CLOSED LOOP TEST METHOD AND APPARATUS FOR DUPLEX DATA TRANSMISSION MODEM

摘要

A duplex data transmission modem is provided having facilities for transmitting data on either a call originate frequency F1 or a call answer frequency F2 while simultaneously receiving data on a call originate frequency F2 and a call answer frequency F1. Control apparatus is provided in the modem for closed loop testing wherein the modem receiver is forced to receive the normal outgoing data modulated carrier signal and return the data signal back to the incoming line and thereby provide loopback on the analog or tone side of the telephone line interface.