DE595949C - Coupling circuit for an audio frequency signal receiver - Google Patents

Description

With telephone lines it is. already known, signals over the telephone lines with audio frequency of z. B. to give 1000 Hz. The call devices responding to such a tone frequency are subject to echo phenomena which are extremely annoying and which can even render the call device ineffective. .
According to the invention, this disadvantage is avoided in that a circuit arrangement for coupling a receiving circuit, for example the circuit of a call device, is provided with the telephone line, which is composed of a longitudinal and cross coupling and which causes the attenuation of the signal currents between the receiving circuit and a part of the line (e.g. the line input) is less · than the attenuation between the receiving circuit and another part of the line (e.g. the line output).

For a better understanding of the principles of the invention, the following is an exemplary embodiment has been described in more detail on the basis of Figs. Fig. 1 shows a known arrangement of a compensating transformer from which the final shape of the embodiment shown in Fig. 6 was developed.

The individual stages of development are shown in Figs. 2, 3 and 4, while Fig. 5 shows one represents simplified circuit for a calculation.

In Fig. Ι a compensation transformer that is connected between input A and output B is shown. Two windings are in series with the line, while the impedance C is connected to the third winding. The line is also bridged by - another impedance D. Such a compensation transformer is often used in amplifier circuits to ^: Compensate the system. Compensation is achieved when the coils are symmetrical and the impedances of input A and output B are equal to each other. The apparent resistances C and D are dimensioned so that their ratio is equal to the transformation ratio of the transformer. These dimensions ensure that signals from input A do not cause any current in output B.

Fig. 2 shows a modification of the circuit according to Fig. 1. The impedance C is disposed in the electrically equivalent position, parallel to the windings in the line, while the secondary · winding of Ausgleichübertragers which previously contained the impedance C, then in series with the consumer S, for example a call device, in a bridge of the line · and thus parallel to the impedance D.

ι I 'I-

Fig. 3 represents a graphic repetition of Fig. 2. If the impedance C is brought to a small value and the value of the impedance D is large, then D, which is parallel to the series connection of secondary winding and consumer 5 ", can without large effect on the rest of the network can be omitted, which is indicated by the fact that D is drawn with a dashed line.

Fig. 4 shows a further stage of development. Here the impedance D has been completely omitted and the series-connected winding has been placed at one end of the main winding instead of the center tap.

If one refers to one of these figures, preferably to figure 4, it can be seen that the call device in this ao arrangement is connected to two voltages at the same time. One of these voltages is the voltage between the two wires; the other is proportional to the current through impedance C. The first of the voltages always has the same direction, regardless of whether the transmission is from A or B ; However, the second voltage changes its direction with the direction of transmission, so that the first-mentioned voltage is increased in the case of currents coming from A and decreased in the case of currents coming from B.

According to the qualitative explanation above, it is evident that echoes or signals from output B differ in their effects from those from input ./4. It is of course desirable that this difference be as pronounced as possible up to the limit that the echoes from B have no effect on the call setup at all. The following conditions determine the necessary conditions. Considerations according to Fig. 5, in which the apparent resistances from input A and output B are represented by R ₁ and R ₂ , respectively. Parallel to the small series resistance r is a winding that was originally the primary winding of the equalizing transformer. A second winding with impedance Z _{2 is assigned to it} . The transmission ratio of these two windings is n. The impedance Z ₂ is connected in series with the impedance Z _{0 of} the call device. As explained later, one or the other or both of the voltage source ^ ₁ and e _{2 can be present.}

If the condition is met that no current is produced in Z ₀ by e _z , it is evident that Z ₀ can be opened without the currents in the rest of the circuit being disturbed (e ₂ is the only acting voltage). In series with Z _{0 there} are two voltages that must be equal and opposite.

These are

^eab -

no, -

IeT + JR ₂

If one equates these two expressions, then it follows for η

η -

Now Z _{0 is switched on} again and e _{2 is} added to C _1, equal and opposite, so that i ₂ is brought to zero. The current J ₀ is now completely dependent on C ₁ . Since no current flows through the resistor R « , this circuit can be opened without the currents or voltages in the rest of the network being changed.

The current in Z is ₀

'»- R ₁ + Z ₀ + Z,'

where Z ₂ = r · n ° .

It is worth noting that the current I ₀ (the ringing current) has its value independent of the impedance of the output circuit. In the usual circuit of the receiving device (Z ₀ directly between α and b with r = o), the value of i _{0 is} practical

The change in sensitivity of the call facility is therefore indicated by the Current ratio

2Z _n

R ₁ + Z ₀ + Z ₂

When considering the relationships of the windings it is also evident that under the assumption of an ideal transformer, the following relationships exist:

Z ₁ , = rn ² =

is or

In general, there are certain practical considerations which _{limit the value of Z 2} upwards. When you determine this value

r can be determined by one of the relationships given above; if r is determined, then the value of η is given.

Another significant advantage of this circuit arrangement ¹ is that, under these conditions, the losses in voice transmission and therefore the line reflected on the receiving circuit are kept very small.

