Abstract: An analog electronic hybrid circuit having a complex internal impedance includes a coupling transformer. The loss resistances of the transformer are used together with a measuring resistor to establish a predetermined complex internal impedance, thereby providing a balancing network. In one embodiment, nonideal characteristics of the transformer (nonlinearities, parasitics) have only very little effect because the transformer is contained in a feedback loop.

Abstract: A signalling receiver has its signal input (E) connected to a central-office trunk (a, b) in a trunk junctor and includes a variable bandpass filter (BP) connected to a clock line (TL). The signal input (E) is connected via an attenuator (DG) to a variable high-pass filter (HP) which is connected to the clock line (TL) and, via a signal evaluation and conversion unit (SE), to the bandpass filter (BP). A bandwidth switch (BU) is connected to the clock line (TL), the variable bandpass filter (BP), and the attenuator (DG). The cutoff frequency of the high-pass filter (HP) and the midband frequency of the bandpass filter (BP) are adjusted with a clock signal having a frequency related to the signal frequency to be received, the cutoff frequency being lower than the midband frequency.

Abstract: There is disclosed a line circuit for connecting a subscriber set to a switching facility to obtain an impedance match. The subscriber set is connected to first and second subscriber terminals by a two-wire line which presents a complex terminating impedance to said switching facility. A constant current source is connected between the first and second terminals for supplying the subscriber set with a constant direct current. There is a control current source coupled between the first and second terminals for supplying the subscriber set with an alternating current with the control current source having a control input. The first and second terminals are connected to respective first and second inputs of a differential amplifier whose output is coupled to a transmit line. The control input of the control current source is coupled to a receive line.