page_title: Low-frequency radio range
hierarchical_section_title: Low-frequency radio range
caption_attribution_description: English: Low frequency radio range signal diagram
context_page_description: The low-frequency radio range, also known as the four-course radio range, LF/MF four-course radio range, A-N radio range, Adcock radio range, or commonly "the range", was the main navigation system used by aircraft for instrument flying in the 1930s and 1940s, until the advent of the VHF omnidirectional range, beginning in the late 1940s. It was used for en route navigation as well as instrument approaches and holds.
  Based on a network of radio towers which transmitted directional radio signals, the radio range defined specific airways in the sky. Pilots navigated using low-frequency radio by listening to a stream of automated "A" and "N" Morse codes. For example, they would turn the aircraft to the right when hearing an "N" stream, to the left when hearing an "A" stream, and fly straight ahead while hearing a steady tone.
  As the VOR system was phased in around the world, low-frequency radio range was gradually phased out, mostly disappearing by the 1970s. There are no remaining operational facilities today. At its maximum deployment, there were nearly 400 stations exclusively using low-frequency radio range in the U.S. alone.
context_section_description: The low-frequency radio range, also known as the four-course radio range, LF/MF four-course radio range, A-N radio range, Adcock radio range, or commonly "the range", was the main navigation system used by aircraft for instrument flying in the 1930s and 1940s, until the advent of the VHF omnidirectional range (VOR), beginning in the late 1940s. It was used for en route navigation as well as instrument approaches and holds.
  Based on a network of radio towers which transmitted directional radio signals, the radio range defined specific airways in the sky. Pilots navigated using low-frequency radio by listening to a stream of automated "A" and "N" Morse codes. For example, they would turn the aircraft to the right when hearing an "N" stream ("dah-dit, dah-dit, ..."), to the left when hearing an "A" stream ("di-dah, di-dah, ..."), and fly straight ahead while hearing a steady tone.
  As the VOR system was phased in around the world, low-frequency radio range was gradually phased out, mostly disappearing by the 1970s. There are no remaining operational facilities today. At its maximum deployment, there were nearly 400 stations exclusively using low-frequency radio range in the U.S. alone.
caption: Low-frequency radio range audio signals: N stream, A stream and combined uniform tone (simulated sounds)
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