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An electronic future : generation two ...

Electronics pioneers

The following people were eminent figures in electronics:

Walter H. Brattain, William Shockley and Robert Noyce

Engineer testing the trial Empress PCM tandem exchange, 1960s

Pulse Code Modulation (PCM) patented (1937) : turning speech into pulses

In 1937 an English engineer, Alec Reeves, working in Paris for the International Standard Electric Company, patented the Pulse Code Modulation (PCM) transmission system. PCM turns the human voice into electronically coded sequences of digital pulses which are then transmitted and turned back into speech at the far end.

This was a visionary concept, underlying the digital systems of today. But Reeves's ideas were well in advance of his time. The techniques he described for coding and decoding signals could not be realised in practical form until suitable components, particularly transistors, became available.

Engineers working on Highgate Wood exchange, 1962

Highgate Wood digital trial (1962) : a magnificent failure

Development of electronic exchange systems proved more difficult than originally thought. It was realised that, to prove the technology, an experimental exchange would need to be constructed.

The first design for an electronic switching system focused on pulse-amplitude modulation (PAM) and time-division multiplex (TDM) digital transmission. The 'working' exchange intended to prove the design was installed at Highgate Wood in 1963, with a different manufacturer allotted to design and build each of the main elements.

But it quickly became clear that PAM techniques were uneconomic and difficult to achieve with the technology and components then available. The main problem was digital electronics 'crosstalking' with switch contact points that were still working in analogue mode. This meant, for example, that sometimes the exchange systems would ring numbers, seemingly of their own volition...

Although Highgate Wood was not a success it did help prove which elements of electronic switching were worth developing and which should be abandoned.

Hullbridge

First production electronic exchange (1966) : Derbyshire's world-beater

The limitations of electronic switching demonstrated by the trial electronic exchange at Highgate Wood in the 1960s, persuaded designers to adopt a solution that used electronics to control miniature relay switches called 'reed relays'.

Development was concentrated in this area, leading eventually to the successful TXE2 and later the TXE4 systems - 'TXE' meaning Telephone Exchange, Electronic.

The first fully operational production TXE2 reed relay exchange was opened at Ambergate, Derbyshire, in 1966. This was the first electronic telephone exchange in Europe - and the first small-to-medium sized one in the world.

Empress PCM exchange at Earl's Court, 1968

Empress - the first all-digital exchange (1968) : showing the way

The GPO embraced the idea of digital transmission enthusiastically. From 1964 it installed more than 7,000 pulse code modulation (PCM) wideband systems on existing copper cables. Four years later it inaugurated the world's first all-digital PCM switching centre in London.

The Empress telephone exchange, near Earl's Court, was opened on September 11, 1968, with an inaugural call from the then Postmaster-General, John Stonehouse, to the Mayor of Hammersmith.

Empress was the first exchange in the world to switch PCM signals from one group of lines to another in digital form. Now Empress solved this problem - and demonstrated that an integrated PCM transmission and switching system was capable of working fully within the existing network of Strowger, Reed-Electronic and Crossbar systems. 

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featured story

100 years of automatic switching!
In 1912 the GPO installed Britain's first automatic telephone exchange in Epsom.

Discover the early days of the telephone...