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156-684: The AN/ARC-5 Command Radio Set is a series of radio receivers, transmitters, and accessories carried aboard U.S. Navy aircraft during World War II and for some years afterward. It is described as "a complete multi-channel radio transmitting and receiving set providing communication and navigation facilities for aircraft. The LF-MF-HF components are designed to transmit and receive voice, tone-modulated, and continuous wave (cw) signals." Its flexible design provided AM radiotelephone voice communication and Modulated continuous wave (MCW) and Continuous wave (CW) Morse code modes, all of which are typical capabilities in other Navy aircraft communication sets of

312-471: 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

468-463: A dual conversion superheterodyne , and one with three IFs is called a triple conversion superheterodyne . The main reason that this is done is that with a single IF there is a tradeoff between low image response and selectivity. The separation between the received frequency and the image frequency is equal to twice the IF frequency, so the higher the IF, the easier it is to design an RF filter to remove

624-418: 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

780-407: A product detector using a so-called beat frequency oscillator , and there are other techniques used for different types of modulation . The resulting audio signal (for instance) is then amplified and drives a loudspeaker. When so-called high-side injection has been used, where the local oscillator is at a higher frequency than the received signal (as is common), then the frequency spectrum of

936-497: 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

1092-414: A spark gap . The output signal was at a carrier frequency defined by the physical construction of the gap, modulated by the alternating current signal from the alternator. Since the output frequency of the alternator was generally in the audible range, this produces an audible amplitude modulated (AM) signal. Simple radio detectors filtered out the high-frequency carrier, leaving the modulation, which

1248-474: 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

1404-427: A "supersonic heterodyne" between the station's carrier frequency and the regenerative receiver's oscillation frequency. When the first receiver began to oscillate at high outputs, its signal would flow back out through the antenna to be received on any nearby receiver. On that receiver, the two signals mixed just as they did in the original heterodyne concept, producing an output that is the difference in frequency between

1560-553: A 10.7 MHz IF frequency. In that situation, the RF amplifier must be tuned so the IF amplifier does not see two stations at the same time. If the AM broadcast band receiver LO were set at 1200 kHz, it would see stations at both 745 kHz (1200−455 kHz) and 1655 kHz. Consequently, the RF stage must be designed so that any stations that are twice the IF frequency away are significantly attenuated. The tracking can be done with

1716-515: A 250 ohm tap on the AF transformers which can be connected. ARA/ATA units and equivalent SCR-274-N units are interchangeable between systems, aside from audio impedance differences. However, AN/ARC-5 units generally are not interchangeable with the units of the earlier systems. In contrast to ARA and SCR-274-N receivers, all AN/ARC-5 receivers have automatic volume control and a modified tube complement. The AN/ARC-5 navigation receivers have terminals and

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1872-399: A 455 kHz IF, but a station on 30.910 would also produce a 455 kHz beat, so both stations would be heard at the same time. But it is virtually impossible to design an RF tuned circuit that can adequately discriminate between 30 MHz and 30.91 MHz, so one approach is to "bulk downconvert" whole sections of the shortwave bands to a lower frequency, where adequate front-end tuning

2028-627: 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

2184-609: A check of the dial calibration by giving a visual indication, viewable by raising a small cover, when the oscillator's frequency matches that of an internal crystal. ARA and SCR-274-N. AN/ARC-5. Audio frequency receiver output and modulator sidetone impedance for the ARA/ATA and the AN/ARC-5 is 300 to 600 ohms. In the SCR-274-N "-A" version, the receiver and modulator impedance is 4000 ohms, while "-B" and later version units have

2340-439: A dual-conversion superhet there are two mixers, so the demodulator is called the third detector . The stages of an intermediate frequency amplifier ("IF amplifier" or "IF strip") are tuned to a fixed frequency that does not change as the receiving frequency changes. The fixed frequency simplifies optimization of the IF amplifier. The IF amplifier is selective around its center frequency f IF . The fixed center frequency allows

2496-422: A fixed range of frequencies offered, which resulted in a worldwide de facto standardization of intermediate frequencies. In early superhets, the IF stage was often a regenerative stage providing the sensitivity and selectivity with fewer components. Such superhets were called super-gainers or regenerodynes. This is also called a Q multiplier , involving a small modification to an existing receiver especially for

2652-599: A four-channel crystal-controlled VHF-AM receiver and transmitter for the U.S. Army's SCR-274-N system. The Army did not adopt these VHF components to any extent because of the move to a common British/American VHF capability in the form of the Bendix SCR-522 VHF-AM set. That remained Army policy until the arrival of the AN/ARC-3. The Navy adopted modified versions of the Western Electric units as

2808-474: A frequency that could be amplified by existing systems. For instance, to receive a signal at 1500 kHz, far beyond the range of efficient amplification at the time, one could set up an oscillator at, for example, 1560 kHz. Armstrong referred to this as the " local oscillator " or LO. As its signal was being fed into a second receiver in the same device, it did not have to be powerful, generating only enough signal to be roughly similar in strength to that of

