Superheterodyne detector,

RFfilteringfJi(/)andIFfiltermgH2(/) However,ifdownconversionisusedwith/to > /c.thecomplex envelope at the IF output will be the conjugate of that for the RF input. This means that the sidebands of the IF output win be inverted (i.e., the upper sideband on the RF input wiU become the lower sideband, etc., on the IF output). If /lo < /c, the sidebands are not inverted. In some special applications the local oscillator (LO) frequency is selected to be the carrier frequency ( /lo = fc). and then the superheterodyne receiver becomes a direct-conversion receiver also called a homodyne or a synchrodyne receiver. In this case the IF filter is replaced by a low-pass filter so that the mixer-LPF combination becomes a product detector and the detector stage of Fig. 12.6 is deletecL Thus, the direct-conversion receiver is the same as a TRF receiver with product detection. 

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