The SCR-68 ( SCR was a military term meaning Set, Complete, Radio) was a military

radiotelephone A radiotelephone (or radiophone), abbreviated RT, is a radio communication system for conducting a conversation; radiotelephony means telephony by radio. It is in contrast to ''radiotelegraphy'', which is radio transmission of telegrams (messag ...

used by the

US Army Signal Corps The United States Army Signal Corps (USASC) is a branch of the United States Army responsible for creating and managing communications and information systems for the command and control of combined arms forces. It was established in 1860 by ...

as an aircraft radio in the waning months of World War I.Stoller, H. M Engineering Dept, Western Electric Company, Inc. “Development of Airplane Radiotelepone Set.” The Electric Journal May, 1919. Due to its many problems, primarily its inability to communicate with other radios, like its ground component the SCR-67 or the larger truck mounted SCR-108, over large distances, the SCR-68 quickly became obsolete. Nonetheless, the SCR-68 was one of the first steps towards developing more effective messaging between

pilots An aircraft pilot or aviator is a person who controls the flight of an aircraft by operating its directional flight controls. Some other aircrew members, such as navigators or flight engineers, are also considered aviators because they are ...

and commanders, even beyond military usage.

Capabilities

The SCR-68 had a few distinct characteristics that separated the SCR-68 from other types of radio. The SCR-68 operated at 750 kHz (400 meter wavelength), using a long wire antenna reeled out behind the aircraft. It could receive and transmit messages over a maximum range of eighteen miles. The

artillery observer An artillery observer, artillery spotter, or forward observer (FO) is a soldier responsible for directing artillery and mortar fire support onto a target. An artillery observer usually accompanies a tank or infantry unit. Spotters ensure that ...

(

navigator A navigator is the person on board a ship or aircraft responsible for its navigation.Grierson, MikeAviation History—Demise of the Flight Navigator FrancoFlyers.org website, October 14, 2008. Retrieved August 31, 2014. The navigator's prim ...

) managed the SCR-68, receiving and relaying messages for the pilot. During World War I, most planes were two-person open-cockpit aircraft. Instead of communicating between themselves in the air, the pilot and the observer sent messages through the SCR-68 where the headphones would eliminate most outside noises. Like a private

telephone line A telephone line or telephone circuit (or just line or circuit industrywide) is a single-user circuit on a telephone communication system. It is designed to reproduce speech of a quality that is understandable. It is the physical wire or oth ...

, the pilot and observer could communicate with each other; however, this action prevented the SCR-68 from receiving any transmissions.Hill, Biggin. Western Electric Aviation Radio Telephone- Report on tests made by Royal Air Force. Bureau of Steam Engineering. May 21, 1918. (Historical memo)

Problems

Advancements with the SCR-68 were marred by its flaws. Military tests by British soldiers reported the difficulty of getting the proper balance with the oscillating and control values. The SCR-68 range was reliable within a five-mile radius, a serious issue when the airplane needed to travel long distances. Another issue with the SCR-68 was the static noise that came from the “ripples” in the generator commutation. The noise was faint and was only considered a problem when receiving messages that exceeded 5 miles. It was later found that metal shielding placed around the wiring helped to prevent this problem.

Origins

The

US Army The United States Army (USA) is the primary land service branch of the United States Department of Defense. It is designated as the Army of the United States in the United States Constitution.Article II, section 2, clause 1 of the United Stat ...

pushed for better technology to gain an advantage in World War I. The US Army asked private American companies to build a device that would establish better communication between

military aircraft A military aircraft is any Fixed-wing aircraft, fixed-wing or rotorcraft, rotary-wing aircraft that is operated by a legal or insurrectionary military of any type. Some military aircraft engage directly in aerial warfare, while others take on su ...

and themselves.

Western Electric Western Electric Co., Inc. was an American electrical engineering and manufacturing company that operated from 1869 to 1996. A subsidiary of the AT&T Corporation for most of its lifespan, Western Electric was the primary manufacturer, supplier, ...

developed the SCR-68 that met qualifications: the radio was condensed to a size that could fit inside the airplane, simple for an Observer to use in flight, and the antenna would not drastically affect the movements of the aircraft. Another problem in the past included a communication device that eliminated the most disturbances from engine noise; the SCR-68 provided that by including a

microphone A microphone, colloquially called a mic (), or mike, is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and publi ...

and a sound-proof helmet. By the summer of 1918, approximately 3,000 units were manufactured and distributed to the US Army.

Parts

Radio Set

Inside the suitcase-shaped box BC-11A was the circuit apparatus used for receiving and transmitting messages. The dials were used to control the frequency of the radio. The flip paddle switched the radio from receive to transmit and vice versa. The dimensions of the box were 17 inches by 10 inches by 7 inches and weighed 21 pounds.

Intercom

The BC-10 (SCR-57) intercom control box for switching between onboard communication and ground communication.

Antenna

The A-21 retractable antenna was located in the rear of the aircraft and was expanded by the air observer while in flight. It could reel out to 300 feet in length, was made out of two copper wires and weighed 19.5 pounds. Depending on the amount of antenna allowed behind the airplane, the antenna functioned at a

wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

of 750 kHz.Schultz, Mike. Western Electric SCR-68 Aircraft Transceiver. Reverse Time Pag

/ref>

Generator

The GN-1

wind-powered Wind power is the use of wind energy to generate useful work. Historically, wind power was used by sails, windmills and windpumps, but today it is mostly used to generate electricity. This article deals only with wind power for electricity ge ...

generatorLieut.-Col. Slaughter, Nugent H. “Radio-Telephone Development in Army” Electrical World, Volume 74 New York: McGraw-Hill, 1919. Pgs 340-343. was located on the braces of the landing gear, to gather adequate wind power and not hinder any other parts of the aircraft. The generator, as well as three 22.5 volt batteries located in the BC-11, provided a plate voltage at 300 volts and a filament voltage at 30 volts. The wind-powered generator was not very efficient, requiring the airplane to travel at fast speeds in order for the generator to work properly.

Other

• T-3 Single button Chest

microphones A microphone, colloquially called a mic (), or mike, is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and publi ...

for sending messages • HS-1

Headphones Headphones are a pair of small loudspeaker drivers worn on or around the head over a user's ears. They are electroacoustic transducers, which convert an electrical signal to a corresponding sound. Headphones let a single user listen to an ...

, to eliminate external sounds

Notes

References

* Handbook, Radio pamphlet No.20 is the original manual.

External links

* https://web.archive.org/web/20090205020349/http://gordon.army.mil/OCOS/Museum/ScrComponents/scrPart1.asp SCR-list * https://web.archive.org/web/20090206080333/http://gordon.army.mil/OCOS/Museum/bc1.asp BC-list * http://www.footnote.com/image/#22404650 Gorrells History * http://www.footnote.com/image/#24303018 post war report * http://www.footnote.com/image/#24302991 installed in DH-4 * http://uv201.com/Radio_Pages/Pre-1921/scr68.htm * http://uv201.com/Radio_Pages/Pre-1921/Images/Development%20of%20Airplane%20Radiotelephone%20Set.pdf
army.mil
artillery report * http://sdr.lib.umich.edu/cgi/pt?id=mdp.39015062770162 signal corps storage catalogue 1920 page 515 {{DEFAULTSORT:Scr-68 20th-century military history of the United States Aviation in World War I Military electronics of the United States Military radio systems of the United States World War I military equipment of the United States World War I American electronics cs:Letecká sekce Spojovacího sboru Spojených států it:Aviation Section, U.S. Signal Corps