Radio tuner

Design history and overview

The primary goal of a tuner's design is to exclude noise and amplify the wanted signal. Tuners may be monophonic or stereophonic, and generally output left and right channels of sound. Tuners generally include a tuning knob or keypad to adjust the frequency, i.e. the intended radio station, measured in megahertz (e.g., 101.1 MHz). Mistuning is the greatest source of distortion in FM reception. Some models realize manual tuning by means of mechanically operated ganged variable capacitors. Often, several sections are 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 the front-end tuner, for electronic tuning. Modern radio tuners use a superheterodyne receiver with tuning selected by adjustment of the frequency of a local oscillator. This system shifts the radio frequency of interest to a fixed frequency so that it can be tuned with a fixed-frequency band-pass filter. Still later, frequency synthesizer then software-defined radio methods were used, with microprocessor control.