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Large Horizontal Loop Antennas

April 26th Fact-of-the-Day

Large horizontal loops are popular HF antennas for good reasons. They tend to have generally similar feed impedances at both odd and even harmonic frequencies (although usually higher at even), in contrast to center-fed dipoles which have low feed impedances at odd harmonics and very high feed impedances at even harmonics. Two-wavelength loops have slightly lower radiation takeoff angles than dipoles. However, there are several common misconceptions about loops. One is that their radiation patterns are omni-directional on all HF bands. Their radiation patterns are rarely circular on any band and change from band-to-band as much as dipole radiation patterns change, only differently. Another misconception is that loop shape doesn't matter. Loop shape has big effects on the radiation patterns of loops larger than one wavelength at the operating frequency. ©2005 Martek International All rights reserved.

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