Receiver (radio)
Encyclopedia
A radio receiver converts signals from a radio antenna
to a usable form. It uses electronic filter
s to separate a wanted radio frequency
signal from all other signals, the electronic amplifier
increases the level suitable for further processing, and finally recovers the desired information through demodulation
and decoding
. Information carried on a radio signal may represent sound, images or data.
In consumer electronics
, the terms radio and radio receiver are often used specifically for receivers designed for the sound signals transmitted by radio broadcasting services – historically the first mass-market commercial radio application.
, a preamplifier
, and a power amplifier
all on the same chassis. Audiophiles will refer to such a device as an integrated receiver, while a single chassis that implements only one of the three component functions is called a discrete component. Some audio purists still prefer three discreet units - tuner, preamplifier and power amplifier - but the integrated receiver has, for some years, been the mainstream choice for music listening. The first integrated stereo
receiver was made by the Harman Kardon
company, and came onto the market in 1958. It had undistinguished performance, but it represented a breakthrough to the "all in one" concept of a receiver, and rapidly improving designs gradually made the receiver the mainstay of the marketplace. Many radio receivers also include a loudspeaker
.
s are a common component in a high-fidelity
or home-theatre
system. The receiver is generally the nerve centre of a sophisticated home-theatre system providing selectable inputs for a number of different audio components like record players, compact-disc players and CD-RW
recorders, and tape decks ( like video cassette recorders (VCR) and video
components (DVD player
s and DVD recorder
s, video game console
s, and television set
s).
With the decline of gramophone record
vinyl discs, modern receivers tend to omit inputs for phonograph
turntables, which have separate requirements of their own. All other common audio/visual components can use any of the identical line-level inputs on the receiver for playback, regardless of how they are marked (the "name" on each input is mostly for the convenience of the user.) For instance, a second CD player can be plugged into an "Aux
" input, and will work the same as it will in the "CD" input jacks.
Some receivers can also provide digital signal processor
s (DSP) to give a more realistic auditory illusion
of listening in a concert hall. Digital audio
S/PDIF
and USB connections are also common today. The home theater receiver, in the vocabulary of consumer electronics, comprises both the 'radio receiver' and other functions, such as control, sound processing, and power amplification. The standalone radio receiver is usually known in consumer electronics as a tuner.
Some modern integrated receivers can send audio out to seven loudspeakers and an additional channel for a subwoofer
and often include connections for headphones
. Receivers vary greatly in price, and support stereophonic
or surround sound
. A high-quality receiver for dedicated audio-only listening (two channel stereo) can be relatively inexpensive; excellent ones can be purchased for $300 United States or less. Because modern receivers are purely electronic
devices with no moving parts unlike electromechanical
devices like turntables and cassette decks, they tend to offer many years of trouble-free service. In recent years, the home theater in a box
has become common, which often integrates a surround-capable receiver with a DVD player. The user simply connects it to a television, perhaps other components, and a set of loudspeakers.
s that are typically monoaural and receive the AM, FM, and/or short wave broadcast band
s. FM, and often AM, radios are sometimes included as a feature of portable DVD
/CD, MP3 CD
, and USB key players, as well as cassette player/recorder
s.
AM/FM stereo car radios
can be a separate dashboard mounted component or a feature of in car entertainment
systems.
A Boombox
(or Boom-box)—also sometimes known as a Ghettoblaster or a Jambox, or (in parts of Europe) as a "radio-cassette"—is a name given to larger portable stereo systems capable of playing radio stations and recorded music, often at a high level of volume.
Self-powered portable radios, such as clockwork radio
s are used in developing nations or as part of an emergency preparedness kit.
was the first person to prove electromagnetic waves existed, in 1887 a German named Heinrich Hertz demonstrated these new waves by using spark gap
equipment to transmit and receive radio or "Hertzian waves", as they were first called. The experiments were not followed up by Hertz. The practical applications of the wireless communication and remote control technology were implemented by Nikola Tesla
.
The world's first radio receiver (thunderstorm register) was designed by Alexander Stepanovich Popov
, and it was first seen at the All-Russia Exhibition 1896
. He was the first to demonstrate the practical application of electromagnetic (radio) waves, although he did not care to apply for a patent for his invention.
A device called a coherer
became the basis for receiving radio signals. The first person to use the device to detect radio waves was a Frenchman named Edouard Branly
, and Oliver Lodge popularised it when he gave a lecture in 1898 in honour of Hertz. Lodge also made improvements to the coherer.
Many experimenters at the time believed that these new waves could be used to communicate over great distances and made significant improvements to both radio receiving and transmitting apparatus. In 1895 Marconi demonstrated the first viable radio system, leading to transatlantic radio communication in December 1901. The honor was later contested as he was found to be using equipment and designs of other experimenters that held the patents at that time.
John Ambrose Fleming
's development of an early thermionic valve to help detect radio waves was based upon a discovery of Thomas Edison
's (called "The Edison effect", which essentially modified an early light bulb). Fleming called it his "oscillation valve" because it acted in the same way as water valve in only allowing flow in one direction. While Fleming's valve was a great stride forward it would take some years before thermionic, or vacuum tube
technology was fully adopted.
Around this time work on other types of detectors
started to be undertaken and it resulted in what was later known as the cat's whisker. It consisted of a crystal
of a material such as galena
with a small springy piece of wire brought up against it. The detector was constructed so that the wire contact could be moved to different points on the crystal, and thereby obtain the best point for rectifying
the signal and the best detection. They were never very reliable as the "whisker" needed to be moved periodically to enable it to detect the signal properly.
, a competitor to Marconi, set about to develop receiver technology that did not infringe any patents to which Marconi had access. He took out a number of patents in the period between 1905 and 1907 covering a variety of developments that culminated in the form of the triode
valve in which there was a third electrode
called a grid. He called this an audion tube
. One of the first areas in which valves were used was in the manufacture of telephone
repeaters, and although the performance was poor, they gave significant improvement in long distance telephone receiving circuits.
With the discovery that triode valves could amplify signals it was soon noticed that they would also oscillate, a fact that was exploited in generating signals. Once the triode was established as an amplifier it made a tremendous difference to radio receiver performance as it allowed the incoming signals to be amplified. One way that proved very successful was introduced in 1913 and involved the use of positive feedback in the form of a regenerative detector. This gave significant improvements in the levels of gain that could be achieved, greatly increasing selectivity, enabling this type of receiver to outperform all other types of the era. With the outbreak of the First World War, there was a great impetus to develop radio receiving technology further. An American named Irving Langmuir
helped introduce a new generation of totally air-evacuated "hard" valves. H. J. Round
undertook some work on this and in 1916 he produced a number of valves with the grid connection taken out of the top of the envelope away from the anode
connection.
