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Alberta Online Encyclopedia
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Alberta's Telephone Heritage
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Electricity

The telephone system uses a 48-volt direct current (or 48-volt DC) to send the voice signal on the talking circuit.

The signal to sound the telephone bell is carried on the "ringer circuit," which uses 110-volt alternating current (or 110-volt AC).

In the 1890s, power for the talking circuit came from batteries that were included in each telephone and in the switchboard. Later, the "common battery" system used direct current from batteries in the telephone office.

Churchill Wire CentreEarly telephone systems used electrical currents travelling through the ground as part of the circuit. This arrangement was subject to interference from other electrical installations such as streetcars and electric street lighting, resulting in poor sound transmission. When metallic circuits added another wire instead of using the ground, signal quality improved. It was well worth the cost of the extra wire.

An electric current travelling through an open pair of wires must have the position of the wires transposed at intervals to avoid "crosstalk interference". This occurs when the signal travelling through one wire injects noise into a neighbouring wire, thus interfering with the sound quality during a telephone conversation.

Wooden wall telephone Often, the rural networks operated by farmer co-operatives or "mutuals" used less expensive equipment and materials. Barbed wire fence lines might be used to carry the signal instead of erecting tall poles. In the absence of other electrical currents, a ground return was quite satisfactory. When new technology was introduced in Alberta’s cities in the 1950s, rural systems had to be upgraded to work effectively with the new systems.

Sculptured Relief Because the voltage in these old systems was different from the newer 110-volt AC that was becoming a standard for most electrical equipment, the telephone company had to transform the power from the grid to 48 volts DC for use in its own network. This transformation also made it generally possible to use the telephone during power failures.


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