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Dipole Antenna for FM radio Now a days the FM radio stations are popular, because of their high clarity and increased band width. The FM-Stereo system is an enhancement of the original FM monaural system and is capable of transmitting two independent audio channels via one frequency modulated RF carrier. In case of a monophonic FM transmission, the highest audio frequency transmitted is 15,000 Hz. But it is possible to transmit modulating frequencies up to 75 KHz, i.e. more than the hearing range of our ears. The modulating frequency spectrum. space between 15 and 75 KHz is used to transmit the second channel of audio information required for FM stereo transmissions

A simple dipole antenna can be used for improving the reception of FM broad cast signal. A dipole is typically a length of conductor split into two portions and signal is taken from the split. The dipole is actually an electrical half wavelength of wire at the frequency of interest, since the impedance under this condition is theoretically 72 ohms resistive and is a good match to a 50-75 ohm source or load generally presented by interfacing equipment such as receivers and transmitters designed to work into this range of impedances. It has a nominal 3dB gain over an isotropic source.

A coaxial cable must be used for best result, a twisted pair cable will attenuate the signal and reduce the out put increase the distortion. If use a Balun transformer, it will provide best impedance matching .
Length of the antenna required

where

L=length of the antenna
C=velocity of light 3X108
f=frequency in Hz
Vf=velocity factor=0.95

There a Half wave dipole for 98MHz (is the band centre of FM band) L=1.454 meter =4.77 feet The dipole would then consist of two lengths of wire of each 0.727meters or 2.385feet inches, as in the figure