When did the first transmission of speech occur with a telephone?
A telephone is a device that allows for the simultaneous sending and receiving of human speech. In addition to being affordable and easy to use, telephones provide a quick and intimate means of contact. There are billions of phones in use worldwide.
When was the telephone patented?
Alexander Graham Bell filed for a telephone patent in the United States on February 14, 1876. Bell was granted U.S. Patent 174,465 on March 7, 1876. Given that it covered both the telephone instrument and the idea of a telephone system, this patent is frequently referred to as the most valuable ever to be granted by the U.S. Patent Office.
When was the telephone introduced to the public?
At the Philadelphia Centennial Exposition in June 1876, one of the first telephone demonstrations took place.
Who is credited as the inventor of the telephone?
Since he was granted the first patent, Alexander Graham Bell is recognized as the person who invented the telephone.
When did the first transmission of speech occur with a telephone?
Alexander Graham Bell and Thomas Watson exchanged speech via a telephone on March 10, 1876, and Bell recorded the conversation in his lab notes, writing, "Mr. Watson—come here—I want to see you."
Telephone: a device intended to transmit and receive human speech simultaneously. The telephone is an instantaneous, personal form of communication that cannot be attained through any other medium. It is also economical and easy to use. It has thus emerged as the most extensively utilized telecommunications gadget globally. There are billions of phones in use worldwide.
Working Components of the Telephone
The telephone instrument consists of the same functional parts that it has had since its inception: a power supply, a switch hook, a dialer, a ringer, a transmitter, a receiver, and an anti-sidetone circuit. Each of these elements is explained in turn below.
Power Source
The electric current used to power the telephone circuit in the early experimental phones was produced at the transmitter by an electromagnet that was triggered by the speaker's voice. Bell's patented design was the first to build a transmitter that functioned on a direct current supplied by a separate power source. This was because the system would not be able to generate enough voltage to produce audible speech in remote receivers. Batteries found within telephone instruments served as the initial sources, but since the 1890s, the local switching office has been the source of current generation. The local loop, a two-wire circuit, is used to supply the current. 48 volts is the standard voltage.
Since the little battery inside the portable phone powers the low-wattage radio transmitters, cordless phones signify a return to individual power sources. The battery of the phone gets refilled via contacts with the base unit while it is not in use. A transformer connected to a regular electrical outlet powers the base unit.
Switch hook
The telephone instrument is connected to the direct current source via the local loop by means of the switch hook. The receiver on an early telephone was hanging on a hook, and it opened and closed a metal contact to activate the switch. This technique is still widely used, but instead of the hook, the combined handset—which encloses the transmitter and receiver—is held on a cradle. Transistor relays have taken the place of metal contacts' mechanical action in certain contemporary electronic devices.
Contact with the local loop is lost when the phone is "on hook." Current passes through the loop and contact is restored when it is off hook. The switching office uses a
low-frequency "dial tone"—actually, two simultaneous tones at 350 and 440 hertz—to indicate that contact has been restored.
Dialer
The user enters the party's number they want to call using the dialer. The dialer generates signals that turn on switches at the local office, creating a transmission line to the person being phoned. There are two types of dialers: rotary and push-button.
Developed in the 1890s, the conventional rotary dialer revolves against a spring's tension before being released, at which point it returns to its initial position at a speed managed by a mechanical governor. Direct current to the switching office is interrupted, or pulsed, by the return rotation of a switch, which causes the switch to open and close. The duration of each pulse is roughly one-tenth of a second, and the quantity of pulses indicates the number being called.
The 1960s saw the introduction of push-button dialing, in which hitting a button produces a "dual-tone" signal unique to the number being entered. The switching office detects and decodes the low and high frequencies that make up each dual tone. Dual tones, as opposed to low-frequency rotary pulses, are able to pass through the telephone system, enabling automated features to be activated at the other end of the line using push-button phones.
A capacitor and resistor stop dialing signals from entering the ringer circuit in both push-button and rotary systems.
Ringer
The ringer sounds an audible tone or ring to notify the user that a call is coming in. There are two kinds of ringers: electronic and mechanical. The switching office generates a 20-hertz, 75-volt alternating current that activates both types. Typically, the ringer is turned on in two-second bursts, interrupted by four-second pauses.