2964-421: 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

3120-548: 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

3276-877: A high IF frequency. The first IF stage uses a crystal filter with a 12 kHz bandwidth. There is a second frequency conversion (making a triple-conversion receiver) that mixes the 81.4 MHz first IF with 80 MHz to create a 1.4 MHz second IF. Image rejection for the second IF is not an issue as the first IF has a bandwidth of much less than 2.8 MHz. To avoid interference to receivers, licensing authorities will avoid assigning common IF frequencies to transmitting stations. Standard intermediate frequencies used are 455 kHz for medium-wave AM radio, 10.7 MHz for broadcast FM receivers, 38.9 MHz (Europe) or 45 MHz (US) for television, and 70 MHz for satellite and terrestrial microwave equipment. To avoid tooling costs associated with these components, most manufacturers then tended to design their receivers around

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3432-696: 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 the International Telecommunication Union (ITU), which allocates frequency bands in

3588-493: 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

3744-595: 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

3900-403: 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 a controller device control

4056-427: 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,

4212-411: A multi-section variable capacitor or some varactors driven by a common control voltage. An RF amplifier may have tuned circuits at both its input and its output, so three or more tuned circuits may be tracked. In practice, the RF and LO frequencies need to track closely but not perfectly. In the days of tube (valve) electronics, it was common for superheterodyne receivers to combine the functions of

4368-432: A narrow-band receiver can have a fixed tuned RF amplifier. In that case, only the local oscillator frequency is changed. In most cases, a receiver's input band is wider than its IF center frequency. For example, a typical AM broadcast band receiver covers 510 kHz to 1655 kHz (a roughly 1160 kHz input band) with a 455 kHz IF frequency; an FM broadcast band receiver covers 88 MHz to 108 MHz band with

4524-499: A non-linear component to produce both sum and difference beat frequency signals, each one containing the modulation in the desired signal. The output of the mixer may include the original RF signal at f RF , the local oscillator signal at f LO , and the two new heterodyne frequencies f RF  +  f LO and f RF  −  f LO . The mixer may inadvertently produce additional frequencies such as third- and higher-order intermodulation products. Ideally,

4680-691: A pre-World War II Navy equipment nomenclature. The major units of the ARA are five receivers covering 0.19 to 9.1 MHz, each unit with its own dynamotor power supply. The major units of the ATA are five transmitters covering 2.1 to 9.1 MHz, using a common transmitter dynamotor/screen modulator unit. Most units were made by the Aircraft Radio Corporation (USN manufacturer's code CBY). Many units were also made by Stromberg-Carlson (USN manufacturer's code CCT). To equip US Army Air Corps planes,

4836-470: 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

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4992-420: 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

5148-459: 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

5304-410: A receiver system that used this effect to produce audible Morse code output using a single triode. The output of the amplifier taken at the anode was connected back to the input through a "tickler", causing feedback that drove input signals well beyond unity. This caused the output to oscillate at a chosen frequency with great amplification. When the original signal cut off at the end of the dot or dash,

5460-673: 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

5616-446: 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,

5772-441: 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

5928-453: A switch to connect a DU-series direction finding loop to the receiver, and have a special audio line for an MX-19/ARC-5 adapter to allow the receiver to serve as an LF/MF localizer for the Navy's short-lived AN/ARN-9 Air-Track (related to ZA, ZAX) instrument landing system. These two capabilities were rarely if ever utilized. Otherwise, equivalent receivers of all three systems can interchange as

6084-673: A team of maintenance engineers to keep them running. Nevertheless, the strategic value of direction finding on weak signals was so high that the British Admiralty felt the high cost was justified. Although a number of researchers discovered the superheterodyne concept, filing patents only months apart, American engineer Edwin Armstrong is often credited with the concept. He came across it while considering better ways to produce RDF receivers. He had concluded that moving to higher "short wave" frequencies would make RDF more useful and

6240-416: 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

6396-652: 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

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6552-409: A unit. Few transmitter components of the AN/ARC-5 are interchangeable with ATA or SCR-274-N equivalent units. Mechanically, the transmitter rear power connector is slightly different, so inserting the wrong transmitter in a rack can damage either the rack or the transmitter power connector. Electrically, AN/ARC-5 transmitters use high-level final amplifier plate modulation, and the output tank circuit

6708-435: 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

6864-472: A wide frequency range (e.g. scanners and spectrum analyzers) a first IF frequency higher than the reception frequency is employed in a double conversion configuration. For instance, the Rohde & Schwarz EK-070 VLF/HF receiver covers 10 kHz to 30 MHz. It has a band switched RF filter and mixes the input to a first IF of 81.4 MHz and a second IF frequency of 1.4 MHz. The first LO frequency

