Building the JWP CityGo 4:1 Balun
A balun is simple and easy to make even the less experienced hams can do it. If you are going to build one do some homework first and choose the correct design for your project, with some extra thought it can be a project to be proud of. Below is a list of parts that I chose to make my CityGo 4:1 balun.
1 x IP65 transparent top plastic box L80mm W55mm H30mm. £6.50
1 x T140-43 ferrite toroid £3.50
1 x Panel mount SO239 £1
1 x Pair of binding posts £1.25 Crimp connectors
heat-shrink & wire £0.50
Total cost £12.75
Start by carefully marking the box for drilling and mounting the binding posts and SO239 making sure all nuts are tight but exercising care not to overtighten or you will damage the box.
Winding the toroid :
10 to 12 turns is sufficient to give a reasonable SWR for most tuners from 3.5mhz to 30mhz. Every time the wire passes through the centre of the toroid counts as one turn. Start by putting a small wire tie on the toroid and passing the wire through the centre making sure it is held firmly in place by the wire tie.
Depending on the thickness of wire you choose continue to wind 10 to 12 turns onto the toroid then using another wire tie to secure the end. Using a larger wire tie around tightly the circumference you can remove the first two ties, see below.
Using the diagram for guidance connect all wires paying some attention to detail you can get a good finish. Build it to the same spec that you would purchase.