With the introduction of the early Bell telephones came the traditional mechanical ringer. It is made up of a magnet, a metal clapper, and two bells that are near to one another. When an alternating current flows through a coil of wire, the magnetic attraction applied to the clapper changes, causing it to vibrate loudly and quickly against the bells. A switch that presses a mechanical damper against the bells mutes the volume.
The ringer current in contemporary electronic ringers, which were first developed in the 1980s, is routed via an oscillator, which modifies the current to precisely the frequency needed to activate a piezoelectric transducer, which is an apparatus composed of a crystalline substance that vibrates in response to an electric current. It is possible to connect the transducer to a tiny loudspeaker that has volume control.
The telephone is on hook, but the ringer circuit stays linked to the local loop. Because the ringer circuit is designed with a high electrical impedance to prevent draining power from the transmitter-receiver circuit when the telephone is in use, a higher voltage is required to activate the ringer. After the handset has been turned on, a capacitor stops direct current from going through the ringer.
Sender
The transmitter, which is housed in the mouthpiece of the phone handset, is basically a tiny microphone. It transforms the speaker's vocal vibrations into changes in the direct current that the power supply sends through the set.
A fixed electrode and a diaphragm-activated electrode are separated by a thin layer of carbon granules in conventional carbon transmitters, which were created in the 1880s. The carbon conducts electricity against a specific resistance. The movable electrode is forced to apply varying pressure to the carbon layer as a result of the diaphragm vibrating in response to the speaker's voice. The electrical resistance of the carbon layer varies with changes in the carbon layer, which in turn causes variations in the electric current.
The carbon layer is swapped out in contemporary electret transmitters, which date back to the 1970s, for a thin plastic sheet with a conductive metallic coating on one side. An electric field is maintained between that coating and another metal electrode by the plastic. Speech-induced vibrations cause the electric field to fluctuate, which causes slight voltage differences. In order to be transmitted over the phone line, the voltages are amplified.
Receiver
The telephone's handset's earpiece houses the receiver. It reproduces human speech by converting fluctuating electric current into sound waves using electromagnetic concepts that were understood in Bell's day. It is made up of two main components: a permanent magnet with pole pieces coiled with insulated fine wire coils and a diaphragm powered by magnetic material placed close to the pole pieces. The speech currents that flow
through the coils alter the diaphragm's permanent magnet's attraction, allowing it to vibrate and emit sound waves.
The electromagnetic system's design has been continuously enhanced over time. The most popular kind of receiver was first used in the Bell system in 1951. Its diaphragm, which is made up of an armature with a ring form and a central cone attached, is pushed like a piston to provide effective response over a large frequency range. In order to mimic natural speech, telephone receivers are made to respond accurately to tones with frequencies between 350 and 3,500 hertz, which is a smaller dynamic range than what the human ear can detect.
Anti-sidetone circuit
The transformers, resistors, and capacitors that make up the anti-sidetone circuit serve a variety of purposes. The main purpose is to lessen sidetone, the annoying sound that comes from the speaker's voice as it passes from the transmitter via the receiver. By placing a transformer between the transmitter and reception circuits and dividing the transmitter signals into two channels, the anti-sidetone circuit reduces the ringing. Nearly all of the divided signals with opposing polarities cancel each other out as they cross over to the reception circuit at the transformer. Conversely, the speech signal from the other end of the line travels a single, uninterrupted path to reach the transformer and passes through it without any problems.
The low electrical impedance of the telephone instrument's circuits and the greater electrical impedance of the telephone line are matched by the anti-sidetone circuit. Impedance matching makes it possible for the system's current to flow more effectively.