7020-405: A yellow circle-S stamped on the front panel. Such receivers were not remotely tuned by the pilot, but were instead lock-tuned to the associated transmitter's frequency before take-off. AN/ARC-5 navigation receivers are not so stabilized, and if installed in the rack a control that allows remote tuning is required. Because of these characteristics, AN/ARC-5 close equivalents to the control boxes of

7176-413: 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

7332-703: 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

7488-468: Is 81.4 to 111.4 MHz, a reasonable range for an oscillator. But if the original RF range of the receiver were to be converted directly to the 1.4 MHz intermediate frequency, the LO frequency would need to cover 1.4-31.4 MHz which cannot be accomplished using tuned circuits (a variable capacitor with a fixed inductor would need a capacitance range of 500:1). Image rejection is never an issue with such

7644-445: 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

7800-448: Is a type of radio receiver that uses frequency mixing to convert a received signal to a fixed intermediate frequency (IF) which can be more conveniently processed than the original carrier frequency . It was invented by French radio engineer and radio manufacturer Lucien Lévy . Virtually all modern radio receivers use the superheterodyne principle. Early Morse code radio broadcasts were produced using an alternator connected to

7956-433: 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

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8112-438: Is basically another self-contained superheterodyne receiver, most likely with a standard IF of 455 kHz. Microprocessor technology allows replacing the superheterodyne receiver design by a software-defined radio architecture, where the IF processing after the initial IF filter is implemented in software. This technique is already in use in certain designs, such as very low-cost FM radios incorporated into mobile phones, since

8268-482: Is because it is easier and less expensive to get high selectivity at a lower frequency using tuned circuits. The bandwidth of a tuned circuit with a certain Q is proportional to the frequency itself (and what's more, a higher Q is achievable at lower frequencies), so fewer IF filter stages are required to achieve the same selectivity. Also, it is easier and less expensive to get high gain at a lower frequencies. However, in many modern receivers designed for reception over

8424-410: 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

8580-427: 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

8736-426: Is easier to arrange. For example, the ranges 29 MHz to 30 MHz; 28 MHz to 29 MHz etc. might be converted down to 2 MHz to 3 MHz, there they can be tuned more conveniently. This is often done by first converting each "block" up to a higher frequency (typically 40 MHz) and then using a second mixer to convert it down to the 2 MHz to 3 MHz range. The 2 MHz to 3 MHz "IF"

8892-455: Is important to understand that this gradual movement to VHF was not accomplished overnight, and there were still pockets of documented HF command set employment through war's end, especially in smaller aircraft. In terms of longevity, the AN/ARR-2 continued into service well into the 1950s, and the beacon band R-23A/ARC-5 receiver was still to be found in some older US Navy aircraft as late as

9048-565: 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

9204-417: 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

9360-410: Is necessary to suppress the image frequency , and may also serve to prevent strong out-of-passband signals from saturating the initial amplifier. A local oscillator provides the mixing frequency; it is usually a variable frequency oscillator which is used to tune the receiver to different stations. The frequency mixer does the actual heterodyning that gives the superheterodyne its name; it changes

9516-404: Is recovered and then further amplified. AM demodulation requires envelope detection , which can be achieved by means of rectification and a low-pass filter (which can be as simple as an RC circuit ) to remove remnants of the intermediate frequency. FM signals may be detected using a discriminator, ratio detector , or phase-locked loop . Continuous wave and single sideband signals require

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9672-415: Is required. The output of the antenna may be very small, often only a few microvolts . The signal from the antenna is tuned and may be amplified in a so-called radio frequency (RF) amplifier, although this stage is often omitted. One or more tuned circuits at this stage block frequencies that are far removed from the intended reception frequency. To tune the receiver to a particular station, the frequency of

9828-436: Is shunt high voltage fed. The two earlier systems use less effective screen modulation, and the output circuit is series high voltage fed. The only electrical components of the AN/ARC-5 transmitter system that are interchangeable with the earlier systems are the dynamotor and the antenna relay. Unlike earlier systems, none of the AN/ARC-5 control boxes have audio jacks for the microphone, headphone, or key. A separate jack box

9984-416: Is that by changing the LO frequency you can tune in different stations. For instance, to receive a signal at 1300 kHz, one could tune the LO to 1360 kHz, resulting in the same 60 kHz IF. This means the amplifier section can be tuned to operate at a single frequency, the design IF, which is much easier to do efficiently. Armstrong put his ideas into practice, and the technique was soon adopted by

10140-524: 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

10296-478: Is used instead. AN/ARC-5 transmitter control boxes contain no Morse key. The broadcast band receiver in all of these command sets is intended to host a homing adapter for the Navy ZB/YE homing system. The homing adapter demodulates a signal near 246 MHz that is modulated with a broadcast band carrier. The output is sent to the broadcast band receiver tuned to the modulating frequency to further demodulate

10452-522: 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 Superhet A superheterodyne receiver , often shortened to superhet ,

