  We present simulations of the Cosmic Microwave Background Radiation (CMBR)
power spectrum for a class of mixed, non-Gaussian, primordial random fields. We
assume a skew positive mixed model with adiabatic inflation perturbations plus
additional isocurvature perturbations possibly produced by topological defects.
The joint probability distribution used in this context is a weighted
combination of Gaussian and non-Gaussian random fields, such as: P(delta) =
(1-alpha)f_{1}(delta) + alpha*f_{2}(delta), where f_{1}(delta) is a Gaussian
distribution, f_{2}(delta) is a non-Gaussian general distribution, and alpha is
a scale dependent mixture parameter. Results from simulations of CMBR
temperature and polarisation power spectra show a distinct signature for very
small deviations (~ 0.1%) from a pure Gaussian field. We discuss the main
properties of such mixed models as well, their predictions and suggestions on
how to apply them to small scale CMBR observations. A reduced chi^2 test shows
that the contribution of an isocurvature fluctuation field is not ruled out in
actual CMB observations, even in WMAP first-year sky map.