(TRF) represented a major improvement in performance over what had been available before, it still fell short of the needs for some of the new applications. To enable receiver technology to meet the needs placed upon it a number of new ideas started to surface. One of these was a new form of direct conversion receiver. Here an internal or local oscillator was used to beat with the incoming signal to produce an audible signal that could be amplified by an audio amplifier
.
H. J. Round
developed a receiver he called an autodyne
in which the same valve was used as a mixer and an oscillator, Whilst the set used fewer valves it was difficult to optimise the circuit for both the mixer and oscillator functions.
The next leap forward in receiver technology was a new type of receiver known as the superheterodyne, or supersonic heterodyne receiver. A Frenchman named Lucien Levy was investigating ways in which receiver selectivity could be improved and in doing this he devised a system whereby the signals were converted down to a lower frequency where the filter bandwidths could be made narrower. A further advantage was that the gain of valves was considerably greater at the lower frequencies used after the frequency conversion, and there were fewer problems with the circuits bursting into oscillation
.
The idea for developing a receiver with a fixed intermediate frequency amplifier and filter is credited to Edwin Armstrong
of the United States. Working for the American Expeditionary Force
in Europe during 1918, Armstrong thought that if the incoming signals was mixed with a variable frequency oscillator (the "local oscillator"), a lower-frequency fixed tuned amplifier could be used. Armstrong's original receiver consisted of a total of eight vacuum tubes. Several tuned circuits could be cascaded to improve selectivity, and being set on a fixed frequency they did not all need to be changed in line with one another. The filters could be preset and left correctly tuned. Armstrong was not the only person working on the idea of a superheterodyne receiver. Alexander Meissner
in Germany had taken out a patent for the idea six months before Armstrong, but since Meissner did not prove the idea in practice, and he did not build a superheterodyne radio, the invention
is credited to Armstrong.
The need for the increased performance of the superheterodyne receiver was first experienced in North America, and by the late 1920s most radio sets were superheterodyne receivers. However, in Europe the number of broadcast stations did not start to rise as rapidly until later. Even so, by the mid-1930s virtually all receiving sets in Europe as well were using the superheterodyne principle. In 1926, the tetrode
valve was introduced, and enabled further improvements in performance.
In 1939 the outbreak of war gave a new impetus to receiver development. During this time a number of classic communications receiver
s were designed. Some like the National HRO
are still sought by enthusiasts today and although they are relatively large by today's standards, they can still give a good account of themselves under current crowded band conditions.
In the late 1940s the transistor
was discovered. Initially the devices were not widely used because of their expense, and the fact that valves were being made smaller, and performed better. However by the early 1960s portable transistor broadcast receivers (transistor radio
s) were hitting the market place. These radios were ideal for broadcast reception on the long and medium wave bands. They were much smaller than their valve equivalents, they were portable and could be powered from batteries
. Although some valve portable receivers were available, batteries for these were expensive and did not last for long. The power requirements for transistor radios were very much less, resulting in batteries lasting for much longer and being considerably cheaper.
in the late 1950s. This enabled radio receiver technology to move forward even further. Integrated circuits enabled high performance circuits to be built for less cost, and significant amounts of space could be saved.
As a result of these developments new techniques could be introduced. One of these was the frequency synthesizer
that was used to generate the local oscillator signal for the receiver. By using a synthesizer it was possible to generate a very accurate and stable local oscillator signal. Also the ability of synthesizers to be controlled by microprocessor
s meant that many new facilities could be introduced apart from the significant performance improvements offered by synthesizers.
can be performed by software instead. The benefit is that software is not affected by temperature, physical variables, electronic noise and manufacturing defects.
While today's radios are amazing pieces of modern technology, filled with low- power, high performance, integrated circuits crammed into the smallest spaces, the basic principle of the radio receiver is practically always the superheterodyne one, the same idea which was developed by Edwin Armstrong back in 1918. For really high-performance receivers, such as satellite communications receivers and military/naval receivers, two-stage ("double conversion") and even three-stage ("triple conversion") superheterodyne processing is frequently used. Single-conversion receivers are rather simple-minded in their nature.
, is the use of digital means to process signals and is coming into wide use in modern shortwave receivers. It is the basis of many areas of modern technology including cell phones, CD players, video recorders and computers. A digital signal is essentially a stream or sequence of numbers that relay a message through some sort of medium such as a wire. The primary benefit of DSP hardware in shortwave receivers is the ability to tailor the bandwidth of the receiver to current reception conditions and to the type of signal being listened to. A typical analog only receiver may have a limited number of fixed bandwidths, or only one, but a DSP receiver may have 40 or more individually selectable filters.
Some PC radios have the great advantage of being field upgradable by the owner. New versions of the DSP firmware
can be downloaded from the manufacturer's web site and uploaded into the flash memory
of the radio. The manufacturer can then in effect add new features to the radio over time, such as adding new filters, DSP noise reduction, or simply to correct bugs.
A full-featured radio control program allows for scanning and a host of other functions and, in particular, integration of databases in real-time, like a "TV-Guide" type capability. This is particularly helpful in locating all transmissions on all frequencies of a particular broadcaster, at any given time. Some control software designers have even integrated Google Earth
to the shortwave databases, so it is possible to "fly" to a given transmitter site location with a click of a mouse. In many cases the user is able to see the transmitting antennas where the signal is originating from.
or GUI interface PC to the radio has unlimited flexibility, any number of new features can be added by the software designer.Features that can be found in advanced control software programs today include a band table, GUI controls corresponding to traditional radio controls, local time clock and a UTC clock, signal strength meter, an ILG database for shortwave listening with lookup capability, scanning capability, text-to-speech interface, and integrated Conference Server.
front-end or traditional radio that supplies an IF
to the SDR. SDR's can go far beyond the usual demodulation
capability of typical, and even high-end DSP shortwave radios. They can for example, record large swaths of the radio spectrum to a hard drive for "playback" at a later date. The same SDR that one minute is demodulating a simple AM broadcast may also be able to decode an HDTV broadcast in the next. A well known open-source project called GNU Radio
is dedicated to evolving a high-performance SDR. All the source code for this SDR is freely downloadable and modifiable by anyone.
