Dipole its symmetric system with ~72ohm in center.

**Wiki:**

The dipole is any one of a class of antennas producing a radiation pattern approximating that of an elementary electric dipole with a radiating structure supporting a line current so energized that the current has only one node at each end.

The most commonly used is the center-fed **half-wave dipole** which is just under a half-wavelength long. The radiation pattern of the half-wave dipole is maximum perpendicular to the conductor, falling to zero in the axial direction, thus implementing an omnidirectional antenna if installed vertically, or (more commonly) a weakly directional antenna if horizontal

A half-wave dipole antenna consists of two quarter-wavelength conductors placed end to end for a total length of approximately *L* = λ/2. The current distribution is that of a standing wave, approximately sinusoidal along the length of the dipole, with a node at each end and an antinode (peak current) at the center (feedpoint)

**How to build half-wave dipole antenna for hf:**

**1.**Need 2 copper wire 1-4mm diameter and **λ/4**– use this table:

**Wavelength table**

Band | MHz | λ | λ/2 | λ/4 |

160 meter | 1,81 MHz | 165,75 Meter | 82,87 Meter | 41,44 Meter |

80 meter | 3,6 MHz | 83,33 Meter | 41,66 Meter | 20,83 Meter |

60 meter | 5,35 MHz | 56,07 Meter | 28,04 Meter | 14,02 Meter |

40 meter | 7,1 MHz | 42,25 Meter | 21,13 Meter | 10,56 Meter |

30 meter | 10,1 MHz | 29,70 Meter | 14,85 Meter | 7,43 Meter |

20 meter | 14,15 MHz | 21,20 Meter | 10,60 Meter | 5,30 Meter |

17 meter | 18,1 MHz | 16,57 Meter | 8,29 Meter | 4,14 Meter |

15 meter | 21,2 MHz | 14,15 Meter | 7,08 Meter | 3,54 Meter |

12 meter | 24,95 MHz | 12,02 Meter | 6,01 meter | 3,00 Meter |

10 meter | 28,4 MHz | 10,56 Meter | 5,28 Meter | 2,64 Meter |

Note that the shortening factor of the wire is not included in the table. So the antenna will be about 5% shorter in reality.

**2.** Balun 1:1 (without balun you will be have many common mode. Balun need for current symmetry and choke commonmode)

**3.** Coax 50ohm 1/2 lamda length (Half-wave coax repeater) – use this link for calculate coax length: (use Freq and shortening factor anly) – https://docs.google.com/spreadsheets/d/1Ww9v5mr89MIzynbZVK-7KeMNxyqpsoXb5VZy7sDfUOY/edit?usp=sharing

Balun 1:1 (without balun you will be have many common-mode. Balun need for current symmetry and choke common-mode)

**Balun:**

Balun is an electrical device that converts between a balanced signal and an unbalanced signal. Our dipole its strongly balanced device, our coax its unbalanced device.

Balun materials:

**Wire copper or silverplated (much better) 0.5-0.7mm 100-300wt**

Core:

FT140-43 – 1-10 mhz 10-24 mhz 30-54mhz

FT140-52 – 1-3 mhz 3-30 mhz 54mhz

**Wire copper or silverplated (much better) 1.2-1.5mm 500-1000wt**

Core:

FT240-43 – 1-10 mhz 10-24 mhz 30-54mhz

FT240-52 – 1-3 mhz 3-30 mhz 54mhz

FT240-K – 1-3mhz 3-54mhz