Loop test method for modems in two-wire operation - has line insulating switches and unity gain loop amplifier

摘要

The loop-test method for modems operating in the two-wire mode is suitable for modems with both single and two-frequency operation. - The test unit comprises two pairs of change-over contacts (K2-3,K4-5) inserted between the modem (M) and the connecting points for the data input and output terminal equipment e.g. teleprinter (103,104). A contact on the output side of the modem (K1) connects the termination network (G1) either with the data channel (U) or with a test loop. - The test loop consists of a termination network (G2) and matching amplifier having a gain of 1 (V). for modems with two-frequency operation, the amplifier is replaced by a frequency converter. The test circuit allows the required loop to be established without the need for access to the actual modem circuitry.