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
to a usable form. It uses electronic filter
Electronic filter
Electronic filters are electronic circuits which perform signal processing functions, specifically to remove unwanted frequency components from the signal, to enhance wanted ones, or both...
s to separate a wanted radio frequency
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
signal from all other signals, the electronic amplifier
Electronic amplifier
An electronic amplifier is a device for increasing the power of a signal.It does this by taking energy from a power supply and controlling the output to match the input signal shape but with a larger amplitude...
increases the level suitable for further processing, and finally recovers the desired information through demodulation
Demodulation
Demodulation is the act of extracting the original information-bearing signal from a modulated carrier wave.A demodulator is an electronic circuit that is used to recover the information content from the modulated carrier wave.These terms are traditionally used in connection with radio receivers,...
and decoding
Digital-to-analog converter
In electronics, a digital-to-analog converter is a device that converts a digital code to an analog signal . An analog-to-digital converter performs the reverse operation...
. Information carried on a radio signal may represent sound, images or data.
In consumer electronics
Consumer electronics
Consumer electronics are electronic equipment intended for everyday use, most often in entertainment, communications and office productivity. Radio broadcasting in the early 20th century brought the first major consumer product, the broadcast receiver...
, the terms radio and radio receiver are often used specifically for receivers designed for the sound signals transmitted by radio broadcasting services – historically the first mass-market commercial radio application.
Types of radio receivers
Various types of radio receivers may include:- Consumer audioSoundSound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
and high fidelityHigh fidelityHigh fidelity—or hi-fi—reproduction is a term used by home stereo listeners and home audio enthusiasts to refer to high-quality reproduction of sound or images, to distinguish it from the poorer quality sound produced by inexpensive audio equipment...
audio receivers and AV receiverAV receiverAV receivers or audio-video receivers are one of the many consumer electronics components typically found within a home theatre system. Their primary purpose is to amplify sound from a multitude of possible audio sources as well as route video signals to your TV from various sources. The user may...
s used by home stereoSTEREOSTEREO is a solar observation mission. Two nearly identical spacecraft were launched into orbits that cause them to respectively pull farther ahead of and fall gradually behind the Earth...
listeners and audio and home theatre system enthusiasts as well as audiophileAudiophileAn audiophile is a person who enjoys listening to recorded music, usually in a home. Some audiophiles are more interested in collecting and listening to music, while others are more interested in collecting and listening to audio components, whose "sound quality" they consider as important as the...
s.
- Communications receiverCommunications receiverA communications receiver is a type of radio receiver used as a component of a radio communication link.-Features:Commercial communications receivers are characterised by high stability and reliability of performance, and are generally adapted for remote control and monitoring...
s, used as a component of a radio communication link, characterized by high stability and reliability of performance.
- Simple crystal radio receiverCrystal radio receiverthumb|Boy listening to a modern crystal radioA crystal radio receiver, also called a crystal set or cat's whisker receiver, is a very simple radio receiver, popular in the early days of radio. It needs no battery or power source and runs on the power received from radio waves by a long wire antenna...
s (also known as a crystal set) which operate using the power received from radio waves.
- Satellite televisionSatellite televisionSatellite television is television programming delivered by the means of communications satellite and received by an outdoor antenna, usually a parabolic mirror generally referred to as a satellite dish, and as far as household usage is concerned, a satellite receiver either in the form of an...
receivers, used to receive television programming from communication satellites in geosynchronous orbitGeosynchronous orbitA geosynchronous orbit is an orbit around the Earth with an orbital period that matches the Earth's sidereal rotation period...
.
- Specialized-use receivers such as telemetryTelemetryTelemetry is a technology that allows measurements to be made at a distance, usually via radio wave transmission and reception of the information. The word is derived from Greek roots: tele = remote, and metron = measure...
receivers that allow the remote measurement and reporting of information.
- Measuring receiverMeasuring ReceiverIn telecommunication, a measuring receiver or measurement receiver is a calibrated laboratory-grade radio receiver designed to measure the characteristics of radio signals. The parameters of such receivers can usually be adjusted over a much wider range of values than is the case with other radio...
s (also: measurement receivers) are calibrated laboratory-grade devices that are used to measure the signal strength of broadcasting stations, the electromagnetic interferenceElectromagnetic interferenceElectromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...
radiation emitted by electrical products, as well as to calibrate RF attenuators and signal generators.
- ScannersScanner (radio)A scanner is a radio receiver that can automatically tune, or scan, two or more discrete frequencies, stopping when it finds a signal on one of them and then continuing to scan other frequencies when the initial transmission ceases....
are specialized receivers that can automatically scan two or more discrete frequencies, stopping when they find a signal on one of them and then continuing to scan other frequencies when the initial transmission ceases. They are mainly used for monitoring VHF and UHF radio systems.
- Internet radio deviceInternet radio deviceAn Internet radio device, also called network music player is a hardware device that is capable of receiving and playing streamed media from either Internet radio stations or a home network.-Background:...
Consumer audio receivers
In the context of home audio systems, the term "receiver" often refers to a combination of a tunerTuner (radio)
A radio tuner is a subsystem that receives radio broadcasts and converts them into audio-frequency signals which can be fed into an amplifier driving a loudspeaker. FM tuner, AM tuner, Digital Audio Broadcasting DAB tuner, etc. are types of radio tuner dealing with transmissions using different...
, a preamplifier
Preamplifier
A preamplifier is an electronic amplifier that prepares a small electrical signal for further amplification or processing. A preamplifier is often placed close to the sensor to reduce the effects of noise and interference. It is used to boost the signal strength to drive the cable to the main...
, and a power amplifier
Amplifier
Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
all on the same chassis. Audiophiles will refer to such a device as an integrated receiver, while a single chassis that implements only one of the three component functions is called a discrete component. Some audio purists still prefer three discreet units - tuner, preamplifier and power amplifier - but the integrated receiver has, for some years, been the mainstream choice for music listening. The first integrated stereo
STEREO
STEREO is a solar observation mission. Two nearly identical spacecraft were launched into orbits that cause them to respectively pull farther ahead of and fall gradually behind the Earth...
receiver was made by the Harman Kardon
Harman Kardon
harman/kardon is a division of Harman International Industries and manufactures home and car audio equipment.Founded in 1953 by Dr. Sidney Harman and Bernard Kardon — two men with a deep interest in music and the arts — the company helped create the high-fidelity audio industry. Their first product...
company, and came onto the market in 1958. It had undistinguished performance, but it represented a breakthrough to the "all in one" concept of a receiver, and rapidly improving designs gradually made the receiver the mainstay of the marketplace. Many radio receivers also include a loudspeaker
Loudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
.