10608-442: The image frequency and must be rejected by the tuned circuits in the RF stage. The image frequency is 2  f IF higher (or lower) than the desired frequency f RF , so employing a higher IF frequency f IF increases the receiver's image rejection without requiring additional selectivity in the RF stage. To suppress the unwanted image, the tuning of the RF stage and the LO may need to "track" each other. In some cases,

10764-504: 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

10920-509: 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

11076-400: 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

11232-439: The "short wave" amplification problem, as the "difference" output still retained its original modulation, but on a lower carrier frequency. In the example above, one can amplify the 100 kHz beat signal and retrieve the original information from that, the receiver does not have to tune in the higher 300 kHz original carrier. By selecting an appropriate set of frequencies, even very high-frequency signals could be "reduced" to

11388-531: 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

11544-489: The 1930s, improvements in vacuum tube technology rapidly eroded the TRF receiver's cost advantages, and the explosion in the number of broadcasting stations created a demand for cheaper, higher-performance receivers. The introduction of an additional grid in a vacuum tube, but before the more modern screen-grid tetrode, included the tetrode with two control grids ; this tube combined the mixer and oscillator functions, first used in

11700-522: The 1970s. After World War II, surplus HF receivers and transmitters of the AN/ARC-5 family were extensively used in amateur radio stations. According to CQ magazine publisher Wayne Green , they first appeared for public purchase in March 1947, with thousands eventually becoming available, making them "by far the most popular surplus item to appear on the market." Green's magazine alone published some 47 articles on converting command sets to amateur use over

11856-426: The 1980s, multi-component capacitor-inductor filters had been replaced with precision electromechanical surface acoustic wave (SAW) filters . Fabricated by precision laser milling techniques, SAW filters are cheaper to produce, can be made to extremely close tolerances, and are very stable in operation. The received signal is now processed by the demodulator stage where the audio signal (or other baseband signal)

12012-611: The AN/ARC5 series is almost identical to the former units but both receivers and transmitters are somewhat different electrically. A receiver and transmitter were added that provide four-channel crystal-controlled VHF-AM operation, along with a rarely encountered set of transmitters that provide coverage of 0.5 to 2.1 MHz. The main units of both the Navy and the Army systems were usually installed in three-receiver racks and two-transmitter racks. Units not in service could be stored on board

12168-414: The AN/ARR-2, an all-in-one homing receiver that replaced the broadcast band receiver and external homing adapter and had other enhancements as well. The R-4A/ARR-2 uses the same dynamotor as the AN/ARC-5 sets, fits in the same racks, and can be controlled by special AN/ARC-5 control boxes. The AN/ARR-2 replaced the earlier R-24/ARC-5 and R-1/ARR-1 combo in AN/ARC-5 installations. Western Electric developed

12324-627: The ARA/ATA and SCR-274-N are rare or never existed. The most common AN/ARC-5 receiver remote control box is the C-38/ARC-5, which allows control only of audio volume of the VHF and MF/HF receivers. No power, mode, or frequency controls are present. The C-38 also has controls for the R-4A homing receiver. A common AN/ARC-5 transmitter control box C-30A/ARC-5 has controls for selecting the MF/HF transmitter or

12480-460: The ARC5 as a driver for an ultrasonic nebulizer. Radio 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 a transmitter to a receiver, by modulating the radio signal (impressing an information signal on

12636-474: 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

12792-459: The IF bandpass filter removes all but the desired IF signal at f IF . The IF signal contains the original modulation (transmitted information) that the received radio signal had at f RF . The frequency of the local oscillator f LO is set so the desired reception radio frequency f RF mixes to f IF . There are two choices for the local oscillator frequency because of the correspondence between positive and negative frequencies. If

12948-523: The R-28/ARC-5 receiver and T-23/ARC-5 transmitter. The T-126/ARC-5 is a late variant of the T-23 which allowed the four channels to be grouped in a 100 to 146 MHz tuning range, smaller than the T-23's. A typical installation of ARA/ATA or SCR-274-N sets would consist of a 3.0 to 6.0 MHz, a .19 to .55 MHz, and a 6.0 to 9.1 MHz receiver in a three-unit rack. Any two transmitters covering

13104-457: The US Army adopted in 1941 a reduced set of radios from the ARA/ATA range. Designated SCR-274-N, these Army radios were electrically almost identical to their ARA/ATA counterparts, except for receiver output and modulator sidetone audio transformer output impedance. Structurally and in appearance, they were virtually identical except for most later units being left unpainted aluminum in contrast to

13260-596: 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

13416-604: The VHF transmitter, and a switch to select the channel for both the VHF transmitter and receiver. Mode controls are normally set for voice and covered. The typical AN/ARC-5 three-receiver, two-transmitter installation reflects system capabilities that are quite sophisticated compared to the earlier systems, allowing VHF homing, four channel VHF-AM communications, and one channel MF/HF-AM communications. All unnecessary controls have been eliminated to simplify operation of this more capable system. Aircraft Radio Corporation, along with Stromberg-Carlson, made most AN/ARC-5 units except for

