The SCR-277 was a mobile, trailer mounted radio range set for radio guidance of aircraft. It was standardized by the U.S. Army in June 1941.
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The SCR-277 was used as a navigation aid and included radio range homing equipment for broadcasting tone identification signals to aircraft fitted with standard command sets but without a radio compass, within a range of approximately 300 miles. It included the BC-467 transmitter with an RF output power of 800 watts, the BC-468 Goniometer, and BC-342 receiver. Frequencies utilized were 200-400 KHz for transmission and 1.5-18 MHz for reception.[1] It was powered by a single PE-90 generator.
In operation the transmitter sends out signals coded "A" or "N" in each of the four quadrants around the beacon. The signals overlap on the range, providing the pilot of the aircraft an indication of his position in relation to location of the beacon. Thus, if he is heading toward the beacon he will receive an aural signal coded "A" or "N" if he is between the beam, and when he is on the beam he will receive "AN" signal. Over land areas the beacon has a range of about 300 miles, while over water areas the range is extended to about 1,000 miles. Charts prepared for air navigation show the position and the orientation of the various beacons.[2]