US2214212A - Telephone substation - Google Patents

Description

Sept. 10, 1940. ms 2,214,212

TELEPHONE SUBSTATION Filed latch 14, 1958 INVENTOR. JOHN H. V0 5 5 ATTORNEYS.

Patented Sept. 10, 1940 z mg m UNlTED sr'rs TELEPHONE SUBSTATION John Henry Voss, Downers Grove, lllL, assignor to Associated Electric Laboratories, End, Chicago, 111., a corporation of Delaware Application March 14, 1938, Serial No. 195,812 25 Claims. (Cl. 179-81) The present invention relates to substation apthe invention to provide in a substation circuit paratus and has for one of its objects the proviof the character described apparatus whereby the sion of an improved arrangement for incorporatsame anti-side tone impedance network may be ing an auxiliary loud speaking sound reproducing utilized to prevent sound transmitted to the unit in the telephone substation circuit. transmitter from being reproduced by the substa- 5 A substation of the character mentioned contion receiver or by the auxiliary sound reproducventionally comprises a telephone transmitter ing unit. and receiver, a hook or cradle switch, a ringing In the illustraetd embodiment of the invention, device, and an auxiliary loud speaking sound rethe substation circuit is shown as comprising a producing unit arranged for alternative use with transmitter, a receiver and an anti-side imped- 1 the telephone receiver. When the substation is to ance network arranged to be interconnecetd to be used in a system of the automatic type, there form a substation circuit. The anti-side tone is also included in the circuit thereof a dial operimpedance network is, when the receiver is conated impulsing device for transmitting switch nected in the substation circuit, operative to control impulses over the associated line to the prevent audio frequency energy generated by the 15 line terminating exchange. In this type of suboperation of the transmitter from being delivered station circuit it is desirable to provide apparatus to the receiver. Also included in the substation for preventing operation of the transmitter from is an auxiliary sound reproducing device and effecting operation of the receiver when the reswitching means comprising the usual receiverceiver is connected for use, and for preventing operated hook switch, for substituting this auxili- 20 operation of the transmitter from efiecting operary sound reproducing unit for the receiver in the ation of the auxiliary sound reproducing unit substation circuit. In accordance with one feawhen this unit is connected for use. It is also ture of the invention, the switching means, the desirable to provide circuit apparatus so arranged anti-side tone impedance network, and the sound that voltage or current transients occasioned by reproducing unit are so connected and arranged 25 operation of the impulsing device are not transthat the anti-side tone impedance network is also mitted to the receiver or the auxiliary sound reoperative to prevent audio frequency energy genproducing unit for reproduction. Various arerated by the operation of the transmitter from rangements have in the past been utilized for being delivered to the auxiliary sound reproducaccomplishing these purposes and while, for the ing unit when this unit is operatively included in 30 most part, these prior arrangements are perfectly the circuit. The auxiliary sound reproducing satisfactory in operation, they are, in the usual unit comprises a vacuum tube amplifier and a instance, rather complicated in character, and loud speaker or translating device connected in expensive. For example, it has been more or less tandem in the order named, and there is included conventional practice to provide separate cirin the amplifier input circuit the secondary wind- '35 cuits associated respectively with the receiver and ing of a voltage amplifying coupling transformer. the auxiliary sound reproducing unit for preventi e substation is equipped for automatic service, ing voice frequency energy generated by operation a dial controlled impulsing device being provided of the transmitter from being delivered to the refor transmitting switch control impulses by way 40 ceiver and the auxiliary sound reproducing unit of the associated line to the line terminating ex- 40 for reproduction. change. In accordance with a further feature of It is an object of the present invention to prothe invention, there is provided an arrangement vide a telephone substantion circuit which is for effectively short-circuiting the secondary equipped to provide amplified reproduction of winding of the coupling transformer during the audio frequency currents transmitted to the suboperation of the impulsing device, thereby to pre- '45 station, and which is of simple and economical vent voltage transients occasioned by operation arrangement and requires a minimum amount of of the device from being amplified by the vacuum circuit equipment. tube amplifier and delivered to the loud speaker.

It is a further object of the invention to provide The novel features believed to be characterisin a substation circuit of the character mentioned tic of the invention are set forth with particu- 50 an improved arrangeme t for preventing tranlarity in the appended claims. The invention,

sient voltages or currents occasoined by operation bothas to organization and method of operaof the impulsing device from being reproduced tion, together with further objects and advanclicks by the auxiliary sound reproducing unit. tages thereof, will best be understood by refera It is a still further and more specific object of ence to the specification, taken in connection 55 ranged that the dial mechanism and l2.

with the accompanying drawing, in which there is illustrated in partially schematic form an automatic telephone system having incorporated therein a substation connected and arranged in accordance with the present invention.

