AN / ARC - 5 The AN / ARC - 5 Command Radio Set is a series of radio receivers , transmitters , and accessories used to provide two - way Morse code and AM radiotelephone communication for U . S . Navy aircraft during World War II and the years following . 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 Navy ARA / ATA , not the later AN / ARC - 5 . History . The AN / ARC - 5 command set 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 tube s , they were compact , rugged and light weight . Many became surplus after the war and were often converted for amateur radio use . The term " ARC - 5 " has come to be a generic , though incorrect , term for all similar 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 , with initial deployment in 1940 . The designations ARA and ATA are 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 , the US Army adopted in 1941 a reduced set of these radios known as the SCR - 274 - N that was electrically almost identical to their ARA / ATA equivalents , except for receiver output and modulator sidetone audio transformer output impedance . It was mechanically almost identical except for most later units being left unpainted aluminum in contrast to the black wrinkle finish of the Navy sets . The designation SCR - 274 - N is a pre - World War II Army equipment nomenclature . The Army did not acquire a receiver covering 1 . 5 to 3 . 0 MHz , nor a transmitter covering 2 . 1 to 3 . 0 MHz . Initially , the Army did not acquire a 3 . 0 to 4 . 0 MHz transmitter , nor a 0 . 52 to 1 . 5 MHz receiver , but need to communicate on the common civil airfield frequency of 3 . 105 MHz plus 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 . 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 the aircraft , just as one would store tuning units of other types of radio equipment . In late 1943 , the U . S . Navy fielded an improved and more flexible set of radios known under the new Joint Army - Navy ( JAN ) nomenclature of AN / ARC - 5 . 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 . Specifications . 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 . ( 1 ) Also component of RAV system . ( 2 ) Also component of RAT system . ( 3 ) Also component of RAT - 1 and RAV systems . ( * ) 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 ) . 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 receiver and modulator impedance is 4000 ohms , while " - B " and later version units have 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 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 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 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 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 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 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 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 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 the R - 28 receiver and T - 23 transmitter . The T - 126 / ARC - 5 is a late variant of the T - 23 which allows the four channels to be grouped lower in a 100 to 146 MHz tuning range than does the T - 23 . 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 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 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 , and the last an MF / HF communication receiver . The transmitter rack would hold a VHF T - 23 and an MF / HF transmitter corresponding to the MF / HF receiver . AN / ARC - 5 communications receivers usually have a yellow circle - S stamped on the front panel to indicate that the receiver is a frequency - stabilized version . 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 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 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 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 was later re - designated the AN / ARC - 4 . By 1943 they began 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 ARC for evaluation purposes , shown in the above chart , but by that time ( latter part of 1944 ) channelized equipment became 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 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 the 1970s . LF / MF / HF receivers all use a similar same 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 gives a visual indication , viewable by raising a small cover , when the oscillator ' s frequency matches that of an internal crystal , thus allowing a check of the dial calibration .