The mixer's job is to precisely tune a particular frequency.
When you tune your radio, you are tuning both the local oscillator in the mixer and the rough RF filter. The audio signal is then amplified and passed through your speakers. It would be cost-prohibitive to build a sharp, yet variable filter.įinally, this IF is passed through a demodulator, which recovers the original audio signal. Since the IF filter never changes frequencies, it's economical to build it to be very sharp and very high quality. The mixer is followed by some sharp IF filters that select out just one channel. The IF is specific to your radio - it was selected by the engineers who made the radio. The process of converting from RF (radio frequency) to IF (intermediate frequency) is sometimes called "mixing down to IF." The beat frequency is sometimes called an intermediate frequency, or IF. The beat frequency is much lower than the radio-frequency carrier, and is easier for the subsequent electronics to handle. The interference of the two waves produces beats. The mixer sums the incoming signal with a pure tone (sine wave) from a local oscillator with an adjustable frequency. The mixer is really the heart and soul of the tuner. In most radios, the filtered radio-frequency channel is passed through a mixer (called a heterodyne in the old days). This filter does not need to be very good - it just needs to prevent power in channels far away from the desired chanel from reaching the next stage of tuning, the mixer. The vicinity of a specific carrier frequency is called a channel. This circuit is a bandpass filter, and admits frequencies only in the vicinity of the desired carrier frequency. The first stage of radio reception is a radio-frequency filter, usually made with an RLC with a variable capacitance or inductance. The result is that an identical modulated radio-frequency signal is induced in the antenna. This modulated carrier is transmitted from one antenna on a tower to another on your car. A radio signal is a carrier signal - a pure sine wave of some specific frequency - modulated in either frequency or in amplitude by an audio-frequency signal.
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