|Slim Jim Antenna|
|The Slim Jim antenna is a simple but effective antenna for VHF or UHF frequencies. I first learned about the Slim Jim when I was in England and needed a good antenna to use for 2 meters. Brian Elliot, G4MEO, lent me a magazine which had an article written by F. C. Judd, G2BCX, on how to build the Slim Jim. Brian also gave me some small-diameter aluminum tubing so that I could build one.|
|The Slim Jim gets its name due to its slender construction and that it uses a J-integrated matching stub, much like a J pole. It has a 3/4 wave element with a 1/4 wave matching stub. It is similar to the J pole but has an element folded back over down toward the matching stub. The feedpoint is also in the same spot as a regular J pole, between the main element and the matching stub.
The first Slim Jim I built was somewhat crude as it was my first antenna I ever built, but yet it worked great. It had a flat VSWR over the entire 2 meter band, and on up into the higher VHF frequencies.
|I have since given the original Slim Jim I built away to a ham who needed a good antenna, but I have since built others using 300 Ohm TV twinlead. It is a simple matter to cut a length of the twinlead, solder the conductors on both ends together, cut a notch and attatch a coaxial cable.|
|Once the basic construction of the twinlead Slim Jim is completed, the entire thing can be installed into a length of 1/2" PVC pipe. PVC caps can be installed at both ends to keep out moisture, but first make sure to drill a hole in the bottom cap to run the cable through. I also used a plastic grommet in the cap to keep the antenna relatively watertight. I used epoxy to attach the end caps and to seal them up. If the antenna is going to be used indoors or installed in an attic, the PVC pipe is not needed. It can be attached to a rafter with a nail and some string or fishing line.|
|The picture at left shows my Slim Jim mounted on the top of the wooden post to which my antenna mast is mounted. Ideally the antenna should be mounted as high up as possible and away from other metal objects, but in this configuration I am just using it as a scanner antenna to listen to local stations. it is mounted to the wooden post with a couple of plastic clamps used to mount PVC pipe to a wall. An alterative way to mount the antenna is to use a PVC T-junction at the feedpoint and run the cable through it. The antenna can then be mounted on the side of a tower.|
|The Slim Jim can be constructed for any VHF or UHF band, and if a long enough section of twinlead is used, one could also be constructed for HF use as well.|
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