The Homebrew Slim Jim Antenna Gain

I’ve been searching for information regarding the radiation angle and the gain of slim jim antenna, but found none of it. So I decided to build the model of the antenna inside the ever useful MMANA-GAL software to get the information I needed myself.

From what I can surmise, the slim jim has a slightly lower radiation angle than vertical dipole antenna and is easier to mount, thus it is suitable to use for point-to-point communication VHF-UHF operation. It has a gain of about 2.8dBi-3.2dBi in free space and 4.8-5.8dBi when mounted at about 30feet from the ground. Here’s the result of MMANA-GAL :

Slim Jim 9w2wtf

Slim Jim mounted 30 feet above ground
Slim Jim Antenna gain

Slim Jim in free space

My Homebrew 2 meter VHF Antennas

Here are the photos of my homebrew 2 meter VHF antennas. One is 6 element OWA yagi and another is a 2 meter Slim Jim for omnidirectional operation

OWA Yagi 6 element

Slim Jim antenna

OWA Yagi 6 element

The homebrew slim jim antenna was previously featured on my blog as well as its plan. The OWA Yagi 6 element antenna plan can be obtained from this post : 6 Element OWA Yagi Antenna for 2 Meter band plan

Panduan SOP dan QSO Radio Amatur Berbahasa Melayu

Berikut merupakan fail PDF yang mengandungi Panduan berQSO yang diterjemahkan kedalam bahasa melayu oleh 9w2ssl.

Antara informasi yang boleh dijadikan panduan semasa mengendalikan komunikasi radio di udara termasuklah komunikasi simpleks, panduan penggunaan pancar-ulang dan kaedah mengendalikan roundtable


Download file tersebut – Amateur Radio Standard Operating Procedure berbahasa melayu

Howto – 2 Meter Slim Jim antenna from Ordinary Wires

Slim Jim (J Integrated Match J-Pole) is probably the most easiest and powerful 2 meter antenna to build provided you have the exact measurement and material to build it.

This how to will show you how to build a 2 meter slim jim antenna from ordinary insulated copper wire commonly used for carrying AC (alternate current) electricity in your household.

Slim Jim construction basic
I am not only going show you the measurement of slim jim antenna for specific frequency, but I’m going to show you how to calculate slim jim antenna by your own using the basic formula below.

Basic Slim Jim Idea

The figure above shows that the longest side of slim jim is 3/4 wavelength long and the shorter side of the slim jim consist of 1/2 wavelength and 1/4 wavelength long seperated by a gap.

The feedline (coax cable) is normally connected 1/20 wavelength from the bottom of the slim jim antenna with the center conductor connected to the longest side and the shield/braid is connected to the shorter side.

Building the Slim Jim antenna
This guide assume you want to build a slim jim antenna that centered on 146MHz.

The formula for calculating wavelength in metric system is 300/(freq MHz)

Using the formula from the figure, we have :

300/146 = 2.055 M
Wavelength = 205.5 cm

Wavelength x copper wire velocity factor = 205.5 cm x 0.94
= 193.17 cm

3/4 wavelength = 193.17 x 0.75
= 144.88 cm (57″)

1/2 wavelength = 193.17 x 0.5
= 96.585 cm (38″)

1/4 wavelength minus gap = 193.17 x 0.25 – 2.6 cm
= 45.69 cm (18″)

Coax tap = 193.17 x 1/20
= 9.6 cm (3 3/4″)

Building Materials

  • 3/4″ diameter PVC (20mm) – 6 feet (180 cm)
  • ordinary insulated copper wire for carrying altenate current (AC) – 11 feet (3.40 meter)
  • Cable ties


  • Soldering iron
  • Glue gun
  • Somthing to make a hole on PVC pipe

Wire Slim Jim Building Steps

  • First take the PVC pile and measure it according to the 3/4 wavelength formula above (144.88 cm).
  • Make two holes at the opposite side of the pipe. This hole is used for putting the copper wire through the pipe. Repeat this step 144.88 cm away from the top hole. Both of these holes will hold the copper wire.
  • Insert the wire through the hole until both end reaches each other on one side of the PVC pipe. Then measure the length of the wire and cut the wire on that side so the setup resembles the figure above.
  • Cut the wire insulation (but leave the wire uncut) 1/20 wavelength away (9.6 cm) from the bottom of the PVC pipe, again refer the figure above.
  • Solder the center of the coax cable at the longest side of the slim jim (3/4 wavelength part) and the braid/shield at the shorted part of the antenna.
  • Test the antenna using SWR meter to ensure that its SWR is at minimum or within acceptable level.
  • There you go, you’ve build yourself your own 2 meter Omnidirectional Slim Jim antenna for less than USD2 (RM 6.00)

2 Meter Wire Slim Jim Antenna in action


mypapit homebrew 2 meter slim jim

Portable 2 Meter Slim Jim antenna using 300 Ohm Twinlead

300Ohm slim jim antenna diagram plan

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.

Basic Slim Jim conceptual plan

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.

Important Notes

  • 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

  1. Easy to construct
  2. Has radiation angle almost parallel to the ground which makes your transmission goes farther than 5/8 or ground plane antennas
  3. Wideband
  4. Portable; Easy to carry, store and deployed
  5. Can be use during emergency situation
  6. Light and flexible

Completed Antenna
Here is a screenshot of my own completed slim jim antenna which I use with my Icom V8 portable radio.

Completed slim jim 300ohm coax

Upon connecting this antenna to your portable radio, you can feel its differences when compared to using the stock rubber duck or telescoping antenna.

2 Meter Amateur Radio Slim Jim Plan

Here are the plan I use for constructing and experimenting with Slim Jim antenna on 2 Meter VHF Amateur band. The measurement used are designed to center around 144-148 MHz radio frequency, which is used by amateur radio world wide.

FYI this is the plan that I use to construct my first ham radio antenna using PVC pipe and aluminium tube.

2 Meter Slim Jim Plan

Credit to Pak Halim and Azmeer for giving this plan and showing me how to construct a proper antenna.

2 Meter Slim Jim using 300 Ohm tv cable (Ribbon Antenna)
Here’s the plan that I use for constructing Slim Jim antenna for portable radio (ICOM V8).

ham radio 2 meter slim jim ribbon antenna

Both design are meant to be fed with 50-Ohm impedance coax feed line (RG-58/RG-8/RG-213) to obtain the most optimized results

2 Meter Amateur Radio Slim Jim Project

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).

slim jim mypapit

slim jim papit

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 :

  1. Aluminium tube 8mm diameter, sold in 10 feet (can be obtained from hardware store, 10feet, RM10)
  2. U PVC Pipe (15mm-20mm) for holding with T junction, RM4
  3. SO-239 connector (for mobile rig), RM10
  4. 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):

  1. Bosch hand drill for drilling pipes and aluminium tube ( RM100)
  2. Rivet / Riveter for attaching coax cable to antenna (RM 20)
  3. Bender (RM 30)
  4. some wire cutter
  5. Hack saw for cutting pipes and aluminum (RM 3)
  6. 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.

SWR Reading

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.