Home Links My Slim Jim's My Gear How to's Files E-Mail Handmade Slim Jim Antenna's by N9TAX Let me start by saying that since discovering the slim jim antenna design I have really come to respect these antennas. The design uses a matching system like a j-pole antenna. This is called the j integrated match (jim) the antenna itself is very slim hence the name Slim Jim. Designs for these antennas date back to the early 1930's the best I can tell. I have found them in QST magazine as far back as the 1940's. I started building these antennas and selling them because I saw no one else with a commercial product like this and I figured that I would help fill a gap. The antennas have become a great success thanks to a lot of hard work and some very dedicated customers. Before I get into the specifics of the antennas I first want to thank everyone who has purchased or helped promote this wonderful product. Without you none of this would be possible. The basic Slim Jim is an end fed folded dipole. It has a radiation pattern peaking between 5 and 8 degrees above the horizon. It is this and this alone that makes this one of the best terrestrial communications antennas I have ever seen for the price. The layout of the antenna is as follows. The top section is 1/2 wave the bottom is 1/4 wave matching section. The antenna is fed near the bottom and the feedpoint impedance is 50 ohms. Ladder line was an excellent choice for these antennas as it presented two well spaced parallel conductors and is virtually indestructable. You can hang the antenna in many places. The only exception is near metal objects. They will interfere with the tuning and performance of the antenna. Hanging it up against drywall or plaster as many people do will also affect the antenna but if this is your only option it will still perform adequately. Open free space is the best of all options and as with all antennas will yield the best performance. Enter the Dual Band antenna. After many requests for a dual band version of this antenna. I searched the internet and books high and low to no avail. I then began research on what it would take to make this antenna perform well on 2m and 70cm. What I came up with was a trapped end fed folded dipole. The secret formula I will leave for the history books. But this design yields excellent results compared to many other dual band antennas. The best I can tell there is no compromise to the performance on 2 meters in fact some claim it works better on 2 than the single band vhf (I have yet to scientifically prove that). Some ask well dont j-poles resonate on the third harmonic of 145mhz anyway? First this antenna is in the j-pole family but is not a true j-pole.  Second J-poles will resonate on 440 without traps but realistically for lack of a better term they suck. If anyone tries to sell you an un-modified j-pole and says it is a dual band antenna they are wrong they dont work, I have seen swr of 3:1 on unmodified j-poles on the 70cm band! So what are my SWR's Well I have a really nice meter that spits out some great charts to show the band sweeps on these antennas. Here is the 2m side. And the 440 plot Just a little disclaimer here this plot was taken with N connectors throughout the system. Your mileage will vary a bit with other connectors. Dont get me wrong this antenna will perform fine with pl-259's but they do introduce impedance bumps at higher frequencies. The Bow One thing I get a lot of requests for is a way to rigidly mount this antenna for mast or tower mounting. Most people want to mount the antennas inside pvc. This makes them extremely hard to tune because the dilectric constant of pvc is anything but constant hi hi. I have developed a solution that may not be the prettiest but is definitely usable. I call it the bow and anyone can build one. It consists of a piece of 3/4" pvc about a 6" longer than the antenna two 90 degree elbows another foot of pvc and a few zip ties. Basically you drill holes in the ends of the long piece of pvc and bow it to the length of the antenna and zip tie the ends to the holes you just made. Affix the elbows as on the bottom to bring the short piece parallel with the antenna and you have a rigid mount that will not interfere with the antenna's tuning. Here is a photo of mine on my tower. I'll tell you what that thing really talks up there I have worked repeaters over 100 miles away. The antennas are available with an assortment of different connectors and with or without long coax cable. The VHF only antennas are custom tunable from 130 - 225 mhz at no extra charge. Thank you for your interest in my antenna. Joe N9TAX The link below will take you to my webstore where you can buy one.