Hi-Fi / Home theater
Today AV receiverAV receiver
AV receivers or audio-video receivers are one of the many consumer electronics components typically found within a home theatre system. Their primary purpose is to amplify sound from a multitude of possible audio sources as well as route video signals to your TV from various sources. The user may...
s are a common component in a high-fidelity
High fidelity
High fidelity—or hi-fi—reproduction is a term used by home stereo listeners and home audio enthusiasts to refer to high-quality reproduction of sound or images, to distinguish it from the poorer quality sound produced by inexpensive audio equipment...
or home-theatre
Home cinema
Home cinema, also commonly called home theater, are home entertainment set-ups that seek to reproduce a movie theater experience and mood with the help of video and audio equipment in a private home....
system. The receiver is generally the nerve centre of a sophisticated home-theatre system providing selectable inputs for a number of different audio components like record players, compact-disc players and CD-RW
CD-RW
A CD-RW is a rewritable optical disc. It was introduced in 1997, and was known as "CD-Writable" during development. It was preceded by the CD-MO, which was never commercially released....
recorders, and tape decks ( like video cassette recorders (VCR) and video
Video
Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...
components (DVD player
DVD player
A DVD player is a device that plays discs produced under both the DVD-Video and DVD-Audio technical standards, two different and incompatible standards. These devices were invented in 1997 and continue to thrive...
s and DVD recorder
DVD recorder
A DVD recorder , is an optical disc recorder that uses Optical disc recording technologies to digitally record analog signal or digital signals onto blank writable DVD media...
s, video game console
Video game console
A video game console is an interactive entertainment computer or customized computer system that produces a video display signal which can be used with a display device to display a video game...
s, and television set
Television set
A television set is a device that combines a tuner, display, and speakers for the purpose of viewing television. Television sets became a popular consumer product after the Second World War, using vacuum tubes and cathode ray tube displays...
s).
With the decline of gramophone record
Gramophone record
A gramophone record, commonly known as a phonograph record , vinyl record , or colloquially, a record, is an analog sound storage medium consisting of a flat disc with an inscribed, modulated spiral groove...
vinyl discs, modern receivers tend to omit inputs for phonograph
Phonograph
The phonograph record player, or gramophone is a device introduced in 1877 that has had continued common use for reproducing sound recordings, although when first developed, the phonograph was used to both record and reproduce sounds...
turntables, which have separate requirements of their own. All other common audio/visual components can use any of the identical line-level inputs on the receiver for playback, regardless of how they are marked (the "name" on each input is mostly for the convenience of the user.) For instance, a second CD player can be plugged into an "Aux
Jack (connector)
In electronics and electrical assemblies, the term jack commonly refers to a surface-mounted connector, often, but not always, with the female electrical contact or socket, and is the "more fixed" connector of a connector pair...
" input, and will work the same as it will in the "CD" input jacks.
Some receivers can also provide digital signal processor
Digital signal processor
A digital signal processor is a specialized microprocessor with an architecture optimized for the fast operational needs of digital signal processing.-Typical characteristics:...
s (DSP) to give a more realistic auditory illusion
Auditory illusion
An auditory illusion is an illusion of hearing, the aural equivalent of an optical illusion: the listener hears either sounds which are not present in the stimulus, or "impossible" sounds...
of listening in a concert hall. Digital audio
Digital audio
Digital audio is sound reproduction using pulse-code modulation and digital signals. Digital audio systems include analog-to-digital conversion , digital-to-analog conversion , digital storage, processing and transmission components...
S/PDIF
S/PDIF
S/PDIF is a digital audio interconnect used in consumer audio equipment over relatively short distances. The signal is transmitted over either a coaxial cable with RCA connectors or a fiber optic cable with TOSLINK connectors. S/PDIF interconnects components in home theaters and other digital high...
and USB connections are also common today. The home theater receiver, in the vocabulary of consumer electronics, comprises both the 'radio receiver' and other functions, such as control, sound processing, and power amplification. The standalone radio receiver is usually known in consumer electronics as a tuner.
Some modern integrated receivers can send audio out to seven loudspeakers and an additional channel for a subwoofer
Subwoofer
A subwoofer is a woofer, or a complete loudspeaker, which is dedicated to the reproduction of low-pitched audio frequencies known as the "bass". The typical frequency range for a subwoofer is about 20–200 Hz for consumer products, below 100 Hz for professional live sound, and below...
and often include connections for headphones
Headphones
Headphones are a pair of small loudspeakers, or less commonly a single speaker, held close to a user's ears and connected to a signal source such as an audio amplifier, radio, CD player or portable Media Player. They are also known as stereophones, headsets or, colloquially, cans. The in-ear...
. Receivers vary greatly in price, and support stereophonic
Stereophonic sound
The term Stereophonic, commonly called stereo, sound refers to any method of sound reproduction in which an attempt is made to create an illusion of directionality and audible perspective...
or surround sound
Surround sound
Surround sound encompasses a range of techniques such as for enriching the sound reproduction quality of an audio source with audio channels reproduced via additional, discrete speakers. Surround sound is characterized by a listener location or sweet spot where the audio effects work best, and...
. A high-quality receiver for dedicated audio-only listening (two channel stereo) can be relatively inexpensive; excellent ones can be purchased for $300 United States or less. Because modern receivers are purely electronic
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
devices with no moving parts unlike electromechanical
Electromechanics
In engineering, electromechanics combines the sciences of electromagnetism, of electrical engineering and mechanics. Mechanical engineering in this context refers to the larger discipline which includes chemical engineering, and other related disciplines. Electrical engineering in this context...
devices like turntables and cassette decks, they tend to offer many years of trouble-free service. In recent years, the home theater in a box
Home theater in a box
A "home theater in a box" is an integrated home theater package which "bundles" together a combination DVD player/ multi-channel amplifier , speaker wires, connection cables, a remote control, a set of five or more surround sound speakers and a low-frequency...
has become common, which often integrates a surround-capable receiver with a DVD player. The user simply connects it to a television, perhaps other components, and a set of loudspeakers.
