We report experimental results from the high-power auroral simulation facility showing that the lower D region can be heated so as to produce either a single, narrowband ELF/VLF radiation signal at the modulation frequency or a signal containing the modulation frequency and many odd harmonics. The measurements are compared to a new 2 1/2-dimensional simulation code that models the lower D region and the Earth ionospheric waveguide. The simulation spectra show good agreement with the observations. Rapidly switching the HF power off and on leads to perturbing currents in the D region that vary in time in a square wave type pattern. This generates an ELF/VLF wave with high, odd harmonics observed up to n=13 (f=nf0, where f0 is the modulating frequency). A more smoothly changing power variation generates a narrowband signal at f0. Simulations show how the D region affects the spectral shape. From these results we find that the heating should occur at a low altitude in the D region (approximately 75 km). Using the simulation results, we determine that the D region current needed to produce the magnetic field spectrum with the odd harmonics has a square wave time variation. ¿ American Geophysical Union 1996