A nice beginning are some of the articles is the link below.
In particular the “A Software Defined Radio for the Masses“ articles by Gerald Youngblood found towards the bottom of the page. http://www.arrl.org/tis/info/sdr.html
Articles how Quadrature signals work.
http://www.dspguru.com/info/tutor/quadsig.htm
HP article on the basics of IQ digital data from/to a radio. http://www.home.agilent.com/agilent/redirector.jspx?action=ref&cname=AGILENT_EDITORIAL&ckey=1000000348%3Aepsg%3Aapn&lc=eng&cc=US
A free book on how DSP works, an excellent book.
Math Simulation software SciLab, software for analyzing data and plotting the results, very capable, can work with .WAV files as data. http://www.scilab.org/
Modeler for SciLab
SciLab Tricks and tips.
http://kiwi.emse.fr/SCILAB/sci-bot/book1.htm
SciLab Toolboxes
http://www.scilab.org/contrib/index_contrib.php?page=listdyn.php&order=date
Octave another math modeler
http://www.gnu.org/software/octave/
Talk and models by Phil Hartman from talk at Dayton, it uses Excel to model SDR software, a good source of equations for the programs mentioned above. http://www.hamsdr.com/dnld.aspx