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144-470: Radio receivers are essential components of all systems that use radio . The information produced by the receiver may be in the form of sound, video ( television ), or digital data . A radio receiver may be a separate piece of electronic equipment, or an electronic circuit within another device. The most familiar type of radio receiver for most people is a broadcast radio receiver, which reproduces sound transmitted by radio broadcasting stations, historically

288-411: A battery and relay . When the incoming radio wave reduced the resistance of the coherer, the current from the battery flowed through it, turning on the relay to ring a bell or make a mark on a paper tape in a siphon recorder . In order to restore the coherer to its previous nonconducting state to receive the next pulse of radio waves, it had to be tapped mechanically to disturb the metal particles. This

432-471: A directional antenna transmits radio waves in a beam in a particular direction, or receives waves from only one direction. Radio waves travel at the speed of light in vacuum and at slightly lower velocity in air. The other types of electromagnetic waves besides radio waves, infrared , visible light , ultraviolet , X-rays and gamma rays , can also carry information and be used for communication. The wide use of radio waves for telecommunication

576-441: A feedback control system which monitors the average level of the radio signal at the detector, and adjusts the gain of the amplifiers to give the optimum signal level for demodulation. This is called automatic gain control (AGC). AGC can be compared to the dark adaptation mechanism in the human eye ; on entering a dark room the gain of the eye is increased by the iris opening. In its simplest form, an AGC system consists of

720-418: A microphone , a video signal representing moving images from a video camera , or a digital signal consisting of a sequence of bits representing binary data from a computer. The modulation signal is applied to a radio transmitter . In the transmitter, an electronic oscillator generates an alternating current oscillating at a radio frequency , called the carrier wave because it serves to generate

864-497: A radar screen . Doppler radar can measure a moving object's velocity, by measuring the change in frequency of the return radio waves due to the Doppler effect . Radar sets mainly use high frequencies in the microwave bands, because these frequencies create strong reflections from objects the size of vehicles and can be focused into narrow beams with compact antennas. Parabolic (dish) antennas are widely used. In most radars

1008-414: A radio , which receives audio programs intended for public reception transmitted by local radio stations . The sound is reproduced either by a loudspeaker in the radio or an earphone which plugs into a jack on the radio. The radio requires electric power , provided either by batteries inside the radio or a power cord which plugs into an electric outlet . All radios have a volume control to adjust

1152-413: A radio frequency (RF) amplifier to increase its strength to a level sufficient to drive the demodulator; (3) the demodulator recovers the modulation signal (which in broadcast receivers is an audio signal , a voltage oscillating at an audio frequency rate representing the sound waves) from the modulated radio carrier wave ; (4) the modulation signal is amplified further in an audio amplifier , then

1296-575: A rectifier which converts the RF signal to a varying DC level, a lowpass filter to smooth the variations and produce an average level. This is applied as a control signal to an earlier amplifier stage, to control its gain. In a superheterodyne receiver, AGC is usually applied to the IF amplifier , and there may be a second AGC loop to control the gain of the RF amplifier to prevent it from overloading, too. In certain receiver designs such as modern digital receivers,

1440-632: A transmitter connected to an antenna which radiates oscillating electrical energy, often characterized as a wave . They can be received by other antennas connected to a radio receiver ; this is the fundamental principle of radio communication. In addition to communication, radio is used for radar , radio navigation , remote control , remote sensing , and other applications. In radio communication , used in radio and television broadcasting , cell phones, two-way radios , wireless networking , and satellite communication , among numerous other uses, radio waves are used to carry information across space from

1584-409: A wireless modem , is applied as input to a computer or microprocessor , which interacts with human users. In the simplest type of radio receiver, called a tuned radio frequency (TRF) receiver , the three functions above are performed consecutively: (1) the mix of radio signals from the antenna is filtered to extract the signal of the desired transmitter; (2) this oscillating voltage is sent through

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1728-474: A " push to talk " button on their radio which switches off the receiver and switches on the transmitter. Or the radio link may be full duplex , a bidirectional link using two radio channels so both people can talk at the same time, as in a cell phone. One way, unidirectional radio transmission is called simplex . This is radio communication between a spacecraft and an Earth-based ground station, or another spacecraft. Communication with spacecraft involves

1872-627: A Service Regulation specifying that "Radiotelegrams shall show in the preamble that the service is 'Radio ' ". The switch to radio in place of wireless took place slowly and unevenly in the English-speaking world. Lee de Forest helped popularize the new word in the United States—in early 1907, he founded the DeForest Radio Telephone Company, and his letter in the 22 June 1907 Electrical World about

2016-443: A cable, as with rooftop television antennas and satellite dishes . Practical radio receivers perform three basic functions on the signal from the antenna: filtering , amplification , and demodulation : Radio waves from many transmitters pass through the air simultaneously without interfering with each other and are received by the antenna. These can be separated in the receiver because they have different frequencies ; that is,

2160-412: A controller device control the actions of a remote device. The existence of radio waves was first proven by German physicist Heinrich Hertz on 11 November 1886. In the mid-1890s, building on techniques physicists were using to study electromagnetic waves, Italian physicist Guglielmo Marconi developed the first apparatus for long-distance radio communication, sending a wireless Morse Code message to

2304-442: A digital communication channel is the capacity excluding the physical layer protocol overhead, for example time division multiplex (TDM) framing bits , redundant forward error correction (FEC) codes, equalizer training symbols and other channel coding . Error-correcting codes are common especially in wireless communication systems, broadband modem standards and modern copper-based high-speed LANs. The physical layer net bitrate

2448-417: A distance of 3500 km (2200 miles), which was received by a coherer. However the usual range of coherer receivers even with the powerful transmitters of this era was limited to a few hundred miles. The coherer remained the dominant detector used in early radio receivers for about 10 years, until replaced by the crystal detector and electrolytic detector around 1907. In spite of much development work, it

2592-605: A filter increases with its center frequency, so as the TRF receiver is tuned to different frequencies its bandwidth varies. Most important, the increasing congestion of the radio spectrum requires that radio channels be spaced very close together in frequency. It is extremely difficult to build filters operating at radio frequencies that have a narrow enough bandwidth to separate closely spaced radio stations. TRF receivers typically must have many cascaded tuning stages to achieve adequate selectivity. The Advantages section below describes how

2736-472: A format sometimes abbreviated like "16bit / 44.1kHz". CD-DA is also stereo , using a left and right channel , so the amount of audio data per second is double that of mono, where only a single channel is used. The bit rate of PCM audio data can be calculated with the following formula: For example, the bit rate of a CD-DA recording (44.1 kHz sampling rate, 16 bits per sample and two channels) can be calculated as follows: The cumulative size of

