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

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Christopher Resuello 2024-4-18

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https://ww2.mathworks.cn/matlabcentral/answers/2108851-why-does-my-frequency-division-multiplexer-demultiplex-to-negative-and-not-the-message-signal

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