DE1060441B - Circuit arrangement for telephone subscriber stations with Rückhoerdaempfung for automatic operation - Google Patents

Description

At telephone subscriber stations with back loss for automatic operation are today very high demands. They have to be cheap to manufacture, and most importantly, they should be easy to manufacture thanks to high operational reliability, good voice transmission, radio interference protection and freedom from background noise distinguish. Furthermore, the listener, the alarm clock and the simulation should be against direct current be locked. Low manufacturing costs and operational reliability can be achieved by the switching elements housed in the station are limited to a minimum. It is Z. B. a telephone subscriber station known that only contains a single capacitor to power the alarm clock, the handset and to block the line simulation against direct current. However, it has the disadvantage that in the Dialing the number of the alarm clock rings and also emits high-frequency impulses that interfere with radio reception be, at another known telephone subscriber station, which has two capacitors, the annoying ringing when dialing a number is prevented by the alarm clock when you pick up the Microphone is disconnected from the line by a contact; but it does not contain any means for Interference suppression of the number dialing impulse contact. Telephone subscriber stations are also known in which the number dial pulse contact is suppressed by a capacitor, but the alarm clock is not optional can be connected to the speech circuit or to the alarm clock circuit.

The subject of the invention forming telephone subscriber station with back hearing loss for automatic operation, which is used to match the impedance of the handset, microphone and line with a speech current transformer with three co-directional windings, corresponds to the requirements regarding Operational safety, good voice transmission, radio interference protection and freedom from background noise. she contains the known switching elements in a combination that all without additional means avoids the above-mentioned disadvantages of known telephone subscriber stations. It is marked through the joint application of the following features:

a) that the dial pulse contact in which the microphone and the one containing a fork contact Parallel branch is arranged,

b) that the second wire can optionally be connected to the speech circuit via a further fork contact or can be connected to the alarm clock circuit.

An example embodiment of the subject matter of the invention is shown schematically in the drawing. The telephone subscriber station contains the alarm clock W, the microphone M, the handset H and the circuit arrangement
for telephone subscriber stations

with back loss
for automatic operation

Applicant:

Albiswerk Zurich AG,
Zurich, Switzerland)

Representative: Dr. M. Eule, patent attorney,
Munich 13, Kurfürstenplatz 2

Claimed priority:
Switzerland from January 3, 1957

Urs Ender, Niederwil, Aargau (Switzerland),
has been named as the inventor

Replica resistor R and a transformer with three co-directional windings Ul, U2 and! 73. The switching elements mentioned are interconnected in such a way that the impedance of the earpiece, microphone and line is matched. The simulation resistor R, which can represent a line or receiver simulation, is used for back hearing loss. A number switch with the pulse contact nsi and the short-circuit contact nsa is provided for the selection of participants. Furthermore, two fork contacts Gl and G 2 and a capacitor C are available. A and -B are the connection points of the subscriber line.

The speech circuit runs from connection point A via the actuated hook switch G1 and the transformer winding? 71, then branches into the microphone and receiver circuit, with the microphone M, the number dial pulse contact nsi and the fork contact G 2 in one branch and the Receiver H, the transformer windings! 72 and! 73 and the capacitor C are connected in series, and then leads to the common connection point B. The receiver circuit also contains the simulation resistor R, which is connected in parallel to receiver H and transformer winding! 72.

When the telephone subscriber station is in the idle state, the alarm clock W is connected to the subscriber line via the hook switch Gl and the capacitor C

909 559/297

I 060

tied together. When the microphone is picked up, the fork contacts Gl and G 2 are actuated, as a result of which the speech circuit is connected to the subscriber line. The alarm clock W is switched off by the hook switch contact Gl from the line. The impulses that arise when dialing a number subsequently cannot make the alarm clock ring. The capacitor C blocks the handset circuit against direct current. This is important insofar as, on the one hand, the power output by the microphone depends on the direct current flowing through it. On the other hand, a direct current flow through the listener, if it exceeds a certain value, is undesirable because it pre-magnetizes the listener and thus worsens its sensitivity.

When dialing numbers, the microphone M and the listener H are bridged in a known manner by the short-circuit contact nsa , so that the number dialing pulse contact nsi from the connection point A via the fork switch contact Gl, the transformer winding Ul, the short-circuit contact nsa, the number dialing pulse contact nsi and the fork contact G 2 periodically interrupts the circuit running after the connection point B. Because the fork contact G 2 and the short-circuit contact nsa are closed when dialing the number, the chain formed from the capacitor C and the transformer windings U 2 and U 3 is parallel to the number dialing pulse contact nsi. The capacitor C prevents sparking at the number dialing pulse contact nsi and thus suppresses the interference. At the moment when the microphone is lifted or hung up, the short-circuit contact nsa is open; but the capacitor C is still in series with the transformer winding U 3, the resistor R and the microphone M parallel to the fork contact G 2, so that sparking is prevented at this contact as well. All contacts have either direct current or alternating ringing current flowing through them; no one only leads the flow of speech. There is therefore no increase in the contact resistance because the relatively high voltages repeatedly break through the oxide skin that forms on the contacts.

Claims (1)

Claim: Circuit arrangement for telephone subscriber stations with back loss for automatic Operation that uses an autotransformer for the mutual impedance matching of the receiver, microphone and line with three windings in the same direction as a voice current transformer, and those in series with a first transformer winding two parallel branches are provided, one branch of which is the microphone and a fork contact and its other branch at least one transformer winding and one capacitor in series contains and in which the microphone is connected to the junction point connected to the first transformer winding and the capacitor at the junction point connected to the one line wire are connected, characterized by the common application of the following mentioned features: a) that the number disk pulse contact (nsi) is arranged in which the microphone and the parallel branch containing a fork contact (G2), b) that the second line wire (A) can be connected either to the speech circuit or to the alarm clock circuit via a further fork contact (Gl). Documents considered:.
German Patent No. 880 152;
Swiss Patent No. 302 743;
British Patent No. 665 081;
German patent application S 31154 VIIIa / 21a ² (published on July 28, 1955). 1 sheet of drawings © 909 559/297 6.59