2880-421: A given bandwidth than analog modulation , by using data compression algorithms, which reduce redundancy in the data to be sent, and more efficient modulation. Other reasons for the transition is that digital modulation has greater noise immunity than analog, digital signal processing chips have more power and flexibility than analog circuits, and a wide variety of types of information can be transmitted using

3024-548: A government license, such as the general radiotelephone operator license in the US, obtained by taking a test demonstrating adequate technical and legal knowledge of safe radio operation. Exceptions to the above rules allow the unlicensed operation by the public of low power short-range transmitters in consumer products such as cell phones, cordless phones , wireless devices , walkie-talkies , citizens band radios , wireless microphones , garage door openers , and baby monitors . In

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3168-587: A large economic cost, but it can also be life-threatening (for example, in the case of interference with emergency communications or air traffic control ). To prevent interference between different users, the emission of radio waves is strictly regulated by national laws, coordinated by an international body, the International Telecommunication Union (ITU), which allocates bands in the radio spectrum for different uses. Radio transmitters must be licensed by governments, under

3312-614: A length of PCM audio data (excluding a file header or other metadata ) can be calculated using the following formula: The cumulative size in bytes can be found by dividing the file size in bits by the number of bits in a byte, which is eight: Therefore, 80 minutes (4,800 seconds) of CD-DA data requires 846,720,000 bytes of storage: where MiB is mebibytes with binary prefix Mi, meaning 2 = 1,048,576. The MP3 audio format provides lossy data compression . Audio quality improves with increasing bitrate: For technical reasons (hardware/software protocols, overheads, encoding schemes, etc.)

3456-543: A limited range of its transmitter. The range depends on the power of the transmitter, the sensitivity of the receiver, atmospheric and internal noise , as well as any geographical obstructions such as hills between transmitter and receiver. AM broadcast band radio waves travel as ground waves which follow the contour of the Earth, so AM radio stations can be reliably received at hundreds of miles distance. Due to their higher frequency, FM band radio signals cannot travel far beyond

3600-595: A metal conductor called an antenna . As they travel farther from the transmitting antenna, radio waves spread out so their signal strength ( intensity in watts per square meter) decreases (see Inverse-square law ), so radio transmissions can only be received within a limited range of the transmitter, the distance depending on the transmitter power, the antenna radiation pattern , receiver sensitivity, background noise level, and presence of obstructions between transmitter and receiver . An omnidirectional antenna transmits or receives radio waves in all directions, while

3744-427: A more limited information-carrying capacity and so work best with audio signals (speech and music), and the sound quality can be degraded by radio noise from natural and artificial sources. The shortwave bands have a greater potential range but are more subject to interference by distant stations and varying atmospheric conditions that affect reception. In the very high frequency band, greater than 30 megahertz,

3888-442: A paper tape machine. The coherer's poor performance motivated a great deal of research to find better radio wave detectors, and many were invented. Some strange devices were tried; researchers experimented with using frog legs and even a human brain from a cadaver as detectors. By the first years of the 20th century, experiments in using amplitude modulation (AM) to transmit sound by radio ( radiotelephony ) were being made. So

4032-470: A primitive spark-gap transmitter . Experiments by Hertz and physicists Jagadish Chandra Bose , Oliver Lodge , Lord Rayleigh , and Augusto Righi , among others, showed that radio waves like light demonstrated reflection, refraction , diffraction , polarization , standing waves , and traveled at the same speed as light, confirming that both light and radio waves were electromagnetic waves, differing only in frequency. In 1895, Guglielmo Marconi developed

4176-420: A public audience. Analog audio is the earliest form of radio broadcast. AM broadcasting began around 1920. FM broadcasting was introduced in the late 1930s with improved fidelity . A broadcast radio receiver is called a radio . Most radios can receive both AM and FM. Television broadcasting is the transmission of moving images by radio, which consist of sequences of still images, which are displayed on

4320-459: A radio signal is usually concentrated in narrow frequency bands called sidebands ( SB ) just above and below the carrier frequency. The width in hertz of the frequency range that the radio signal occupies, the highest frequency minus the lowest frequency, is called its bandwidth ( BW ). For any given signal-to-noise ratio , an amount of bandwidth can carry the same amount of information ( data rate in bits per second) regardless of where in

4464-489: A receiver that is typically colocated with the transmitter. In radio navigation systems such as GPS and VOR , a mobile navigation instrument receives radio signals from multiple navigational radio beacons whose position is known, and by precisely measuring the arrival time of the radio waves the receiver can calculate its position on Earth. In wireless radio remote control devices like drones , garage door openers , and keyless entry systems , radio signals transmitted from

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4608-533: A recipient over a kilometer away in 1895, and the first transatlantic signal on 12 December 1901. The first commercial radio broadcast was transmitted on 2 November 1920, when the live returns of the Harding-Cox presidential election were broadcast by Westinghouse Electric and Manufacturing Company in Pittsburgh, under the call sign KDKA . The emission of radio waves is regulated by law, coordinated by

4752-673: A reference to the radiotelegraph and radiotelegraphy . The use of radio as a standalone word dates back to at least 30 December 1904, when instructions issued by the British Post Office for transmitting telegrams specified that "The word 'Radio'... is sent in the Service Instructions." This practice was universally adopted, and the word "radio" introduced internationally, by the 1906 Berlin Radiotelegraphic Convention, which included

4896-613: A related problem is DC offset of the signal. This is corrected by a similar feedback system. Radio waves were first identified in German physicist Heinrich Hertz 's 1887 series of experiments to prove James Clerk Maxwell's electromagnetic theory . Hertz used spark-excited dipole antennas to generate the waves and micrometer spark gaps attached to dipole and loop antennas to detect them. These primitive devices are more accurately described as radio wave sensors, not "receivers", as they could only detect radio waves within about 100 feet of

5040-446: A screen on a television receiver (a "television" or TV) along with a synchronized audio (sound) channel. Television ( video ) signals occupy a wider bandwidth than broadcast radio ( audio ) signals. Analog television , the original television technology, required 6 MHz, so the television frequency bands are divided into 6 MHz channels, now called "RF channels". The current television standard, introduced beginning in 2006,

5184-422: A second goal of detector research was to find detectors that could demodulate an AM signal, extracting the audio (sound) signal from the radio carrier wave . It was found by trial and error that this could be done by a detector that exhibited "asymmetrical conduction"; a device that conducted current in one direction but not in the other. This rectified the alternating current radio signal, removing one side of

