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Slim Jim Antenna

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




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4 Comments


Unknown member
May 08, 2023

This is the very first antenna I ever built. I was VK6MJS. Good antenna and so easy to build.

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Unknown member
May 08, 2023
Replying to

Me too Stanley, my first attempt at an Antenna.. The first worked so well I made another and I still have them. I used one at the Antennapalooza.


Cheers.

Craig.

😀

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Unknown member
May 08, 2023

Wow this antenna takes me back many many years. At the time it was classed the most efficient 2 metre antenna, also very broad band. A few years ago I built a new one which is sitting doing nothing in my garage. It is the perfect antenna for 2 metres if you live in a sensitive antenna area with (winging neighbours). The reason? it can fit in a 65 mm plastic pipe and when fitted at roof gutter level or higher, attracts little or no attention. Let me know if any member is interested in building one as I would be pleased to bring mine to the club and take it apart so members can see how easy it is…

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Unknown member
May 08, 2023
Replying to

Hi Roy,


Spread the word around at the club, I'm sure many would be keen to build them.

😀

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