EFData Modem Processor Board PL/3970-2
EFData Modem Processor Board PL/3970-2 this board comes from our squirrel infested attic. It is almost impossible to find additional information and so much of this description is guesswork.
Based on the format of the board we assume that it belongs to the SDM 6000/9000 series of modems that have separate cards for modulation and demodulation.
This is the demodulator board.