Slim Jim Antenna was designed by late Fred Judd. It uses a matching system similar to j-pole antenna. It is the most effective antenna when compared to other ground plane antennas.
It has two electric poles charged positive and negative.
Use this online slim jim antenna design calculator to find the actual wavelength, overall length, half wave radiator section, quarter wave radiation section, feed point, gap and spacing of Slim Jim antenna by providing the frequency and velocity factor.
slim jim antenna design calculator
Actual Wavelength = 300 / f Wavelength Considering Velocity Factor = 300 * v / f
Overall Length = 22500 * v / f
Half Wave Radiator Section = 30000 * (0.5 * v) / f
Quarter Wave Matching Section = 30000 * (0.25 * v) /f
50Ω Feed Point = 30000 * (0.025 * v) / f Gap = 300 / f
Spacing = 30000 * 0.02175 / f
Where, v = Velocity Factor f = Frequency
Example
If the frequency and velocity factor is 30 MHz and 10 vf, then Actual Wavelength = 300 / 30 Actual Wavelength = 10 m Wavelength Considering Velocity Factor = (300x10) / 30 WCVF = 100 m Overall Length = 22500 x 10 / 30 OL = 7510 cm Half Wave Radiator Section = 30000 * (0.5 * 10) / 30 HWRS = 5000 cm Quarter Wave Matching Section = 30000 * (0.25 * v) / f QWMS = 2500 cm 50Ω Feed Point = 30000 * (0.025 * 10) / 30 50Ω FP = 250 cm Gap = 300 / 30 Gap = 10 cm Spacing = 30000 * 0.02175 / 30 Spacing = 21.75 cm
Hope that is of help.. Craig vk3ncr
