In-building power line transmission measurements show potential for low attenuation propagation above 30 MHz. These measurements show that frequency bands can exist having low or minimum attenuation above 100 MHz. A simple high-frequency propagation model for analysis of in-building communications up to 900 MHz, which can be implemented using a commercial circuit simulator, is described. This physics-based model is extracted using broadband data from both time-and frequency-domain network transmission (S21) measurements. The novelty of this modeling approach is that different propagation modes such as electromagnetic coupling, waveguide propagation through the wiring conduit, and fading are included. An RF circuit model in a simulator environment is useful for analyzing a wide range of communication problems at the circuit, subsystem, and system levels.