Telephone
A telephone, colloquially referred to as a phone, is a telecommunications device that enables two or more users to conduct a conversation when they are too far apart to be easily heard directly.
The essential elements of a telephone are a microphone (transmitter) to speak into and an earphone (receiver) which reproduces the voice at a distant location.
In later decades, the analog cellular system evolved into digital networks with greater capability and lower cost.
Convergence in communication services has provided a broad spectrum of capabilities in cell phones, including mobile computing, giving rise to the smartphone, the dominant type of telephone in the world today.
As with other influential inventions such as radio, television, the light bulb, and the computer, several inventors pioneered experimental work on voice transmission over a wire and improved on each other's ideas.
Charles Bourseul, Antonio Meucci, Johann Philipp Reis, Alexander Graham Bell, and Elisha Gray, amongst others, have all been credited with the invention of the telephone.
The sound-powered dynamic variants survived in small numbers through the 20th century in military and maritime applications, where its ability to create its own electrical power was crucial.
Early telephones used a single wire for the subscriber's line, with ground return used to complete the circuit (as used in telegraphs).
The earliest dynamic telephones also had only one port opening for sound, with the user alternately listening and speaking (or rather, shouting) into the same hole.
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 in appreciating the potential.
Some local farming communities that were not connected to the main networks set up barbed wire telephone lines that exploited the existing system of field fences to transmit the signal.
Disadvantages of single-wire operation such as crosstalk and hum from nearby AC power wires had already led to the use of twisted pairs and, for long-distance telephones, four-wire circuits.
[21] What turned out to be the most popular and longest-lasting physical style of telephone was introduced in the early 20th century, including Bell's 202-type desk set.
[24] Stations are usually connected via twisted pair wires to reduce electrical interference, and can be positioned at considerable distances from each other in the order of several kilometers.
Using 1mm core diameter twisted-pair wiring, some sound-powered telephone systems can operate a pair of handsets positioned up to 48km (30 miles) apart.
They are often used for communications in airports, railways and public utilities, mining, ski slopes, bridges, sporting arenas and shipyards.
Because they operate at low voltages, they are suitable for use in situations where there is a risk of explosions or fire, such as chemical plants, oil and gas works, arsenals, mines and quarries.
The customer equipment may be an analog telephone adapter (ATA) which translates the signals of a conventional analog telephone; an IP Phone, a dedicated standalone device; or a computer softphone application, utilizing the microphone and headset devices of a personal computer or smartphone.
Base stations include a radio transceiver which enables full-duplex, outgoing and incoming signals and speech with the handsets.
The base station often includes a microphone, audio amplifier, and a loudspeaker to enable hands-free speakerphone conversations, without needing to use a handset.
[39] Over time, these networks evolved, with each new generation (2G, 3G, 4G, and beyond) offering improved data transmission capabilities and more advanced features for mobile communication.
These include text messaging, calendars, alarm clocks, personal schedulers, cameras, music players, games and later, internet access and smartphone functionality.
As their functionality has increased over the years, many types of mobile phone, notably smartphones, require an operating system to run.
[40][41] Before the era of smartphones, mobile phones were generally manufactured by companies specializing in telecommunications equipment, such as Nokia, Motorola, and Ericsson.
Since the advent of smartphones, mobile phone manufacturers have also included consumer electronics companies, such as Apple, Samsung and Xiaomi.
Smartphones offer the ability to access internet data through the cellular network and via wi-fi, and usually allow direct connectivity to other devices via Bluetooth or a wired interface, such as USB or Lightning connectors.
Typically, smartphones feature such tools as cameras, media players, web browsers, email clients, interactive maps, satellite navigation and a variety of sensors, such as a compass, accelerometers and GPS receivers.
Therefore, they can work in most geographic locations on the Earth's surface, as long as open sky and the line-of-sight between the phone and the satellite is provided.
Satellite phones provide similar functionality to terrestrial mobile telephones; voice calling, text messaging, and low-bandwidth Internet access are supported through most systems.
Satellite phones are popular on expeditions into remote locations, hunting, fishing, maritime sector, humanitarian missions, business trips, and mining in hard-to-reach areas, where there is no reliable cellular service.
