Telephone

Telephone list for Brno City Municipality

---

Speech currents passing through the coils vary the attraction of the permanent magnet for the diaphragm, causing it to vibrate and produce sound waves. Through the years the design of the electromagnetic system has been continuously improved. In the most common type of receiver, introduced in the Bell system in , the diaphragm, consisting of a central cone attached to a ring-shaped armature , is driven as a piston to obtain efficient response over a wide frequency range.

Telephone receivers are designed to have an accurate response to tones with frequencies of to 3, hertz—a dynamic range that is narrower than the capabilities of the human ear but sufficient to reproduce normal speech. The anti-sidetone circuit is an assemblage of transformers, resistors, and capacitors that perform a number of functions.

The anti-sidetone circuit accomplishes this reduction by interposing a transformer between the transmitter circuit and the receiver circuit and by splitting the transmitter signals along two paths. When the divided signals, having opposite polarities, meet at the transformer, they almost entirely cancel each other in crossing to the receiver circuit. The speech signal coming from the other end of the line, on the other hand, arrives at the transformer along a single, undivided path and crosses the transformer unimpeded.

Impedance matching allows a more efficient flow of current through the system. Beginning in the early 19th century, several inventors made a number of attempts to transmit sound by electric means. The first inventor to suggest that sound could be transmitted electrically was a Frenchman, Charles Bourseul, who indicated that a diaphragm making and breaking contact with an electrode might be used for this purpose.

In the s Italian American inventor Antonio Meucci had electrical devices in his home called telettrofoni that he used to communicate between rooms, though he did not patent his inventions. By Johann Philipp Reis of Germany had designed several instruments for the transmission of sound. The transmitter Reis employed consisted of a membrane with a metallic strip that would intermittently contact a metallic point connected to an electrical circuit.

As sound waves impinged on the membrane, making the membrane vibrate, the circuit would be connected and interrupted at the same rate as the frequency of the sound. The fluctuating electric current thus generated would be transmitted by wire to a receiver, which consisted of an iron needle that was surrounded by the coil of an electromagnet and connected to a sounding box. The fluctuating electric current would generate varying magnetic fields in the coil, and these in turn would force the iron needle to produce vibrations in the sounding box.

In the s two American inventors, Elisha Gray and Alexander Graham Bell , each independently, designed devices that could transmit speech electrically. An electromagnetic coil was located near each of the reeds. When a reed in the transmitter was vibrated by sound waves of its resonant frequency—for example, hertz—it induced an electric current of corresponding frequency in its matching coil. Thus, simple tones could be transmitted. In the spring of Gray realized that a receiver consisting of a single steel diaphragm in front of an electromagnet could reproduce any of the transmitted tones.

Gray, however, was initially unable to conceive of a transmitter that would transmit complex speech vibrations and instead chose to demonstrate the transmission of tones via his telegraphic device in the summer of However, since Bell too had no transmitter, the membrane device was never constructed. Following some earlier experiments, Bell postulated that, if two membrane receivers were connected electrically, a sound wave that caused one membrane to vibrate would induce a voltage in the electromagnetic coil that would in turn cause the other membrane to vibrate.

Working with a young machinist, Thomas Augustus Watson , Bell had two such instruments constructed in June An application for a U. Several hours later that same day, Gray filed a caveat on the concept of a telephone transmitter and receiver. A caveat was a confidential , formal declaration by an inventor to the U. Patent Office of an intent to file a patent on an idea yet to be perfected; it was intended to prevent the idea from being used by other inventors. At this point neither Gray nor Bell had yet constructed a working telephone that could convey speech.

On March 7, , Bell was awarded U. This patent is often referred to as the most valuable ever issued by the U. Patent Office, as it described not only the telephone instrument but also the concept of a telephone system. Gray had earlier come up with an idea for a transmitter in which a moving membrane was attached to an electrically conductive rod immersed in an acidic solution.