5328-441: A smaller bandwidth than the old analog channels, saving scarce radio spectrum space. Therefore, each of the 6 MHz analog RF channels now carries up to 7 DTV channels – these are called "virtual channels". Digital television receivers have different behavior in the presence of poor reception or noise than analog television, called the " digital cliff " effect. Unlike analog television, in which increasingly poor reception causes

5472-416: A television (video) signal has a greater data rate than an audio signal . The radio spectrum , the total range of radio frequencies that can be used for communication in a given area, is a limited resource. Each radio transmission occupies a portion of the total bandwidth available. Radio bandwidth is regarded as an economic good which has a monetary cost and is in increasing demand. In some parts of

5616-400: A transmitter to a receiver, by modulating the radio signal (impressing an information signal on the radio wave by varying some aspect of the wave) in the transmitter. In radar, used to locate and track objects like aircraft, ships, spacecraft and missiles, a beam of radio waves emitted by a radar transmitter reflects off the target object, and the reflected waves reveal the object's location to

5760-652: A transmitter to control the actions of a device at a remote location. Remote control systems may also include telemetry channels in the other direction, used to transmit real-time information on the state of the device back to the control station. Uncrewed spacecraft are an example of remote-controlled machines, controlled by commands transmitted by satellite ground stations . Most handheld remote controls used to control consumer electronics products like televisions or DVD players actually operate by infrared light rather than radio waves, so are not examples of radio remote control. A security concern with remote control systems

5904-447: A variable R ) is the number of bits that are conveyed or processed per unit of time. The bit rate is expressed in the unit bit per second (symbol: bit/s ), often in conjunction with an SI prefix such as kilo (1 kbit/s = 1,000 bit/s), mega (1 Mbit/s = 1,000 kbit/s), giga (1 Gbit/s = 1,000 Mbit/s) or tera (1 Tbit/s = 1,000 Gbit/s). The non-standard abbreviation bps

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6048-435: A variety of license classes depending on use, and are restricted to certain frequencies and power levels. In some classes, such as radio and television broadcasting stations, the transmitter is given a unique identifier consisting of a string of letters and numbers called a call sign , which must be used in all transmissions. In order to adjust, maintain, or internally repair radiotelephone transmitters, individuals must hold

6192-413: Is amplified in the transmitter and applied to a transmitting antenna which radiates the energy as radio waves. The radio waves carry the information to the receiver location. At the receiver, the radio wave induces a tiny oscillating voltage in the receiving antenna which is a weaker replica of the current in the transmitting antenna. This voltage is applied to the radio receiver , which amplifies

6336-703: Is spoofing , in which an unauthorized person transmits an imitation of the control signal to take control of the device. Examples of radio remote control: Radio jamming is the deliberate radiation of radio signals designed to interfere with the reception of other radio signals. Jamming devices are called "signal suppressors" or "interference generators" or just jammers. During wartime, militaries use jamming to interfere with enemies' tactical radio communication. Since radio waves can pass beyond national borders, some totalitarian countries which practice censorship use jamming to prevent their citizens from listening to broadcasts from radio stations in other countries. Jamming

6480-453: Is 125 Mbit/s, due to the 4B5B (four bit over five bit) encoding. In this case, the gross bit rate is equal to the symbol rate or pulse rate of 125 megabaud, due to the NRZI line code . In communications technologies without forward error correction and other physical layer protocol overhead, there is no distinction between gross bit rate and physical layer net bit rate. For example,

6624-444: Is a transmitter and receiver combined in one unit. Below is a list of a few of the most common types, organized by function. A radio receiver is connected to an antenna which converts some of the energy from the incoming radio wave into a tiny radio frequency AC voltage which is applied to the receiver's input. An antenna typically consists of an arrangement of metal conductors. The oscillating electric and magnetic fields of

6768-445: Is a digital format called high-definition television (HDTV), which transmits pictures at higher resolution, typically 1080 pixels high by 1920 pixels wide, at a rate of 25 or 30 frames per second. Digital television (DTV) transmission systems, which replaced older analog television in a transition beginning in 2006, use image compression and high-efficiency digital modulation such as OFDM and 8VSB to transmit HDTV video within

6912-433: Is an audio transceiver , a receiver and transmitter in the same device, used for bidirectional person-to-person voice communication with other users with similar radios. An older term for this mode of communication is radiotelephony . The radio link may be half-duplex , as in a walkie-talkie , using a single radio channel in which only one radio can transmit at a time, so different users take turns talking, pressing

7056-596: Is an advanced radio technology which debuted in some countries in 1998 that transmits audio from terrestrial radio stations as a digital signal rather than an analog signal as AM and FM do. Its advantages are that DAB has the potential to provide higher quality sound than FM (although many stations do not choose to transmit at such high quality), has greater immunity to radio noise and interference, makes better use of scarce radio spectrum bandwidth, and provides advanced user features such as electronic program guide , sports commentaries, and image slideshows. Its disadvantage

7200-435: Is applied to a loudspeaker or earphone to convert it to sound waves. Although the TRF receiver is used in a few applications, it has practical disadvantages which make it inferior to the superheterodyne receiver below, which is used in most applications. The drawbacks stem from the fact that in the TRF the filtering, amplification, and demodulation are done at the high frequency of the incoming radio signal. The bandwidth of

7344-410: Is called "tuning". The oscillating radio signal from the desired station causes the tuned circuit to resonate , oscillate in sympathy, and it passes the signal on to the rest of the receiver. Radio signals at other frequencies are blocked by the tuned circuit and not passed on. A modulated radio wave, carrying an information signal, occupies a range of frequencies . The information ( modulation ) in

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7488-427: Is called an uplink , while a link that transmits data from the spacecraft to the ground is called a downlink. Radar is a radiolocation method used to locate and track aircraft, spacecraft, missiles, ships, vehicles, and also to map weather patterns and terrain. A radar set consists of a transmitter and receiver. The transmitter emits a narrow beam of radio waves which is swept around the surrounding space. When

7632-442: Is called the intermediate frequency (IF). The IF signal also has the modulation sidebands that carry the information that was present in the original RF signal. The IF signal passes through filter and amplifier stages, then is demodulated in a detector, recovering the original modulation. The receiver is easy to tune; to receive a different frequency it is only necessary to change the local oscillator frequency. The stages of

7776-428: Is first mixed with one local oscillator signal in the first mixer to convert it to a high IF frequency, to allow efficient filtering out of the image frequency, then this first IF is mixed with a second local oscillator signal in a second mixer to convert it to a low IF frequency for good bandpass filtering. Some receivers even use triple-conversion . At the cost of the extra stages, the superheterodyne receiver provides

