<P> Sensitivity to the image frequency can be minimised only by (1) a filter that precedes the mixer or (2) a more complex mixer circuit that suppresses the image . In most receivers this is accomplished by a bandpass filter in the RF front end . In many tunable receivers, the bandpass filter is tuned in tandem with the local oscillator . </P> <P> Image rejection is an important factor in choosing the intermediate frequency of a receiver . The farther apart the bandpass frequency and the image frequency are, the more the bandpass filter will attenuate any interfering image signal . Since the frequency separation between the bandpass and the image frequency is 2 f I F (\ displaystyle 2f_ (\ mathrm (IF)) \!), a higher intermediate frequency improves image rejection . It may be possible to use a high enough first IF that a fixed - tuned RF stage can reject any image signals . </P> <P> The ability of a receiver to reject interfering signals at the image frequency is measured by the image rejection ratio . This is the ratio (in decibels) of the output of the receiver from a signal at the received frequency, to its output for an equal - strength signal at the image frequency . </P> <P> It is difficult to keep stray radiation from the local oscillator below the level that a nearby receiver can detect . The receiver's local oscillator can act like a low - power CW transmitter . Consequently, there can be mutual interference in the operation of two or more superheterodyne receivers in close proximity . </P>

Explain principle and working of simple and superheterodyne receiver