Data terminal interface circuit to a telephone transmission line

Claim 1

A circuit arrangement for connecting a data terminal for sending and/or receiving data signals to a transmission line connected to telephone equipment, via which line, telephone signals are transmitted in a first frequency range and data signals in a second higher frequency range, and to which the telephone equipment and the data terminal are connected via a filter arrangement, which includes a lowpass filter lying in the transmission, the transmission line having a first, relatively high characteristic impedance for the transmission of the telephone signals and a lower, second characteristic impedance for the transmission of the data signals, the lowpass filter being designed so that on the side connected with the transmission line which is opposite the side connected with the telephone equipment, there is provided a capacitive termination and, in the transmission line, a line transformer which comprises at least one transformer winding for coupling with the data terminal as a coupling winding, characterized in that the line transformer (U3) is connected by its respective coupling winding (w7) directly with the data terminal (DG), and the capacitive termination (C7) of the lowpass filter (TP) is rated so that its a-c resistance in said second frequency range is at most in the order of magnitude of the characteristic impedance of the transmission line for that frequency range but is preferably lower than this characteristic impedance.