Creation of the Telephone Device
Earliest Audio Transmitters
A number of inventors tried their hand at electric sound transmission starting in the early 1800s. Charles Bourseul, a French inventor, was the first to propose that sound could be transferred electrically. He suggested that this could be accomplished by using a diaphragm that made and broke contact with an electrode. Although he did not receive a
patent for his innovations, Italian American inventor Antonio Meucci employed electrical devices called teletrofono in his home during the 1850s to communicate between rooms. German inventor Johann Philipp Reis created a number of sound-transmission devices before 1861. Reis's transmitter was a membrane with a metallic strip that was attached to an electrical circuit and would periodically make contact with a metallic point.The circuit would connect and disconnect at the same rate as the sound's frequency as sound waves impinged on the membrane and caused it to vibrate. The resulting variable electric current would be sent by wire to a receiver, which consisted of an iron needle attached to a sounding box and encircled by an electromagnet coil. The coil's changing magnetic fields, caused by the erratic electric current, would compel the iron needle to vibrate inside the sounding box. Thus, Reis's device was able to send a basic tone but was unable to replicate the intricate waveforms involved in speech.
Gray and Bell: Speech Transmission
The Initial Gadgets
Elisha Gray and Alexander Graham Bell, two American innovators, separately created devices that could transmit speech electrically in the 1870s. A collection of metallic reeds adjusted to various frequencies served as the transmitter and receiver of Gray's first invention, a harmonic telegraph. Every reed had an electromagnetic coil next to it. Sound waves at the transmitter's resonance frequency, 400 hertz, for example, caused a reed to vibrate, which in turn caused an electric current in the matching coil to flow at the same frequency. All the coils in the receiver were connected to this coil, but only the reed tuned to the frequency of the transmitting reed would vibrate in response to the electric current. Simple tones could be communicated.
Bell, on the other hand, had also thought of employing the harmonic telegraph concept for speech transmission, and in the summer of 1874, he developed an analogous membrane receiver to Gray's. But Bell didn't have a transmitter either, thus the membrane device was never built. Bell proposed, based on some previous tests, that if two membrane receivers were electrically connected, a sound wave causing one membrane to vibrate would cause an electromagnetic coil to generate a voltage, which would then force the other membrane to vibrate. Together with a young machinist named Thomas Augustus Watson, Bell ordered the construction of two of these instruments in June 1875. On June 3, 1875, the apparatus was tested; while no comprehensible words were sent, "speechlike" sounds were audible at the other end.
Two hours before Elisha Gray's rival device was announced, on February 14, 1876, Alexander Graham Bell filed the telephone patent at the USPTO. The phone for Bell is located on the table to the right.On February 14, 1876, a U.S. patent application based on Bell's work was submitted. Gray filed a disclaimer on the idea of a telephone transmitter and receiver a few hours later that same day. An inventor who wants to keep an idea undeveloped from being used by others would submit a formal, secret declaration to the U.S. Patent Office stating that they intended to file a patent on it. This document was known as a caveat. Neither Bell nor Gray had succeeded in building a functional phone that could transmit speech at this time. Gray's caveat was overruled and Bell's patent application approved due to its earlier filing date. Bell was granted U.S. Patent 174,465 on March 7, 1876. Given that it covered both the telephone instrument and the idea of a telephone system, this patent is frequently referred to as the most valuable ever to be granted by the U.S. Patent Office.
The Quest for an Effective Transmitter
Gray had previously developed a transmitter concept that involved attaching a moving membrane to an electrically conducting rod that was submerged in an acidic solution. When sound waves struck the membrane, a second conductive rod submerged in the fluid would move in relation to one another. Changes in the two rods' distance from one another would result in changes in electric resistance and, ultimately, in changes in the electric current. Longer cables could be used between the transmitter and the receiver since the variable-resistance transmitter had the ability to really enhance the sound broadcast, unlike the magnetic coil kind of transmitter.
Once more, Bell developed a similar "liquid" transmitter concept. Bell was able to transmit voice to Watson for the first time on March 10, 1876, using this device, which he recorded in his lab notes as "Mr. Watson—come here—I want to see you." Shortly afterward, the telephone was first shown in public. Its design was reminiscent of the previous magnetic coil membrane units previously mentioned. At the Philadelphia Centennial Exposition in June 1876, one of the first protests took place. Shortly after, more testing and equipment improvement took place. Bell tested his telephone in both directions on October 9, 1876, covering a distance of 5 kilometers (2 miles) between Cambridgeport, Massachusetts, and Boston. The first telephone to be used for commerce
was installed in May 1877 when phones were installed in the offices of clients of the E.T. Holmes burglar alarm firm.
