In this paper we present a didactical activity based on modelling an engineering problem known as Blind Source Separation (BSS) and the results of its implementation in a linear algebra course in a Mexican university. The problem had previously been analysed from an institutional point of view, carrying out the notion of the matrix map T(x)=Ax. In the frame of APOS theory we propose a genetic decomposition for this concept, in order to analyze students' constructions related to it, and at the same time, using the BSS context as a reference to connect mathematical constructions with a real life situation.