Another conductive rod was immersed in the solution, and, as sound waves impinged on the membrane, the two rods would move with respect to each other. Variations in the distance between the two rods would produce variations in electric resistance and, hence, variations in the electric current. In contrast to the magnetic coil type of transmitter, the variable-resistance transmitter could actually amplify the transmitted sound, permitting use of longer cables between the transmitter and the receiver.

Watson—come here—I want to see you. One of the earliest demonstrations occurred in June at the Centennial Exposition in Philadelphia.

Further tests and refinement of equipment followed shortly afterward. On October 9, , Bell conducted a two-way test of his telephone over a 5-km 2-mile distance between Boston and Cambridgeport, Massachusetts. In May the first commercial application of the telephone took place with the installation of telephones in offices of customers of the E.

Holmes burglar alarm company. The poor performance of early telephone transmitters prompted a number of inventors to pursue further work in this area. Among them was Thomas Alva Edison , whose design for a voice transmitter consisted of a cavity filled with granules of carbonized anthracite coal. The carbon granules were confined between two electrodes through which a constant electric current was passed.

One of the electrodes was attached to a thin iron diaphragm, and, as sound waves forced the diaphragm to vibrate, the carbon granules were alternately compressed and released. As the distance across the granules fluctuated, resistance to the electric current also fluctuated, and the resulting variations in current were transmitted to the receiver.

The telephone instrument continued to evolve over time, as can be illustrated by the succession of American instruments described below. The concept of mounting both the transmitter and the receiver in the same handle appeared in in instruments designed for use by telephone operators in a New York City exchange. The earliest telephone instrument to see common use was introduced by Charles Williams, Jr.

Designed for wall mounting, this instrument consisted of a ringer, a hand-cranked magneto for generating a ringing voltage in a distant instrument , a hand receiver, a switch hook, and a transmitter. Various versions of this telephone instrument remained in use throughout the United States as late as the s. As is noted in the section Switching , the telephone dial originated with automatic telephone switching systems in Desk instruments were first constructed in Patterned after the wall-mounted telephone, they usually consisted of a separate receiver and transmitter.

The ringer and much of the telephone electronics remained in a separate box, on which the transmitter-receiver handle was cradled when not in use. The first telephone to incorporate all the components of the station apparatus into one instrument was the so-called combined set of Need a new phone for home? You can find a phone that suits your home decor too, with a variety of styles and colours available beyond the standard white or black finishes.

Shop our telephone accessories range for extention kits and adaptors. If you need a phone for on the go we can help you out too. We have Android tablets from the budget to the high spec. As well as being a media system and internet browsing device you can easily get productive on a tablet thanks to the ever-expanding range of powerful apps. And for those of you that need a bit more processing power we also have desktop PCs. Argos logo — link to home page. 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.

The Edison patents kept the Bell monopoly viable into the 20th century, by which time the network was more important than the instrument. Early telephones were locally powered, using either a dynamic transmitter or by the powering of a transmitter with a local battery.

Navigation menu

One of the jobs of outside plant personnel was to visit each telephone periodically to inspect the battery. During the 20th century, telephones powered from the telephone exchange over the same wires that carried the voice signals became common. Early telephones used a single wire for the subscriber's line, with ground return used to complete the circuit as used in telegraphs.

Working components of the telephone

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. Sometimes the instruments were operated in pairs at each end, making conversation more convenient but also more expensive.

The telephone instrument

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 in appreciating the potential.

Signalling began in an appropriately primitive manner. The user alerted the other end, or the exchange operator , by whistling into the transmitter. Exchange operation soon resulted in telephones being equipped with a bell in a ringer box , first operated over a second wire, and later over the same wire, but with a condenser capacitor in series with the bell coil to allow the AC ringer signal through while still blocking DC keeping the phone " on hook ".

Telephones connected to the earliest Strowger switch automatic exchanges had seven wires, one for the knife switch , one for each telegraph key , one for the bell, one for the push-button and two for speaking. Large wall telephones in the early 20th century usually incorporated the bell, and separate bell boxes for desk phones dwindled away in the middle of the century. Rural and other telephones that were not on a common battery exchange had a magneto 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 networks set up barbed wire telephone lines that exploited the existing system of field fences to transmit the signal. In the s 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 required the user to operate a separate switch to connect either the voice or the bell.

