# Which type of balun to use for unbalanced line (Coax) to a dipole antenna?

How can I choose a balun for the transformation? What to look carefully? Generally I see on commercial baluns that one input for unbalanced coax and two output. Does that two output mean one for the ground and other goes to the antenna?

• Can you show an example?
– JRE
Commented Jun 11, 2021 at 12:59
• Transformation of impedance? Or balance of what? Commented Jun 11, 2021 at 13:01
• @TonyStewartEE75 Transformation of unbalanced signal to balanced signal.
– Xant
Commented Jun 11, 2021 at 13:06
• Show diagram and spectral impedances (f) required to define CM choke. Commented Jun 11, 2021 at 13:11

Which type of balun to use for unbalanced line (Coax) to a dipole antenna?

If you are connecting to a dipole, you need an balanced output because that is what dipoles work best with.

If you are interfacing to coax you need an unbalanced input because coax is an unbalanced transmission medium.

Generally I see on commercial baluns that one input for unbalanced coax and two output.

That's correct the "bal" part of "balun" will be the output and the "un" part of "balun" is the unbalanced port (suitable for coax).

Does that two output mean one for the ground and other goes to the antenna?

No, of course not. If you grounding one of the balanced outputs then you are unbalancing it and making it largely unsuitable for the dipole antenna. You are defeating the whole point of using a balun.

• Thank you, Andy. So, always will be two feed point on the dipole? What should I look at carefully for the selection ?
– Xant
Commented Jun 11, 2021 at 13:28
• There are always two feed wires on a dipole antenna (a half wave antenna) and they are balanced. On a monopole (quarter wave antenna) there are also two feed wires but one will be ground/earth hence the feed is unbalanced @antfellow Commented Jun 11, 2021 at 13:37