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
Results
A professional looking folded dipole ready to mount and use.
Hi, I’m in the process of building a folded dipole with a 4:1 balun centered on 437.2MHz for a college project. I am writing you to ask if you have any performance data for the folded dipole shown on this page. I ask because my 4nec2 simulations for a resistance of 200ohms do not agree with the dimensions of your folded dipole. At 437.2MHz 4nec2 optimizes my length at 242mm.
Thank You,
Michael
P.S. my professor’s call sign is WB9AWX
Hi Michael,
I have emailed you a reply.
Matt