DUPLEX DATA TANSMISSION MODEM UTILIZING AN INJECTED TONE FOR SHIFTING POWER WITHIN THE TRANSMIT SPECTRUM

摘要

D-1799 Application for Patent of John A.C. Bingham and Ronald K. Maxwell for DUPLEX DATA TRANSMISSION MODEM UTILIZING AN INJECTING TONE FOR SHIFTING POWER WITHIN THE TRANSMIT SPECTRUM A full duplex communication system including a pair of full duplex modems. Each modem has both a call originate mode of operation and a call answer mode of operation. In the call originate mode outgoing data is transmitted by modulation of a carrier frequency F2 and incoming data is received by demodulation of a data modulating carrier of frequency F1. When in the answer mode of operation, the data is received on frequency F2 and transmitted on frequency F1. Means are provided for injecting a carrier frequency F6 in the outgoing data transmission path. The frequency F6 is near the midpoint between F1 and F2. The amplitude is such that the distribution of power within the transmission band is balanced so that the power in the frequency band set aside for single frequency signaling systems does not exceed the power in the remainder of the transmission band. This prevents the false operation of signal frequency systems triggered by the transmission of certain bit patterns, which could result in improper billing, intermittent transmission interruptions, insertion of a band elimination filter in the transmission path or the complete disconnection of a call.