Abstract: The invention relates to a synchronous modulation system using amplitude modulation, which basically consists of a modulator and a demodulator able to transmit digital signals at double the frequency of its carrier wave. For this purpose, the system uses analog and digital circuits that combine to modulate, separately, the positive half and the negative half of the carrier sine wave, such that in a single cycle of the carrier wave, two different information bits can be sent. The demodulator-modulator unit can be easily combined with other units to form wired or wireless communication systems and even optical or sonic systems with minimal generation of parasitic harmonics, resulting in a minimum bandwidth requirement for operation.