The Dipole was invented by Heinrich Rudolph Hertz it is a relatively simple antenna using wire. The feeder is connected to a Balun which in turn is connected to the two antenna “legs” one being the ground the other the live leg. Usually dipoles are either 1/2 or 1/4 wave. Dipoles can be mounted horizontally or vertically.
Notice in the above diagram the 75Ω Feedline, we use 50Ω for amateur radio.
One thing of note: a Dipole is often called a Reference Antenna, as it is omni-directional and has 0db gain
Here is a JavaScript Dipole Calculator
Fig 1. Displays a chart showing the lobes of a standard 1/2 wave dipole whilst Fig 2. shows an SWR plot of the same Dipole (Based on a Freespace height of 20m (for 20m)
These where created in MMANA-GAL
To the right is a nested dipole made back in 2010 in a afternoon of boredom, the trick to nesting is a common feed point for all the lengths. The frequency will automatically choose the right wire!
The measurements below are for one leg of the dipole, so ideally you cut TWO lengths the same. Always cut slightly long and use a tuner to get the trimming right.
4m (70mhz) – 70.300 – 3ft. 3 – 31/32in. or 1.015 M
6m (50mhz) – 50.100 – 4ft. 8 – 1/16in. or 1.424 M
10m (28mhz) – 28.225 – 8ft. 3 – 1/2in. or 2.527 M
12m (24mhz) – 24.925 – 9ft. 4 – 11/16in. or 2.862 M
15m (21mhz) – 21.000 OR SEE 40m – 11ft. 1 – 23/32in. or 3.396 M
17m (18mhz) – 18.100 – 12ft. 11 – 5/32in. or 3.941 M
20m (14mhz) – 14.125 – 16ft. 6 – 13/16in. or 5.049 M
30m (10mhz) – 10.140 – 23ft. 0 – 15/16in. or 7.034 M
40m ( 7mhz) – 7.100 – 32ft. 11 – 1/2in. or 10.046 M
60m ( 5mhz) – 5.350 – 43ft. 8 – 7/8in. or 13.331 M
80m (3.5mhz) – 3.600 – 65ft. 0 – 1/32in. or 19.812 M
160m (1.8mhz) – 1.840 – 127ft. 2 – 3/32in. or 38.763 M
40m Will tune perfectly for 15m!