The Telephone

  
Alexander Graham Bell 
Internet
Satellites
 
 

In 1877, American Alexander Graham Bell realized that producing speech with this method would require a steady electric current. He produced the first device capable of sending and receiving quality, comprehensible human speech. His device consisted of identical transmitters and receivers, which contained flexible metal diaphragms and a horseshoe magnet with a wire coil. Sounds would strike the diaphragm causing vibrations in the magnetic field, which generated a variable electric current that travelled to the receiver where it was reproduced. 

Today’s Telephone 
Early telephones had no dial to automatically connect to your intended location. You had to tell the operator who you wished to talk to, and she (the job of telephone operator was strictly a female occupation) would connect a wire into the required connector on a large switchboard, linking you directly to the telephone. As telephone usage increased, this proved inefficient, and mechanical alternatives were devised. An electronic dial transmitted a unique series of current impulses that were associated by the switching station with a particular telephone, and connected it. 

Today, new telephones have a 12 button keypad. Each row and column sends a specific tone, identified in the diagram included with this article. For example, if you press the 7, the telephone sends signals of 1209 Hz (hertz) and 852 Hz. This replaced rotary dial telephones because it was faster, less prone to errors, and enables the user to input information to a computerized system, such as a voicemail service. There are over 600 million telephone numbers in operation today, allowing you to talk to people all over the world. 

Step by Step 
To talk to someone on the telephone, you pick up the phone’s handset, which lifts the switch hook, forming a direct-current circuit between the phone and a switching centre. When this happens, a relay in the centre closes, indicating your phone is "off the hook". Now anyone who dials your phone will receive a busy signal. The switching centre also sends a steady "dial tone" to your phone to inform you it is ready to handle your call. You dial the phone by pushing the required sequence of buttons. 

In North America, every telephone has a corresponding telephone number. First, there is a one digit International code ("1" in United States and Canada), followed by a three digit area code, then a three digit exchange code, and finally a four digit code representing the actual telephone. If the call is "local" within the same exchange code area as your phone, only the last seven digits of the number are required. 

Each button you dial sends a signal to the switching system. The provide information needed to link you to the appropriate connection. The switching system links to the switching machine that handles the other phone’s connection, choosing the quickest available route along the telephone’s network of phone lines. If the phone you wish to connect to is currently in use, a rapid on/off tone, called a busy signal, is sent to your phone. If you can connect, the other phone will ring to indicate someone is calling. When the person picks up their handset, their switch hook is released, shutting off the ringing current and allowing the sounds on both ends to flow between phones. This complete connection usually takes less only seconds. 

Advances 
Sometimes connecting to far off places can be difficult. In 1927 you could make an overseas call to Europe with a radio-telephone service, but this proved to be expensive. In 1956 technical advancements made it possible for an underwater telephone cable to be placed between Newfoundland, Canada, and Scotland. There are several types of telephone wires used to form the telephone network. Coaxial cable, also used in cable television connections, usually consisting of 22 thin copper tubes sheathed in polyethylene and lead, can handle 132 000 connections at a time. Fibre optic cables, which are made of extremely clear thin glass, use a laser or LED (light-emitting diode) to create tiny beams of light that travel many times faster than electric currents, can handle larger volumes of information. But not all telephone signals travel on wires. Microwave relay stations send data at super-high frequencies through the air in straight lines to other relay stations. Similar technology is implemented on a much larger scale using satellites. 

Future Phones 
While the telephone isn’t becoming obsolete, today there are more two-way communication technologies are being offered to consumers. Large conference centres offer have offered businesses direct video-telephone services for years, and mobile cellular and PCS (Personal Communication System) phones allow people to carry their phone in their pocket where ever they go. New telephone services like voice-mail, call return, and 3-way calling are available in most areas to extend the usefulness of phones, and of course, the Internet, the fastest growing communication technology, is continuing to increase in speed and usefulness, enabling a virtually limitless array of communication applications for millions of users.