Abstract: A modem coupling circuit comprising: (a) a transformer 1 having a core 1a including a gap formed therein, primary windings N1a, N1b constituting a bifilar wound coil which is wound around the core 1a, forming a single layer and connected to power lines L1, L2, and a secondary winding N2 connected to a transmitting circuit 2 and a secondary winding N3 connected to a receiving circuit 3, the secondary windings N2, N3 holding the single layer of the primary windings between; (b) a coupling capacitor C1 connected to a middle point between first ends of the primary windings, the first ends being not connected to the power lines L1, L2; (c) current limiting resistances R1a, R1b connected to the primary windings N1a, N1b having a bifilar construction; (d) drive resistances R2a, R2b connected to the secondary winding for transmission N2; and (e) terminating resistances R3a, R3b connected to the secondary winding for reception N3.

Abstract: A modem coupling circuit comprising: (a) a transformer 1 having a core 1a including a gap formed therein, primary windings N1a, N1b constituting a bifilar wound coil which is wound around the core 1a, forming a single layer and connected to power lines L1, L2, and a secondary winding N2 connected to a transmitting circuit 2 and a secondary winding N3 connected to a receiving circuit 3, the secondary windings N2, N3 holding the single layer of the primary windings between; (b) a coupling capacitor C1 connected to a middle point between first ends of the primary windings, the first ends being not connected to the power lines L1, L2; (c) current limiting resistances R1a, R1b connected to the primary windings N1a, N1b having a bifilar construction; (d) drive resistances R2a, R2b connected to the secondary winding for transmission N2; and (e) terminating resistances R3a, R3b connected to the secondary winding for reception N3.

Abstract: A transmission apparatus such as a modem has a receiving unit which receives information and a clock-supplying unit which supplies a clock signal to the receiving unit. It further has an instantaneous dropout detection unit which detects the occurrence of an instantaneous dropout on the receiving circuit and a clock supply control unit which stops the supply of a clock to the receiving unit for a prescribed amount of time when the instantaneous dropout detection unit detects an instantaneous dropout, the stopping of the clock supply causing holding of receiving parameters and the restarting of clock supply causing restarting of the receiving operation.

Abstract: A transmission apparatus, connected via a hybrid circuit to a line, such as a modulator-demodulator which can perform stable echo cancellation, whether the level of the far-end echo is high or not, provided with a transmission unit which generates a transmission signal to be transmitted to the line via the hybrid circuit, a reception unit which receives the reception signal supplied from the line via the hybrid circuit, and a superimposing means for superimposing the reception signal applied to the hybrid circuit onto the transmission signal. The transmission signal onto which the reception signal is superimposed by the superimposing means is transmitted to the line via the hybrid circuit.

Abstract: In a modem, after scrambling data which are time-divided into main data and secondary data, a 2 W-4 W conversion circuit sends the data to the two-wire line. An estimated echo component is subtracted from a signal which is available from the 2 W-4 W conversion circuit. Following this, the signal from the 2 W-4 W conversion circuit is demodulated, descrambled and separated into main data and secondary data. A generator polynomial for scrambling is different from a generator polynomial for descrambling. The modem comprises a line-trouble-detect part which samples data of the secondary channel, by multipoint sampling, to obtain the secondary data and detects the number of inversion points in the descrambled secondary channel data per unit time period. The line-trouble-detect part outputs a line-trouble signal which indicates that there is a trouble on the line if the number of detected inversion points is more than a predetermined number.