Adcock antenna
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The Adcock antenna is an antenna array consisting of four equidistant vertical elements which can be used to transmit or receive directional radio waves.
Diagram from Adcock's 1919 patent, depicting a four-element monopole antenna array; active antenna segments are marked in red.
27-meter (90-foot) diagonal spacing Japanese Adcock direction finder installation for 2 MHz in Rabaul
Low-frequency radio range
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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.
Doolittle's instrument panel
The vibrating reed, developed in the 1920s, was a simple, panel-mounted instrument with "turn left-right" indicator.
Early low-frequency radio station based on crossed loop antennas; later installations used Adcock antennas for improved performance.