retroelectro
Engineering silence: the telephone and the negative feedback amplifier Written by: David Ray, Cyber City Circuits
altogether, selling Western Electric to Bell Telephone. Western Electric became the manufacturing division of Bell Telephone for the next fifty years, and many of the world’s great innovations came out of the team at Western Electric. The proliferation of telephones throughout the developed parts of this country was very quick. It soon surpassed telegraph line production, and Bell Telephone was at the center of it all. Long-distance phone calls Eventually, phone lines would stretch across the country, including the transcontinental telephone line (1914), which had amplifier stations all along the way. Every ten to twenty miles, there would be a repeater station. As with the transatlantic cable, once
the telephone was used over long distances, new problems began to appear. ■ Signal attenuation – as the electrical signals traveled through the telephone lines, they experienced attenuation, requiring the use of many amplifier stations and, in some cases, manned relay stations ■ Noise from the repeaters – each repeater was designed around high-voltage vacuum tubes, and each one carried with it some intrinsic thermal noise or ‘hiss.’ Each station would amplify the noise from every station before it, and eventually, the noise would rival the intended voice signal, making it unintelligible. The distortion in a string of amplifiers would increase in direct proportion to the number of amplifiers ■ Poor quality telephone lines
The telephone is 150 years old and has undergone many different incarnations. From Elisha Gray’s first version, playing the violin over telegraph lines to modern smartphone computers that no longer need a line to charge. At every step, innovations in the telephone have driven technological advancements. Innovations in transmission lines, switchboards, touch-tone systems, audio filters, FSK modems, and more. Just like when they stretched telegraph lines
across the ocean, pulling telephone lines across the country also led to new and unique problems emerging along the way. This is the story of distortion and noise and how a man named Harold Black solved it. Western Electric and the telephone Elisha Gray first invented the telephone in 1875. His company, Western Electric Manufacturing Company in
Various tunes, including ‘Yankee Doodle’, ‘Robin Adair’, ‘Auld Lang Syne’, and others, were transmitted a mile and heard by a room full of ladies and gentlemen as loudly and tunefully as if they had been in the same room where they were played. These demonstrations were nationwide news. Everyone was excited about the prospect of actual voice communication, but Gray’s telephone could only transmit music from an instrument, like the violin. Alexander Graham Bell, a Scottish immigrant, was a dedicated servant to those who suffered from deafness and hearing loss. He and his engineer, Thomas Watson, worked for months to develop a method for the deaf to communicate using the telegraph or a similar device. Working on this problem, Bell and Watson had developed a way to send a voice message over telegraph wires and files, for which they were granted a patent in March 1876, fifteen months after Gray first demonstrated his telephone. Within a few weeks of applying,
Elisha Gray and his first telephone.
Bell was awarded the patent for the telephone. Around the same time, Gray sold his interest in the Western Electric Manufacturing Company to the telegraph giant, Western Union. Now owning the patent applications and caveats filed by Gray, Western Union sued Bell Telephone over this patent dispute. Western Union lost the lawsuit and, as part of the judgment, was forced to exit the telephone industry Retro Electro fun fact: the official story goes that Gray filed for a patent on his telephone within moments of Bell, but Bell’s application was awarded while Gray’s was not because Bell’s was earlier in the day. Newspapers would allege, a decade later, that Bell bribed the patent examiner, Mr. Wilber, with a $100 bill (half of a month’s pay for an examiner) for his ‘favoritism’ in this matter.
Chicago, had worked in the telegraph industry for years, manufacturing all kinds of equipment. Gray retired from his administrative duties at Western Electric the year before to focus on his own research. He began holding demonstrations in January 1875.
Alexander Graham Bell (Left) with his engineer Thomas Watson (Right).
Harold S Black while testing his new system in 1930.
we get technical
20
21
Powered by FlippingBook