7920-565: Is in radio clocks and watches, which include an automated receiver that periodically (usually weekly) receives and decodes the time signal and resets the watch's internal quartz clock to the correct time, thus allowing a small watch or desk clock to have the same accuracy as an atomic clock. Government time stations are declining in number because GPS satellites and the Internet Network Time Protocol (NTP) provide equally accurate time standards. A two-way radio

8064-417: Is mainly due to their desirable propagation properties stemming from their longer wavelength. In radio communication systems, information is carried across space using radio waves. At the sending end, the information to be sent is converted by some type of transducer to a time-varying electrical signal called the modulation signal. The modulation signal may be an audio signal representing sound from

8208-804: Is not the case for modern modulation systems used in modems and LAN equipment. For most line codes and modulation methods: More specifically, a line code (or baseband transmission scheme) representing the data using pulse-amplitude modulation with 2 N {\displaystyle 2^{N}} different voltage levels, can transfer N {\displaystyle N} bits per pulse. A digital modulation method (or passband transmission scheme) using 2 N {\displaystyle 2^{N}} different symbols, for example 2 N {\displaystyle 2^{N}} amplitudes, phases or frequencies, can transfer N {\displaystyle N} bits per symbol. This results in: An exception from

8352-537: Is not the degree of amplification but random electronic noise present in the circuit, which can drown out a weak radio signal. After the radio signal is filtered and amplified, the receiver must extract the information-bearing modulation signal from the modulated radio frequency carrier wave . This is done by a circuit called a demodulator ( detector ). Each type of modulation requires a different type of demodulator Many other types of modulation are also used for specialized purposes. The modulation signal output by

8496-669: Is often used to replace the standard symbol bit/s, so that, for example, 1 Mbps is used to mean one million bits per second. In most computing and digital communication environments, one byte per second (symbol: B/s ) corresponds to 8 bit/s. When quantifying large or small bit rates, SI prefixes (also known as metric prefixes or decimal prefixes) are used, thus: Binary prefixes are sometimes used for bit rates. The International Standard ( IEC 80000-13 ) specifies different symbols for binary and decimal (SI) prefixes (e.g., 1 KiB /s = 1024 B/s = 8192 bit/s, and 1 MiB /s = 1024 KiB/s). In digital communication systems,

8640-408: Is possible without bit errors for a certain physical analog node-to-node communication link . The channel capacity is proportional to the analog bandwidth in hertz. This proportionality is called Hartley's law . Consequently, the net bit rate is sometimes called digital bandwidth capacity in bit/s. The term throughput , essentially the same thing as digital bandwidth consumption , denotes

8784-437: Is provided by the network equipment or protocols, we have the following relation: for a certain communication path. These are examples of physical layer net bit rates in proposed communication standard interfaces and devices: In digital multimedia, bit rate represents the amount of information, or detail, that is stored per unit of time of a recording. The bitrate depends on several factors: Generally, choices are made about

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8928-445: Is that it is incompatible with previous radios so that a new DAB receiver must be purchased. As of 2017, 38 countries offer DAB, with 2,100 stations serving listening areas containing 420 million people. The United States and Canada have chosen not to implement DAB. DAB radio stations work differently from AM or FM stations: a single DAB station transmits a wide 1,500 kHz bandwidth signal that carries from 9 to 12 channels from which

9072-405: Is the datarate measured at a reference point in the interface between the data link layer and physical layer, and may consequently include data link and higher layer overhead. In modems and wireless systems, link adaptation (automatic adaptation of the data rate and the modulation and/or error coding scheme to the signal quality) is often applied. In that context, the term peak bitrate denotes

9216-524: Is the one-way transmission of information from a transmitter to receivers belonging to a public audience. Since the radio waves become weaker with distance, a broadcasting station can only be received within a limited distance of its transmitter. Systems that broadcast from satellites can generally be received over an entire country or continent. Older terrestrial radio and television are paid for by commercial advertising or governments. In subscription systems like satellite television and satellite radio

9360-530: Is usually accomplished by a powerful transmitter which generates noise on the same frequency as the target transmitter. US Federal law prohibits the nonmilitary operation or sale of any type of jamming devices, including ones that interfere with GPS, cellular, Wi-Fi and police radars. ELF 3 Hz/100 Mm 30 Hz/10 Mm SLF 30 Hz/10 Mm 300 Hz/1 Mm ULF 300 Hz/1 Mm 3 kHz/100 km Bit rate In telecommunications and computing , bit rate ( bitrate or as

9504-450: The FM broadcast bands between about 65 and 108 MHz in the very high frequency (VHF) range. The exact frequency ranges vary somewhat in different countries. FM stereo radio stations broadcast in stereophonic sound (stereo), transmitting two sound channels representing left and right microphones . A stereo receiver contains the additional circuits and parallel signal paths to reproduce

9648-595: The International Telecommunication Union (ITU), which allocates frequency bands in the radio spectrum for various uses. The word radio is derived from the Latin word radius , meaning "spoke of a wheel, beam of light, ray". It was first applied to communications in 1881 when, at the suggestion of French scientist Ernest Mercadier  [ fr ] , Alexander Graham Bell adopted radiophone (meaning "radiated sound") as an alternate name for his photophone optical transmission system. Following Hertz's discovery of

9792-413: The amplitude (voltage or current) of the signal. In most modern receivers, the electronic components which do the actual amplifying are transistors . Receivers usually have several stages of amplification: the radio signal from the bandpass filter is amplified to make it powerful enough to drive the demodulator, then the audio signal from the demodulator is amplified to make it powerful enough to operate

9936-452: The ionosphere without refraction , and at microwave frequencies the high-gain antennas needed to focus the radio energy into a narrow beam pointed at the receiver are small and take up a minimum of space in a satellite. Portions of the UHF , L , C , S , k u and k a band are allocated for space communication. A radio link that transmits data from the Earth's surface to a spacecraft

10080-413: The longwave range, and between 526 and 1706 kHz in the medium frequency (MF) range of the radio spectrum . AM broadcasting is also permitted in shortwave bands, between about 2.3 and 26 MHz, which are used for long distance international broadcasting. In frequency modulation (FM), the frequency of the radio signal is varied slightly by the audio signal. FM broadcasting is permitted in

10224-410: The physical layer gross bitrate , raw bitrate , data signaling rate , gross data transfer rate or uncoded transmission rate (sometimes written as a variable R b or f b ) is the total number of physically transferred bits per second over a communication link, including useful data as well as protocol overhead. In case of serial communications , the gross bit rate is related to

