This enables us to match antennas with a 200 Ohm impedance to the 50 Ohm required for modern Radio equipment. It will also let us connect a balanced antenna to an unbalanced load.
Some people struggle with these kinds of schematics. So I have included the one below. which gives people a better idea of how it is made.
To construct this project, you will need some supplies:-
1 X SO239 socket.
about 3 meters of Enamel coated wire.
Cable ties and insulating tape.
Solder and soldering iron.
some optional items, depending on how you plan to use it :-
weatherproof box ( Waterproof and UV resistant. )
Here we have our T200-2 Toroid. You need two lengths about 1 meter long of wire. I have used brown and blue wire here. So you can see what’s going on. We begin by fixing the start of the windings with a cable tie.
The windings we are going to use are called Bifilar. You can see in this image and in the diagram above, the two wires are looped around the toroid. You should prevent the wires from over lapping each other. To cover 160m through to 6m ( 1.8Mhz – 50 Mhz ) you will need to loop the wire 13 times around. This is not overly critical. At the end you should be left with helical windings and 4 wires.
Now its time to start making our transformer. We need to connect the end of winding 1 ( brown wire ) to the start of winding 2 ( blue wire ). As you can see, the end of winding 1 can be cut short but the start of winding 2 should be left as long as possible. I have removed some of the Insulation. If you are using enamelled coated wire, you will need to sand some of the enamel off.
Now we have the completed transformer, we are going to mount it into a box, so we can use it outside. I have used a small electrical conduit box from a local DIY store. Its cheap and designed to be used outside. This makes it waterproof and UV resistant. Another good point is that there are entry holes prepared for cable. I simply had to poke one out. This can be seen in the picture, along with the SO239 socket. The socket is reused.
This picture shows how we are making connections in our box. I have wrapped tape around the connection we made at the end of winding 1 and start of winding 2.( where the brown wire and blue wire go into the black tape) This is then connected to the outside of the SO239. The end of winding 2 ( single blue wire ) is soldered to the inside of the SO239 a second wire is also soldered to connect to our antenna. This wire and the Start of Winding 1 ( brown wire) is our connection to the unbalanced antenna.
On this occasion I built this 4-1 Balun for a single use. To be used with a Off Centre Fed Dipole antenna. So I have not added screw posts. I have taken the antennas driven elements straight outside. They are soldered onto the start of winding 1 ( brown wire ) and end of winding 1 / start of winding 2 ( where the blue and brown wire go into tape above) Hopefully this is clear.
Here you can see I have used silicone sealant to fix the transformer to the box and make all the screw holes and SO239 watertight. I have also placed some foam on top of the transformer. This will keep it tightly in place when we screw the lid down. More silicone the better !
Here is the finished project. As I mentioned before I built this one for use with an Off centre Fed dipole. which is attached ! It can be found here : http://www.m0zpk.co.uk/40-meter-off-centre-fed-dipole/ If you want it for other purposes, such as a delta loop. Fit screw pegs. This will enable you to experiment.