Pulse Code Modulation

In the 1930s the necessity to convert analogue data to digital format for computer use was unknown - there were no computers capable of using it. However the idea was seen by Alec Reeves as a means of communicating with perfect fidelity - no errors could arise in a system based on ones and noughts. In 1938 he filed a patent in France that introduced the concept of digital communication which he called Pulse Code Modulation. It is now commonplace for computers, radio, television, CDs, recording and so on.

Although the idea had military application for coded transmissions, it was totally impractical for commercial use as it required racks of valves to implement. By the time transistors and integrated circuits made it practicable, the patents had run out.

When Alec Reeves invented pulse code modulation in 1937 a prediction that the GPO would issue a commemorative postage stamp on the subject in 1969 would probably have struck him as unlikely.

The significance of the invention, although clear enough to Reeves, was not widely appreciated at the time. Furthermore, it was to be many years before the advent of the transistor would make it a practical proposition. Even in 1969, well over a quarter of a century later, it is only just beginning to come into widespread use in the UK telecommunications network.

Reeves and many others in telecommunications became convinced that PCM and associated digital systems eventually will be the principal methods of transmitting not only speech, but all forms of information from one point to another by wire, radio, or optical links. In most electronics laboratories in the 1960s onwards prediction of the future was being taken perfectly seriously and what might have been described as "science fiction thinking" a year or two previously was then considered to be legitimate scientific activity. Alec Reeves has given a good deal of thought to the future of telecommunications when asked to give lectures in the late 1960s and came up with some fascinating prospects.

For his work on PCM he won
The Ballantine Medal of the Franklin Institute (1965) Press release
The City of Columbus Gold Medal (1966)
PCM was commemorated on a shilling (5p) postage stamp (1969)

Below is reproduced the letter of congratulations war written by Harold S Geneen, the controversial president of ITT. It is followed by another from Group Captain E. Fennessey, and finally another from ITT head office inviting him to a company sponsored trip and various comments are written on it by STL management.

Further Reading

Principles of Pulse Code Modulation by Kenneth W. Cattermole
Click here to get a copy - only available second hand now. But you will find a review here, or indeed could write your own.

Elliptical Fiber Waveguides, (The Artech House Optoeletronics Library), by Richard B. Dyott, begins with an historical overview, and then provides detailed coverage of specific waveguide and fiber modes, including all relevant specifications and data currently available.
UK/European buyers
Buyers in Rest of the World

Optical Fibre Communications by C.P. Sandbank
Click here to get a copy - only available second hand now. But you may find a review here, or indeed could write your own.

He had a child-like delight in these company trips, and when one was arranged he would skip along the corridors of STL if he thought that no one was looking. Note that these letters were written in the days before computers, hence if they are more than a few lines long typos are altered rather than re-done. [If you re-typed a long letter to correct one typo, the chances are you'd introduce another.] When Alec Reeves finally left STL, his laboratory occupied about 1000 sq feet. That entire space was taken with one of the world's first word processors, intended for writing the most special and complicated scientific reports without error. Ironically, it was manufactured in Germany.

This carbon copy of a response to another congratulatory letter exemplified Alec Reeves' attitude to invention and also his sense of fun.