Differential propagation effects are a key element in the design and use of dual-channel radars for meteorological measurements. Particularly in the case of circularly polarized signals, these effects determine the maximum ranges to which certain measurement objectives can be accomplished. For various purposes one may want to assume either that propagation effects are negligible or that they dominate backscattering effects in the received signals. Approximate and exact representations of the averaged signal parameters and the spectral functions are given for cases in which propagation effects are predominant. The cross-spectrum of the two received signals and the spectral power ratio can be used under some conditions to separate scattering and propagation effects.