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Broadband multilevel QAM modulator
Complete multilevel QAM modulator, combining input signal filtration stage and modulation stage, implemented in digital signal processing technique in programmable logic device (FPGA). Input is digital data, output are digital samples, modulated at intermediate frequency. Modulator needs only to be connected to fast DAC converter and simple analog filter. Block diagram 
Modulator has two inputs: serial digital data (TxD) and its clock (TxC). Input data is being filtered by a lowpass filter and then modulated with choosen modulation parameters. At output, the modulated signal is represented as digital samples. Connected DAC converter and lowpass filter, transforms digital output signal into analog signal. "REQUEST/READY" signals are used to initiate restart sequence, allowing receiver to restore synchronization. Pictures on the right side show spectrum of modulated signal, for 9216 kbit/s transmission speed (modulation speed 2304 kbaud) and QAM16 modulation. Carrier frequency is 9.22 MHz. |