After making a batch of nice folded dipole elements on my diy jig, I needed to work out how to mount them and  feed them with 50 Ohm coax. The feed point impedance should be 200 Ohms so I needed a 4:1 balun.

A 4:1 coax balun is easy to make and, using this tool, I worked out the size of the coax loop for my balun centred on 434.000 Mhz.

You will need

length of RJ58 coax
Maplin project box – Order code SC78K
BNC socket
Silicone sealant

Step 1

Drill holes in the project box to suit the elements of the dipole, the bnc socket and the coax balun.

Step 2

Insert the element, BNC socket and both ends of the balun.

Step 3

Solder the parts together as per the balun diagram.

Step 4

Apply a small amount of silicone to the areas around the holes in the box.

Step 5

Screw the box cover into place


A professional looking folded dipole ready to mount and use.

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