Dipole antenna

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The most basic of all antennas, the dipole is popular for TV reception because of its predictability. A freestanding half-wave dipole has a torroidal (doughnut-shaped) reception pattern, and has a terminal impedance of 75 ohms. But if this 75-ohm antenna is connected directly to 75-ohm coaxial cable without a 1-to-1 balun, some signal picked up by the dipole will flow onto the outside of the shield conductor where it will be retransmitted and lost. (Also some signal picked up by the shield will flow onto the dipole, disrupting the gain, the radiation pattern, and the impedance. This could be an improvement, but more likely it is the opposite.)

The dipole is 75-ohms at only one frequency. For other frequencies its terminal impedance will include some reactance, which will prevent a good match with the feed-line. See impedance. See