13572-569: The Western Electric VHF units. The AN/ARC-5 certainly represents the climax development of the pre-war MF/HF command set. But its VHF AN/ARC-5 set and the AN/ARR-2 homing adapter presaged a move toward higher frequencies. During World War II, the Navy began a slow movement toward VHF-AM for command functions in theaters where it made sense, beginning with the Western Electric WE-233A commercial airline set which

13728-401: 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 a recipient over

13884-405: 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

14040-994: The aircraft, just as one would store tuning units of other types of radio equipment. The following is a table of ARA/ATA, SCR-274-N, and AN/ARC-5 major components that could comprise a typical three-receiver, two-transmitter installation, with other configurations also being possible. In addition, several miscellaneous components are listed. A blank in the component ID column indicates that no equivalent unit existed for that system. A.R.C. refers to Aircraft Radio Corporation. Notes: (*) A (basic model) or B (1st revision). (†) No letter (basic model) or A (revision). (‡) A (basic model) or AM (field modified to remove vacuum capacitor). LF/MF/HF receivers all use an almost identical 6-tube superhet design: r.f. amplifier (12SK7), converter (12K8), two i.f. stages (two 12SK7's, or 12SK7/12SF7), diode detector/ BFO (12SR7), and one audio stage (12A6). Transmitters use four tubes: 1626 oscillator, two 1625 finals, and 1629 magic-eye tuning. The latter allows

14196-510: The anticipated USAAF use of the AN/ARR-1 homing adapter (see below) compelled adding these units to the SCR-274-N. Early Army units were made by Aircraft Radio Corporation, but the vast majority was made by Western Electric, plus a few by Colonial Radio and others. In late 1943, the U.S. Navy fielded an improved and more flexible set of its ARA/ATA radios under the new Joint Army-Navy (JAN) nomenclature of AN/ARC-5. Structurally and in appearance,

14352-414: 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

14508-422: The black wrinkle finish of the Navy sets. The designation SCR-274-N is a pre-World War II Army equipment nomenclature. The Army never acquired the ARA 1.5 to 3.0 MHz receiver, nor the ATA 2.1 to 3.0 MHz transmitter. Initially, it did not acquire the 3.0 to 4.0 MHz transmitter, nor the 0.52 to 1.5 MHz receiver, but the need to communicate on the common civil airfield frequency of 3.105 MHz plus

14664-486: The carrier for voice messages or for a Morse code letter indicating to the pilot his bearing from the homing transmitter. All broadcast band receivers came with a power adapter to supply power to the homing adapter. The adapter under the Navy nomenclature system is the ZB-series. The identical unit under JAN nomenclature is the AN/ARR-1. This system was used by both the Navy extensively and the Army much less so. To put

14820-668: 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,

14976-466: 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

15132-480: The desired frequency ranges would be in the transmitter rack. The two transmitters would be fixed-tuned before take-off, with the pilot able to select the desired transmitter and control the mode (Voice, MCW, CW) at the transmitter control box. The receivers were tuned at the pilot's control box by electrical cables and long mechanical tuning shafts, allowing remote control of power, mode, frequency, and volume. AN/ARC-5 set composition and control differed markedly from

15288-432: The detection process, only the beat frequency would exit the receiver. By selecting two carriers close enough that the beat frequency was audible, the resulting Morse code could once again be easily heard even in simple receivers. For instance, if the two alternators operated at frequencies 3 kHz apart, the output in the headphones would be dots or dashes of 3 kHz tone, making them easily audible. Fessenden coined

15444-412: The difference at 100 kHz and the sum at 700 kHz. This is the same effect that Fessenden had proposed, but in his system the two frequencies were deliberately chosen so the beat frequency was audible. In this case, all of the frequencies are well beyond the audible range, and thus "supersonic", giving rise to the name superheterodyne. Armstrong realized that this effect was a potential solution to

15600-483: The dots and dashes would normally be inaudible, or "supersonic". Due to the filtering effects of the receiver, these signals generally produced a click or thump, which were audible but made determining dots from dashes difficult. In 1905, Canadian inventor Reginald Fessenden came up with the idea of using two Alexanderson alternators operating at closely spaced frequencies to broadcast two signals, instead of one. The receiver would then receive both signals, and as part of

15756-506: The earlier systems. Three-unit receiver racks were still predominant, but the receiver line-up was quite different. One receiver would usually be a R-4A homing receiver, another the VHF R-28/ARC-5, and the last an MF/HF communication receiver. The transmitter rack would hold a VHF T-23/ARC-5 and an MF/HF transmitter corresponding to the MF/HF receiver. Frequency-stabilized versions of the AN/ARC-5 communications receivers usually have

