DE430965C - Intermediate amplifier circuit for telephone lines - Google Patents

Description

The invention relates to a repeater circuit for telephone lines from the kind where the line line is used for speaking in one direction or the other is switched and which is based on the fact that the amplifier circuit to prevent the risk of whistling alternately ready for operation at a rate of change that does not affect speech communication ίο one or the other speech direction can be switched.

It has already been proposed that the amplifier circuit be switched on and off by means of a rotating contact device which alternately short-circuits the receiving sides of the amplifier. Experiments have shown that the damping of the whistle cycle by short-circuiting an amplifier is not sufficient, but at a high \ ^? amplification, enough current can get into the other line section and into the whistle cycle via the second non-closed amplifier to cause the circuit to whistle. Closer investigations have now shown that this deficiency is due to the contact resistance on the brushes of the contact device, which are located in the short-circuit line. This contact resistance causes corresponding voltage differences in the ends of the receiving winding and, as a result, a response of the amplifier. The numerical amplification possibility with such an arrangement must not exceed the attenuation by the short circuit, otherwise the whistling occurs. One is therefore not free to choose the number of reinforcements.

According to the invention, this disadvantage is thereby eliminated or to a minimum reduced that either the influence of the contact resistance on the brushes Parallel connection of several brushes is reduced or apart from the receiving side as well the transmitter side of the amplifier is short-circuited.

Some exemplary embodiments of the invention are illustrated in the drawing.

Fig. Ι corresponds to the circuit according to the main patent. A rotating contact device α alternately shorts with the contact brushes O ₁ , l> 2, b _s , b ± the receiving sides C ₁ , c _{2 of} the amplifiers d _v d ₂ acting in different directions during very small periods of time, so that amplified speech flow alternately in the flows in one direction or the other. With this arrangement there is now the disadvantage that current in the receiving windings of the amplifier e _lt e due to the contact resistance on the brush. _{z can} flow and therefore the short-circuited amplifier comes into its own and under certain circumstances the whistling disturbance can occur.

Fig. 2 shows an amplifier circuit in which to remedy this drawback or to enable a higher gain not only on the receiving side, but also the transmission side is short-circuited.

The circuit according to Fig. 2 differs from that according to Fig. 1 only in that the brush sets V ₁ , V ₂ , b ' _s , b \ have been added, which serve to short-circuit the transmission sides i _v i _{2 of} the two amplifiers. This results in a much higher damping than z. B. achieved by connecting two brushes in parallel on the receiving side, since these only have an additive effect, but in the case of Fig. 2 they are multiplicative.

A circuit arrangement for tube amplifiers, which in principle is the same as that shown in FIG. 2, is illustrated in FIG. This embodiment differs from the embodiments according to FIGS. 1 and 2 in that only one brush b is provided for the reception and transmission circuit

*) The patentsitcher named the following as the inventors:

Friti Luschen in Betiin-Südende and Dr.phil. nat. Carl A. Hartmann in Berlin-Siemensstadt.

and the contact device consists of a drum separated by insulation material in two halves k _t , k ₂ , each half carrying consecutive contacts /, f - f _v f \ , via which the receiving and transmitting sides of the two amplifiers are alternately short-circuited will. What is also remarkable about this arrangement is that there is only one interruption point to be closed by the brushes and therefore the contact resistance in each short-circuit circuit is only half as great and the damping of the whistling cycle is consequently twice as great as in the embodiment according to Fig. 1. The This circuit works as follows.

The brush may consist of two conducting with each \ other associated halves V _1, V ₁ consist, of which the one on the contact segment k _t, k and the other on the contact segment ₂ is adjustable.

In the illustrated position of the brush, the primary winding of the transformer ^ _{1 is} short-circuited via the brush halves V ₁ , as is the secondary winding of the transformer Zi ₁ via the connecting line between the primary winding of the input transformer g _t and the secondary winding of the output transformer It ₁ and via the brush V ₁ . Therefore, if speech current arrives from the telephone line section indicated on the left in the drawing, it flows via the brush part V ₁ , the connecting line Z ₁ between the upstream and downstream transformer and the secondary winding of the output transformer via b '\ back into the left-hand long-distance line section. The primary winding of the input transformer of ^ ₁ is thus short-circuited, as is the secondary winding of the output transformer via the ^; Brush part V ₁ . Speech current arriving from the right flows via the primary winding of the transformer h ₂ , the connecting line L, the brush V ₁ back into the long-distance line section on the right. The increased current flows from the secondary winding g ₂ via the brush V ₁ into the long-distance line j section on the left. :

If the brushes reach the contacts / ', j f \, then the amplifier d _{2 is} short-circuited on both sides, while the amplifier O _{1 is} switched to ready to receive and forwards the telephone currents arriving from the left in an amplified manner. The brush is always chosen expediently so that its width slightly exceeds that of the insulation layer between two consecutive contact segments, so that both amplifiers are never connected to the line, otherwise whistling can occur. Of course, instead of short-circuiting the receiving side or the receiving and transmitting side, the receiving side could also be interrupted by a suitable contact device. The different sets of corresponding lamellae can be spatially arranged on the drum with respect to one another in such a way that capacitive reactions are no longer to be feared. You can z. B. on the drum the * one set offset from the other in the axial direction.

The primary winding of the input transformer and the secondary winding of the output transformer both amplifiers are conductively connected to each other and z. B. to the heating battery placed for the purpose of having a common zero point for both brush halves and thus potential differences between to prevent the two parts of the brush.

Claims (4)

Patent Claims: ι. Repeater circuit for telephone lines, in which the line line for speaking in one direction or the other by means of a contact device is switched, characterized in that the contact device is not only the receiving, but also short-circuits the transmission side of the amplifier to be put out of operation. 2. Repeater circuit according to claim 1, characterized in that the contact device from two to a center plane through an insulating layer separate half-drums and the short circuit by a single brush for receiving and transmitting side is effected. 3. intermediate amplifier circuit according to claim 1, characterized in that the primary winding of the input transformer and the secondary winding of the output transformer of both amplifiers Connected to one another conductively on one side and connected to one pole of the local battery to achieve a common zero point for both brush halves. 4. Repeater circuit according to claim 3, characterized in that the width of the brush exceeds that of the insulating layer between two contact blades. 1 sheet of drawings.