  We give a new lower bound on the expansion coefficient of an edge-vertex
graph of a $d$-regular graph. As a consequence, we obtain an improvement on the
lower bound on relative minimum distance of the expander codes constructed by
Sipser and Spielman. We also derive some improved results on the vertex
expansion of graphs that help us in improving the parameters of the expander
codes of Alon, Bruck, Naor, Naor, and Roth.
