Superheterodyne

The superhet radio or to give it its full name the super heterodyne receiver is one of the  most popular forms of receiver in use today. Virtually all broadcast radios, televisions  and many more types of receiver use the superhet or super heterodyne principle. First developed at the end of the First World War, with its invention credited to the American Edwin Armstrong, the use of the superhet has grown ever since the concept was first discovered. 

"A super heterodyne receiver contains a combination of amplification with frequency mixing, and is by far the most popular architecture for a microwave receiver "

To heterodyne means to mix two signals of different frequencies together, resulting in a "beat" frequency. Actually, two signals are always created, the sum frequency and the difference frequency. These are referred to as the two sidebands. The sum frequency is the upper sideband, and the difference frequency is the difference sideband. In most microwave receivers, the upper sideband is ignored .

Principle and motivation for the use of the super-heterodyne
receiver
The super-heterodyne receiver is a special type of receiver that in addition to demodulating
the incoming signal, does carrier-frequency tuning(selection of the desired signal),f ilter-ing(separation of the desired signal from interference) and ampli cation.
Selectivity is a measure of how well a receiver can select a desired station while excluding
all others.
By converting the Radio Frequency(RF) signal to a xed Intermediate Frequency(IF),
the super-heterodyne receiver provides improved selectivity. It is much easier, (and much
more cost-e ective) to implement a band-pass lter with good selectivity at a xed center
frequency, rather than to improve the selectivity of the RF ampli er(which has a variable
center frequency).
 

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