Abstract: A method for avoiding self-oscillation in a four-wire loop in conjunction with echo cancellation is effected with the aid of an adaptive filter (15). Self-oscillation is avoided for both long and short connections and also when signalling with narrow-band signals, by restricting the permitted range of the coefficients of the adaptive filter in a manner such that the absolute value of the filter transfer function will be sufficiently small so that amplification in the four-wire loop is less than one. This is achieved by limiting the absolute value of the filter transfer function (1Hcal), to a value which is smaller than a determined function of the echo transfer function (H.sub.fa) in the far-end of the loop and the echo transfer function (H.sub.ne) in the near-end of the loop.

Abstract: The invention relates to echo elimination in a subscriber line circuit having digital signal processing. Echo elimination is effected with the aid of a digital balance filter which is connected in an interface where the sampling frequency, e.g. 16 kHz, is higher than the original sampling frequency, e.g. 8 kHz, of transmitted signals. The requisite size of the balance filter can be reduced by sampling the filter at the same frequency, e.g. 8 of kHz, as the original sampling frequency of the transmitted signals.

Abstract: The present invention relates to a method and an arrangement for supplying direct current to a telephone line. According to the invention, the current supply characteristic is programmable. The arrangement comprises a direct current supply circuit which detects the line voltage and supplies a line current in accordance with a preprogrammed current supply characteristic. The circuit includes a first more high-voltage part and a second more low-voltage part, in which programming of the current supply characteristic takes place. For the purpose of achieving programming, a first resistive component having a programmable resistance is arranged essentially parallel with a capacitor in the second part. The first resistive component determines the supply resistance of the circuit for low line currents.

Abstract: The present invention relates to an apparatus in ringing signaling to a called subscriber. Connection and disconnection of the signal takes place with the aid of the apparatus. The problem solved by the invention is that of current transients being generated on disconnection of the signal, these transients causing a disturbing clicking noise in the engaged telephone of a subscriber in a neighboring channel. The apparatus solving the problem includes a two-way switching circuits (10) connected in series with an AC voltage generator (2), said circuit disconnecting the AC voltage to a bell (1) when the current through the bell has its zero crossing, and a discharge circuit (11) for the discharging the bell before it is connected via a relay (3) to a SLIC circuit (4), such that the voltage across the bell is within the SLIC circuit voltage interval when the relay (3) connects the bell to the SLIC circuit (4), which occures when said signal is disconnected.

Abstract: A simplified balancing impedance (Z.sub.2) included in a transformer fork has a constant capacitor (C.sub.5) connected in series with the termination resistor (R.sub.1). The variable capacitance in the balancing impedance contains a resistor-capacitor network (R.sub.2, C.sub.6 ; R.sub.3 C.sub.7, C.sub.8 -C.sub.11) connected in parallel with the termination resistance. The constant capacitor and the center point capacitor (C.sub.2) on the balancing side of the fork can thus be replaced by one capacitor.

Abstract: A pilot receiver memory unit is described which is included in a carrier frequency system for storing the control value to the regulating amplifier of each group demodulator in the receiver. The memory unit utilizes a circulating digital shift register having a number of sections equal to the number of space-divided groups. The digital contents of each section which determines the control value can be changed in dependence on determination signals which are supplied through logic means to the register. The control value is converted to analog form before being supplied to the group amplifiers.