15912-570: 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

16068-413: 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

16224-592: 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

16380-533: The following 10 years, reprinting them in a compendium in 1957. Interest has continued into the 21st century. The T-16 and T-17 transmitters which operated in the standard broadcast band were very hard to find on the surplus market but were used by some as low power "pirate" AM stations with the addition of a modulation transformer in the B+ line and a suitable audio amplifier which was a 50 watt PA, guitar, or 'HI-FI home entertainment amplifier. The tuning system would allow

16536-618: 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

16692-410: The image frequency from the input and achieve low image response . However, the higher the IF, the more difficult it is to achieve high selectivity in the IF filter. At shortwave frequencies and above, the difficulty in obtaining sufficient selectivity in the tuning with the high IFs needed for low image response impacts performance. To solve this problem two IF frequencies can be used, first converting

16848-403: The incoming radio frequency signal to a higher or lower, fixed, intermediate frequency (IF). The IF band-pass filter and amplifier supply most of the gain and the narrowband filtering for the radio. The demodulator extracts the audio or other modulation from the IF radio frequency. The extracted signal is then amplified by the audio amplifier. To receive a radio signal, a suitable antenna

17004-466: The input frequency to a high IF to achieve low image response, and then converting this frequency to a low IF to achieve good selectivity in the second IF filter. To improve tuning, a third IF can be used. For example, for a receiver that can tune from 500 kHz to 30 MHz, three frequency converters might be used. With a 455 kHz IF it is easy to get adequate front end selectivity with broadcast band (under 1600 kHz) signals. For example, if

17160-436: The inventor, and his US Patent 1,342,885 was issued on 8 June 1920. After various changes and court hearings Lévy was awarded US patent No 1,734,938 that included seven of the nine claims in Armstrong's application, while the two remaining claims were granted to Alexanderson of GE and Kendall of AT&T. The antenna collects the radio signal. The tuned RF stage with optional RF amplifier provides some initial selectivity; it

17316-400: The latter monopolizing the market for superheterodyne receivers until 1930. Because the original motivation for the superhet was the difficulty of using the triode amplifier at high frequencies, there was an advantage in using a lower intermediate frequency. During this era, many receivers used an IF frequency of only 30 kHz. These low IF frequencies, often using IF transformers based on

17472-412: The local oscillator and the mixer in a single tube, leading to a savings in power, size, and especially cost. A single pentagrid converter tube would oscillate and also provide signal amplification as well as frequency mixing. The mixer tube or transistor is sometimes called the first detector , while the demodulator that extracts the modulation from the IF signal is called the second detector . In

17628-454: The local oscillator frequency is less than the desired reception frequency, it is called low-side injection ( f IF = f RF − f LO ); if the local oscillator is higher, then it is called high-side injection ( f IF = f LO − f RF ). The mixer will process not only the desired input signal at f RF , but also all signals present at its inputs. There will be many mixer products (heterodynes). Most other signals produced by

17784-441: The local oscillator is controlled by the tuning knob (for instance). Tuning of the local oscillator and the RF stage may use a variable capacitor , or varicap diode . The tuning of one (or more) tuned circuits in the RF stage must track the tuning of the local oscillator. The signal is then fed into a circuit where it is mixed with a sine wave from a variable frequency oscillator known as the local oscillator (LO). The mixer uses

17940-431: The location of the transmitter, so one requires linear amplification to allow the strength of the original signal, often very weak, to be accurately measured. To address this need, RDF systems of the era used triodes operating below unity. To get a usable signal from such a system, tens or even hundreds of triodes had to be used, connected together anode-to-grid. These amplifiers drew enormous amounts of power and required

18096-402: 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

18252-416: The mid-1930s, superheterodynes using much higher intermediate frequencies (typically around 440–470 kHz) used tuned transformers more similar to other RF applications. The name "IF transformer" was retained, however, now meaning "intermediate frequency". Modern receivers typically use a mixture of ceramic resonators or surface acoustic wave resonators and traditional tuned-inductor IF transformers. By

18408-556: The military. It was less popular when commercial radio broadcasting began in the 1920s, mostly due to the need for an extra tube (for the oscillator), the generally higher cost of the receiver, and the level of skill required to operate it. For early domestic radios, tuned radio frequency receivers (TRF) were more popular because they were cheaper, easier for a non-technical owner to use, and less costly to operate. Armstrong eventually sold his superheterodyne patent to Westinghouse , which then sold it to Radio Corporation of America (RCA) ,

18564-408: The mixer (such as due to stations at nearby frequencies) can be filtered out in the IF tuned amplifier ; that gives the superheterodyne receiver its superior performance. However, if f LO is set to f RF  +  f IF , then an incoming radio signal at f LO  +  f IF will also produce a heterodyne at f IF ; the frequency f LO  +  f IF is called

