Hello home builders, this is a vertically polarized omnidirectional free space antenna which offers
approximately 1.8dB of gain. It has a radiation efficiency 50% better than a
ground-plane antenna due to its low radiation angle. The slim jim antenna is a very old design from the 30's
and plenty of information can be found about it on the net. This site however, will actually show you how to
build your slim jim antenna from Home Depot items!
Antenna Description: Basically it is an end-fed folded dipole operated vertically. The matching
stub provides a low impedance feed point (50 ohms) at the base and couples to
the antenna section at high impedance at one end. As with all folded dipoles,
the currents in each leg are in phase, whereas in the matching stub they in
phase opposition, so little or no radiation occurs from this. Correctly matched, the VSWR (Voltage Standing Wave
Ratio -Steve) will be much less than 1.5:1, and remains so across the band.
