A binary model for symbiotic stars is examined, in order to account for their radio properties. The system is comprised of a cool, mass-losing star and a hot companion. Radio emission arises in the portion of the stellar wind photoionized by the hot star. Computer simulations for the case of uniform mass loss at constant velocity show that when less than half the wind is ionized, optically thick spectral indices greater than +0.6 are produced. Model fits to radio spectra allow the binary separation, wind density, and ionizing photon luminosity to be calculated. The model is applied to the symbiotic star H1 - 36. Some predictions and further tests of the model are pointed out.