Simultaneous multifrequency scintillation data observed at a mid-latitude station of transmission from the ATS 6 radio beacon experiments are used to find the power spectra of amplitude scintillation. With the frequency spacing of 40, 140, and 360 MHz, weak and strong scintillations are often observed. Single-scatter scintillation theory is applied to interpret the weak scintillation data, and the theory correctly predicts the spectral shape. For strong scintillations the spectra no longer show a distinct break frequency at which the spectra begin to roll off. Because of decorrelation by multiple scattering there is also broadening at the high-frequency portion of the spectrum, even though the slope of the high-frequency asymptote remains about the same as that in the weak scintillation case. Some of these features are compared with predictions based on the multiple-scatter scintillation theory.