Another common place one can see dipoles is as antennas for the FM band – these are folded dipoles. The tips of the antenna are folded back until they almost meet at the feedpoint, such that the antenna comprises one entire wavelength. The main advantage of this arrangement is an improved bandwidth over a standard half-wave dipole.
The Length of folded dipole
* La = 145 / freq ( MHz )
Length of coil
* for 75 ohm cable : Lb = La x 0.8
* for 50 ohm cable: Lb = La x 0.66
Using a 3 – 12 V lightbulb we can make a symmetrical antenna. Hold the lightbulb and touch the folded dipole, move from end point to middle. If the lightbulb goes off in the middle everythimg is ok.
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