<P> More complex transmissions like PAL / NTSC (TV), DAB (digital radio), DVB - T / DVB - S / DVB - C (digital TV) etc. use a wider frequency bandwidth, often with several subcarriers . These are transmitted inside the receiver as an intermediate frequency (IF). The next step is usually either to process subcarriers like real radio transmissions or to sample the whole bandwidth with A / D at a rate faster than the Nyquist rate that is at least 2 times the IF frequency . </P> <P> The tuner can also refer to a radio receiver or standalone audio component that are part of an audio system, to be connected to a separate amplifier . The verb tuning in radio contexts means adjusting the radio receiver to receive the desired radio signal carrier frequency that a particular radio station uses . </P> <P> The simplest tuner consists of an inductor and capacitor connected in parallel, where the capacitor or inductor is made to be variable . This creates a resonant circuit which responds to an alternating current at one frequency . Combined with a detector, also known as a demodulator (diode D1 in the circuit), it becomes the simplest radio receiver, often called a crystal set . </P> <P> Older models would realize manual tuning by means of mechanically operated ganged variable capacitors . Often several sections would be provided on a tuning capacitor, to tune several stages of the receiver in tandem, or to allow switching between different frequency bands . A later method used a potentiometer supplying a variable voltage to varactor diodes in the local oscillator and tank circuits of front end tuner, for electronic tuning . </P>

What type of circuit is used to tune a radio