Several innovators decided to continue their research in this field because of the inadequate performance of the first telephone transmitters. One of them was Thomas Alva Edison, whose voice transmitter design from 1886 had a chamber filled with carbonized anthracite coal grains. A steady electric current was run between the two electrodes, which contained the carbon granules.A thin iron diaphragm was fixed to one of the electrodes, and as sound waves caused the diaphragm to vibrate, the carbon granules were compressed and released alternately. Variations in resistance to the electric current resulted from variations in the distance across the granules, and these variations in current were relayed to the receiver. Because Edison's carbon transmitter was so straightforward, affordable, long-lasting, and efficient, it served as the model for all subsequent telephone transmitter designs up until the 1970s.
Development of the Modern Instrument
The series of American instruments that follow serve as examples of how the telephone instrument changed over time. The idea of putting the transmitter and receiver in the same handle first surfaced in devices made for New York City exchange telephone operators in 1878. Charles Williams, Jr. introduced the first telephone apparatus into widespread usage in 1882. This device, which was meant to be mounted on the wall, included a hand-cranked magneto (used to produce a ringing voltage in a different device), a hand receiver, a switch hook, and a transmitter.As late as the 1950s, different iterations of this telephone device were still in use across the country. The telephone dial began with automatic telephone switching systems in 1896, as mentioned in the section on switching.
The first desk instruments were made in 1897. They were designed to resemble wall-mounted telephones and often had a separate transmitter and receiver. But the combined transmitter-receiver E1A handset, released by the American Telephone & Telegraph Company (AT&T) in 1927, changed all of that.When not in use, the transmitter-receiver handle was restrained on a separate box that housed the majority of the telephone circuitry and the ringing. The so-called combination set of 1937 was the first telephone to merge every part of the station machinery into a single device. There were over 25 million of these instruments made before a new design took their place in
1949. With notable advancements in audio quality, mechanical design, and physical construction, the 1949 telephone was an entirely new device. In 1963, push-button versions of this set were introduced.The telephone dial has been replaced by a keypad that may typically be set to produce dual-tone signals, akin to AT&T's Touch-Tone system, or pulses resembling those of the dial mechanism. Lastly, the telephone instrument now has a variety of additional features available, such as speed-dialing multiple phone numbers and last-number recall.
Cordless Telephones
In a house or office, cordless telephones replace traditional telephone instruments and allow for extremely restricted movement, up to 100 meters (330 ft). They function as a wireless extension to the current home or business wiring because they communicate with a base unit that is directly inserted into an existing telephone jack. The original cordless phones used two frequencies, 1.7 megahertz and 49 megahertz, using analog modulation techniques. In the late 1990s, phones operating in the 902–928 megahertz band started to appear. Cordless phones first functioned over two frequencies in the 46– and 49–megahertz bands in the 1980s. These phones used spread-spectrum modulation, digital modulation, or analog modulation. These days, some digital cordless phones function in the gigahertz range, such as 5.8 gigahertz. Broadly speaking, consumers have benefited from increased quality and range with every new generation of cordless phones.
Personal Communication Systems
The personal communication system (PCS) is a wireless service that is accessible in several nations across the globe. The term "PCS" refers to all wireless communication methods that are linked to the public switched telephone network, including mobile phones and aeronautical public correspondence systems. However, the fundamental idea behind PCS is that it offers omnipresent service to roaming users, minimal subscriber terminal costs and service fees, and small, light, and discrete personal portable devices.
The second-generation cordless telephony (CT-2) system, which went into operation in the UK in 1991, was the first PCS to be deployed. The CT-2 system was intended to function as a telepoint system from the beginning. When using telepoint systems, a user with a portable unit could dial a base station a few hundred meters away to make calls (but not receive them). The base unit charged subscribers for calls and functioned as a public pay phone connected to the PSTN. The popular GSM digital cellular system
Cordless Telephones
In a house or office, cordless telephones replace traditional telephone instruments and allow for extremely restricted movement, up to 100 meters (330 ft). They function as a wireless extension to the current home or business wiring because they communicate with a base unit that is directly inserted into an existing telephone jack. The original cordless phones used two frequencies, 1.7 megahertz and 49 megahertz, using analog modulation techniques. In the late 1990s, phones operating in the 902–928 megahertz band started to appear. Cordless phones first functioned over two frequencies in the 46– and 49–megahertz bands in the 1980s. These phones used spread-spectrum modulation, digital modulation, or analog modulation. These days, some digital cordless phones function in the gigahertz range, such as 5.8 gigahertz. Broadly speaking, consumers have benefited from increased quality and range with every new generation of cordless phones.
