The Superheterodyne receiver (or to give it its full name, The Supersonic Heterodyne Receiver – usually these days shortened to superhet) was invented by Edwin Armstrong in 1918. Edwin Howard Armstrong Edwin Howard Armstrong (December 18, 1890 - January 31, 1954) was an American electrical engineer and inventor. ... 1918 was a common year starting on Tuesday (see link for calendar). ...

The Super Heterodyne principle, as used in radio receivers, allows certain obstacles in high performance radio design to be overcome. Tuned radio frequency (TRF) receivers suffered from poor frequency stability, and poor selectivity, as even filters with a high Q factor have a wide bandwidth at radio frequencies. Regenerative and super-regenerative receivers offer better sensitivity but suffer from stability and selectivity problems. The Tuned Radio Frequency Receiver (short TRF) was invented by Edwin Armstrong in 1918. ... The word selectivity has more meanings: Selectivity Electronic selectivity This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... The term filter may refer to: A device to separate mixtures. ... The Q factor or quality factor is a measure of the quality of a resonant system. ... Analog Bandwidth is the width, usually measured in hertz, of a frequency band f2 − f1. ...

In radios using the principle, all signal frequencies are converted typically to a constant lower frequency before detection. This constant frequency is called the intermediate frequency, or IF. In typical AM (Medium Wave) home receivers, that frequency is 455 kHz, for FM VHF receivers, it is usually 10.7 MHz. Amplitude modulation (AM) is a form of modulation in which the amplitude of a carrier wave is varied in direct proportion to that of a modulating signal. ... Frequency modulation (FM) is a form of modulation which represents information as variations in the instantaneous frequency of a carrier wave. ... Very high frequency (VHF) is the radio frequency range from 30 MHz (wavelength 10 m) to 300 MHz (wavelength 1 m). ...

Super Heterodyne receivers "beat" or heterodyne a frequency from a local oscillator (within the receiver) with the incoming signal. The user tunes the radio by adjusting the set's oscillator frequency and/or the tuning of the incoming signals. This heterodyning results in a higher and a lower frequency than that of the incoming frequency. Either the higher or the lower (typically) is chosen as the IF, which is amplified and then demodulated (reduced to just audio frequencies through a speaker). In telecommunications, to heterodyne is to generate new frequencies by mixing two or more signals in a nonlinear device such as a vacuum tube, transistor, or diode mixer. ... An electronic oscillator is an electronic circuit that produces a repetitive electronic signal, often a sine wave or a square wave. ...

Almost all receivers in use today utilize this method. The diagram below shows the basic elements of a single conversion superhet receiver. In practice not every design will have all these elements, nor does this convey the complexity of other designs, but the essential elements of a local oscillator and a mixer followed by a filter and IF amplifier are common to all superhet circuits.

Superheterodyne receiver block diagram – A smaller and cleaned-up PNG version of Image:Superhet. ...

The advantage to this method is that most of the radio's signal path has to be sensitive to only a narrow range of frequencies. Only the front end (the part before the frequency converter stage) needs to be sensitive to a wide frequency range. For example, the front end might need to be sensitive to 1–30 MHz, while the rest of the radio might need to be sensitive only to 455 kHz, a typical IF frequency.

Sometimes, to overcome obstacles such as image response, more than one IF is used. In such a case, the front end might be sensitive to 1–30 MHz, the first half of the radio to 5 MHz, and the last half to 50 kHz. Two frequency converters would be used, and the radio would be a "Double Conversion Super Heterodyne". Image Response (or more correctly, Image Response Rejection Ratio, or IMRR) is a measure of performance of a radio receiver, particularly one that operates on the super-heterodyne principle. ...

Super Heterodyne receivers have superior characteristics in both frequency stability and selectivity. It is much easier to stabilize an oscillator than a filter, especially with modern frequency synthesiser technology, and IF filters can give much narrower passbands at the same Q factor than an equivalent RF filter. A fixed IF also allows the use of a crystal filter in very critical designs such as radiotelephone receivers which have exceptionally high selectivity. A frequency synthesiser is an electronic system for generating any of a range of frequencies from a single fixed timebase or oscillator. ... The Q factor or quality factor is a measure of the quality of a resonant system. ... A Crystal Filter is a special form of quartz crystal used in electronics systems, in particular communications devices. ... A radiotelephone is a communications device that allows two or more people to talk using radio. ...

Radio transmitters also use Super Heterodyne technology. The design of a Super Heterodyne transmitter is similar to that of a Super Heterodyne receiver except each stage of the signal path is reversed. In communications and information processing, a transmitter (sometimes abbreviated XMTR) is an object (source) which sends information to an observer (receiver). ...

The next evolution of Super Heterodyne receiver design is the software defined radio architecture, where the IF processing after the initial IF filter is implemented in software. A software-defined radio (SDR) system is a radio communication system which uses software for the modulation and demodulation of radio signals. ... Computer software (or simply software) refers to one or more computer programs and data held in the storage of a computer for some purpose. ...

See also

• Automatic Gain Control
• Demodulator
• VFO

Automatic gain control (AGC) is an electronic system found in many types of devices. ... A demodulator is an electronic circuit used to recover the information content from the carrier wave of a signal. ... Acronym for: Variable Frequency Oscillator Any radio receiver or transmitter that works by the superheterodyne principle, and which can be tuned across various frequencies, will need a VFO. Altering the frequency of this VFO will control the frequency to which the radio is tuned. ...

External links

• Radio Receiver Technology A selection of articles describing various aspects of the superhet radio