18720-472: 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

18876-403: The original signal will be reversed. This must be taken into account by the demodulator (and in the IF filtering) in the case of certain types of modulation such as single sideband . To overcome obstacles such as image response , some receivers use multiple successive stages of frequency conversion and multiple IFs of different values. A receiver with two frequency conversions and IFs is called

19032-540: The original signal. As a result, any number of simple amplification systems could be used. One method used an interesting side-effect of early triode amplifier tubes. If both the plate (anode) and grid were connected to resonant circuits tuned to the same frequency and the stage gain was much higher than unity , stray capacitive coupling between the grid and the plate would cause the amplifier to go into oscillation. In 1913, Edwin Howard Armstrong described

19188-471: The oscillation decayed and the sound disappeared after a short delay. Armstrong referred to this concept as a regenerative receiver , and it immediately became one of the most widely used systems of its era. Many radio systems of the 1920s were based on the regenerative principle, and it continued to be used in specialized roles into the 1940s, for instance in the IFF Mark II . There was one role where

19344-490: The period. It was an improvement of the Navy's ARA/ATA command set. Similar units designated SCR -274-N were used in U.S. Army aircraft. The Army set is based on the ARA/ATA, not the later AN/ARC-5. The ARA/ATA and SCR-274-N series are informally referred to as "ARC-5", despite small differences that render all three series incompatible. Like the AN/ARC-5, the ARA/ATA and SCR-274-N had AM voice communication and two-way MCW and CW Morse code capability. The AN/ARC-5 command set

19500-505: 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

19656-541: The preferred technology to reduce aircrew "fiddling" with controls, so it was not pursued beyond the evaluation quantities. By late war, the discovery of "ducting" in the lower VHF band (that allowed Japanese tactical radio intercepts over long distances under certain conditions) drove development of the AN/ARC-12 (UHF version of the AN/ARC-1) and AN/ARC-27 sets in currently-used UHF-AM military aircraft band. However, it

19812-646: The problem of image rejection. Even later, however, low IF frequencies (typically 60 kHz) were again used in the second (or third) IF stage of double or triple-conversion communications receivers to take advantage of the selectivity more easily achieved at lower IF frequencies, with image-rejection accomplished in the earlier IF stage(s) which were at a higher IF frequency. In the 1920s, at these low frequencies, commercial IF filters looked very similar to 1920s audio interstage coupling transformers, had similar construction, and were wired up in an almost identical manner, so they were referred to as "IF transformers". By

19968-410: The purpose of increasing selectivity. The IF stage includes a filter and/or multiple tuned circuits to achieve the desired selectivity . This filtering must have a band pass equal to or less than the frequency spacing between adjacent broadcast channels. Ideally a filter would have a high attenuation to adjacent channels, but maintain a flat response across the desired signal spectrum in order to retain

20124-456: The quality of the received signal. This may be obtained using one or more dual tuned IF transformers, a quartz crystal filter , or a multipole ceramic crystal filter . In the case of television receivers, no other technique was able to produce the precise bandpass characteristic needed for vestigial sideband reception, such as that used in the NTSC system first approved by the US in 1941. By

20280-451: 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,

20436-409: 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

20592-451: 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

20748-415: 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 a receiver that is typically colocated with the transmitter. In radio navigation systems such as GPS and VOR ,

20904-456: 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

21060-449: The received station, although in practice LOs tend to be relatively strong signals. When the signal from the LO mixes with the station's, one of the outputs will be the heterodyne difference frequency, in this case, 60 kHz. He termed this resulting difference the " intermediate frequency " often abbreviated to "IF". In December 1919, Major E. H. Armstrong gave publicity to an indirect method of obtaining short-wave amplification, called

21216-416: The regenerative system was not suitable, even for Morse code sources, and that was the task of radio direction finding , RDF. The regenerative system was highly non-linear, amplifying any signal above a certain threshold by a huge amount, sometimes so large it caused it to turn into a transmitter (which was the entire basis of the original IFF system ). In RDF, the strength of the signal is used to determine

21372-459: The rig to be loaded into almost any kind of vertical or dipole antenna for neighborhood and beyond AM broadcasting. The on air fidelity of the unit was very good. One T-17 was used on 1580 by three different operators at three different locations in the Chicago suburbs as a pirate station in the 1960s with the local FCC office raiding each station at its location. The last raided operator repurposed

21528-481: 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

21684-412: The self-resonance of iron-core transformers , had poor image frequency rejection, but overcame the difficulty in using triodes at radio frequencies in a manner that competed favorably with the less robust neutrodyne TRF receiver. Higher IF frequencies (455 kHz was a common standard) came into use in later years, after the invention of the tetrode and pentode as amplifying tubes, largely solving

21840-415: The so-called autodyne mixer. This was rapidly followed by the introduction of tubes specifically designed for superheterodyne operation, most notably the pentagrid converter . By reducing the tube count (with each tube stage being the main factor affecting cost in this era), this further reduced the advantage of TRF and regenerative receiver designs. By the mid-1930s, commercial production of TRF receivers

