Superheterodyne receiver: Difference between revisions

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The Super Heterodyne receiver was invented by Edwin Armstrong in 1918.

The Super Heterodyne (sometimes shortened to superhet) principle as used in radio receivers allows certain obstacles to 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.

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 a typical AM (Medium Wave) home receivers, that frequency is 455 kHz, for FM VHF receivers, it is usually 10.7 MHz.

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).

Almost all receivers in use today utilize this method.

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".

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.

Radio transmitters also use Super Heterodyne technology. The design of a Super Heterodyne transmitter is similar to that of a Super Heterodyne receiver which each stage of the signal path reversed.

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.

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 The '''Super Heterodyne receiver''' was invented by [[Edwin Armstrong]] in [[1918]].
-The Super Heterodyne principle as used in radio receivers allows certain obstacles to 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.
+The Super Heterodyne (sometimes shortened to ''superhet'') principle as used in radio receivers allows certain obstacles to high performance [[radio]] design to be overcome. Tuned Radio Frequency (TRF) receivers suffered from poor [[frequency stability]], and poor [[selectivity]], as even [[filter]]s with a high [[Q factor]] have a wide [[bandwidth]] at radio frequencies.
-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 modern home receivers, that frequency is 455 kHz.
+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 a typical AM (Medium Wave) home receivers, that frequency is 455 kHz, for FM VHF receivers, it is usually 10.7 MHz.
-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).
+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).
 Almost all receivers in use today utilize this method.
-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, which is a typical IF frequency.
+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".
+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".
-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|frequency synthesiser]] technology, and IF filters can give much narrower passbands at the same [[Q factor]] than an equivalent RF filter.
+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|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.
 [[Radio transmitter]]s also use Super Heterodyne technology. The design of a Super Heterodyne transmitter is similar to that of a Super Heterodyne receiver which each stage of the signal path reversed.