Modem for rf subscriber telephone system

A MODEM INCLUDING MODULATOR AND DEMODULATOR SECTIONS. A BIT STERAM IS CONVERTED INTO A PHASE MODULATED INTERMEDIATE FREQUENCY (IF) SIGNAL AND DIGITALLY FILTERED. WHEN CONVERTED INTO AN ANALOG SIGNAL,THE MODULATED SIGNAL IS CENTERED ABOUT A PREDETERMINED FREQUENCY AND DEVIATES IN ACCORDANCE WITH THE VALUE OF THE PHASE MODULATED SYMBOL. THE ANALOG SIGNAL IS FILTERED AND PASSED TO A MIXER FOR UP CONVERSION. THE DEMODULATOR INCLUDES A MICROPROCESSOR WHICH INCLUDES MEANS FOR STORING FILTERED COEFFICIENTS FOR USE IN FILTERING RECEIVED DIGITAL SIGNALS. THE MODEM IS OPERABLE IN A TRAINING MODE WHEREIN A SEQUENCE OF PREDETERMINED SYMBOLS IS PROVIDED TO THE MODULATOR SECTION AND THE RESULTANT PHASE MODULATED INTERMEDIATE FREQUENCY SIGNAL IS DEMODULATED TO ADJUST THE STORED FILTERED COEFFICIENTS UNTIL THE RECONSTRUCTED PHASE MODULATED SYMBOLS CORRESPOND TO THE SEQUENCE OF PREDETERMINED SIGNALS. (FIGURE 1A).