Before the turn of the century, news-bearing messengers traveled by horse, stagecoach, or foot. Even the telegraph, which could transmit information long distances "instantly," still relied on people to decode and hand-deliver the message. Depending on where the recipient was located, an "urgent" message could take five minutes or weeks to arrive. Telephoning was not much faster. People had to wait for open lines, there was no long-distance service, and transmission was poor and unreliable.
In the 20th century, engineers began transforming a fledgling technology of copper wire, wooden poles, and primitive transmitters into a complex system of fiber optics, satellites, and digital technology. With astonishing persistence and unparalleled innovation, they transformed the heart of this system - the telephone - into the cornerstone of a communications revolution.
Today's messengers are electricity, laser-produced light beams, and microwaves. They carry images, computer data, and conversations with unprecedented accuracy and reliability at lightning speed. The telephone is now the gateway to the fax machine and the Internet for millions, and the tool that connects friends and family conveniently and economically, no matter where in the world they may be. The technical challenges faced and met by engineers to achieve these feats have been formidable, and they weave an interesting story of trial and error.
Long-distance technology had arrived in 1892 with the invention of a signal amplifier, but many innovations were necessary before telephoning would truly cover long distances. The triode vacuum tube, invented in 1906 by American Lee De Forest, further amplified electrical signals to make long distance feasible, and the use of the loading coil, which connected to the cable every mile or so, increased speaking ranges to approximately 1,000 miles. Plans to connect the east and west coasts of the United States began in 1914 and the job was completed a year later.
The technical focus for the next several decades was on improving transmission quality and expanding automatic switching systems. Innovations included high quality insulated wire and coaxial cable technology. High-reliability vacuum-tube circuits and coaxial cable vastly improved the transmission quality in an undersea cable that linked North America and Europe. Improved automatic-switching systems included direct distance dialing, which further reduced the need for operators.
From the 1970s on, as computer and electronics technology developed, engineers began transforming the telephone into an invaluable multifunctional tool. They added features like call forwarding and call waiting, caller ID, automatic answering and message-recording, stored numbers, and others.
Most recently, laser and fiber optic technology has made a dramatic difference in the efficiency of the telephone system. In 1975 engineers developed the first commercial continuous-wave semiconductor laser. Smaller than a grain of sand, this remarkable device made it possible to transmit optically encoded telephone conversations over fiber-optic cables. Today, a single optical fiber combined with amplifiers can carry tens of millions of phone conversations in one thousandth of a second.
Other new technologies are transforming the global telephone system. New digital exchanges route some 1.5 million calls per hour through a vast array of cables, optical fibers, and radio and microwave links. The switch from analog systems to digital has overcome many of the problems associated with sending electrical signals over long distances, such as noise, distortion, and weakening of signals.
In remote places in India and Africa, the use of solar cells is now making it possible to introduce phones without a large-scale electrical distribution system. As the developing world becomes more technologically advanced, these countries will be able to leapfrog early technologies and take immediate advantage of the new systems. Indeed, many nations are already doing so with digital satellite downloading.
Mobile phones were introduced in St. Louis in 1945, but the technology wasn't fully developed until recently. Today, hexagonal base stations are central to cellular phones. Every 15 minutes each base station beams out a message asking all the activated handsets within its cell to report in. This enables the central computers to know where to route a call when a handset is phoned. Systems that use radio waves for transmission via a network of satellites and terrestrial-based antennas allow people to use a digital telephone anywhere on Earth.
By 1915, it had taken 39 years to go from a single telephone in Boston to 11 million nationwide. Today, estimates put that number closer to 200 million, plus an additional 80 million cell phones. Thomas Edison noted then that the invention had "annihilated time and space, and brought the human family in closer touch." The most dramatic changes in access time, distance, line capacity, and clarity have occurred in the last quarter of this century. What would Edison think of human potential now?