Personal Communication Systems
The personal communication system (PCS) is a wireless service that is accessible in several nations across the globe. The term "PCS" refers to all wireless communication methods that are linked to the public switched telephone network, including mobile phones and aeronautical public correspondence systems. However, the fundamental idea behind PCS is that it offers omnipresent service to roaming users, minimal subscriber terminal costs and service fees, and small, light, and discrete personal portable devices.
The second-generation cordless telephony (CT-2) system, which went into operation in the UK in 1991, was the first PCS to be deployed. The CT-2 system was intended to function as a telepoint system from the beginning. When using telepoint systems, a user with a portable unit could dial a base station a few hundred meters away to make calls (but not receive them). The base unit charged subscribers for calls and functioned as a public pay phone connected to the PSTN. The popular GSM digital cellular system
replaced the CT-2 system, which was rendered obsolete due to its restricted coverage (see mobile telephone).
Concurrently, the DECT (Digital Enhanced Cordless Telecommunications, formerly known as Digital European Cordless Telephone) system of personal communication was being developed by the European Conference on Posts and Telecommunications (CEPT). Originally intended to serve office environments with cordless telephone service, the DECT system's functionality quickly expanded to encompass telepoint services and campus-wide communications. By 1999, DECT accounted for half of the cordless market in Europe.
The Personal Handy-Phone System (PHS), a PCS that was released to the public in Japan in 1994, was partially based on the DECT ideas. The PHS gained traction as a cellular system substitute in urban areas. With the ability to handle data flow at speeds of 32 and 64 kilobits per second, it might serve as a fast wireless modem for Internet access.
The Federal Communications Commission (FCC) in the US offered many licenses in the 1.85–1.99 GHz band for use in PCS applications between 1994 and 1995.
The Telephone Network
Reviewing the steps involved in placing a single call on a conventional wired telephone can aid in understanding the multitude of ideas represented in the public switched telephone network (PSTN). A phone subscriber initiates a call by pulling the phone "off-hook," indicating to the nearby central office that they need service. The dial tone is the response from the central office, which has been continuously monitoring the phone line (a procedure known as attending). The customer enters the phone number of the person being called after hearing the dial tone. The entered number is stored by the central office, which also converts it into the location of the equipment and a path to it. Additionally, the central office verifies if the called party's line is already in use, or "busy." If the number of the called party is located in the same central office, the call is considered intraoffice; if it is located in a different central office, an interoffice call is necessary. The central office switch will manage the call process in its entirety if it is an intra office call. If the call is interoffice, it will be routed across a long-distance network to either a central office that is close by or a central office that is far away. When it comes to interoffice communications, a different signaling network is used to manage the call
flow across numerous switches and phone trunks. The telephone switch will display a busy signal until the called party returns to the "on-hook" state, assuming the call is intraoffice and the called party's line is busy and does not have call waiting (which allows the current call to be suspended). The called party's line will be alerted, or "rung," if it is not busy or if call waiting is available. An audio signal alerting the calling party to the ringing will be sent back at the same time as the line is rang.Ringing will stop and a voice path will be established through the switching system to both the calling and called parties if the called party answers by going off-hook. Until one of the parties gets back on the hook, the voice path is maintained. Call charging is recorded at that point, and the voice path is cut off.
It is clear from the previously given example that telephone networks are made up of four main parts:
1.Switching as needed between trunks and telephone sets.
2.Signaling is done when necessary both between central offices and between telephone sets.
3. Transmission, both within and between central offices and between the central switching office and customers' phone sets.This section goes over each of these key telephone system components one at a time.
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