The First Commercial Instruments

The first telephones were technically diverse. Some have used a transmitter of liquid, some had a metal diaphragm which induces a current in the solenoid wound around a permanent magnet, and others were "dynamic" - their membrane vibration of a coil of wire in the field of a permanent magnet or the coil vibrate the diaphragm. Sound-powered dynamic type survived in small amounts throughout the 20th century in military and maritime applications where its ability to create its own electrical power was crucial. Most, however, used the Edison / Berliner carbon transmitter, which was much stronger than the other, even though it required an induction coil which was an impedance matching transformer to make it compatible with the impedance of the line. Edison patents kept the Bell monopoly viable into the 20th century, when the network is more important than the instrument.

Early telephones were locally made using either a dynamic transmitter or by the powering of a transmitter with a local battery. One of the tasks of outside plant personnel was to visit each telephone periodically to inspect the battery. During the 20th century, "common battery" operation came to dominate, powered by "talk battery" from the telephone exchange over the same wires that carry voice signals.

The first telephones used a single wire for the subscriber's line, with ground return used to complete the circuit (as used in telegraphs). The first mobile dynamic also had one port opening for sound, with the user alternately listening and speaking (or rather, shouting) into the same hole. Sometimes the instruments were operated in pairs at each end, making conversation easier, but also more expensive.

At first, the benefits of a telephone exchange were not exploited. Instead telephones were leased in pairs to a subscriber, who had to arrange for a telegraph contractor to construct a line between them, for example between a home and a shop. Users who wanted the ability to speak to several different locations would need to obtain and set up three or four pairs of telephones. Western Union, already using telegraph exchanges, quickly extended the principle to its telephones in New York City and San Francisco, and Bell was not slow to appreciate the potential.

Signaling began appropriately primitive. The user alerted the other end, or the exchange operator, by whistling into the transmitter. Foreign exchange transaction soon resulted in cell being equipped with a bell in a box ring, initially operated by a second wire, and later on the same wire, but with a capacitor (condenser) in series with the coil bell to allow the AC ringer signal through while still blocking DC (keeping the phone "on hook"). Phones connected to the first Strowger automatic exchanges had seven son, one for the knife switch, one for each telegraph key, one for the bell, one for the push-button and two for speaking. Mobile Great Wall in the early 20th century usually incorporated the bell, and separate bell boxes for desk phones narrowed the gap in the middle of the century.

Rural telephony and others who were not on a common battery exchange had a magneto or hand-cranked generator to produce a high voltage alternating signal to ring the bells of other telephones on the line and to alert the operator . Some local farming communities that were not connected to the main network set up barbed wire telephone lines that have exploited the current system of fences field to transmit the signal.

In the 1890 a new smaller style of telephone was introduced, packaged in three parts. The transmitter stood on a stand, known as a "candlestick" for its shape. When not in use, the receiver hung on a hook with a switch in it, known as a "switchhook." Previous telephones necessary for the user to operate a separate switch to connect either the voice or the bell. With the new kind, the user is less likely to leave the phone "off the hook". In phones connected to magneto exchanges, the bell, induction coil, battery and magneto were in a separate bell box or "ringer box". In phones connected to common battery exchanges, the box bell was installed in an office or any other place out of the way, because it does not need a battery or magneto.

Cradle designs were also used at this time, having a handle with the receiver and transmitter attached, now called a handset, separate from the cradle base that housed the magneto crank and other parts. They were larger than the "candlestick" and more popular.

Disadvantages of single wire operation such as crosstalk and hum from nearby AC power son had already led to the use of twisted pairs and, for long distance telephones, four circuits son. Users in the early 20th century did not place long distance calls from their own telephones but made an appointment to use a special test its long distance telephone booth furnished with the latest technology.

This proved to be the most popular and longest lasting physical style of telephone was introduced in the early 20th century, including Bell Model 102. A transmitter of carbon granules and an electromagnetic receiver are united in a single molded plastic handle, which is not used when sitting in a cradle in the base unit. The wiring diagram model 102 shows the direct connection of the receiver to the line, while the transmitter was induction coupled with the energy supplied by a local battery. The coupling transformer, battery, and ringer were in a separate envelope. The mode dial at the base of the line current by repeatedly interrupted very briefly disconnecting the line 1-10 times for each digit, and the hook switch (in the center of the diagram) disconnected the line the transmitter battery while the phone was out of the cradle.

After the 1930 the base also enclosed the bell and induction coil, which avoids the distinctive ring box old. Power was supplied to each subscriber line by central office batteries instead of a local battery, which required periodic maintenance. For the next half century, the network behind the telephone became progressively larger and much more efficient, but after the phone was added the instrument itself changed little until American Telephone & Telegraph Company (AT & T) introduced touch-tone dialing in the 1960.