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

Btw, the guy in the blue shirt maintaining the repeater is 9W2USF, Handle: Amiruddin.

Gunung Keriang Repeater Team

You can get the rest of the photos here – RGK Repeater Gunung Keriang Photos, all of the photos taken from 9W2DOT website

Step I

First get a ATX PC power supply from the nearest computer store. Price is around RM30-70.

Make sure it could supply sufficient current. Look at the label. We need at least 10-17amp at 12V for a sufficient operation of mobile rig. Lower Ampere rating means that your mobile rig cant transmit with a typical HiGH setting (50w).

Step 2

Look for ATX power connector. It should look like this.

Look for black and green wire at the ATX connector. The wire position is 4th from the top left side of the connector and 4th from the bottom right side from the connector as pictured above.

Cut the black and green wire. Trim all the other wires as we wont need them.

Tie both Black and Green wire together.

Connect both Green and Black wire to bypass the PC Power Supply unit. Insulate it with some tape. and switch on the power supply. If the fan is running, that means you’ve successfully completed this step!

Step 3.

Turn off the power supply. Look for HDD, CDROM power connector, as pictured above.

Cut all wire from the connector.

Separate 2 black wires and one yellow wire. Combine both black wires together.

Look for an extra mobile rig power connector, this can be obtained from electronic shops car accessories, or car battery shop.

Connect the yellow wire (+12 volt DC) to the positive terminal at the power connector as pictured above. Connect both black wires together and put it to the negative terminal as picture above too.

Step 4

Cut all unnecessary wires, connector, and leave the power supply with just the rig power connector like this. It will look much more presentable and neatly prepared.

You can test the output voltage of this power supply by testing it with Voltmeter/Multimeter. Here you can see that the power supply output voltage is about 12V, which is suffiecient to power a mobile rig (13.8V +/- 15%).

Step 5

Finally, connect the power supply to your mobile rig to power it up. Enjoy your QSO!

FAQ: Nice, but my mobile rig require 13.8VDC to operate, this PSU only supplies 12V, it won’t work
Actually it can work. Mobile rigs requires 13.8 +/- 15% VDC to work (check your rig manual). and that gives a range about 11.7V – 15.8V of stable voltage potential. So a 12V power supply with sufficient current (15A and above) is definitely sufficient to power the mobile rigs.

Acknowledgments
This howto has been translated directly from Malay version original article published in Forum Anak Perlis written by me.

You can refer there for a complete malay version of the guide if you find the English version is confusing.

As an amateur radio operator I usually monitor local repeater (145.525 MHz -0.600, tone: 103.5) and local simplex on 145.425 MHz mostly during night time.

I use an Icom v8 and Icom IC V8000 as my communication equipment. My hobby includes antenna homebrewing and finding the most energy efficient way to transmit as far as possible using the least power.

That’s all for now. Thanks for visiting. I can be reached at 9w2wtf@please.name.my, or 9w2wtf@mypapit.net

73 to all

For example :

If you are transmitting on 145 MHz frequency with 65 Watt of power using 15 meter RG-58 cable, the maximum effective power radiated by your antenna is just about half of the transmitting power (36.156 MHz).

But when you switch to RG-8 cable, the loss would be significantly lower, and your antenna would radiate 54 Watt of power.

Since the power loss is significant, it is advisable that you consider the choice of your feedline before setting up your station. In emergency or QRP situation, every 1 Watt counts.

If you have no other choice other than to use RG-58 cable, it is advisable to put your antenna as high as possible with the shortest amount of cable possible. This will save your rig a lot of hard work, and may actually get your signal to travel further than before

How much power loss in your feedline ? Check it at Coax Cable and Line Loss Calculator website

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.

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.

Calculation
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

Tools

• 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

Actually both PL-259 and SO-239 are collectively known as UHF connector.

PL-259

Pictured above is commonly called the UHF male connector. Usually come in two version, one for lighter cable like RG-58, and another for heavier braid coax RG-8, RG-213.

SO-239

Also known as UHF female. If you bought a mobile or base amateur radio rig, yours are likely to have this kind of connector.

Both PL-259 connector and SO-239 fits together and is collectivly called the UHF type connection.

So hope that would clear up confusion associated with SO-239, PL-259 connector. Both of them are known as UHF connector but with different names for male/female jack. That’s all for today folks!

Due to the enourmous size of 3 element Yagi and the current working condition on 10/11 meter band, I decided to accept the advice of 9W2RZL and thinking of constructing a directional antenna right after I obtain the 11/10 meter rig (which is maybe around April).

Moxon antenna might suit my need as it is :

• directional
• has gain of around 5 dBi
• Compact and Light weight
• Easy to construct
• designed for 50 Ohm impedance
• Wideband
• Great F/B ratio, useful for blanking noise

Here is the plan for the 10 meter Moxon antenna, centered on 28.5 MHz frequency.

Dimensions

• A – 382.43 cm (150 1/2 inch)
• B – 57.13 cm (22 1/2 inch)
• C – 11.02 cm (4 3/8 inch)
• D – 71.06 cm (28 1/4 inch)
• E – 139.76 cm (55 inch)

These calculation are made for 12 gauge wire using L. B. Cebik Moxon Calculator tool. The Moxon on the above photo belong to Mark Rabel

Radiation Pattern Lobes

Dimensions (in inches)
Element, Length, Space from Reflector

Reflector – 40.52, —-
Driver – 39.96, 10.13
Director 1 – 37.38, 14.32
Director 2 – 36.31 25.93
Director 3 – 36.31, 37.28
Director 4 – 34.96 , 54.22

Calculated Center of gravity 23.87 inches

Dimensions (in cm)
Element, Length, Space from Reflector

Reflector – 102.92, —-
Driver – 101.50, 25.73
Director 1 – 94.95, 36.37
Director 2 – 92.23, 65.86
Director 3 – 92.23, 94.69
Director 4 – 88.80 , 137.72

Calculated Center of gravity :60.66 cm

The plan for the antenna has been taken from LB Cebik website. More article will follow that covers our construction of this Yagi antenna along with our reports of its improvement.

Congratulations to those who has passed the examination! See you on the air!