Superheterodyne Receiver

The Supersonic Heterodyne receiver, or Superheterodyne receiver uses frequency mixing to convert a received signal to a fixed intermediate frequency (IF) which can be more conveniently processed than the original carrier frequency. At the cost of an extra frequency converter stage, the superheterodyne receiver provides superior selectivity and sensitivity compared with simpler designs.

So, the incoming radio signal is mixed with a local oscillator to produce sum and difference frequency components. The lower frequency difference component called the intermediate frequency (IF), is separated from the other components by fixed tuned amplifier stages set to the intermediate frequency. The tuning of the local oscillator is mechanically ganged to the tuning of the signal circuit or radio frequency (RF) stages so that the difference intermediate frequency is always the same fixed value.

How it works

The antenna collects the radio signal. The tuned RF stage with optional RF amplifier provides some initial selectivity and prevent strong out-of-passband signals from saturating the initial amplifier. A local oscillator provides the mixing frequency. The oscillator is typically a variable frequency oscillator which is used to tune the receiver to different stations. The frequency mixer then changes the incoming radio frequency signal to a higher or lower, fixed, intermediate frequency (IF). The IF band-pass filter and amplifier supply most of the gain and the narrowband filtering for the radio. The demodulator extracts the audio or other modulation from the IF radio frequency. Finally, the extracted signal is then amplified by the audio amplifier.