A standard dipole, at reasonable heights, provides you with a 2:1 SWR bandwidth of around 7%. While that's plenty of bandwidth on 20 Meters (14.175 MHz, 0.992 MHz BW), it tends to be a little light on 80 Meters (3.75 MHz, 0.262 MHz BW). However, if you were to make a dipole appear thicker, the bandwidth would increase and feed impedance will be modified. Using the method provided in the diagram below, bandwidth can be increased to about 13% and provide a better match to 50 Ω coax.
|Fat (Broadbanded) Dipole|
The diagram below shows all of the dimensions for a Fat Dipole. The diagram is also a calculator. If you change the frequency at the top of the diagram, the dimensions will be adjusted. The top of the diagram shows the Fat Dipole itself with the associated dimensions. A #14 Copperweld wire is suggested because it is strong, doesn't stretch, and is light. This will work with any other kind of wire but may get a little heavy with the larger gauges. A center support might be in order to support the weight.
The Spacer is detailed in the middle of the drawing. This can be made from wood or plastic but must be strong to support the spacing between the wires. I only show Spacers in the center and at the ends, but you may want to add more of them to keep the wires spaced properly. But note, that will increase the weight.
The bottom of the diagram contains a small table that lists some common Amateur frequencies and the associated Length, Spacing, and effective Bandwidth. If you want to see other frequencies, use the Frequency Input area at the top of the diagram.