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Adcock Antennas

December 17th Fact-of-the-Day

Small, perfectly-balanced vertical loop antennas are useful for vertically polarized radio signal direction finding, because they have a figure-of-eight receiving pattern with two sharp nulls where the output goes to zero. Unfortunately, in those two null directions they are sensitive to horizontally polarized waves and ionospheric refraction polarization shifts commonly rotate signals transmitted from vertically polarized antennas so that returning skywaves are not perfectly vertical. In 1919 F. Adcock was granted British Patent 130490 for his solution to that problem which involved removing the top and bottom horizontal portions of a vertical rectangular loop, so that only the two vertical sides remained. That proved to greatly reduce sensitivity to horizontally polarized waves and caused 'Adcock Antennas' to replace loops in many sea and air radio navigation applications. ©2004 Martek International All rights reserved.


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