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I have a resonant half wave dipole which is one continuous length and not separated in the middle, fed using a gamma match, and with the braid of the coax joined to the exact electrical center of the dipole.

How does this gamma match arrangement act as a balun ?

Does AC current flow back down the outside of the coax if i don't use an rf choke ?

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The gamma match was discussed at length in a previous Ham Stack Exchange answer. Current flow on the shield is, theoretically, prevented by its connection to a point of zero potential - the center of the element - as long as the center of the antenna is, in fact, a point of zero potential. Since any construction asymmetries and the antenna's environment may cause current imbalance that could produce voltage imbalance, it is possible that current will flow on the outside of the shield. Whether the current magnitude is sufficient to distort the antenna pattern or interact with other structures must be evaluated on a case-by-case basis.

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  • $\begingroup$ HI Brian and thank you for your excellent answer, That makes perfect sense. $\endgroup$ – Andrew Oct 29 '18 at 9:19

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