A 138.8 MHz backscatter radar has been deployed at Arecibo Observatory in Puerto Rico to monitor modifications to the ionospheric F region produced by a high-power, HF (3--5 MHz) radio wave. This radar provides a new diagnostic tool for examining wave production in the plasma at long (~1 m) wavelengths. When high-power radio waves are transmitted, strongly enhanced ion-acoustic waves are detected. The temporal development of the HF-enhanced ion waves at 138.8 MHz exhibits an ''overshoot'' behavior similar to that of HF-induced Langmuir waves and ion waves monitored in the past with the Arecibo 430 MHz radar. ¿ American Geophysical Union 1987