The ratio of x to o mode radiation produced when an x mode wave strikes a steep density gradient is determined for wave and plasma parameters typical of those observed in the auroral kilometric radiation source region. We find that the waves reflected from or transmitted through the density gradient generally have an o mode component 20 dB or more weaker than the x mode component. This agrees with the ratio of x to o mode intensity observed in auroral kilometric radiation signals near the auroral plasma cavity by both the DE 1 and ISIS 1 spacecraft.