  Modern digital crosscorrelators permit the simultaneous measurement of all
four Stokes parameters. However, the results must be calibrated to correct for
the polarization transfer function of the receiving system. The transfer
function for any device can be expressed by its Mueller matrix. We express the
matrix elements in terms of fundamental system parameters that describe the
voltage transfer functions (known as the Jones matrix) of the various system
devices in physical terms and thus provide a means for comparing with
engineering calculations and investigating the effects of design changes. We
describe how to determine these parameters with astronomical observations. We
illustrate the method by applying it to some of the receivers at the Arecibo
Observatory.
