Why does my Frequency Division Multiplexer demultiplex to negative and not the message signal?

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Christopher Resuello
评论： Yukthi S 2024-5-31
Hi,
I'm working on a project that involves on the practice of communication techniques, designed in simulink. I'm trying to design a Frequency Divison Multiplexer that multiplex 3 modulated signals (AM modulated signals), then demultiplex to obtain the original signals back. However, when designing the demodulation circuit to remove the carrier signal, I'm not sure why its giving a negative amplitude and not the orginal message signals.
I'm confused if its my demodulation circuit or its just the characeristic of an Frequency Divison Multiplexer.
Note: From the multiplexer and modulation, there aren't any issues as its responding with the correct waveform of modulation and multiplex form.
Perameters:
Input 1 - 1volt, 100Hz message, 3kHz carrier, Sine
input 2 - 1volt, 150Hz message, 2.5Khz Carrier, Sine
input 3 - 1volt, 50Hz message, 1.2Khz Carrier, Sine
Saturation (for all) - 0 lower limit, 3 upper limit
Filter Desginer1 - Butterworth, Lowpass, filter order 3, pass band 3kHz
Filter Designer2 - Butterworth, Low pass, filter order 3, pass band 2.5kHz
Filter Designer3 - Butterworth, Low pass, filter order 3, pass band 1.2Khz
Constant (for all) = -0.3055
Figure 1: Circuit Diagram of Demultiplexer & Demodulation
Figure 2: Scope from the Demultiplex, saturation then the Low Pass Filter Output from order.
Figure 2: scope output from the demodulation stage of the cirucit

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