Portable radios
Portable radios include simple transistor radioTransistor radio
A transistor radio is a small portable radio receiver using transistor-based circuitry. Following their development in 1954 they became the most popular electronic communication device in history, with billions manufactured during the 1960s and 1970s...
s that are typically monoaural and receive the AM, FM, and/or short wave broadcast band
Broadcast band
A Broadcast band is a segment of the radio spectrum used for broadcasting.-See also:* North American broadcast television frequencies* Dead air* Internet radio* radio networks* Music radio* Old-time radio* Radio astronomy* Radio programming...
s. FM, and often AM, radios are sometimes included as a feature of portable DVD
DVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....
/CD, MP3 CD
MP3 CD
An MP3 CD is a Compact Disc that contains digital audio in the MP3 file format. Discs are written in the Yellow Book standard data format , as opposed to the Red Book standard audio format ....
, and USB key players, as well as cassette player/recorder
Compact Cassette
The Compact Cassette, often referred to as audio cassette, cassette tape, cassette, or simply tape, is a magnetic tape sound recording format. It was designed originally for dictation, but improvements in fidelity led the Compact Cassette to supplant the Stereo 8-track cartridge and reel-to-reel...
s.
AM/FM stereo car radios
Car audio
Car audio/video , auto radio, mobile audio, 12-volt and other terms are used to describe the sound or video system fitted in an automobile. While 12-volt audio and video systems are also used, marketed, or manufactured for marine, aviation, and buses, this article focuses on cars as the most common...
can be a separate dashboard mounted component or a feature of in car entertainment
In car entertainment
In-Car Entertainment, , is a collection of hardware devices installed into automobiles, or other forms of transportation, to provide audio and/or audio/visual entertainment, as well as automotive navigation systems...
systems.
A Boombox
Boombox
Boombox is a colloquial expression for a portable cassette or CD player. Other terms known are ghetto blaster, jambox, or radio-cassette. It is a device capable of receiving radio stations and playing recorded music , usually at relatively high volume...
(or Boom-box)—also sometimes known as a Ghettoblaster or a Jambox, or (in parts of Europe) as a "radio-cassette"—is a name given to larger portable stereo systems capable of playing radio stations and recorded music, often at a high level of volume.
Self-powered portable radios, such as clockwork radio
Clockwork radio
A windup radio or clockwork radio is a radio that is powered by human muscle power rather than batteries or the electrical grid. In the most common arrangement, an internal electrical generator is run by a mainspring, which is wound by a hand crank on the case. Turning the crank winds the spring...
s are used in developing nations or as part of an emergency preparedness kit.
History of radio receivers
Early development
While James Clerk MaxwellJames Clerk Maxwell
James Clerk Maxwell of Glenlair was a Scottish physicist and mathematician. His most prominent achievement was formulating classical electromagnetic theory. This united all previously unrelated observations, experiments and equations of electricity, magnetism and optics into a consistent theory...
was the first person to prove electromagnetic waves existed, in 1887 a German named Heinrich Hertz demonstrated these new waves by using spark gap
Spark gap
A spark gap consists of an arrangement of two conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the voltage difference between the conductors exceeds the gap's breakdown voltage, a spark forms,...
equipment to transmit and receive radio or "Hertzian waves", as they were first called. The experiments were not followed up by Hertz. The practical applications of the wireless communication and remote control technology were implemented by Nikola Tesla
Nikola Tesla
Nikola Tesla was a Serbian-American inventor, mechanical engineer, and electrical engineer...
.
The world's first radio receiver (thunderstorm register) was designed by Alexander Stepanovich Popov
Alexander Stepanovich Popov
Alexander Stepanovich Popov was a Russian physicist who was the first person to demonstrate the practical application of electromagnetic waves....
, and it was first seen at the All-Russia Exhibition 1896
All-Russia exhibition 1896
The All-Russia industrial and art exhibition 1896 in Nizhny Novgorod was held from May 28 till October 1 , 1896. The 1896 exhibition was the biggest pre-revolution exhibition in Russian Empire and was organized with the money allotted by Nicholas II, Emperor of Russia...
. He was the first to demonstrate the practical application of electromagnetic (radio) waves, although he did not care to apply for a patent for his invention.
A device called a coherer
Coherer
The coherer was a primitive form of radio signal detector used in the first radio receivers during the wireless telegraphy era at the beginning of the twentieth century. Invented around 1890 by French scientist Édouard Branly, it consisted of a tube or capsule containing two electrodes spaced a...
became the basis for receiving radio signals. The first person to use the device to detect radio waves was a Frenchman named Edouard Branly
Edouard Branly
Édouard Eugène Désiré Branly was a French inventor, physicist and professor at the Institut Catholique de Paris. He is primarily known for his early involvement in wireless telegraphy and his invention of the Branly coherer around 1890.-Biography:The coherer was the first widely used detector for...
, and Oliver Lodge popularised it when he gave a lecture in 1898 in honour of Hertz. Lodge also made improvements to the coherer.
Many experimenters at the time believed that these new waves could be used to communicate over great distances and made significant improvements to both radio receiving and transmitting apparatus. In 1895 Marconi demonstrated the first viable radio system, leading to transatlantic radio communication in December 1901. The honor was later contested as he was found to be using equipment and designs of other experimenters that held the patents at that time.
John Ambrose Fleming
John Ambrose Fleming
Sir John Ambrose Fleming was an English electrical engineer and physicist. He is known for inventing the first thermionic valve or vacuum tube, the diode, then called the kenotron in 1904. He is also famous for the left hand rule...
's development of an early thermionic valve to help detect radio waves was based upon a discovery of Thomas Edison
Thomas Edison
Thomas Alva Edison was an American inventor and businessman. He developed many devices that greatly influenced life around the world, including the phonograph, the motion picture camera, and a long-lasting, practical electric light bulb. In addition, he created the world’s first industrial...
's (called "The Edison effect", which essentially modified an early light bulb). Fleming called it his "oscillation valve" because it acted in the same way as water valve in only allowing flow in one direction. While Fleming's valve was a great stride forward it would take some years before thermionic, or vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
technology was fully adopted.
Around this time work on other types of detectors
Detector (radio)
A detector is a device that recovers information of interest contained in a modulated wave. The term dates from the early days of radio when all transmissions were in Morse code, and it was only necessary to detect the presence of a radio wave using a device such as a coherer without necessarily...
started to be undertaken and it resulted in what was later known as the cat's whisker. It consisted of a crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
of a material such as galena
Galena
Galena is the natural mineral form of lead sulfide. It is the most important lead ore mineral.Galena is one of the most abundant and widely distributed sulfide minerals. It crystallizes in the cubic crystal system often showing octahedral forms...
with a small springy piece of wire brought up against it. The detector was constructed so that the wire contact could be moved to different points on the crystal, and thereby obtain the best point for rectifying
Rectifier
A rectifier is an electrical device that converts alternating current , which periodically reverses direction, to direct current , which flows in only one direction. The process is known as rectification...
the signal and the best detection. They were never very reliable as the "whisker" needed to be moved periodically to enable it to detect the signal properly.
