The SCR-300 was a portable

radio Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a tr ...

transceiver In radio communication, a transceiver is an electronic device which is a combination of a radio ''trans''mitter and a re''ceiver'', hence the name. It can both transmit and receive radio waves using an antenna, for communication purposes. Thes ...

used by US Signal Corps in

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...

. This

backpack A backpack—also called knapsack, schoolbag, rucksack, rucksac, pack, sackpack, booksack, bookbag or backsack—is, in its simplest frameless form, a fabric sack carried on one's back and secured with two straps that go over the shoulders ...

-mounted unit was the first radio to be nicknamed a "

walkie talkie A walkie-talkie, more formally known as a handheld transceiver (HT), is a hand-held, portable, two-way radio transceiver. Its development during the Second World War has been variously credited to Donald Hings, radio engineer Alfred J. Gross, ...

History

In 1940,

Motorola Motorola, Inc. () was an American multinational telecommunications company based in Schaumburg, Illinois, United States. After having lost $4.3 billion from 2007 to 2009, the company split into two independent public companies, Motorola ...

(then the Galvin Manufacturing Company) received a contract from the

War Department War Department may refer to: * War Department (United Kingdom) * United States Department of War (1789–1947) See also * War Office, a former department of the British Government * Ministry of defence * Ministry of War * Ministry of Defence * D ...

to develop a portable, battery powered voice radio receiver/

transmitter In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the ...

for field use by

infantry Infantry is a military specialization which engages in ground combat on foot. Infantry generally consists of light infantry, mountain infantry, motorized infantry & mechanized infantry, airborne infantry, air assault infantry, and mar ...

units. The project engineering team consisted of

Daniel E. Noble Daniel Earl Noble (October 4, 1901 – February 16, 1980) was an American engineer, and executive vice chairman of the board of Motorola, who is known for the design and installation of the nation's first statewide two-way FM radio communicatio ...

, who conceived of the design using

frequency modulation Frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. The technology is used in telecommunications, radio broadcasting, signal processing, and computing. In analog ...

, Henryk Magnuski who was the principal

RF engineer Radio-frequency (RF) engineering is a subset of electronic engineering involving the application of transmission line, waveguide, antenna and electromagnetic field principles to the design and application of devices that produce or use signals ...

, Marion Bond, Lloyd Morris, and Bill Vogel. The SCR-300 operated in the 40.0 to 48.0 MHz frequency range, and was channelized. Along with other mobile FM tank and artillery radios such as the

SCR-508 The SCR-508 radio was a mobile Signal Corps Radio used by the U.S. Army during World War II, for short range ground communications. The SCR-508 series radio represented the Army's commitment to both FM and crystal tuning, and was used extensively ...

(20.0 to 27.9 MHz) and the SCR-608 (27.0 to 38.9 MHz), the SCR-300 marked the beginning of the transition of

combat-net radio In telecommunication, a combat-net radio (CNR) is a radio operating in a network that (a) provides a half-duplex circuit and (b) uses either a single radio frequency or a discrete set of radio frequencies when in a frequency hopping mode. CNRs ...

from low-HF AM/CW to low-

VHF Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter. Frequencies immediately below VHF ...

FM. Although a relatively large backpack-carried radio rather than a handheld model, the SCR-300 was described in War Department Technical Manual TM-11-242 as "primarily intended as a walkie-talkie for foot combat troops", and so the term "

walkie-talkie A walkie-talkie, more formally known as a handheld transceiver (HT), is a hand-held, portable, two-way radio transceiver. Its development during the Second World War has been variously credited to Donald Hings, radio engineer Alfred J. Gross, ...

" first came into use. The final acceptance tests took place at

Fort Knox Fort Knox is a United States Army installation in Kentucky, south of Louisville and north of Elizabethtown. It is adjacent to the United States Bullion Depository, which is used to house a large portion of the United States' official gold re ...

