Abstract: A multiple tone signal is demodulated and synchronization is obtained by precisely locating frame boundaries in order to ensure reliable communication in the presence of anomalies such as Doppler shift, multipath propagation, and additive electronic noise. One such signal, TADIL-A or Link-11, employs multiple tone audio waveforms that are used to modulate RF carriers for the transmission of digital data. Initially, the signal is frequency divided and classified to determine if the incoming frame is a preamble, data or noise. For preamble frames, a digital filter is used to extract the 605 Hz tone in the time domain, and the resulting real-valued signal is passed through a first Hilbert transform to generate the corresponding imaginary complex-valued signal. Unfiltered data frames are passed through a second Hilbert transform and the output is multiplied by the complex conjugate of the stored Doppler reference signal to produce a Link-11 Signal stripped of Doppler.