Cognitive Radio and signal intelligence (SIGINT) applications require radios to perform situation-awareness functions, as spectrum sensing to detect the spectral occupation. In more advanced systems, for SIGINT and for interference cancellation purposes, a radio receiver may need to classify an otherwise unknown signal without prior information about its modulation type, and rapidly synthesize, prototype, and deploy a suitable demodulator. The Rapid Radio framework uses a signal analysis stage to obtain the parameters of the signal of interest, to quickly prototype a suitable radio demodulator using the reconfiguration features and processing capabilities of FPGAs. This paper presents the techniques devised to perform the Automatic Modulation Classification stage of the framework, considering its interaction with the parameter estimation and signal synchronization stages, and presents performance results obtained under simulation conditions as well as in over-the-air transmissions.