This will be my next homebrew project, a morse practice oscillator circuit. 9W2AZV and I are going to build this as we are preparing ourselves to perfect our Morse code sending/receiving skills.
In the spirit of amateur radio/ham, we will homewbrew the equipment using easily obtainable parts from our nearest electronic stores.
Here’s the circuit
We are still thinking of the easiest and cheapest way to homebrew the keyer, but we are considering to use discarded/faulty computer mouse as our first keyer.
As a bonus, we thought of hooking this keyer straight to PC serial port, so we could use it with XChat CWirc plugin to enable us to test our Morse skill on the irc.
With the amount of work i’m having this week, I would estimate that this project would be completed by the end of March. So stay tune for photos!
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.
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″)
- 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
Short on a good and reliable antenna for your amateur radio operation ?
Here’s how to make a simple 2 meter amateur radio antenna from ordinary tv antenna (Rabbit Ears Antenna).
For your information these antenna can be bought from local tv store at around RM4 a piece (less than USD2).
The best thing about these antenna that it has terminating point (screw) which you can screw in your coax cable to each dipole leg, as shown in the (rather blurry) photo.
After that, extend the telescoping element to the desired length to match your transmitting frequency.
Usually amateur radio operator working on 2 meter VHF would use antenna with vertical polarisation. In this case, you need to spread the dipole to vertical position like pictured above, connect it to your transceiver and be amaze by its transmitting (or receiving) power.
Main Advantage of This Antenna
- Embarassingly easy to construct
- Can be adjusted to any frequency, because of its adjustable telescopic element
As you can see, the rabbit ear tv antenna can also make a good antenna during emergency situation. Its adjustable telescopic elements made it easy to reconfigure the antenna to transmit on different frequencies.
ps : You can use this dipole calculator, if you unsure about the dipole length.
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.
Here is a 6 element yagi my friend and I have built for experimenting with directional antenna. Theoritically the antenna has about 10dBi gain in its main lobe and a good Front-to-Back ratio, a perfect substitute if you don’t have means to get the popular V24 Silverthunder antenna.
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.