ίο On the other hand, however, the specified dimensioning of the impedance Z ₂ (Fig. 5) has the consequence that a transmission of alternating currents, z. B. ringing currents, through this impedance into the line is only possible with considerable losses. Likewise, for the currents coming from the line section A , e.g. ringing currents, which are to be transmitted into the coupled circuit (receiving circuit), the impedance is of a disturbing magnitude, provided that the circuit is dimensioned so that the transmission losses for the speech currents are low. It is therefore desirable, if not even necessary, that the impedance Z _{2 is} removed from the receiving circuit as soon as it has served its purpose. This can be accomplished in a number of ways, one arrangement of which is shown in Figure 6. It mainly consists of a changeover relay 11 which can short-circuit _{the impedance Z 2 through contacts.} When incoming signals arrive, the circuit of the calling equipment would give rise to echo phenomena, if arrangements similar to those described above are not assigned to the line. When the call signs are of sufficient duration to energize some relays in the call device X , relay 11 is energized, which _{short-circuits the impedance Z 2} and creates a more convenient route for the call flows. The character coming from the output side with a lower number of periods, for example with 20 periods, is now also transmitted more strongly. On the other hand, energize the characters with a low number of periods arriving from the output side, the relay 11, so that the higher periodic call stream of z. B.

1000 Hz can be sent into the input line A without having to go through the high impedance Z _3. If the call has not responded properly, ie if it is exposed to echo phenomena, the circuit corresponds to that shown in Fig. 5.

Because of the required line symmetry, the small series resistance is divided and each half was placed in a wire of the line; the same is true of the transformer windings been proceeded.

The call device Z shown in Fig. 6 can in its internal structure the known Call converter circuits that are used in the transition from the trunk line to the local line and vice versa are used, so that a more detailed representation of the circuit is unnecessary. About the one from the left coming long-distance line, which usually contains amplifiers, the call or signal currents with a frequency of z. B. 1000 Hz are transmitted, while for the local line leading to the right, currents of, for example 20 Hz can be used.

The primary purpose of the call facility X is to transmit call or signal flows at a lower frequency to the local line (20 Hz) when receiving call or signal streams from the long-distance line (1000 Hz). In a corresponding manner, when calling or signaling currents are received from the local line (20 Hz), corresponding currents of higher frequency (1000 Hz) are to be transmitted into the long-distance line.

During the call transmission, the relay 11 is energized via the line 5 ¹ in both cases, so that the otherwise passing speech wires are interrupted and the resistance of the call or signal circuit connected to the trunk line (1000 Hz) is reduced to avoid unnecessary losses. In the idle state, the relay 11 is de-energized, and it occurs when receiving call or signal currents from the trunk line (1000 Hz), the special effect of the transmitter circuit according to the invention, through which a disruption of the reception of the call or signal currents from the local line reflected currents is prevented. As soon as the incoming call or signal currents over the trunk have worked for a short time, a switching device occurs within the call device X , which causes the relay 11 to respond. In this way, interference with both the higher-frequency and the lower-frequented circuits is avoided during the call transmission.

When receiving low-frequency call or signal currents from the local line (20 Hz), interference with reception due to echo phenomena is less to be feared, see above that at this point the use of a transformer circuit according to the invention does not appear necessary.

Since the embodiment of the invention described above is specifically on relates to the arrangement of a call circuit in a transmission line, is express pointed out that the invention is more general as it is a device

tang contains through which any auxiliary or main circuits with a Transmission line can be connected in such a way that this main circuit noticeably more receptive to signals from one direction than to signals from the other Direction is made, with such facilities that the transmission from ordinary telephone streams

ίο is not noticeably influenced, d. H. so that a large attenuation in the voice transmission is avoided.

This invention offers yet another important outlook that becomes apparent when considering the

> 5 Fig. 5 becomes apparent. The circuit arrangement is such that by an _{EMF generated in the impedance Z 2} signals can be transmitted through the transformer in such a way that in the impedance at one end of the line, z. B. R ₁ , there is a greater amplitude than in the impedance at the other end of the line, e.g. B. i? ₂ .

Claims (6)

Patent claims: i. Coupling circuit for an audio frequency signal receiver, e.g. B. call converter, to a double telephone line, on both sides of which the coupling circuit located parts a transmission of audio frequency signals "(ringing currents) can take place in both transmission directions, thereby indicates that the input circuit of the audio frequency signal receiver has a longitudinal and a cross coupling of such Size connected to the line is that only in the one direction of transmission audio frequency signal streams arriving via the line (ringing streams) can effectively influence the audio frequency signal receiver (call converter), while it is influenced by audio frequency signal currents flowing in the other direction over the line (ringing currents) is prevented. 2. Circuit arrangement according to claim i, characterized in that the Input circuit of the audio frequency signal receiver (call converter) parallel to Double line lies and contains at least one winding of a transformer, of which at least one further winding is connected in series with the line. 3. Circuit arrangement according to claim 2, characterized in that to the transformer winding in series with the line has an ohmic resistance is connected in parallel. 4. Circuit arrangement according to claim 2 and 3, characterized in that that the ratio of the number of turns in the input circuit of the audio frequency signal receiver (Rufumetzers) lying transformer winding to the winding lying in series with the line about equal to the ratio of the impedance of the line to the parallel resistance of those in series with the line Winding is. 5. Circuit arrangement according to claim i, characterized in that Switching means are provided by which the coupling device is rendered ineffective after its function has been fulfilled will. 6. Circuit arrangement according to claim 5, characterized in that the Switching means are dependent on the audio frequency signal receiver (call converter) itself. 1 sheet of drawings