why the SSB receiver re-injects the missing carrier? Why add the carrier back in after downshifting the incoming modulated signal instead of before why the SSB receiver re-injects the missing carrier? Why add the carrier back in after downshifting the incoming modulated signal instead of before Solution Re-injection of carrier is done by BFO,this re-injection of carrier allows easy de-modulation of RF and even IF signal also.if injected carrier is at the wrong frequencyrelative to the station then the audiio will become disorted..