10368-400: The radio spectrum into 12 bands, each beginning at a wavelength which is a power of ten (10 ) metres, with corresponding frequency of 3 times a power of ten, and each covering a decade of frequency or wavelength. Each of these bands has a traditional name: It can be seen that the bandwidth , the range of frequencies, contained in each band is not equal but increases exponentially as

10512-416: The source information rate , also known as the entropy rate . The bitrates in this section are approximately the minimum that the average listener in a typical listening or viewing environment, when using the best available compression, would perceive as not significantly worse than the reference standard. Compact Disc Digital Audio (CD-DA) uses 44,100 samples per second, each with a bit depth of 16,

10656-531: The 1920s with the introduction of broadcasting. Electromagnetic waves were predicted by James Clerk Maxwell in his 1873 theory of electromagnetism , now called Maxwell's equations , who proposed that a coupled oscillating electric field and magnetic field could travel through space as a wave, and proposed that light consisted of electromagnetic waves of short wavelength . On 11 November 1886, German physicist Heinrich Hertz , attempting to confirm Maxwell's theory, first observed radio waves he generated using

10800-474: The Earth's atmosphere has less of an effect on the range of signals, and line-of-sight propagation becomes the principal mode. These higher frequencies permit the great bandwidth required for television broadcasting. Since natural and artificial noise sources are less present at these frequencies, high-quality audio transmission is possible, using frequency modulation . Radio broadcasting means transmission of audio (sound) to radio receivers belonging to

10944-596: The US, these fall under Part 15 of the Federal Communications Commission (FCC) regulations. Many of these devices use the ISM bands , a series of frequency bands throughout the radio spectrum reserved for unlicensed use. Although they can be operated without a license, like all radio equipment these devices generally must be type-approved before the sale. Below are some of the most important uses of radio, organized by function. Broadcasting

11088-443: The above factors in order to achieve the desired trade-off between minimizing the bitrate and maximizing the quality of the material when it is played. If lossy data compression is used on audio or visual data, differences from the original signal will be introduced; if the compression is substantial, or lossy data is decompressed and recompressed, this may become noticeable in the form of compression artifacts . Whether these affect

11232-694: The above is some self-synchronizing line codes, for example Manchester coding and return-to-zero (RTZ) coding, where each bit is represented by two pulses (signal states), resulting in: A theoretical upper bound for the symbol rate in baud, symbols/s or pulses/s for a certain spectral bandwidth in hertz is given by the Nyquist law : In practice this upper bound can only be approached for line coding schemes and for so-called vestigial sideband digital modulation. Most other digital carrier-modulated schemes, for example ASK , PSK , QAM and OFDM , can be characterized as double sideband modulation, resulting in

11376-400: The achieved average useful bit rate in a computer network over a logical or physical communication link or through a network node, typically measured at a reference point above the data link layer. This implies that the throughput often excludes data link layer protocol overhead. The throughput is affected by the traffic load from the data source in question, as well as from other sources sharing

11520-409: The advantage of greater selectivity than can be achieved with a TRF design. Where very high frequencies are in use, only the initial stage of the receiver needs to operate at the highest frequencies; the remaining stages can provide much of the receiver gain at lower frequencies which may be easier to manage. Tuning is simplified compared to a multi-stage TRF design, and only two stages need to track over

11664-405: The air simultaneously without interfering with each other because each transmitter's radio waves oscillate at a different rate, in other words, each transmitter has a different frequency , measured in hertz (Hz), kilohertz (kHz), megahertz (MHz) or gigahertz (GHz). The receiving antenna typically picks up the radio signals of many transmitters. The receiver uses tuned circuits to select

11808-438: The amplitude of the modulation does not vary with the radio signal strength, but in all types the demodulator requires a certain range of signal amplitude to operate properly. Insufficient signal amplitude will cause an increase of noise in the demodulator, while excessive signal amplitude will cause amplifier stages to overload (saturate), causing distortion (clipping) of the signal. Therefore, almost all modern receivers include

11952-431: The antenna is mixed with an unmodulated signal generated by a local oscillator (LO) in the receiver. The mixing is done in a nonlinear circuit called the " mixer ". The result at the output of the mixer is a heterodyne or beat frequency at the difference between these two frequencies. The process is similar to the way two musical notes at different frequencies played together produce a beat note . This lower frequency

12096-414: The beam strikes a target object, radio waves are reflected back to the receiver. The direction of the beam reveals the object's location. Since radio waves travel at a constant speed close to the speed of light , by measuring the brief time delay between the outgoing pulse and the received "echo", the range to the target can be calculated. The targets are often displayed graphically on a map display called

12240-462: The bit transmission time T b {\displaystyle T_{\text{b}}} as: The gross bit rate is related to the symbol rate or modulation rate, which is expressed in bauds or symbols per second. However, the gross bit rate and the baud value are equal only when there are only two levels per symbol, representing 0 and 1, meaning that each symbol of a data transmission system carries exactly one bit of data; for example, this

12384-601: The carrier cycles, leaving a pulsing DC current whose amplitude varied with the audio modulation signal. When applied to an earphone this would reproduce the transmitted sound. Below are the detectors that saw wide use before vacuum tubes took over around 1920. All except the magnetic detector could rectify and therefore receive AM signals: Radio Radio is the technology of communicating using radio waves . Radio waves are electromagnetic waves of frequency between 3  hertz (Hz) and 300  gigahertz (GHz). They are generated by an electronic device called

12528-501: The connection establishment phase due to adaptive modulation  – slower but more robust modulation schemes are chosen in case of poor signal-to-noise ratio . Due to data compression, the actual data transmission rate or throughput (see below) may be higher. The channel capacity , also known as the Shannon capacity, is a theoretical upper bound for the maximum net bitrate, exclusive of forward error correction coding, that

12672-668: The continuous waves which were needed for audio modulation , so radio was used for person-to-person commercial, diplomatic and military text messaging. Starting around 1908 industrial countries built worldwide networks of powerful transoceanic transmitters to exchange telegram traffic between continents and communicate with their colonies and naval fleets. During World War I the development of continuous wave radio transmitters, rectifying electrolytic, and crystal radio receiver detectors enabled amplitude modulation (AM) radiotelephony to be achieved by Reginald Fessenden and others, allowing audio to be transmitted. On 2 November 1920,

12816-466: The customer pays a monthly fee. In these systems, the radio signal is encrypted and can only be decrypted by the receiver, which is controlled by the company and can be deactivated if the customer does not pay. Broadcasting uses several parts of the radio spectrum, depending on the type of signals transmitted and the desired target audience. Longwave and medium wave signals can give reliable coverage of areas several hundred kilometers across, but have

