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