Slinky Dipole Antenna
Description
My custom designed slinky antenna. People have been making slinky dipoles for longer than i have been around, but i decided to design some parts to make assembly easier. I included a picture of the exact slinky i used. I bought mine from Walmart and it has an inner diameter of about 62mm (2.4 in). I have 3 options for the center piece, SMA, BNC, and SO239, pick which one you need. I have not printed the BNC or SO239 models, i just stole the SO239 measurements from another model on thingiverse, and looked up the BNC online, so i cant guarantee those are exactly right. Assembly should be pretty simple with the incuded pictures. The main picture doesnt inclue the "end crank" as i havent printed them yet. I will update when i finish and take a good picture. i used #6 screws which are about 3.3mm diameter. i just tapped threads into the center piece, but you could run a long one through the center and use a nut on the other side. the center piece has a hole on top for an eyelet if you wanted to hang this, and a 22mm hole in the bottom that fits a 1/2 pvc pipe with an OD of .84". i read that brass slinkys work better for this, but are a bit more expensive so i opted for the cheap one, although i hear they rust if left outside. the paracord spool has a tensioner on the bottom of it, see the remix i tagged for pictures on how this works. I didnt actually remix his model per se, but i did basically copy it in my design. (thanks mikeaj) This has 550 paracord strung through it so the slinkys dont have to hold the weight. They would probably bend if you tried. The "paracord clip" goes on before the "end crank" so you can lock the end in place. you can then use the knob on the crank to spin the end crank and wind the slink up onto it thus electrically shortening your antenna. I didnt even bother with aligator clips or anything, either the spring in the slinky holds them together enough to short out, or they couple and it achieves the same effect anyway. I am still a little new to the RF world so i am no expert, but the more turns that are after the crank and not streched, the higher the resonant frequency goes. With just 2 slinkys this is resonant for me at about 8MHz and 26MHz. If you stretch them out more it lowers the frequency, but not that much after you get to about 7 feet per slinky. I have read online not to stretch them more than about 15 feet each or they might permanently deform. If i shorten it with the crank i can shift those 2 dips up to the 20 meter and 10 meter bands. i plan on getting 2 more slinkys, soldering them to the ends of these two and seeing if i can tune other bands as well. if you have any questions please comment on here as i check it semi regularly, and if you make it, please post a make with some pictures, it makes me smile.
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