98-684: 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
196-463: 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
294-407: 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
392-414: 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
490-427: 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
588-553: 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
686-515: 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
784-399: 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
882-609: 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
980-439: 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
1078-422: 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
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#17327810219651176-599: 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
1274-474: 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
1372-877: 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
1470-411: 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
1568-432: 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
1666-499: 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,
1764-691: 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,
1862-410: 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,
1960-453: 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
2058-673: 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
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#17327810219652156-409: 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
2254-472: 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
2352-405: 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
2450-468: 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
2548-448: 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
2646-438: 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
2744-482: 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
2842-426: 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"
2940-455: 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
3038-410: 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
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3136-404: 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
3234-415: 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
3332-436: 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
3430-416: 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
3528-478: 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
3626-442: 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,
3724-439: 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
3822-489: 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
3920-522: 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
4018-426: 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)
AN/ARC-5 - Misplaced Pages Continue
4116-611: 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
4214-414: 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
4312-627: 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
4410-573: The ARC5 as a driver for an ultrasonic nebulizer. Radio Too Many Requests If you report this error to the Wikimedia System Administrators, please include the details below. Request from 172.68.168.226 via cp1108 cp1108, Varnish XID 224693351 Upstream caches: cp1108 int Error: 429, Too Many Requests at Thu, 28 Nov 2024 08:03:42 GMT Superhet A superheterodyne receiver , often shortened to superhet ,
4508-459: 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
4606-523: 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
4704-457: 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
4802-604: 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
4900-569: 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
4998-994: 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
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#17327810219655096-510: 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,
5194-422: 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
5292-486: 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
5390-480: 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
5488-432: 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
5586-412: 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
5684-483: 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
5782-506: 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
5880-533: 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
5978-410: 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
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#17327810219656076-403: 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
6174-466: 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
6272-436: 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
6370-400: 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
6468-412: 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
6566-454: 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
6664-441: 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
6762-431: 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
6860-416: 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
6958-556: 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) ,
7056-408: 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
7154-403: 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
7252-540: 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
7350-471: 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
7448-490: 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
7546-541: 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
7644-646: 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
7742-410: 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
7840-504: 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
7938-449: 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
8036-416: 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
8134-459: 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
8232-412: 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
8330-415: 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
8428-423: 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
8526-523: 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
8624-403: 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
8722-445: 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
8820-462: 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
8918-427: 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,
9016-441: 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
9114-410: 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
9212-600: 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
9310-402: 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
9408-505: 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,
9506-509: 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
9604-472: 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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