This paper proposes an observer-based approach for robust chaotic communication with high power plaintext signals. The convergence rate of synchronization can be assigned by appropriately selecting the observer gains. The proposed scheme is carefully designed so that the encrypted signal does not deteriorate the synchronization. The proposed method significantly improves the frequency-domain characteristics of the transmitted secret message. This has the effect of preventing the extraction of the secret message using filtering techniques; hence improved security. Computer simulations show that the synchronization between the transmitter and the receiver is robust for different amplitude values of the information signal even in the presence of external disturbances. The synchronization between the transmitter and the receiver is maintained and the message signal is exactly recovered even for the various types of waveforms (square, trapezoidal, sinusoidal) of plaintext message and while varying the duty cycle and the rising and falling times of the signal.