Principle of operation thumb|upright=2.0|Block diagram of a typical single-conversion superheterodyne receiver. The diagram has blocks that are common to superheterodyne receivers, with only the RF amplifier being optional. Red parts are those that handle the incoming radio frequency (RF) signal; green are parts that operate at the intermediate frequency (IF), while blue parts operate at the modulation (audio) frequency. The dotted line indicates that the local oscillator and RF filter must be tuned in tandem. thumb|upright=1.6|How a superheterodyne radio works. The horizontal axes are frequency f. The blue graphs show the voltage spectra of the radio signals at various points in the circuit. The red graphs show the transfer functions of the filters in the circuit; the thickness of the red bands shows the fraction of signal from the previous graph that passes through the filter at each frequency. The incoming radio signal from the antenna (top graph) consists of the desired radio signal S1 plus others at different frequencies. The RF filter (2nd graph) removes any signal such as S2 at the image frequency LO - IF, which would otherwise pass through the IF filter and interfere. The remaining composite signal is applied to the mixer along with a local oscillator signal (LO) (3rd graph). In the mixer the signal S1 combines with the LO frequency to create a heterodyne at the difference between these frequencies, the intermediate frequency (IF), at the mixer output (4th graph). This passes through the IF bandpass filter (5th graph) and then is amplified and demodulated (demodulation is not shown). The unwanted signals create heterodynes at other frequencies (4th graph), which are filtered out by the IF filter .
PrinCiPle Of opeRATion THumb|upright=2.0|block diAgraM oF a TYpicAl single-conVErSIOn sUperhEterOdYne receiVer. The diaGrAM HAS blockS tHaT ARE cOmmon to sUperHeterodyne rECeivers, wItH only thE Rf aMPlifieR bEiNg OptionAl. red ParTs ARe thOse That hAnDlE the IncOmING raDio frEQuenCY (RF) SiGnAl; green arE pArts ThaT opErate at the iNTErmeDiatE fReqUEncy (iF), WHIle blue paRts Operate at tHe moduLAtIOn (audIo) frequenCy. thE DOtted line iNDicAtEs thaT the locaL OScillatoR anD rF filtEr mUst be tUned in tANdeM. thumb|upRigHt=1.6|how a supeRHeterodyne Radio WOrks. ThE HOrIZonTal AxeS Are fRequeNcy f. THe blUe grapHS sHOW thE voltAGe sPeCtRa of thE rAdio siGnAls at varioUS PoiNts in THe ciRcUIt. thE rEd Graphs shoW thE Transfer FuNctiOns oF the filTers in The cIrcUiT; tHE thickness oF thE red Bands sHows THe fRaCtIOn of signal frOm The PREvIous graph That paSses THrougH thE fILter aT Each freQuency. tHe iNCOMing rAdIo signal from thE antennA (Top graph) conSists Of tHe dEsIReD radiO SigNaL s1 plus OThErs aT dIfFeReNT freQuenCies. tHe rf fiLter (2Nd grAph) rEmoves aNy sIGnal such aS s2 aT THe imAge fREquency lO - If, which WoulD OtherwIse PASs THrough THe iF filter And intErfere. thE remAiNinG CoMpOsIte sIgNal is apPLieD to the mIxEr along WIth a LOCal osciLlAtor sIgnal (lo) (3Rd GrApH). in the miXeR tHe sIgnaL S1 combiNes WIth the Lo FreqUency To cReate a heTeroDYNe at the diffeRenCe bETween tHese fRequEncIEs, ThE intERmEdiAte FrEQueNcy (iF), At tHE mixeR OUTput (4th graPH) ThIs pASseS throuGh the if bandpAss FilTer (5th graPH) and then iS amPlifiEd and dEmodulaTed (deModulatIon Is not SHoWn). the UnwantED sIgNals CrEatE HeteroDyNes at otHeR fReQUEnciES (4Th graPh), whICh arE FIltered oUt by The IF fiLter .