I have now read several articles on Software Defined Radios written by my fellow Amateurs referring to QSD/QSE without defining the acronyms. Here QSD/QSE are defined: QSD in the context of SDR means Quadrature Sampling Detector and QSE means Quadrature Sampling Exciter; hence they are seen referred to as QSD/QSE. It would be nice if authors would define/describe acronyms when first used in their articles to avoid ambiguity (QSD means "is my keying defective"  as well). Chances are you will find this post while trying to figure out what an author means- hope this helps you.