12960-420: The demodulator is usually amplified to increase its strength, then the information is converted back to a human-usable form by some type of transducer . An audio signal , representing sound, as in a broadcast radio, is converted to sound waves by an earphone or loudspeaker . A video signal , representing moving images, as in a television receiver , is converted to light by a display . Digital data , as in

13104-449: The desired signal. A single tunable RF filter stage rejects the image frequency; since these are relatively far from the desired frequency, a simple filter provides adequate rejection. Rejection of interfering signals much closer in frequency to the desired signal is handled by the multiple sharply-tuned stages of the intermediate frequency amplifiers, which do not need to change their tuning. This filter does not need great selectivity, but as

13248-648: The earphone the signal sounded like a musical tone or buzz, and the Morse code "dots" and "dashes" sounded like beeps. The first person to use radio waves for communication was Guglielmo Marconi . Marconi invented little himself, but he was first to believe that radio could be a practical communication medium, and singlehandedly developed the first wireless telegraphy systems, transmitters and receivers, beginning in 1894–5, mainly by improving technology invented by others. Oliver Lodge and Alexander Popov were also experimenting with similar radio wave receiving apparatus at

13392-399: The encoding bit rate is the goodput that is required to avoid playback interruption. The term average bitrate is used in case of variable bitrate multimedia source coding schemes. In this context, the peak bit rate is the maximum number of bits required for any short-term block of compressed data. A theoretical lower bound for the encoding bit rate for lossless data compression is

13536-570: The existence of radio waves in 1886, the term Hertzian waves was initially used for this radiation. The first practical radio communication systems, developed by Marconi in 1894–1895, transmitted telegraph signals by radio waves, so radio communication was first called wireless telegraphy . Up until about 1910 the term wireless telegraphy also included a variety of other experimental systems for transmitting telegraph signals without wires, including electrostatic induction , electromagnetic induction and aquatic and earth conduction , so there

13680-446: The file size (in bytes) divided by the file transfer time (in seconds) and multiplied by eight. As an example, the goodput or data transfer rate of a V.92 voiceband modem is affected by the modem physical layer and data link layer protocols. It is sometimes higher than the physical layer data rate due to V.44 data compression , and sometimes lower due to bit-errors and automatic repeat request retransmissions. If no data compression

13824-482: The filtering at the lower intermediate frequency. One of the most important parameters of a receiver is its bandwidth , the band of frequencies it accepts. In order to reject nearby interfering stations or noise, a narrow bandwidth is required. In all known filtering techniques, the bandwidth of the filter increases in proportion with the frequency, so by performing the filtering at the lower f IF {\displaystyle f_{\text{IF}}} , rather than

13968-413: The first commercial radio broadcast was transmitted by Westinghouse Electric and Manufacturing Company in Pittsburgh, under the call sign KDKA featuring live coverage of the Harding-Cox presidential election . Radio waves are radiated by electric charges undergoing acceleration . They are generated artificially by time-varying electric currents , consisting of electrons flowing back and forth in

14112-415: The first mass-market radio application. A broadcast receiver is commonly called a "radio". However radio receivers are very widely used in other areas of modern technology, in televisions , cell phones , wireless modems , radio clocks and other components of communications, remote control, and wireless networking systems. The most familiar form of radio receiver is a broadcast receiver, often just called

14256-592: The first radio communication system, using a spark-gap transmitter to send Morse code over long distances. By December 1901, he had transmitted across the Atlantic Ocean. Marconi and Karl Ferdinand Braun shared the 1909 Nobel Prize in Physics "for their contributions to the development of wireless telegraphy". During radio's first two decades, called the radiotelegraphy era, the primitive radio transmitters could only transmit pulses of radio waves, not

14400-534: The following relation: In case of parallel communication , the gross bit rate is given by where n is the number of parallel channels, M i is the number of symbols or levels of the modulation in the i th channel , and T i is the symbol duration time , expressed in seconds, for the i th channel. The physical layer net bitrate , information rate , useful bit rate , payload rate , net data transfer rate , coded transmission rate , effective data rate or wire speed (informal language) of

14544-618: The frequency increases; each band contains ten times the bandwidth of the preceding band. The term "tremendously low frequency" (TLF) has been used for wavelengths from 1–3 Hz (300,000–100,000 km), though the term has not been defined by the ITU. The airwaves are a resource shared by many users. Two radio transmitters in the same area that attempt to transmit on the same frequency will interfere with each other, causing garbled reception, so neither transmission may be received clearly. Interference with radio transmissions can not only have

14688-475: The frequency of the original radio signal f RF {\displaystyle f_{\text{RF}}} , a narrower bandwidth can be achieved. Modern FM and television broadcasting, cellphones and other communications services, with their narrow channel widths, would be impossible without the superheterodyne. The signal strength ( amplitude ) of the radio signal from a receiver's antenna varies drastically, by orders of magnitude, depending on how far away

14832-482: The gross bit rate and net bit rate is affected by the FEC code rate according to the following. The connection speed of a technology that involves forward error correction typically refers to the physical layer net bit rate in accordance with the above definition. For example, the net bitrate (and thus the "connection speed") of an IEEE 802.11a wireless network is the net bit rate of between 6 and 54 Mbit/s, while

14976-472: The gross bit rate is between 12 and 72 Mbit/s inclusive of error-correcting codes. The net bit rate of ISDN2 Basic Rate Interface (2 B-channels + 1 D-channel) of 64+64+16 = 144 kbit/s also refers to the payload data rates, while the D channel signalling rate is 16 kbit/s. The net bit rate of the Ethernet 100BASE-TX physical layer standard is 100 Mbit/s, while the gross bitrate

15120-428: The incoming radio signal is at the resonant frequency, the resonant circuit has high impedance and the radio signal from the desired station is passed on to the following stages of the receiver. At all other frequencies the resonant circuit has low impedance, so signals at these frequencies are conducted to ground. The power of the radio waves picked up by a receiving antenna decreases with the square of its distance from

15264-417: The listener can choose. Broadcasters can transmit a channel at a range of different bit rates , so different channels can have different audio quality. In different countries DAB stations broadcast in either Band III (174–240 MHz) or L band (1.452–1.492 GHz). The signal strength of radio waves decreases the farther they travel from the transmitter, so a radio station can only be received within

15408-402: The longest transmission distances of any radio links, up to billions of kilometers for interplanetary spacecraft . In order to receive the weak signals from distant spacecraft, satellite ground stations use large parabolic "dish" antennas up to 25 metres (82 ft) in diameter and extremely sensitive receivers. High frequencies in the microwave band are used, since microwaves pass through

