The diagnostic and communication possibilities, based on resonant properties of ionospheric magnetoplasma near the Equator, are discussed for a wide spectral range of electromagnetic waves. The utilization of geometrical resonances of both natural and artificial origin and plasma eigenmodes are considered for a model of anisotropic heterogeneous collisional magnetoplasma at low latitudes. The possibilities of linear and non-linear wave transformation and scattering, together with the orthogonality of ionospheric gradients and geomagnetic fields, are illustrated. The threshold and self-oscillation phenomena, stimulated by heating, produced by an equatorial electrojet, photo-electrons and powerful transmitters, are examined.