In this post we provide a calculator that gives the length of an antenna that can be used in the Frequency Modulation (FM) Band.
Example Calculation
The FM band is not a single frequency. Instead it extends from 88 MHz to 108 MHz. For the purpose of the calculation, we can choose the center of the band at 98 MHz.
The length of a quarter wave antenna for FM applications is 76 cm. Also known as Whip antennas, they are used in consumer FM radios such as the one shown in the picture below.
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At 100 MHz, the length is 75 cm. As the frequency increases, the length decreases. For the range 88 MHz to 108 MHz, the length of an FM antenna is between 85 cm and 69 cm.
FM Broadcast stations use Dipole Antennas this calculator provides the length. For the range 88 MHz to 108 MHz, the dipole antenna length is between 162 cm and 132 cm.
The dipole has larger dimensions than a monopole for the same frequency.
Note that the antenna length is independent of the modulation type (in this case frequency modulation) and depends only on the frequency of operation.
Antenna Construction
Antennas on portable FM radios can be extended and contracted. They are called telescopic or telescoping as the structure resembles that of a telescope.
