Modulator and demodulator

The modulator is an abbreviation for adjacent-frequency modulator, often referred to as a radio frequency modulator or a television modulator, and is one of the main devices in the cable TV front-end room. The adjacent frequency modulator is applied to various cable television systems, satellite television systems, residential closed-circuit televisions, monitoring systems, hotel and hotel digital set-top box transformation systems, as well as military and school education audio-visual systems.

A device that recovers an original modulated signal from oscillations or waves generated by modulation. Applied disciplines: Communication technology (a subject); communication principles and basic technologies (two subjects).

It restores the amplified AC voltage to a DC voltage whose magnitude and polarity correspond to the amplitude and phase of the AC voltage. The following figure shows the principle circuit of the demodulator. RL is the load and C is the filter capacitor. Its function is to smooth the output DC voltage. The demodulation switch K and the input AC signal have the same frequency. When Ui is positive, the switch is turned on, and the output is equal to the input voltage UO. After the smoothing of the capacitor C, a smooth DC voltage UO should be obtained. Conversely, if Ui is negative, the switch is turned on, Ui is positive, and the switch is turned off, the output receives a negative pulsating DC voltage UO.

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