The FM transmitters have a very large bandwidth as compared to AM transmitters. In FM transmission, ground wave and sky wave propagation is not possible, and signals in VHF and UHF bands are propagated by line of sight propagation, which restricts the range upto 50 km. A voltage variable reactance device is placed across the tuned or tank circuit of an oscillator which is tuned to the carrier frequency. The modulator makes use of a BJT or FET, which exhibits a variable reactance with change in the modulating signal. The varactor diode is a two terminal device whose capacitance varies with applied voltage. The voltage controlled oscillator is a sinusoidal oscillator. Its frequency is controlled by an external voltage, thus it is a kind of frequency modulator.