A
tuner is a subsystem that receives
radio frequency (RF) transmissions like
radio broadcasts and converts the selected
carrier frequency and its associated
bandwidth into a fixed frequency that is suitable for further processing, usually because a lower frequency is used on the output.
Broadcast FM/
AM transmissions usually feed this
intermediate frequency (IF) directly into a
demodulator that convert the radio signal into
audio-frequency signals that can be fed into an
amplifier to drive a
loudspeaker. More complex transmissions like
PAL/
NTSC (TV),
DAB (digital radio),
DVB-T/
DVB-S/
DVB-C (digital TV) etc. uses 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 the IF frequency.