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Slim Jim Antenna
The Slim Jim is a vertically polarized omnidirectional end-fed antenna having considerable “gain” and this is concentrated almost parallel to ground toward the horizon rather than skyward making it more efficient than a ground plane type antenna by about 50 percent better. It can be built for almost any frequency! ( Below 10 meters it gets VERY tall )
Due to it’s SLIM design, there is very little wind loading. It is fed with 50 ohm coax.
It uses a ‘J ‘ type matching stub (J Integrated Matching = JIM), hense the name SLIM JIM. Credit for the original design goes to F.C. Judd, G2BCX. Since the vertical angle of radiation is so narrow, about 8 degrees toward the horizon, it usually out performs 5/8 λ or groundplane type construction due to their much higher angle of radiation. It is estimated that the Slim Jim appears to have about 6dB gain over a 5/8 λ antenna due to the extreme low angle of radiation.
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