The first observations of HF heater stimulated electromagnetic emissions induced in the low-latitude ionospheric plasma above Arecibo, Puerto Rico, are reported. Many systematic spectral features of the emissions bear a close resemblance to those observed in ionospheric modification experiments in the auroral zone and scale in accordance with detailed theory. This proves that these sideband emissions are not dependent on specific geophysical conditions but are due to fundamental interaction processes in the ionospheric plasma. We also report the discovery of unique, short-lived HF sideband emissions that are less systematic than those observed previously and accompanied by a quenching of the HF enhanced plasma and ion lines in the Arecibo 430 MHz incoherent scatter radar spectra. ¿ American Geophysical Union 1989