Telephone substation apparatus

Claim 2

A telephone substation circuit of the central battery type having a pair of terminals, and a speech of the anti-sidetone type establishing a direct current path across said terminals, said speech circuit including a voice transmitter unit and a voice receiver unit, said substation circuit further comprising: a. a multifrequency generator having a resonant circuit with discretely controllable resonant frequencies and an amplifying means; b. selector means for selecting a descrete resonant frequency of the resonant circuit, the resonant circuit being coupled to the amplifying means in such manner as to render the amplifying means capable of supporting oscillations at said selected frequency; c. switch means, linked to said selector means, for shunting the resonant circuit until actuation of said switch means by operation of said selector means, for removing the shunt so as to place the resonant circuit in series with the voice transmitter unit, said switch means functioning also to enable the amplifying means by connecting the amplifying means to the speech circuit so as to derive an operating voltage therefrom, and to interrupt the flow of direct current through the resonant circuit after said amplifying means has been enabled; whereby the output of said multifrequency generator is coupled to said pair of terminals.

Claim 3

The invention as claimed in claim 1 wherein the switch means is mechanically linked to the selector means to be responsive thereto, and wherein the switch means comprises a set of transfer contacts and a late-break set of contacts, the transfer contacts being used to shunt the resOnant circuit and to enable the amplifying means, and the late-break contacts being used to interrupt the flow of direct current through the resonant circuit so as to initiate oscillations at said selected frequency after said amplifying means has been enabled.

Claim 4

The invention as claimed in claim 2 wherein the break transfer contact being for shunting the resonant circuit and the make transfer contact being for completing a circuit to enable the amplifying means.

Claim 5

A telephone substation circuit of the central battery type including a pair of terminals, an induction coil having a plurality of windings, a line impedance balancing network, a voice receiver unit, and a voice transmitter unit, the voice transmitter unit being serially connected with a winding of the induction coil to form part of a series circuit establishing a direct current path across said terminals, said substation circuit further comprising: a. a multifrequency generator having a resonant circuit with discretely controllable resonant frequencies, a selector means for selecting a discrete resonant frequency and an amplifying means, said resonant circuit being coupled to said amplifying means in such manner as to render said amplifying means capable of supporting oscillation at said selected frequency, b. switch means normally shorting said resonant circuit, said switch means responding to operation of said selector means by removing said short, by inserting the resonant circuit in series with the voice transmitter unit to initiate a flow of direct current through the resonant circuit, by enabling said amplifying means with current derived from a voltage appearing across a series circuit including, said resonant circuit, the voice transmitter unit, and said winding of the induction coil, and by interrupting the flow of direct current through the resonant circuit after said amplifying means has been enabled, c. whereby the output of said multifrequency generator is coupled to said pair of terminals.

Claim 6

A telephone substation circuit of the central battery type including a pair of terminals, an induction coil having a plurality of windings, a line impedance balancing network, a voice receiver unit, and a voice transmitter unit, the voice transmitter unit being serially connected with a winding of the induction coil to form part of a series circuit establishing a direct current path across said terminals, said substation circuit further comprising: a. a multifrequency generator having a resonant circuit with discretely controllable resonant frequencies, a selector means for selecting a discrete resonant frequency and an amplifying means, said resonant circuit being coupled to said amplifying means in such manner as to render said amplifying means capable of supporting oscillation at said selected frequency, b. switch means normally shorting said resonant circuit, said switch means responding to operation of said selector means by removing said short, by inserting the resonant circuit in series with the voice transmitter unit to initiate a flow of direct current through the resonant circuit, by enabling said amplifying means with current derived from a voltage appearing across a series circuit including, said resonant circuit, the voice transmitter unit, and said winding of the induction coil, and by interrupting the flow of direct current through the resonant circuit after said amplifying means has been enabled, c. whereby the output of said multifrequency generator is coupled to said pair of terminals.

Claim 7

The invention as defined in claim 4 wherein the resonant circuit comprises an inductor with a plurality of tap positions and a capacitor for connection to a selected one of said tap positions by the selector means, and wherein the switch means is mechanically linked to the selector means so as to operate with each operation of the selector means, the switch means having a set of transfer contacts and a late-break set of contacts whereby the transfer short the resonant circuit in their unoperated position and allow an operating voltage to enable the amplifying means in their operated position and whereby the late-break pair of contacts interrupt the flow of direct current through the resonant circuit after said amplifying means has been enabled.

Claim 8

In a telephone substation circuit having a speech network including a voice transmitter and a voice receiver; a substation signalling circuit comprising: a resonant circuit having a plurality of selectively controllable resonant frequencies, a shunt in parallel with said resonant circuit for bypassing current around said circuit, the combination of said resonant circuit and said shunt being in series with at least a portion of said speech network; selector means for selecting a resonant frequency of the resonant circuit; amplifying means coupled to the resonant circuit for supporting oscillations at said selected resonant frequency; and switch means, responsive to said selector means, for opening the shunt across the resonant circuit upon actuation of the selector means, to allow a direct current to flow through the resonant circuit, said switch means being operative thereafter to enable the amplifying means and to interrupt said flow of direct current after the amplifying means has been enabled.

Claim 9

In a telephone substation circuit having a speech network including a voice transmitter and a voice receiver; a substation signalling circuit comprising: a resonant circuit having a plurality of selectively controllable resonant frequencies, a shunt in parallel with said resonant circuit for bypassing current around said circuit, the combination of said resonant circuit and said shunt being in series with at least a portion of said speech network; selector means for selecting a resonant frequency of the resonant circuit; amplifying means coupled to the resonant circuit for supporting oscillations at said selected resonant frequency; and switch means, responsive to said selector means, for opening the shunt across the resonant circuit upon actuation of the selector means, to allow a direct current to flow through the resonant circuit, said switch means being operative thereafter to enable the amplifying means and to interrupt said flow of direct current after the amplifying means has been enabled.

Claim 10

The invention as claimed in claim 6 wherein the switch means is mechanically linked to the selector means to be responsive thereto, and wherein the switch means comprises a set of transfer contacts aNd a late-break set of contacts, the transfer contacts being for shunting the resonant circuit and to enable the amplifying means, and the late-break contacts being for interrupting the flow of direct current through the resonant circuit so as to initiate oscillations at said selected frequency after said amplifying means has been enabled.

Claim 11

The invention as claimed in claim 7 wherein the break transfer contact being for shunting the resonant circuit and the make transfer contact being for completing a circuit to enable the amplifying means.