15552-510: The loudness of the audio, and some type of "tuning" control to select the radio station to be received. Modulation is the process of adding information to a radio carrier wave . Two types of modulation are used in analog radio broadcasting systems; AM and FM. In amplitude modulation (AM) the strength of the radio signal is varied by the audio signal. AM broadcasting is allowed in the AM broadcast bands which are between 148 and 283 kHz in

15696-472: The need for legal restrictions warned that "Radio chaos will certainly be the result until such stringent regulation is enforced." The United States Navy would also play a role. Although its translation of the 1906 Berlin Convention used the terms wireless telegraph and wireless telegram , by 1912 it began to promote the use of radio instead. The term started to become preferred by the general public in

15840-520: The net as well as gross bit rate of Ethernet 10BASE-T is 10 Mbit/s. Due to the Manchester line code, each bit is represented by two pulses, resulting in a pulse rate of 20 megabaud. The "connection speed" of a V.92 voiceband modem typically refers to the gross bit rate, since there is no additional error-correction code. It can be up to 56,000 bit/s downstream and 48,000 bit/s upstream . A lower bit rate may be chosen during

15984-465: The net bitrate of the fastest and least robust transmission mode, used for example when the distance is very short between sender and transmitter. Some operating systems and network equipment may detect the " connection speed " (informal language) of a network access technology or communication device, implying the current net bit rate. The term line rate in some textbooks is defined as gross bit rate, in others as net bit rate. The relationship between

16128-433: The perceived quality, and if so how much, depends on the compression scheme, encoder power, the characteristics of the input data, the listener's perceptions, the listener's familiarity with artifacts, and the listening or viewing environment. The encoding bit rate of a multimedia file is its size in bytes divided by the playback time of the recording (in seconds), multiplied by eight. For real-time streaming multimedia ,

16272-505: The picture quality to gradually degrade, in digital television picture quality is not affected by poor reception until, at a certain point, the receiver stops working and the screen goes black. Government standard frequency and time signal services operate time radio stations which continuously broadcast extremely accurate time signals produced by atomic clocks , as a reference to synchronize other clocks. Examples are BPC , DCF77 , JJY , MSF , RTZ , TDF , WWV , and YVTO . One use

16416-451: The radio frequency spectrum it is located, so bandwidth is a measure of information-carrying capacity . The bandwidth required by a radio transmission depends on the data rate of the information (modulation signal) being sent, and the spectral efficiency of the modulation method used; how much data it can transmit in each kilohertz of bandwidth. Different types of information signals carried by radio have different data rates. For example,

16560-409: The radio signal desired out of all the signals picked up by the antenna and reject the others. A tuned circuit (also called resonant circuit or tank circuit) acts like a resonator , similar to a tuning fork . It has a natural resonant frequency at which it oscillates. The resonant frequency of the receiver's tuned circuit is adjusted by the user to the frequency of the desired radio station; this

16704-451: The radio spectrum, the right to use a frequency band or even a single radio channel is bought and sold for millions of dollars. So there is an incentive to employ technology to minimize the bandwidth used by radio services. A slow transition from analog to digital radio transmission technologies began in the late 1990s. Part of the reason for this is that digital modulation can often transmit more information (a greater data rate) in

16848-413: The radio transmitter is, how powerful it is, and propagation conditions along the path of the radio waves. The strength of the signal received from a given transmitter varies with time due to changing propagation conditions of the path through which the radio wave passes, such as multipath interference ; this is called fading . In an AM receiver, the amplitude of the audio signal from the detector, and

16992-410: The radio wave from each transmitter oscillates at a different rate. To separate out the desired radio signal, the bandpass filter allows the frequency of the desired radio transmission to pass through, and blocks signals at all other frequencies. The bandpass filter consists of one or more resonant circuits (tuned circuits). The resonant circuit is connected between the antenna input and ground. When

17136-401: The radio wave push the electrons in the antenna back and forth, creating an oscillating voltage. The antenna may be enclosed inside the receiver's case, as with the ferrite loop antennas of AM radios and the flat inverted F antenna of cell phones; attached to the outside of the receiver, as with whip antennas used on FM radios , or mounted separately and connected to the receiver by

17280-563: The radio wave to demodulate the later amplitude modulated (AM) radio transmissions that carried sound. In a long series of experiments Marconi found that by using an elevated wire monopole antenna instead of Hertz's dipole antennas he could transmit longer distances, beyond the curve of the Earth, demonstrating that radio was not just a laboratory curiosity but a commercially viable communication method. This culminated in his historic transatlantic wireless transmission on December 12, 1901, from Poldhu, Cornwall to St. John's, Newfoundland ,

17424-456: The radio waves that carry the information through the air. The modulation signal is used to modulate the carrier, varying some aspect of the carrier wave, impressing the information in the modulation signal onto the carrier. Different radio systems use different modulation methods: Many other types of modulation are also used. In some types, a carrier wave is not transmitted but just one or both modulation sidebands . The modulated carrier

17568-448: The receiver after the mixer operates at the fixed intermediate frequency (IF) so the IF bandpass filter does not have to be adjusted to different frequencies. The fixed frequency allows modern receivers to use sophisticated quartz crystal , ceramic resonator , or surface acoustic wave (SAW) IF filters that have very high Q factors , to improve selectivity. The RF filter on the front end of

17712-416: The receiver is needed to prevent interference from any radio signals at the image frequency . Without an input filter the receiver can receive incoming RF signals at two different frequencies,. The receiver can be designed to receive on either of these two frequencies; if the receiver is designed to receive on one, any other radio station or radio noise on the other frequency may pass through and interfere with

17856-465: The receiver is tuned to different frequencies it must "track" in tandem with the local oscillator. The RF filter also serves to limit the bandwidth applied to the RF amplifier, preventing it from being overloaded by strong out-of-band signals. To achieve both good image rejection and selectivity, many modern superhet receivers use two intermediate frequencies; this is called a dual-conversion or double-conversion superheterodyne. The incoming RF signal

18000-481: The same digital modulation. Because it is a fixed resource which is in demand by an increasing number of users, the radio spectrum has become increasingly congested in recent decades, and the need to use it more effectively is driving many additional radio innovations such as trunked radio systems , spread spectrum (ultra-wideband) transmission, frequency reuse , dynamic spectrum management , frequency pooling, and cognitive radio . The ITU arbitrarily divides

18144-425: The same network resources. See also measuring network throughput . Goodput or data transfer rate refers to the achieved average net bit rate that is delivered to the application layer , exclusive of all protocol overhead, data packets retransmissions, etc. For example, in the case of file transfer, the goodput corresponds to the achieved file transfer rate . The file transfer rate in bit/s can be calculated as