Valves (Tubes)
An American named Lee de ForestLee De Forest
Lee De Forest was an American inventor with over 180 patents to his credit. De Forest invented the Audion, a vacuum tube that takes relatively weak electrical signals and amplifies them. De Forest is one of the fathers of the "electronic age", as the Audion helped to usher in the widespread use...
, a competitor to Marconi, set about to develop receiver technology that did not infringe any patents to which Marconi had access. He took out a number of patents in the period between 1905 and 1907 covering a variety of developments that culminated in the form of the triode
Triode
A triode is an electronic amplification device having three active electrodes. The term most commonly applies to a vacuum tube with three elements: the filament or cathode, the grid, and the plate or anode. The triode vacuum tube was the first electronic amplification device...
valve in which there was a third electrode
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...
called a grid. He called this an audion tube
Audion tube
The Audion is an electronic amplifying vacuum tube invented by Lee De Forest in 1906. It was the forerunner of the triode, in which the current from the filament to the plate was controlled by a third element, the grid...
. One of the first areas in which valves were used was in the manufacture of telephone
Telephone
The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...
repeaters, and although the performance was poor, they gave significant improvement in long distance telephone receiving circuits.
With the discovery that triode valves could amplify signals it was soon noticed that they would also oscillate, a fact that was exploited in generating signals. Once the triode was established as an amplifier it made a tremendous difference to radio receiver performance as it allowed the incoming signals to be amplified. One way that proved very successful was introduced in 1913 and involved the use of positive feedback in the form of a regenerative detector. This gave significant improvements in the levels of gain that could be achieved, greatly increasing selectivity, enabling this type of receiver to outperform all other types of the era. With the outbreak of the First World War, there was a great impetus to develop radio receiving technology further. An American named Irving Langmuir
Irving Langmuir
Irving Langmuir was an American chemist and physicist. His most noted publication was the famous 1919 article "The Arrangement of Electrons in Atoms and Molecules" in which, building on Gilbert N. Lewis's cubical atom theory and Walther Kossel's chemical bonding theory, he outlined his...
helped introduce a new generation of totally air-evacuated "hard" valves. H. J. Round
H. J. Round
Captain Henry Joseph Round was one of the early pioneers of radio and received 117 patents. He was the first to report observation of electroluminescence from a diode, leading to the discovery of the light-emitting diode...
undertook some work on this and in 1916 he produced a number of valves with the grid connection taken out of the top of the envelope away from the anode
Anode
An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....
connection.
Autodyne and superheterodyne
By the 1920s, the tuned radio frequency receiverTuned radio frequency receiver
A tuned radio frequency receiver is a radio receiver that is usually composed of several tuned radio frequency amplifiers followed by circuits to detect and amplify the audio signal. Prevalent in the early 20th century, it can be difficult to operate because each stage must be individually tuned...
(TRF) represented a major improvement in performance over what had been available before, it still fell short of the needs for some of the new applications. To enable receiver technology to meet the needs placed upon it a number of new ideas started to surface. One of these was a new form of direct conversion receiver. Here an internal or local oscillator was used to beat with the incoming signal to produce an audible signal that could be amplified by an audio amplifier
Audio amplifier
An audio amplifier is an electronic amplifier that amplifies low-power audio signals to a level suitable for driving loudspeakers and is the final stage in a typical audio playback chain.The preceding stages in such a chain are low power audio amplifiers which perform tasks like pre-amplification,...
.
H. J. Round
H. J. Round
Captain Henry Joseph Round was one of the early pioneers of radio and received 117 patents. He was the first to report observation of electroluminescence from a diode, leading to the discovery of the light-emitting diode...
developed a receiver he called an autodyne
Autodyne
The autodyne circuit was an improvement to radio signal amplification using the De Forest Audion vacuum tube amplifier. By allowing the tube to oscillate at a frequency slightly different from the desired signal, the sensitivity over other receivers was greatly improved. The autodyne circuit was...
in which the same valve was used as a mixer and an oscillator, Whilst the set used fewer valves it was difficult to optimise the circuit for both the mixer and oscillator functions.
The next leap forward in receiver technology was a new type of receiver known as the superheterodyne, or supersonic heterodyne receiver. A Frenchman named Lucien Levy was investigating ways in which receiver selectivity could be improved and in doing this he devised a system whereby the signals were converted down to a lower frequency where the filter bandwidths could be made narrower. A further advantage was that the gain of valves was considerably greater at the lower frequencies used after the frequency conversion, and there were fewer problems with the circuits bursting into oscillation
Oscillation
Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...
.
The idea for developing a receiver with a fixed intermediate frequency amplifier and filter is credited to Edwin Armstrong
Edwin Armstrong
Edwin Howard Armstrong was an American electrical engineer and inventor. Armstrong was the inventor of modern frequency modulation radio....
of the United States. Working for the American Expeditionary Force
American Expeditionary Force
The American Expeditionary Forces or AEF were the United States Armed Forces sent to Europe in World War I. During the United States campaigns in World War I the AEF fought in France alongside British and French allied forces in the last year of the war, against Imperial German forces...
in Europe during 1918, Armstrong thought that if the incoming signals was mixed with a variable frequency oscillator (the "local oscillator"), a lower-frequency fixed tuned amplifier could be used. Armstrong's original receiver consisted of a total of eight vacuum tubes. Several tuned circuits could be cascaded to improve selectivity, and being set on a fixed frequency they did not all need to be changed in line with one another. The filters could be preset and left correctly tuned. Armstrong was not the only person working on the idea of a superheterodyne receiver. Alexander Meissner
Alexander Meissner
Alexander Meissner was Austrian engineer and physicist. He was born in Vienna and died in Berlin....
in Germany had taken out a patent for the idea six months before Armstrong, but since Meissner did not prove the idea in practice, and he did not build a superheterodyne radio, the invention
Invention
An invention is a novel composition, device, or process. An invention may be derived from a pre-existing model or idea, or it could be independently conceived, in which case it may be a radical breakthrough. In addition, there is cultural invention, which is an innovative set of useful social...
is credited to Armstrong.
