced with rows of switches.
Later, automatic, relay-operated devices replaced most operators. The Exchange in which I first worked used Step-By Step automatic switching. Its users could dial other local and nearby suburban numbers without needing help from an Operator.
To make calls outside the suburban area (and to some distant suburbs)
they still needed to have a "trunk-call" set up by an Operator. A room upstairs in the Exchange housed several switchboards, each manned (or womaned?) by an Operator. The switchboards were cord-operated. The Operators would connect
the caller to a Trunk line to the distant area using a set of three cords - one connected to answer the caller's line, another to the Trunk line, and the third for monitoring and supervising the call. An Operator at the distant Trunk
Exchange would call the required subscriber if it was within her area or call another area's Operator to extend to that area. The final Operator would test the required number, and, if it was available, connect it to the caller.
The Operators' equipment would indicate when the call was finished so that they could disconnect the equipment, freeing the trunk for other users. Calls were divided into 3-minute segments, and the caller was charged according to their length. It was common to hear the operator enquire, "Three minutes, are you extending?"
The automatic switching mechanisms in the exchange used electro-magnetic relays to perform the signalling, switching, monitoring and disconnecting functions previously carried out by operators.
Each telephone line was permanently connected to a pair of tags on a large frame in the exchange, the Main Distributing Frame, or MDF.
Opposite the rows of tags on which the cable pairs were terminated was another large set of tags, each pair of these being connected to a unique switch called a uniselector. This switch, with a few associated relays (collectively, the "line-equipment") were what determined their telephone number. To create a telephone service a cable pair was allocated a uniselector, providing the subscriber with their unique number.
When a person lifted the receiver to make a call, the relays sensed this and activated the uniselector. The uniselector had a rotating arm that searched between 25 outlets to find a free first-selector.
The function of the first-selector was to advise the caller that they had successfully connected to the equipment (or not), and then to accept and respond to pulses from their telephone that represented the first digit dialled. It would step
vertically according to the number dialled (hence "step-by-step") then an arm would rotate to search a "bank" of outlets on that level that each connected to a second-selector. The second-selector, then in turn a
third and fourth- selector accepted and responded to the second, third and fourth digits.
A final-selector then came into play, and this had several extra functions. It stepped vertically, as with the other selectors, then instead of searching, it rotated horizontally in response to the last digit, so it accepted the last two digits dialled. Each pair of contacts on the final selector was permanently connected to the line equipment of one subscriber. It tested this equipment to ensure it was free and if so, returned a ring-tone to the caller and applied ring current to the called line. When the called party answered, it connected the lines together, provided power for the call, and monitored its progress. When the caller replaced the phone handset it released all of the equipment for the next user.
With this configuration, the exchange equipment could control six stages of ten digits, giving a capacity of 10000 lines.
The equipment operates on 50 volts, and this was supplied from a lead-acid battery comprised of 25 cells, each generating 2 volts. Each cell was, I think, about 600mm tall and about 150mm by 100mm based. The battery was mains-charged, with back-up from a diesel generator. Both the battery and the generator had duplicates on standby.
An exchange team (sometimes of one person) was responsible for the day-to-day running, moving and removal of "jumper-wires" as this became necessary when subscribers changed their locations etc. and for the location and repair of faults
as they occurred. One of the major tools for locating faults, on both external and internal components, was the test-desk. This was a large desk, similar to a switchboard in appearance and size but with meters and other items for
testing. This allowed the incoming line to be isolated from the exchange equipment and tested for open- or short-circuits, foreign earth or battery, or any other abnormal condition, and the line-equipment (uniselector etc.) to be tested. It also
allowed the subscriber to be called, for information about the fault and to test line performance.
When a fault had been analyzed, sometimes temporary measures could be applied to give full or partial service until a complete repair could be made. This may involve a change of cable-pair, or using a "hospital-circuit" which simulated the proper conditions for the line.
For faults within the exchange, a large box, called a Traffic Route Tester (TRT) could be used to simulate calls between various stages of the exchange. It was set to make the same call repeatedly for as long as necessary, and the technician used the results to identify and fix the fault.
A smaller, but no less important tool used both in and out of the exchange was the appropriately-named buttinski, a handset with dial attached and with clips or a plug on the end of its cord. This could be used to call or listen across lines to locate noise or other problems.
Of course, all this doesn't come without a price, and each telephone line had an associated meter that counted the number of calls made from that line. In earlier days the calls were monitored and divided into 3-minute segments, each segment generating an additional meter pulse. The meters were read regularly and the information used for billing.
Time moves on, I guess, and Telephony moves on with it.
Larger cables, some containing 2400 or more pairs of cables, have been replaced by optic-fibre cable in many places. These have many advantages, including
- Little or no interference between adjacent channels
- Less attenuation (diminishing of signal strength) over long distances, so less repeater-stations are needed
- Lower cost (now) than equivalent copper cable
- Much higher capacity per cable
- Can carry data and other services that use higher frequencies
- No environmental damage from earth-leakage current
Balanced against this is the disadvantage of more difficult connection and maintenance of cable.
Subscriber-end equipment has changed to include functions such as caller-identification, auto-answer, message-taking, diversion, call-transfer and many more. Telephone handsets can be hands-free, allowing the user to do other things while conversing; cordless, so the user can visit various rooms and continue to speak. Mobile handsets can be used virtually anywhere, and are compact for easy carrying, and usually incorporate a camera and often, internet access as well.
Exchange equipment has changed dramatically also. From the original "Strowger" step-by-step equipment it advanced through crossbar (still mechanically-switched but much more efficient) to electronic switching and control, with more reliability, simpler maintenance (plug-in replacement of many items), lower power requirements, and better overall performance.