{{Short description|US military portable radio transceiver}} {{Use American English|date=October 2024}} {{Use dmy dates|date=October 2024}} thumb|right|Motorola SCR-300 circa 1940 The '''SCR-300''', designated '''AN/VRC-3''' under the Joint Electronics Type Designation System, was a portable frequency modulated (FM) radio transceiver used by US Signal Corps in World War II. This backpack-mounted unit was the first radio to be nicknamed a "walkie talkie".<ref name="SCR300">{{cite web|last1=Magnuski|first1=H. S.|title=About the SCR-300|url=http://www.scr300.org/|website=SCR300.org|accessdate=2 July 2016}}</ref>
== History == In 1940, Motorola (then the Galvin Manufacturing Company) received a contract from the War Department to develop a portable, battery powered voice radio receiver/transmitter for field use by infantry units. The project engineering team consisted of Daniel E. Noble, who conceived of the design using frequency modulation, Henryk Magnuski who was the principal RF engineer, 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 (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 from low-HF (high frequency) AM/CW (amplitude modulated/ continuous wave) to low-VHF (very high frequency) FM.<ref name="Niesel">{{cite web |last1=Niesel |first1=John |title=The SCR-300 Backpack Radio |url=https://warfarehistorynetwork.com/daily/wwii/the-scr-300-backpack-radio/ |website=warfarehistorynetwork.com |publisher=Sovereign Media |accessdate=28 December 2018 |archive-date=27 October 2019 |archive-url=https://web.archive.org/web/20191027152946/http://warfarehistorynetwork.com/daily/wwii/the-scr-300-backpack-radio |url-status=dead }}</ref>
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" first came into use.<ref name="KaufmannKaufmann2009">{{cite book|author1=J. E. Kaufmann|author2=H. W. Kaufmann|title=The American GI in Europe in World War II: The March to D-Day|url=https://archive.org/details/americangiineuro0001kauf|url-access=registration|quote=SCR-300 walkie talkie.|date=22 September 2009|publisher=Stackpole Books|isbn=978-0-8117-4373-0|pages=[https://archive.org/details/americangiineuro0001kauf/page/51 51]–}}</ref><ref name="nerds-TM II-242">{{cite book |title=TM II-242 - RADIO SET SCR - 300 - A |date=February 26, 1945 |publisher=US War Department |page=1 |url=https://radionerds.com/images/b/b5/TM-11-242.pdf |access-date=February 2, 2025 |chapter=Chapter I - GENERAL}}</ref>
The final acceptance tests took place at Fort Knox, Kentucky 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 World War II.<ref name="Petrakis1991">{{cite book|author=Harry Mark Petrakis|title=The founder's touch: the life of Paul Galvin of Motorola|url=https://archive.org/details/founderstouchlif0000petr_a8r0|url-access=registration|date=1 January 1991|publisher=Motorola University Press, J.G Ferguson Pub. Co.|isbn=978-0-89434-119-9}}</ref><ref name="Sterling2008">{{cite book|author=Christopher H. Sterling|title=Military Communications: From Ancient Times to the 21st Century|url=https://books.google.com/books?id=RBC2nY1rp5MC&pg=PA504|year=2008|publisher=ABC-CLIO|isbn=978-1-85109-732-6|pages=504–}}</ref>
The SCR-300 saw action in the Pacific Theater, beginning in New Georgia 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.<ref name="ThompsonHarris1966">{{cite book|author1=George Raynor Thompson|author2=Dixie R. Harris|title=The Signal Corps: the outcome (mid-1943 through 1945)|url=https://books.google.com/books?id=5tVWAAAAYAAJ&pg=PA667|year=1966|publisher=Office of the Chief of Military History, U.S. Army|pages=667–}}</ref>
The SCR-300 saw heavy use in the Normandy invasion and the Italian campaign. It also became "key equipment" that helped deter confusion in the Battle of the Bulge.<ref name="Yenne">{{cite book|author=Bill Yenne, William Yenne|title=Secret Gear, Gadgets, and Gizmos|url=https://books.google.com/books?id=TbByQl2h0LcC&pg=PA32|publisher=Zenith Imprint|isbn=978-1-61060-744-5|pages=32–}}</ref>
The British adopted the design of the SCR-300 for their own use from 1947 as the "Wireless Set No. 31".<ref name="WarDept1945">{{cite book|author=United States. War Dept|title=Radio Set SCR-300-A, War Department Technical Manual TM 11-242|url=https://books.google.com/books?id=AhotAAAAIAAJ|year=1945|publisher=United States War Dept.}} [http://www.scr300.org/index-tifs.html Alt URL]</ref><ref name="Olive-Drab.com">{{cite web|title=SCR-300 Backpack Radio|url=http://olive-drab.com/od_electronics_scr300.php|website=Olive-Drab.com|publisher=Olive-Drab.com|accessdate=2 July 2016}}</ref>
== Specifications == [[File:Scr300.png|thumb|right|Signal Corps Radio set SCR-300-A]] The SCR-300 was an 18-tube battery operated VHF battlefield radio half-duplex transceiver. It used an FM transmitter section and a double superheterodyne receiver. It incorporated an adjustable squelch circuit, an automatic frequency control circuit, a crystal controlled calibration circuit, easy to use tuning/channel selection, tuning lock to prevent accidental frequency changes, and radio relay or retransmission capability using two SCR-300 units and the appropriate cable assemblies.<ref name="WarDept1945" /><ref>{{cite book|title=Electronics|url=https://books.google.com/books?id=K0QSAAAAIAAJ&pg=RA2-PA204|date=January 1945|publisher=McGraw-Hill Publishing Company|location=New York, New York|chapter=Details of the SCR-300 F-M Walkie-Talkie|last= Noble|first=Daniel E|pp= 204, 209, 212}}</ref>
*Weight: ::With battery BA-70: {{cvt|38.23|lb|lk=in}} ::With battery BA-80: {{cvt|32.23|lb}} *Power supply requirements: ::Filaments: 4.5 volts ::Receiver plate: 90 volts ::Transmitter plate: 150 volts (using additional 60 volt battery) *Antenna: ::AN-130-A: Two section flexible whip, {{convert|33|in|cm|lk=in}} ::AN-131-A: Eight section flexible whip, {{cvt|10|ft|8|in|cm}} *Frequency range: VHF between {{cvt|40-48|MHz}} *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 tubes: ::3A4 (2) ::1T4 (6) ::1L4 (5) ::1R5 (1) ::1A3 (1) ::1S5 (3) *RF Power output: 0.3 watts *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 {{convert|3|mi|lk=in}} (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)
== See also == {{Portal|Electronics}} {{div col|colwidth=15em}} *ARC-5 *AN/PRC-6 *BC-348 *BC-654 *R-390A *SCR-299 *SCR-536 *Signal Corps Radio *Wireless Set No. 19 *Wireless Set No. 18 *Vintage amateur radio *AN/PRC-77 Portable Transceiver *SCR-694 *List of military electronics of the United States {{div col end}}
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== References == {{Reflist}}
== External links == * [https://radionerds.com/images/b/b5/TM-11-242.pdf TM-11-242: RADIO SET SCR - 300 - A]
Category:Amateur radio transmitters Category:Military radio systems of the United States Category:World War II American electronics Category:Military electronics of the United States