SU68680A1 - Method of connecting two-wire subscriber lines to a four-wire or two-channel long-distance communication line - Google Patents

Description

When a two-wire subscriber line is connected to a four-wire or two-channel long-distance line, differential circuits with balanced circuits, echo suppressors, etc., are usually used.

According to the invention, it is proposed to carry out a two-way communication, starting from the subscriber’s apparatus, and for this purpose send a higher frequency current from the station to the subscriber, which is modulated by a microphone, and the resulting sidebands can be used as the transmission band of the conversation from the subscriber.

In this case, the transition of the conversation from the transmission channel to the reception channel is weakened, the communication becomes very stable, and the echoes become less than the value indicated by the ICC standards for the longest signal running time in the circuit.

FIG. 1, 2, 3 and 4 depict the skeleton schemes of devices for drying, demonstration of the proposed method.

12

As can be seen from the diagram shown in FIG. 1, a special termination is added to the four-wire communication system. The subscriber's telephone set is connected to this termination via a two-wire line, as usual, through a switch. The telephone set in the DB systems receives a constant current from the switch to power the microphone. In MB systems, the battery that powers the microphone is located in the device itself.

In addition to direct current, the microphone of the subscriber telephone additionally receives power from the end of the four-wire system with high-frequency current from a special generator G. The frequency of this generator is chosen above the talk frequency band (in the diagram, for example, taken 6400 Hz). During a conversation, the microphone will modulate both the direct current and the high frequency current. For voice transmission of the subscriber, one of the side current modulation frequencies is used.

179

high frequency, which is captured by the input filter F of the transmission channel. If, for example, we consider the conversation spectrum to be the frequency band of 300-2400 Hz and use the upper sideband for transmission from the subscriber, then the filter F should pass frequencies from 6700 to 8800 Hz.

Further, in the transmission channel there is a BM demodulator powered by a carrier frequency from the same generator as the subscriber telephone sets. Consequently, as a result of demodulation, a talk frequency spectrum of 300-2400 Hz is formed, which through the filter F4 enters the transmission channel of the four-wire system.

The conversation from the reception channel of the four-wire system to the subscriber goes through the filter F in the usual frequency band. Thus, at the point of transition from a four-wire communication system to a two-wire line, the transmission and reception go in different frequency bands separated by filters F and Fd. The F-band filter only passes the 6400 Hz carrier frequency. It is needed in order to get rid of harmful modulation of the carrier frequency in the generator by a talk signal from the receive channel, which as a result can interfere with the transmission channel as an interference. When communicating via packed circuits, you can not modulate the incoming call from the subscriber in the transmission channel, but choose the carrier frequency so that the subscriber receives a frequency spectrum that is picked up on the communication channel to transmit the conversation. In this case, a long-distance equipment will not require a modulator. The corresponding scheme of the attachment to the four-wire communication channel is shown in FIG. 2

The proposed method of increasing the stability of communication can also be successfully applied in duplex communication over two-wire circuits (in low-frequency channels) equipped with terminal amplifiers (Fig. 3).

When using the described method in this case, the length of the amplifier can be significantly increased180

plot without danger of zooming.

The balance in the linear differential system should be adjusted only to reduce the local effect.

As the subscriber telephone continues to be powered by constant current, the call, call pick-up and call control systems remain unchanged.

The subscriber’s telephone must undergo some alteration to increase its efficiency at higher frequencies and eliminate the unpleasant carrier whistle on the telephone. To this end, the transformer winding in a special telephone circuit, which is used to reduce the effect of a local effect on the microphone, is shunted by a serial circuit tuned to the carrier frequency, and a parallel loop sequentially connected to the carrier frequency is also sequentially connected to the balanced circuit. These circuits are chosen so that they hardly vary the characteristics of a telephone set during normal use.

Pa figs. Figure 4 shows a schematic diagram of a converted telephone set without calling, burglar and typesetting devices, where it is indicated: L and L - clamps for connecting the line wires, Tr-transformer, T - telephone, M - microphone, BK - balanced circuit.

Subject invention

Claims (3)

1. A method of connecting two-wire subscriber lines to a four-wire or two-channel long-distance communication line, characterized in that in order to separate the two-wire line, the transmission and reception bands from the station send to the subscriber an increased frequency current, which is modulated by a microphone, and the resulting side frequencies are used as talk transmission bands. 2. A device for carrying out the method according to claim 1, characterized in that for switching from a four-wire channel to a two-wire line, two filters with separated passbands and a generator used to power the microphone with an increased frequency current are connected to the latter. 3. In a telephone installation in which the connection of subscriber lines to a long-distance line is carried out according to the method of clause I, application of a telephone set at a subscriber, in which, in order to eliminate whistling and increase recoil, high-frequency power circuits are input tuned to this frequency and switched on: one parallel to one of the windings of the differential transformer, the other in series with balanced resistance. Fig, 1 FIG. 2 End of the prefetched communication system FIG. 3 Oink (N.Ch. channel amplifier FIG. four