Dual-Message Amplitude Modulation (DMAM)

Abstract

In this paper, a new method is proposed for AM modulation of two separate messages (dual message). The proposed method uses only one carrier and does not need any transformer or multiplexer device, while the existing methods need two carriers or a transformer or a multiplexer device for modulating a dual message. The procedure of this modulation is quite simple. First, the carrier signal is divided into positive and negative half cycles. Then, one of the message signals is inserted into positive half cycles by a simple voltage-controlled resistor (e.g., a JFET in the linear region). Another message signal is inserted into negative half cycles using the same process. Finally, the half cycles are added together and the resultant signal would have two different envelopes on negative and positive half cycles. Detection of these two messages is easy too. The demodulator consists of two simple diode detectors. One of them gets the message signal from positive half cycles, and the other gets the negative half cycles signal. Altogether, the most important advantages of this design compared to the existing methods for modulating a dual message are less power consumption and more simplicity of modulating and demodulating procedures and circuits. In addition, this method decreases the cost of the modulator system.