Due to popular searches, I’ve included a diagram to make a flexible slim jim antenna. This antenna is useful to increase the range of your portable radio or as a simple QRP mobile antenna for emergency situation.
In order to proceed with this project you need
- about 165 cm (64 inch) 300 Ohm twinlead cable
- RG-58 coax cable (RG-8, RG-213 might be too big for soldering), any length but keep it shorter than 7 meters for portable radio
- Soldering iron
- Wire cutter
- Connector to your Rig (usually BNC type or UHF Male)
- insulating tape
This is an ideal antenna for first timers to build. It is powerful yet simple to construct, once you get the hang of it you would certainly have no problem to construct other variants of Slim Jim antenna using different material.
This exercise would also prepare you in the world of Amateur Radio where real hams homebrew their own antennas.
- Make sure you solder the center conductor to the longest part of the antenna, and the outer conductor (braid) at the shorter side of the antenna
- If you use this on mobile rig, keep transmission power lower than 50watt to avoid the antenna from being burned away.
- Make sure the antenna is held straight for best transmission and reception. Best way to make sure of that is to hang the antenna at a higher place or strap it to PVC pipe or other non-conductive pole
Advantages of 300ohm Twinlead Slim Jim Antenna
- Easy to construct
- Has radiation angle almost parallel to the ground which makes your transmission goes farther than 5/8 or ground plane antennas
- Portable; Easy to carry, store and deployed
- Can be use during emergency situation
- Light and flexible
Here is a screenshot of my own completed slim jim antenna which I use with my Icom V8 portable radio.
Upon connecting this antenna to your portable radio, you can feel its differences when compared to using the stock rubber duck or telescoping antenna.