18288-456: The same time in 1894–5, but they are not known to have transmitted Morse code during this period, just strings of random pulses. Therefore, Marconi is usually given credit for building the first radio receivers. The first radio receivers invented by Marconi, Oliver Lodge and Alexander Popov in 1894-5 used a primitive radio wave detector called a coherer , invented in 1890 by Edouard Branly and improved by Lodge and Marconi. The coherer

18432-420: The sound volume, is proportional to the amplitude of the radio signal, so fading causes variations in the volume. In addition as the receiver is tuned between strong and weak stations, the volume of the sound from the speaker would vary drastically. Without an automatic system to handle it, in an AM receiver, constant adjustment of the volume control would be required. With other types of modulation like FM or FSK

18576-402: The speaker. The degree of amplification of a radio receiver is measured by a parameter called its sensitivity , which is the minimum signal strength of a station at the antenna, measured in microvolts , necessary to receive the signal clearly, with a certain signal-to-noise ratio . Since it is easy to amplify a signal to any desired degree, the limit to the sensitivity of many modern receivers

18720-467: The superheterodyne receiver overcomes these problems. The superheterodyne receiver, invented in 1918 by Edwin Armstrong is the design used in almost all modern receivers except a few specialized applications. In the superheterodyne, the radio frequency signal from the antenna is shifted down to a lower " intermediate frequency " (IF), before it is processed. The incoming radio frequency signal from

18864-678: The transmitter, and were not used for communication but instead as laboratory instruments in scientific experiments. The first radio transmitters , used during the initial three decades of radio from 1887 to 1917, a period called the spark era , were spark gap transmitters which generated radio waves by discharging a capacitance through an electric spark . Each spark produced a transient pulse of radio waves which decreased rapidly to zero. These damped waves could not be modulated to carry sound, as in modern AM and FM transmission. So spark transmitters could not transmit sound, and instead transmitted information by radiotelegraphy . The transmitter

19008-431: The transmitting antenna also serves as the receiving antenna; this is called a monostatic radar . A radar which uses separate transmitting and receiving antennas is called a bistatic radar . Radiolocation is a generic term covering a variety of techniques that use radio waves to find the location of objects, or for navigation. Radio remote control is the use of electronic control signals sent by radio waves from

19152-404: The transmitting antenna. Even with the powerful transmitters used in radio broadcasting stations, if the receiver is more than a few miles from the transmitter the power intercepted by the receiver's antenna is very small, perhaps as low as picowatts or femtowatts . To increase the power of the recovered signal, an amplifier circuit uses electric power from batteries or the wall plug to increase

19296-426: The tuning range. The total amplification of the receiver is divided between three amplifiers at different frequencies; the RF, IF, and audio amplifier. This reduces problems with feedback and parasitic oscillations that are encountered in receivers where most of the amplifier stages operate at the same frequency, as in the TRF receiver. The most important advantage is that better selectivity can be achieved by doing

19440-457: The two separate channels. A monaural receiver, in contrast, only receives a single audio channel that is a combination (sum) of the left and right channels. While AM stereo transmitters and receivers exist, they have not achieved the popularity of FM stereo. Most modern radios are able to receive both AM and FM radio stations, and have a switch to select which band to receive; these are called AM/FM radios . Digital audio broadcasting (DAB)

19584-464: The visual horizon to about 30–40 miles (48–64 km). Radios are manufactured in a range of styles and functions: Radio receivers are essential components of all systems that use radio . Besides the broadcast receivers described above, radio receivers are used in a huge variety of electronic systems in modern technology. They can be a separate piece of equipment (a radio ), or a subsystem incorporated into other electronic devices. A transceiver

19728-605: The visual horizon; limiting reception distance to about 40 miles (64 km), and can be blocked by hills between the transmitter and receiver. However FM radio is less susceptible to interference from radio noise ( RFI , sferics , static) and has higher fidelity ; better frequency response and less audio distortion , than AM. So in countries that still broadcast AM radio, serious music is typically only broadcast by FM stations, and AM stations specialize in radio news , talk radio , and sports radio . Like FM, DAB signals travel by line of sight so reception distances are limited by

19872-510: The weak radio signal so it is stronger, then demodulates it, extracting the original modulation signal from the modulated carrier wave. The modulation signal is converted by a transducer back to a human-usable form: an audio signal is converted to sound waves by a loudspeaker or earphones, a video signal is converted to images by a display , while a digital signal is applied to a computer or microprocessor, which interacts with human users. The radio waves from many transmitters pass through

20016-412: Was a glass tube with metal electrodes at each end, with loose metal powder between the electrodes. It initially had a high resistance . When a radio frequency voltage was applied to the electrodes, its resistance dropped and it conducted electricity. In the receiver the coherer was connected directly between the antenna and ground. In addition to the antenna, the coherer was connected in a DC circuit with

20160-598: Was a need for a more precise term referring exclusively to electromagnetic radiation. The French physicist Édouard Branly , who in 1890 developed the radio wave detecting coherer , called it in French a radio-conducteur . The radio- prefix was later used to form additional descriptive compound and hyphenated words, especially in Europe. For example, in early 1898 the British publication The Practical Engineer included

20304-414: Was a very crude unsatisfactory device. It was not very sensitive, and also responded to impulsive radio noise ( RFI ), such as nearby lights being switched on or off, as well as to the intended signal. Due to the cumbersome mechanical "tapping back" mechanism it was limited to a data rate of about 12-15 words per minute of Morse code , while a spark-gap transmitter could transmit Morse at up to 100 WPM with

20448-405: Was called a " detector ". Since there were no amplifying devices at this time, the sensitivity of the receiver mostly depended on the detector. Many different detector devices were tried. Radio receivers during the spark era consisted of these parts: The signal from the spark gap transmitter consisted of damped waves repeated at an audio frequency rate, from 120 to perhaps 4000 per second, so in

20592-412: Was done by a "decoherer", a clapper which struck the tube, operated by an electromagnet powered by the relay. The coherer is an obscure antique device, and even today there is some uncertainty about the exact physical mechanism by which the various types worked. However it can be seen that it was essentially a bistable device, a radio-wave-operated switch, and so it did not have the ability to rectify

20736-497: Was switched on and off rapidly by the operator using a telegraph key , creating different length pulses of damped radio waves ("dots" and "dashes") to spell out text messages in Morse code . Therefore, the first radio receivers did not have to extract an audio signal from the radio wave like modern receivers, but just detected the presence of the radio signal, and produced a sound during the "dots" and "dashes". The device which did this

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