Dictionary of Electrical and Electronic Terms
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Superheterodyne Receiver Definition

A Superheterodyne Receiver is a type of receiver that uses a mixer to convert an incoming RF signal into an IF signal for amplification. The most basic superheterodyne receiver would consist of an antenna to receive a radio frequency signal and an RF Mixer to translate the incoming signal into a lower Intermediate Frequency [IF]. An RF filter [shown] might also be included to filter out unwanted radio signals.

A high level block diagram is included as part of the definition of an AM Receiver, and includes the different wave shapes produced by each block or section.

Diagram of a Superheterodyne Receiver
Superheterodyne Receiver

The definition of Superheterodyne covers the translation of a high frequency to a lower frequency, but a standard radio receiver will combine other functions required to receive and translate the signal into a usable format. For example the diagram above shows an additional IF Filter, a Beat Frequency Oscillator and a mixer, along with an audio amplifier and speaker.

The different functions of the receiver are some what self explanatory. The Antenna, which could be any type, is used to receive radio signals over the air [RF signals].

The RF filter [which could be tunable] is used to pass only the signals or frequency band of interest, blocking or filtering all other frequencies.

The RF Mixer accepts the selected signal frequency and combines or mixes that frequency with an oscillator frequency [labeled Variable Frequency Oscillator or VFO], producing an intermediate frequency used by the rest of the circuit. The oscillator frequency is chosen so the combination of that frequency and the RF frequency result in the desired IF frequency.

A mixer will normally output the two input signal frequencies in addition to the mixed or combined frequency. These frequencies must be filtered out so that only the IF frequency remains, which is the combination of the two input frequencies. An IF filter is used to filter out frequencies other than the IF frequency.

A Beat Frequency Mixer is than used to translate the IF frequency down to the audio band, just as the RF mixer produced the IF frequency. The Beat Frequency Oscillator [BFO] is a much lower frequency than the one used by the VFO because a mixer produces the sum and difference of the two input signals. The resultant audio signal is than passed to the audio section of the system.

The audio amplifier block would be comprised of at least a Preamplifier to amplify the low level signals from the detector and a power amplifier which would be used to drive a speaker, both of which would be an Audio Amplifier. The audio portion of the diagram would be part of a receiver system, but is not included in the definition of a superheterodyne receiver.

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