The need for the increased performance of the superheterodyne receiver was first experienced in North America, and by the late 1920s most radio sets were superheterodyne receivers. However, in Europe the number of broadcast stations did not start to rise as rapidly until later. Even so, by the mid-1930s virtually all receiving sets in Europe as well were using the superheterodyne principle. In 1926, the tetrode
Tetrode
A tetrode is an electronic device having four active electrodes. The term most commonly applies to a two-grid vacuum tube. It has the three electrodes of a triode and an additional screen grid which significantly changes its behaviour.-Control grid:...
valve was introduced, and enabled further improvements in performance.
War and postwar developments
Communications receiver
A communications receiver is a type of radio receiver used as a component of a radio communication link.-Features:Commercial communications receivers are characterised by high stability and reliability of performance, and are generally adapted for remote control and monitoring...
s were designed. Some like the National HRO
National HRO
The original National HRO was a 9-tube shortwave general coverage communications receiver manufactured by the National Radio Company of Malden, Massachusetts, USA.-History:...
are still sought by enthusiasts today and although they are relatively large by today's standards, they can still give a good account of themselves under current crowded band conditions.
In the late 1940s the transistor
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
was discovered. Initially the devices were not widely used because of their expense, and the fact that valves were being made smaller, and performed better. However by the early 1960s portable transistor broadcast receivers (transistor radio
Transistor radio
A transistor radio is a small portable radio receiver using transistor-based circuitry. Following their development in 1954 they became the most popular electronic communication device in history, with billions manufactured during the 1960s and 1970s...
s) were hitting the market place. These radios were ideal for broadcast reception on the long and medium wave bands. They were much smaller than their valve equivalents, they were portable and could be powered from batteries
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
. Although some valve portable receivers were available, batteries for these were expensive and did not last for long. The power requirements for transistor radios were very much less, resulting in batteries lasting for much longer and being considerably cheaper.
Semiconductors
Further developments in semiconductor technology led to the introduction of the integrated circuitIntegrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
in the late 1950s. This enabled radio receiver technology to move forward even further. Integrated circuits enabled high performance circuits to be built for less cost, and significant amounts of space could be saved.
As a result of these developments new techniques could be introduced. One of these was the frequency synthesizer
Frequency synthesizer
A frequency synthesizer is an electronic system for generating any of a range of frequencies from a single fixed timebase or oscillator. They are found in many modern devices, including radio receivers, mobile telephones, radiotelephones, walkie-talkies, CB radios, satellite receivers, GPS systems,...
that was used to generate the local oscillator signal for the receiver. By using a synthesizer it was possible to generate a very accurate and stable local oscillator signal. Also the ability of synthesizers to be controlled by microprocessor
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
s meant that many new facilities could be introduced apart from the significant performance improvements offered by synthesizers.
Digital technologies
Receiver technology had been advancing gradually and regularly. Many of the functions performed by a analogue electronicsAnalogue electronics
Analogue electronics are electronic systems with a continuously variable signal, in contrast to digital electronics where signals usually take only two different levels. The term "analogue" describes the proportional relationship between a signal and a voltage or current that represents the signal...
can be performed by software instead. The benefit is that software is not affected by temperature, physical variables, electronic noise and manufacturing defects.
While today's radios are amazing pieces of modern technology, filled with low- power, high performance, integrated circuits crammed into the smallest spaces, the basic principle of the radio receiver is practically always the superheterodyne one, the same idea which was developed by Edwin Armstrong back in 1918. For really high-performance receivers, such as satellite communications receivers and military/naval receivers, two-stage ("double conversion") and even three-stage ("triple conversion") superheterodyne processing is frequently used. Single-conversion receivers are rather simple-minded in their nature.
DSP technology
DSP technology, short for digital signal processingDigital signal processing
Digital signal processing is concerned with the representation of discrete time signals by a sequence of numbers or symbols and the processing of these signals. Digital signal processing and analog signal processing are subfields of signal processing...
, is the use of digital means to process signals and is coming into wide use in modern shortwave receivers. It is the basis of many areas of modern technology including cell phones, CD players, video recorders and computers. A digital signal is essentially a stream or sequence of numbers that relay a message through some sort of medium such as a wire. The primary benefit of DSP hardware in shortwave receivers is the ability to tailor the bandwidth of the receiver to current reception conditions and to the type of signal being listened to. A typical analog only receiver may have a limited number of fixed bandwidths, or only one, but a DSP receiver may have 40 or more individually selectable filters.
PC controlled radio receivers
"PC radios", or radios that are designed to be controlled by a standard PC are controlled by specialized PC software using a serial port connected to the radio. A "PC radio" may not have a front-panel at all, and may be designed exclusively for computer control, which reduces cost.Some PC radios have the great advantage of being field upgradable by the owner. New versions of the DSP firmware
Firmware
In electronic systems and computing, firmware is a term often used to denote the fixed, usually rather small, programs and/or data structures that internally control various electronic devices...
can be downloaded from the manufacturer's web site and uploaded into the flash memory
Flash memory
Flash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...
of the radio. The manufacturer can then in effect add new features to the radio over time, such as adding new filters, DSP noise reduction, or simply to correct bugs.
A full-featured radio control program allows for scanning and a host of other functions and, in particular, integration of databases in real-time, like a "TV-Guide" type capability. This is particularly helpful in locating all transmissions on all frequencies of a particular broadcaster, at any given time. Some control software designers have even integrated Google Earth
Google Earth
Google Earth is a virtual globe, map and geographical information program that was originally called EarthViewer 3D, and was created by Keyhole, Inc, a Central Intelligence Agency funded company acquired by Google in 2004 . It maps the Earth by the superimposition of images obtained from satellite...
to the shortwave databases, so it is possible to "fly" to a given transmitter site location with a click of a mouse. In many cases the user is able to see the transmitting antennas where the signal is originating from.
Radio control software
The field of software control of PC radios has grown rapidly in the last several years, with developers making a number of advances. Since the Graphical User InterfaceGraphical user interface
In computing, a graphical user interface is a type of user interface that allows users to interact with electronic devices with images rather than text commands. GUIs can be used in computers, hand-held devices such as MP3 players, portable media players or gaming devices, household appliances and...
or GUI interface PC to the radio has unlimited flexibility, any number of new features can be added by the software designer.Features that can be found in advanced control software programs today include a band table, GUI controls corresponding to traditional radio controls, local time clock and a UTC clock, signal strength meter, an ILG database for shortwave listening with lookup capability, scanning capability, text-to-speech interface, and integrated Conference Server.
