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Broadband FM modulator
Complete binary FM modulator (256…2304kbit/s) for digital signal transmission implemented in DSP technique. The device has two serial inputs: data and clock. Output consists of digital samples modulated on intermediate frequency. The modulator needs only to be connected to fast DAC 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. Very useful feature of modulator is that it allows to parallely transmit digital, 16 kbit/s EOW channel. Low-pass EOW signal is added to modulated analog signal. Deviation of EOW channel is 18% of main channel deviation. This way of transmitting EOW channel is recomended by STANAG 4212 standard. Pictures on right side, show spectrum od modulated signal for data rates: 2304 kbit/s (top most), 1152 kbit/s, 576 kbit/s and 288 kbit/s. |