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
FIG 1. 20m Dipole Radiation Pattern
FIG 2. 20m Dipole SWR Plot
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!
Nested Dipoles for 10/12/15m
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!