Abstract: A phase locked loop for bringing an oscillator (1) into phase with an incoming signal. In accordance with the invention there are means which on the one hand determine whether the phase difference between the oscillator output signal and the incoming signal is positive or negative and on the other hand in response thereto cause the oscillator (1) to emit either of two output signal frequencies, one of which is predeterminately higher while the other is predeterminately lower than the incoming signal frequency. The oscillator (1) is hereby brought into phase with the incoming signal when the former emits its two output signal frequencies alternatingly.

Abstract: An FIR-type balance filter for preventing, in adaptive echo cancellation in a telecommunication system in which digital information transferred in duplex over a single conductor pair, that the local data transmitter disturbs the local data reception. The filter is thereby arranged so that the total number of links (N) in the filter is divided into at least a first group (I) and a second group (II). The apparatus contains a memory (MI) addressable from the filter links and said first group, there being written into and read from said memory the correction values from and to a correction unit (KB1), sending signals for correcting the filter parameters. The memory (M1) also sends signals to a summing circuit (A2), to which are also supplied the output signals from said second group of filter links, said output signals possibly being originated by table look-up in a further memory, or by vector multiplication. A second correction unit (KB2) corrects the filter parameters in said second group.

Abstract: A method and an apparatus, in a telecommunication system for transmission of digital information in duplex over a signal conductor pair for automatically adjusting a balance filter included in a hybrid coupler circuit with the aid of adaptive echo cancellation so that the local data transmitter does not disturb the local data reception, without utilizing any particular testing procedure in initiating the adaptive echo cancellation. A control signal (.epsilon..sub.k) is formed, with the help of which the correction unit (KB) is caused to generate signals for rapid updating of the balance filter (B) parameters, in spite of that knowledge is lacking in the initiation instant concerning the value of the signal transmitted from the remote end to the apparatus, and that no counteraction between level correction and filter adaption is obtained. The apparatus includes a quantizer (Q) in which a sampled, received signal (r.sub.k) is quantized, an estimated signal (a.sub.