DE1076188B - Circuit arrangement for telephone subscriber stations equipped with fee displays - Google Patents

Description

GERMAN

To display the charges for a telephone call, a display device is generally provided at the subscriber's premises, which is controlled by charge, enimpulsen that reach the subscriber from the control center via the subscriber line. The best known scheme of this type is shown in Fig. 1 of the drawing. By means of a transformer U ₁ provided in a control center Z, the pulses generated by a contact I are sent at a frequency of 50 Hz via two lines α and b, which connect the control center Z to the subscriber T. You have an electrical circuit that contains the following switching elements: earth £ _c in the control center, transformer U ₃ , two capacitors C ₃ and C ₄ , the secondary windings of transformer U ₁ , lines a and b, two capacitors C. ₁ and C ₂ , the transformer U ₂ , the charge indicator G _m and earth E _t at subscriber T. The various parts of this circle must have good symmetry with respect to "earth" so that the charge pulses do not interfere with the telephone conversation.

If one assumes that the transmission of a frequency range for sufficient speech intelligibility from 300 to 3000 Hz is sufficient, so you can use the subscriber line for the symmetrical to be sent charge pulses use a frequency that is outside of the frequency range mentioned is, the separation of the different frequencies by means of additional circles in the manner of Filtering is brought about.

A circuit of this type is shown in Fig. 2, where two low-pass filters, one (TP ₁ ) in the center and the other (TP ₂ ) at the subscriber, with a permeability of up to 3000 Hz, the unhindered passage of the speech frequencies from the Allow central Z to subscriber T and vice versa, but block all frequencies outside this range. The charge pulses generated by a contact / go from the control center Z to the lines α and b via a band filter 5P ₃ and reach the charge indicator G _m at the subscriber T via a band filter 5P ₄ . If one considers that the frequencies of 25 or 50 Hz are required for the alarm clock current far below the speech frequency range of 300 to 3000 Hz and that the filters for low frequencies are also very extensive and expensive, one is forced to use frequencies far for the charge pulses above 3000 Hz, for example in a range from 10,000 to 20,000 Hz.

For these high frequencies, however, the attenuation of the line is so great that only an energy of a few milliwatts are available to operate the number drums of the fee display.

Circuit arrangement

for those equipped with fee indicators

Telephone subscriber stations

Applicant:

SODECO Societe des Compteurs de Geneve, Geneva (Switzerland)

Representative: Dipl.-Ing. R. Müller-Bömer,

Berlin-Dahlem, Podbielskiallee 68, and Dipl.-Ing. H. H. Wey, Munich 23, patent attorneys

Claimed priority:

Switzerland from September 20, 1955

Paul Lüscher, Geneva (Switzerland), has been named as the inventor

The present invention overcomes the aforementioned disadvantages; it uses a common amplifier both for the amplification of the charge impulses and for the amplification of the microphone current. This use of a common amplifier for both purposes was previously unknown; acquaintance Facilities, e.g. B. according to British patent specification 679 875 or according to German patent specification 899 373, used amplifiers either only for the microphone current or only for the charge pulses.

The invention thus relates to a circuit arrangement for equipped with fee displays Telephone subscriber stations in which filters for separate paths of the microphone alternating currents and the Charge pulses are provided, and is characterized in that for the amplification of the microphone alternating currents and the charge pulses a common amplifier is provided, the input of which on the one hand with the subscriber line, on the other hand with the microphone and its output on the one hand is connected to the charge indicator, on the other hand to the subscriber line.

. . . .... 909 757/345

In Fig. 3 of the drawing, an embodiment of the invention is shown; it shows an amplifier V, the input of which is connected on the one hand to the subscriber line L and on the other hand to the microphone JIi, but whose output is connected both to the subscriber line L and to the charge indicator G _m .

Due to the arrangement of the two bandpass filters BP , the path of the charge pulses for the voice frequencies is blocked. The bandpass filters BP only pass frequencies above, for example, 10 kHz. On the other hand, the low-pass filter TP only lets frequencies of 300 to 3000 Hz through. The alternating speech currents and. the charge pulses run in the opposite direction over the line.

The inventive design of the amplifier it is possible to use a single common amplifier to produce two different signals, viz the charge pulses and microphone alternating currents to amplify at the same time.

Claims (1)

Patent claim: Circuit arrangement for telephone subscriber stations equipped with charge indicators, in which filters are provided for separate paths for the alternating microphone currents and the charge pulses, characterized in that a common amplifier is provided for amplifying the alternating microphone currents and the charge pulses, the input of which is connected to the subscriber line (L), on the other hand with the microphone (M) and its output on the one hand with the charge indicator (G _m ), on the other hand with the subscriber line (L). Considered publications:
German Patent No. 899,373;
British Patent No. 679 875. 1 sheet of drawings © 909 7577345 2. 66