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I have as assignment to make a half wave dipole antenna, that radiates at 433 MHz. I am trying to figure out how to use a coaxial cable as transmission line. I know that the coaxial cable is unbalanced and an ideal half wave dipole is balanced. To properly connect these two is a balun required.

The main question I have about the coaxial cable is how do I connect the coaxial cable to the dipole when only the inner conductor transfers the signal? What is the best way to connect it together, taking in consideration that I also need a 180 degrees shifted signal connected to one of the arms of the dipole?

Glenn W9IQ
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Mike576
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1 Answers1

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How do I connect the coaxial cable to the dipole

Using a balun. That's its job.

when only the inner conductor transfers the signal

This is an incorrect assumption. Current always flows in loops, so there is always an equal and opposite current somewhere. In a coaxial cable, the signal is carried by both the inner conductor and the outer conductor (or, in some perspectives, “in the space between them”).

If you connect the inner and outer conductor of a coaxial cable to the two arms of a dipole then the dipole will in fact work as an antenna — but the outer conductor of the cable will also radiate/receive. This is the problem a balun solves. If you ignore it, you will still have an antenna, but possibly not the antenna you intended to design.

Kevin Reid AG6YO
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