Schematic Diagram : Bell 103 Compatible FSK Modem


The following circuit is a modem using MM74HC942, a single chip low-speed modem and compatible with Bell 103 standard.  This modem circuit runs at 300 baud in bidirectional mode (full duplex). The sine wave synthesizer and the frequency of this modem chip generate phase-coherent FSK modulation for best bit accuracy. Circuit diagram :

BELL 103 Compatible FSK Modem Schematic

BELL 103 Compatible FSK Modem Schematic Diagram (click to enlarge)

The single chip modem is perfect for radio telemetry, remote data collection, stand-alone modem, remote-process control, tone signaling system, credit verification, or PoS terminal. The table 1 above shows the tone allocation for the chip. The modem on the end of the line, that initiates the called is called the originate modem. The other one is the answer modem. (source : National Semiconductor Application Notes)


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