With the new kind, the user was 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 ". 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 wires had already led to the use of twisted pairs and, for long distance telephones, four-wire circuits.

Users at the beginning of the 20th century did not place long distance calls from their own telephones but made an appointment to use a special soundproofed long distance telephone booth furnished with the latest technology. 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 type desk set. A carbon granule transmitter and electromagnetic receiver were united in a single molded plastic handle, which when not in use sat in a cradle in the base unit. The circuit diagram of the model shows the direct connection of the transmitter to the line, while the receiver was induction coupled.

In local battery configurations, when the local loop was too long to provide sufficient current from the exchange, the transmitter was powered by a local battery and inductively coupled, while the receiver was included in the local loop. The dial switch in the base interrupted the line current by repeatedly but very briefly disconnecting the line 1 to 10 times for each digit, and the hook switch in the center of the circuit diagram disconnected the line and the transmitter battery while the handset was on the cradle.

In the s, telephone sets were developed that combined the bell and induction coil with the desk set, obviating a separate ringer box. The rotary dial becoming commonplace in the s in many areas enabled customer-dialed service, but some magneto systems remained even into the s.

After World War II, the telephone networks saw rapid expansion and more efficient telephone sets, such as the model telephone in the United States, were developed that permitted larger local networks centered around central offices. Ericsson DBH ca. Modern sound-powered emergency telephone. One type of mobile phone , called a cell phone. The invention of the transistor in dramatically changed the technology used in telephone systems and in the long-distance transmission networks.

With the development of electronic switching systems in the s, telephony gradually evolved towards digital telephony which improved the capacity, quality, and cost of the network. The development of digital data communications method, such as the protocols used for the Internet , it became possible to digitize voice and transmit it as real-time data across computer networks , giving rise to the field of Internet Protocol IP telephony, also known as voice over Internet Protocol VoIP , a term that reflects the methodology memorably.

VoIP has proven to be a disruptive technology that is rapidly replacing traditional telephone network infrastructure.

How Telephones Work

A January Newsweek article suggested that Internet telephony may be "the next big thing. From a customer perspective, IP telephony uses a high-bandwidth Internet connection and specialized customer premises equipment to transmit telephone calls via the Internet, or any modern private data network. The customer equipment may be an analog telephone adapter ATA which interfaces a conventional analog telephone to the IP networking equipment, or it may be an IP Phone that has the networking and interface technology built into the desk-top set and provides the traditional, familiar parts of a telephone, the handset, the dial or keypad, and a ringer in a package that usually resembles a standard telephone set.

In addition, many computer software vendors and telephony operators provide softphone application software that emulates a telephone by use of an attached microphone and audio headset, or loud speaker. Despite the new features and conveniences of IP telephones, some may have notable disadvantages compared to traditional telephones.

Unless the IP telephone's components are backed up with an uninterruptible power supply or other emergency power source, the phone ceases to function during a power outage as can occur during an emergency or disaster when the phone is most needed. Traditional phones connected to the older PSTN network do not experience that problem since they are powered by the telephone company's battery supply, which will continue to function even if there is a prolonged power outage. Another problem in Internet-based services is the lack of a fixed physical location, impacting the provisioning of emergency services such as police, fire or ambulance, should someone call for them.

Unless the registered user updates the IP phone's physical address location after moving to a new residence, emergency services can be, and have been, dispatched to the wrong location. From Wikipedia, the free encyclopedia. For other uses, see Telephone disambiguation. For other uses, see Phone disambiguation. For the handheld personal computer, see Smartphone.

• Imagerie musculosquelettique : pathologies générales (French Edition)
• Tren a Puigcerdà (Catalan Edition)
• Hunter´s Song - Piano
• Kokosöl-Natürliches Mittel für Hautprobleme, Übergewicht, gesundes Haar und eine optimale Gesundheit (German Edition)
• Our Same Word
• La peur sans mémoire : T3 - Men who walk the edge of honor (French Edition)
• My Cat Does My Homework and Other Poems for Children