21996-423: The stages of the IF amplifier to be carefully tuned for best performance (this tuning is called "aligning" the IF amplifier). If the center frequency changed with the receiving frequency, then the IF stages would have had to track their tuning. That is not the case with the superheterodyne. Normally, the IF center frequency f IF is chosen to be less than the range of desired reception frequencies f RF . That

22152-523: The station being received is on 600 kHz, the local oscillator can be set to 1055 kHz, giving an image on (-600+1055=) 455 kHz. But a station on 1510 kHz could also potentially produce an image at (1510-1055=) 455 kHz and so cause image interference. However, because 600 kHz and 1510 kHz are so far apart, it is easy to design the front end tuning to reject the 1510 kHz frequency. However at 30 MHz, things are different. The oscillator would be set to 30.455 MHz to produce

22308-403: The super-heterodyne. The idea is to reduce the incoming frequency, which may be, for example 1,500,000 cycles (200 meters), to some suitable super-audible frequency that can be amplified efficiently, then passing this current through an intermediate frequency amplifier, and finally rectifying and carrying on to one or two stages of audio frequency amplification. The "trick" to the superheterodyne

22464-445: The system into operation on the aircraft, the beacon band receiver would be replaced in the rack by the broadcast band receiver. The antenna post is connected to the output of the homing adapter, and a power cable is connected from the homing adapter to the broadcast band receiver. The normal control that had been used for the beacon band receiver also serves this homing system without further reconfiguration. Western Electric developed

22620-462: The term " heterodyne ", meaning "generated by a difference" (in frequency), to describe this system. The word is derived from the Greek roots hetero- "different", and -dyne "power". Morse code was widely used in the early days of radio because it was both easy to produce and easy to receive. In contrast to voice broadcasts, the output of the amplifier didn't have to closely match the modulation of

22776-431: 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

22932-427: The two signals. For instance, consider a lone receiver that was tuned to a station at 300 kHz. If a second receiver is set up nearby and set to 400 kHz with high gain, it will begin to give off a 400 kHz signal that will be received in the first receiver. In that receiver, the two signals will mix to produce four outputs, one at the original 300 kHz, another at the received 400 kHz, and two more,

23088-441: The war and were often converted for amateur radio use. The term 'ARC-5', while correctly applied to the AN/ARC-5 series, has also come to be a generic, though incorrect, term for the ARA/ATA and SCR-274-N command set units, including those designed by the Aircraft Radio Corporation in the late 1930s. The antecedent of the AN/ARC-5 system was the U.S. Navy's ARA/ATA system, initially deployed in 1940. The designations ARA and ATA are

23244-510: 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

23400-598: 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

23556-410: Was largely replaced by superheterodyne receivers. By the 1940s, the vacuum-tube superheterodyne AM broadcast receiver was refined into a cheap-to-manufacture design called the " All American Five " because it used five vacuum tubes: usually a converter (mixer/local oscillator), an IF amplifier, a detector/audio amplifier, audio power amplifier, and a rectifier. Since this time, the superheterodyne design

23712-600: Was later re-designated the AN/ARC-4. By 1943 they began deploying their own AN/ARC-1 ten-channel VHF-AM set in increasing numbers, but hedged their bets with the AN/ARC-5 VHF sets in certain aircraft. This experimentation even caused them to contract for and officially nomenclature a continuously tunable AN/ARC-5 VHF capability from Aircraft Radio Corporation for evaluation purposes, shown in the above chart, but by that time (latter part of 1944) channelized equipment became

23868-402: Was looking for practical means to build a linear amplifier for these signals. At the time, short wave was anything above about 500 kHz, beyond any existing amplifier's capabilities. It had been noticed that when a regenerative receiver went into oscillation, other nearby receivers would start picking up other stations as well. Armstrong (and others) eventually deduced that this was caused by

24024-505: Was passed on to the user's headphones as an audible signal of dots and dashes. In 1904, Ernst Alexanderson introduced the Alexanderson alternator , a device that directly produced radio frequency output with higher power and much higher efficiency than the older spark gap systems. In contrast to the spark gap, however, the output from the alternator was a pure carrier wave at a selected frequency. When detected on existing receivers,

24180-509: Was used by the US Navy from the latter part of World War II into the post-war era. It was fitted in many different aircraft types for communication between aircraft, navigation, and communication back to base. Units were available that covered much of the MF , HF , and VHF spectrum. Despite the use of octal base vacuum tubes , they were compact, rugged and light weight. Many became surplus after

24336-472: Was used for almost all commercial radio and TV receivers. French engineer Lucien Lévy filed a patent application for the superheterodyne principle in August 1917 with brevet n° 493660. Armstrong also filed his patent in 1917. Levy filed his original disclosure about seven months before Armstrong's. German inventor Walter H. Schottky also filed a patent in 1918. At first the US recognised Armstrong as

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