Generation ofwide-band FM can be done by variousmeans.However, only themost common and conceptually the simplest one, known as the direct method, is considered here. It employs a voltage-controlled oscillator (VCO) as a modulator. A VCO is an oscillator whose oscillation frequency is equal to the resonant frequency of a tuned circuit, as shown in Figure. The frequency can be varied if either the inductance or the capacitance is made voltage-sensitive to the message signal f (t).