Kentucky Kentucky ( , ), officially the Commonwealth of Kentucky, is a state in the Southeastern region of the United States and one of the states of the Upper South. It borders Illinois, Indiana, and Ohio to the north; West Virginia and Virginia ...

in Spring 1942. The performance of the SCR-300 during those tests demonstrated its capacity to communicate through interference and the rugged quality of the design. Motorola was to produce nearly 50,000 of the SCR-300 units during the course of

. The SCR-300 saw action in the Pacific Theater, beginning in

New Georgia New Georgia, with an area of , is the largest of the islands in Western Province, Solomon Islands, and the 200th-largest island in the world. Geography New Georgia island is located in the New Georgia Group, an archipelago including most ...

in August 1943. Colonel Ankenbrandt informed General Meade that "they are exactly what is needed for front line communications in this theater". In his point of view, the main difficulty was keeping them supplied with fresh batteries. The SCR-300 saw heavy use in the

Normandy invasion Operation Overlord was the codename for the Battle of Normandy, the Allied operation that launched the successful invasion of German-occupied Western Europe during World War II. The operation was launched on 6 June 1944 (D-Day) with the Norm ...

and the Italian campaign. It also became "key equipment" that helped deter confusion in the

Battle of the Bulge The Battle of the Bulge, also known as the Ardennes Offensive, was the last major German offensive campaign on the Western Front during World War II. The battle lasted from 16 December 1944 to 28 January 1945, towards the end of the war in ...

. The British adopted the design of the SCR-300 for their own use from 1947 as the "Wireless Set No. 31".Alt URL
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Specifications

The SCR-300 was an 18-tube battery operated

battlefield radio

half-duplex A duplex communication system is a point-to-point system composed of two or more connected parties or devices that can communicate with one another in both directions. Duplex systems are employed in many communications networks, either to allow ...

. It used an FM transmitter section and a double

superheterodyne A superheterodyne receiver, often shortened to superhet, 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 carri ...

receiver. It incorporated an adjustable

squelch In telecommunications, squelch is a circuit function that acts to suppress the audio (or video) output of a receiver in the absence of a strong input signal. Essentially, squelch is a specialized type of noise gate designed to suppress weak s ...

circuit, an

automatic frequency control In radio equipment, Automatic Frequency Control (AFC), also called Automatic Fine Tuning (AFT), is a method or circuit to automatically keep a resonant circuit tuned to the frequency of an incoming radio signal. It is primarily used in radi ...

circuit, a crystal controlled calibration circuit, easy to use tuning/channel selection, tuning lock to prevent accidental frequency changes, and

radio relay Radio stations that cannot communicate directly due to distance, terrain or other difficulties sometimes use an intermediate radio relay station to relay the signals. A radio relay receives weak signals and retransmits them, often in a different di ...

or retransmission capability using two SCR-300 units and the appropriate cable assemblies. *Weight: ::With battery BA-70: ::With battery BA-80: *Power supply requirements: ::Filaments: 4.5

volt The volt (symbol: V) is the unit of electric potential, electric potential difference (voltage), and electromotive force in the International System of Units (SI). It is named after the Italian physicist Alessandro Volta (1745–1827). Defin ...

s ::Receiver plate: 90 volts ::Transmitter plate: 150 volts (using additional 60 volt battery) *Antenna: ::AN-130-A: Two section flexible whip, ::AN-131-A: Eight section flexible whip, *Frequency range: 40 to 48 MHz (40-48 MC) *Channel spacing: 200 kHz *Channel Selection via "TUNING" control, channel display showing channel 0 (40.000 MHz) to channel 40 (48.000 MHz) *Modulation: FM voice *

Vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied. The type known as ...

s: ::3A4 (2) ::1T4 (6) ::1L4 (5) ::1R5 (1) ::1A3 (1) ::1S5 (3) *RF Power output: 0.3

watt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James ...

s *Frequency calibration (crystal oscillator) 4.3 MHz 10th harmonic (43.0 MHz) and 11th harmonic (47.3 MHz) marked on channel display - channel 15 (43.000 MHz) and halfway between channels 36 (47.200 MHz) and 37 (47.400 MHz) *Range: approximately (varied considerably with terrain, location of transmitter and receiver, and antenna used)

War Department Technical Manuals

* TM 11-242 for Radio Set SCR-300-A (1945) * TM 11-983 for PP-114 Vibrator power supply (1945) * TM 11-637 for AN/VRC-3 (1944)

References

{{Reflist Amateur radio transmitters Military radio systems of the United States World War II American electronics Military electronics of the United States