  In this paper we review the application of the matched filter (MF) technique
and its application to detect weak, deterministic, smooth signals in a
stationary, random, Gaussian noise. This is particular suitable in astronomy to
detect emission lines in spectra and point-sources in two-dimensional maps. A
detailed theoretical development is already available in many books (e.g. Kay
1998; Poor 1994; McNicol 2005; Hippenstiel 2002; Macmillan & Creelma 2005;
Wickens 2002; Barkat 2005; Tuzlukov 2001; Levy 2008). Our aim is to examine
some practical issues that are typically ignored in textbooks or even in
specialized literature as, for example, the effects of the discretization of
the signals and the non-Gaussian nature of the noise. To this goal we present
each item in the form of answers to specific questions. The relative
mathematics and its demonstration are kept to a bare simplest minimum, in the
hope of a better understanding of the real performances of the MF in practical
applications. For the ease of formalism, arguments will be developed for
one-dimensional signals. The extension to the two-dimensional signals is
trivial and will be highlighted in dedicated sections.
