SCR-300 Backpack Radio manual, TM 11-242
In 1940, Motorola received a contract to develop a portable, battery powered FM voice receiver/transmitter for the War Department, intended for field use by infantry units. The specifications included a weight limit of 35 pounds, so it could be carried on the back of an individual soldier, with a reliable range of three miles. It also had to be waterproof and be able to withstand tropical fungicides. The result of the design effort met or exceeded all specifications and was released as the Radio Set SCR-300.
The Radio Set SCR-300 and SCR-300-A consisted of an 18-tube, crystal controlled portable receiver and transmitter, along with batteries and accessories such as the case, handset, and two lengths of whip antenna. It had an innovative tuning that sets both receive and transmit frequency in tandem along with integrated calibration. A squelch circuit Was provided to minimize roar in the high-gain circuits when there is no signal. The SCR-300 utilized the frequency band of 40.0 to 48.0 mc divided into 41 channels of 200 kc. The transmitter power was 0.3 watts with a range of 3 miles with the longer antenna.
The BC-1000 was used with the same frequency band in the AN/VRC-3 (used in tanks) so the two sets could intercommunicate between armor and infantry.
The entire SCR-300 assembly weighs between 32 and 38 pounds depending on the batteries used (BA-70 or BA-80).
The Radio Set SCR-300 was issued with War Department Technical Manual TM 11-242, 15 June 1943 and almost fifty thousand SCR-300 Walkie-Talkie units were produced by Motorola during World War II.