Strong Langmuir turbulence effects are investigated during ionospheric modification experiments performed at the Arecibo Observatory. Indirect evidence of Langmuir wave collapse is obtained through the observation of theoretically predicted 'caviton-type' enhanced plasma wave spectra. A typical spectrum consists of a 'free-mode' peak with a frequency that is significantly higher than the heater frequency, and a broad 'caviton continuum' with frequencies below the heater frequency. The generation and dynamics of free modes - freely propagating Langmuir waves radiated by collapsing cavitons during collapse - are discussed. Asymmetries between the frequency shifts and strengths of the upshifted and downshifted free-mode lines and their dependence in the time delay following the onset of heating are explained in terms of the radiation of free Langmuir modes by cavitons and the subsequent propagation of free modes down or up the free Langmuir modes by caviton and the subsequent propagation of free modes down or up the density gradient. Experimental results are compared with theoretical predictions.