Signals and Codes

In this introduction, we take a brief tour of telecommunications through videotelephony.

Optical Telegraphy

Communications signaling is an ancient as the smoke signals and drum beating of early civilizations. The history of modern telecommunications, however, began with the use of the telegraph to transmit signals by transit systems such as railroads.

Experiments on communication with electricity, initially unsuccessful, started in about 1726. Scientists including Laplace, Ampère, and Gauss were involved. The first working telegraph was built by Francis Ronalds in 1816 and used static electricity. Charles Wheatstone and William Fothergill Cooke patented a five-needle, six-wire system, which entered commercial use in 1838. It used the deflection of needles to represent messages and started operating over twenty-one kilometers (thirteen miles) of the Great Western Railway on 9 April 1839.

On the other side of the Atlantic Ocean, Samuel Morse developed a version of the electrical telegraph which he demonstrated on September 2, 1837. Alfred Vail saw this demonstration and joined Morse to develop the register—a telegraph terminal that integrated a logging device for recording messages to paper tape. This was demonstrated successfully over three miles (five kilometers) on January 6, 1838 and eventually over forty miles (sixty-four kilometers) between Washington, D.C. and Baltimore on May 24, 1844. Morse’s most important technical contribution to this telegraph was the simple and highly efficient Morse Code, co-developed with Vail, which was an important advance over Wheatstone’s more complicated and expensive system, and required just two wires. The communications efficiency of the Morse Code preceded that of the Huffman code in digital communications by over 100 years, but Morse and Vail developed the code purely empirically, with shorter codes for more frequent letters.

The submarine cable across the English Channel, wire coated in gutta percha, was laid in 1851. The first successful transatlantic telegraph cable was completed on July 27, 1866, allowing transatlantic telecommunication for the first time.

The electric telephone was invented in the 1870s, it was based on earlier work with harmonic telegraphs. The first commercial telephone services were set up in 1878 and 1879 on both sides of the Atlantic in the cities of New Haven and London. Alexander Graham Bell held the master patent for the telephone that was needed for such services in both countries. As with other great inventions such as radio, television, the light bulb, and the digital computer, several inventors engaged in pioneering experimental work on voice transmission over a wire, and then improved on each other’s ideas. However, the key innovators were Alexander Graham Bell and Gardiner Greene Hubbard, who created the first telephone company, the Bell Telephone Company in the United States, which later evolved into American Telephone & Telegraph (AT&T), which was, at times, the world’s largest phone company.

Telephone technology grew quickly after the first commercial services emerged, with inter-city lines being built and telephone exchanges in every major city of the United States by the mid-1880s. The first transcontinental telephone call occurred on January 25, 1915. Despite this, transatlantic voice communication remained impossible for customers until January 7, 1927 when a connection was established using radio. However, no cable connection existed until TAT-1 was inaugurated on September 25, 1956 providing 36 telephone circuits.

In 1880, Bell and co-inventor Charles Sumner Tainter conducted the world’s first wireless telephone call via modulated light beams projected by photophones. The scientific principles of their invention would not be utilized for several decades, when they were first deployed in military and fiber-optic communications.

The first transatlantic telephone cable (which incorporated hundreds of electronic amplifiers) was not operational until 1956, only six years before the first commercial telecommunications satellite, Telstar, was launched into space.

Over several years starting in 1894, the Italian inventor Guglielmo Marconi worked on adapting the newly discovered phenomenon of radio waves to telecommunication, building the first wireless telegraphy system using them. In December 1901, he established wireless communication between St. John’s, Newfoundland and Poldhu, Cornwall (England), earning him a Nobel Prize in Physics (which he shared with Karl Braun) in 1909. In 1900, Reginald Fessenden was able to wirelessly transmit a human voice.

In 1925, Japanese engineer Kenjiro Takayanagi demonstrated a CRT television with thermal electron emission. In 1927, he increased the television resolution to 100 lines, which was unrivaled until 1931. In 1928, he was the first to transmit human faces in half-tones on television, influencing the later work of Vladimir K. Zworykin.

On March 25, 1925, Scottish inventor John Logie Baird publicly demonstrated the transmission of moving silhouette pictures at the London department store Selfridge’s. Baird’s system relied upon the fast-rotating Nipkow disk, and thus it became known as the mechanical television. His invention formed the basis of semi-experimental broadcasts done by the British Broadcasting Corporation beginning September 30, 1929.

For most of the twentieth century, televisions used the cathode ray tube (CRT) invented by Karl Braun. In 1934, he gave the first public demonstration of the television at Philadelphia’s Franklin Institute and opened his own broadcasting station. John Logie Baird switched from mechanical television and became a pioneer of color television using cathode-ray tubes. After mid-century, the spread of coaxial cable and microwave radio relay allowed television networks to spread across even large countries.