Hi there, sorry for being quiet for a while, but rest assured I was on some knowledge discovery mission to learn about building Slim Jim antenna for two way radio communication (specifically for Amateur radio band).
This antenna is specifically built to resonates within 2 meter amateur radio band (144-148MHz). This antenna has been build with the help of my friend, Amet who is a trained electrician.
Slim Jim Plan that we use
Please refer to 2 Meter Amateur Radio Slim Jim Plan post for more information
Among the items used to construct the antenna are :
- Aluminium tube 8mm diameter, sold in 10 feet (can be obtained from hardware store, 10feet, RM10)
- U PVC Pipe (15mm-20mm) for holding with T junction, RM4
- SO-239 connector (for mobile rig), RM10
- Coax Cable (either RG-8 RM7/m or RG-58 RM2/m, quality varies
Tools that we used are (included with cost if you want to buy them):
- Bosch hand drill for drilling pipes and aluminium tube ( RM100)
- Rivet / Riveter for attaching coax cable to antenna (RM 20)
- Bender (RM 30)
- some wire cutter
- Hack saw for cutting pipes and aluminum (RM 3)
- and oh yes, we *dont use* any torch welder for this one
As you already might guess, the cost for constructing the antenna alone cost slightly less than RM30 (~USD 10, except cable and tool cost), the Slim Jim is mounted on the roof of my house with ordinary TV antenna bracket, with the height of close to 40 feet from the ground.
Why build your own antenna? It is a way for me to better understand about radio wave resonance and to learn more about how to build a radio antenna to tune in to specific frequency, something that commercial antenna lacks, because it is built to tune to a wider range of frequency due to market demand.
This antenna is said to have a gain of 3.2dBi, though I don’t have confirmation about this information.
Here’s the reading I’ve obtained from Diamond SX-200 SWR meter, using 20 watt output power :
- 144 Mhz – 1.2
- 146 Mhz – 1.3
- 148 Mhz – 1.5
The reading is kinda bit off from the center of frequency :p, I know. this is due to my poor handling with aluminium bender. I’ve made it almost an inch longer, so that kinda explains the SWR reading is kinda centered on the lower frequency.
However this is way cheaper than buying a commercial antenna which cost me a lot of bucks, and I surely have more fun!
What can be improved?
Supposed if you want the antenna to resonate better, you could replace aluminum tubing with copper or brass tube and replace RG-58 coax cable with a low loss cable such as RG-213 or RG-8 which was used in this experiment.
What’s next ?
Next I’ll try to construct a ribbon antenna (?), which is a a very flexible antenna to be used with a portable handy radio, when you are traveling and gives you about 3dBi gain when positioned carefully.