Software-defined radios
The next level in radio / software integration are so-called pure "software defined radios". The distinction here is that all filtering, modulation and signal manipulation is done in software, usually by a PC soundcard or by a dedicated piece of DSP hardware. There may be a minimal RFRadio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
front-end or traditional radio that supplies an IF
Intermediate frequency
In communications and electronic engineering, an intermediate frequency is a frequency to which a carrier frequency is shifted as an intermediate step in transmission or reception. The intermediate frequency is created by mixing the carrier signal with a local oscillator signal in a process called...
to the SDR. SDR's can go far beyond the usual demodulation
Demodulation
Demodulation is the act of extracting the original information-bearing signal from a modulated carrier wave.A demodulator is an electronic circuit that is used to recover the information content from the modulated carrier wave.These terms are traditionally used in connection with radio receivers,...
capability of typical, and even high-end DSP shortwave radios. They can for example, record large swaths of the radio spectrum to a hard drive for "playback" at a later date. The same SDR that one minute is demodulating a simple AM broadcast may also be able to decode an HDTV broadcast in the next. A well known open-source project called GNU Radio
GNU Radio
GNU Radio is a free software toolkit for learning about, building, and deploying software-defined radio systems. GNU Radio is released under the GPL version 3 license....
is dedicated to evolving a high-performance SDR. All the source code for this SDR is freely downloadable and modifiable by anyone.
See also
- AV receiverAV receiverAV receivers or audio-video receivers are one of the many consumer electronics components typically found within a home theatre system. Their primary purpose is to amplify sound from a multitude of possible audio sources as well as route video signals to your TV from various sources. The user may...
- Car audioCar audioCar audio/video , auto radio, mobile audio, 12-volt and other terms are used to describe the sound or video system fitted in an automobile. While 12-volt audio and video systems are also used, marketed, or manufactured for marine, aviation, and buses, this article focuses on cars as the most common...
- Crystal radio receiverCrystal radio receiverthumb|Boy listening to a modern crystal radioA crystal radio receiver, also called a crystal set or cat's whisker receiver, is a very simple radio receiver, popular in the early days of radio. It needs no battery or power source and runs on the power received from radio waves by a long wire antenna...
- DemodulationDemodulationDemodulation is the act of extracting the original information-bearing signal from a modulated carrier wave.A demodulator is an electronic circuit that is used to recover the information content from the modulated carrier wave.These terms are traditionally used in connection with radio receivers,...
- Dielectric wireless receiverDielectric wireless receiverDielectric wireless receiver is a type of radiofrequency receiver front-end featuring a complete absence of electronic circuitry and metal interconnects. It offers immunity against damage from intense electromagnetic radiation, produced by EMP and HPM sources...
- Digital Audio Broadcast (DAB)
- Direct conversion receiver
- NeutrodyneNeutrodyneThe Neutrodyne was a particular type of Tuned Radio Frequency radio receiver, in which the instability-causing inter-electrode capacitance of the triode RF tubes is cancelled out or "neutralized"...
- RadarRadarRadar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
- Radar warning receiverRadar warning receiverRadar warning receiver systems detect the radio emissions of radar systems. Their primary purpose is to issue a warning when a radar signal that might be a threat is detected. The warning can then be used, manually or automatically, to evade the detected threat...
- Radiogram (furniture)Radiogram (furniture)In British English, a radiogram is a now old-fashioned piece of furniture that combined a valve radio and record player. The word radiogram is a portmanteau of radio and gramophone....
- Receiver (information theory)Receiver (Information Theory)The receiver in information theory is the receiving end of a communication channel. It receives decoded messages/information from the sender, who first encoded them. Sometimes the receiver is modeled so as to include the decoder. Real-world receivers like radio receivers or telephones can not be...
- Regenerative radio receiver
- Selectivity (electronic)
- Sensitivity (electronics)Sensitivity (electronics)The sensitivity of an electronic device, such as a communications system receiver, or detection device, such as a PIN diode, is the minimum magnitude of input signal required to produce a specified output signal having a specified signal-to-noise ratio, or other specified criteria.Sensitivity is...
- Noise (electronics)Noise (electronics)Electronic noise is a random fluctuation in an electrical signal, a characteristic of all electronic circuits. Noise generated by electronic devices varies greatly, as it can be produced by several different effects...
- DistortionDistortionA distortion is the alteration of the original shape of an object, image, sound, waveform or other form of information or representation. Distortion is usually unwanted, and often many methods are employed to minimize it in practice...
- Satnav
- Superheterodyne receiverSuperheterodyne receiverIn electronics, a superheterodyne receiver uses frequency mixing or heterodyning to convert a received signal to a fixed intermediate frequency, which can be more conveniently processed than the original radio carrier frequency...
- Table radioTable radioTable radio is a term used to describe a small, self-contained radio receiver used as an entertainment device. Most such receivers are limited to radio functions, though some have compact disc or audio cassette players and clock radio functions built in; some models also include shortwave or...
- TelecommunicationTelecommunicationTelecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...
- Television receive-onlyTelevision receive-onlyTelevision receive-only, TVRO, or Big ugly dish , is a term used in North America to refer to the reception of satellite television from FSS-type satellites, generally on C-band analog; free-to-air and unconnected to a commercial DBS provider...
- Transistor radioTransistor radioA transistor radio is a small portable radio receiver using transistor-based circuitry. Following their development in 1954 they became the most popular electronic communication device in history, with billions manufactured during the 1960s and 1970s...
- Tuned radio frequency receiverTuned radio frequency receiverA tuned radio frequency receiver is a radio receiver that is usually composed of several tuned radio frequency amplifiers followed by circuits to detect and amplify the audio signal. Prevalent in the early 20th century, it can be difficult to operate because each stage must be individually tuned...
- Tuner (radio)Tuner (radio)A radio tuner is a subsystem that receives radio broadcasts and converts them into audio-frequency signals which can be fed into an amplifier driving a loudspeaker. FM tuner, AM tuner, Digital Audio Broadcasting DAB tuner, etc. are types of radio tuner dealing with transmissions using different...
Further reading
- Communications Receivers, Third Edition, Ulrich L. Rohde, Jerry Whitaker, McGraw Hill, New York, 2001, ISBN 0-07-136121-9