Referring now to the single figure of the drawing, there is diagrammatically illustrated a telephone system comprising an automatic telephone exchange I0 which may, if desired, constitute a private automatic branch exchange. Terminating at the exchange It! are a plurality of teletwo of which are indicated at H The ends of the lines remote from the exchange [0 terminate in substations of the automatic type, that associated with the line ll being diagrammatically illustrated at A and that associated with the line l2 being indicated gen erally at B. The automatic exchange l8 comprises the usual subscriber controlled automatic switches for setting up connections between the telephone lines of the system. More particularly, these switches are, in accordance with conventional practice, divided into two classes, namely, non-numerical switches such, for example, as line finder or line switches; and numerical switches, such, for example. as selector and connector switches, which respond to impulses transmitted thereto over calling ones of the telephone lines and function to perform the usual line group, subgroup and unit selecting operations. The connector switches at which the lines terminate are, in accordance with conventional practice, equipped to perform the usual auxiliary functions of: testing a selected called line to determine the idle or busy condition thereof, returning busy tone over the calling line in the event a selected called line is found busy, and projecting ringing current over a selected called line to actuate the signal device at the called substation in the event a selected idle at the time it is tested.

Referring now more particularly to the equipment provided at the substation B, this substation comprises switching means in the form of a call-and-answer key l3 for connecting the substation apparatus to the line l2, a ringing or signal device. I 4 connected across the line conductors l6 and H in series with a condenser 15; a transmitter [8, a receiver is, a dial controlled impulsing device 25, and switching means in the form of a hook or.cradle switch 2i. 2| comprises a member 22 for supporting the receiver 19 when not in use, and switch springs 23 to 21, inclusive, which are operative, in response to the removal of the receiver l9 from the supporting member 22, to include the receiver 19 in the substation circuit. The impulsing device 2!! is of the conventional dial operated type and comprises a pair'of impulsing springs 28 and two sets of shunt contact springs 29 and 3b. The springs 29 and the springs 38' are normally restrained to the open circuit positions indicated in the drawing, and are so arcloses the same during operation of the impulsing device. Also included in the substation equipment is an auxiliary sound reproducing unit comprising a vacuum tube amplifier 3i and a translating device or loud speaker 32. The amplifier 3! is provided with an input circuit which includes the secondary winding 33 of a voltage step-up or amplifying transformer 34,'which transformer is more generally designated as a'coupling element. The transformer 36 also includes a primary winding ,35 which is normally. connectedacross phone lines,

one element 36 of an anti-side tone impedance network indicated generally at 31. This network, which is provided for the purpose of preventing audio frequency energy generated by operation of the transmitter 3 from being delivered to the receiver l9 or to the input circuitof the amplifier 3!, further comprises a second inductance element 38 connected in series with that element 36. Both of the elements 36 and 38 are coupled to a third inductance element 39. Also included in the network 31 is a resistor 40 which is provided for the purpose of balancing the resistive impedance of the line l2 and other impedances necessarily connected to this line when the substation B is included in an established telephone connection.

For the purpose of minimizing acoustical coupling between the transmitter I 8 and the auxiliary sound reproducing unit, it is contemplated that these elements of the circuit shall be remotely located with respect to each other. More particularly, the auxiliary sound reproducing unit is remotely located with respect to the re mainder of the substation. apparatus and is connected thereto by means of a cable 42 comprising conductors 43 to 46, inclusive, which are preferably formed of tinsel wire, permitting continuous handling of the cable 42 with a minimum likelihood of breaking the enumerated conductors.

In order to prevent voltage transients occasioned by operation of the impulsing device 20 from being reproduced as clicks by the receiver 55? or the auxiliary sound reproducing unit, the contact sprin s 29 are arranged to complete a path for at least partially short-circuiting the primary winding of the transformer 34 when the hook switch 2! occupies the position shown in the drawing, and for short-circuiting the receiver 59 when this receiver is removed from its supporting member 22 to permit the switch 2i to assume its off-normal position. As a further expedient for preventing such transient voltages from being reproduced by the auxiliary sound reproducing device, there is provided a path for effectively short-circuiting the input circuit or, more particularly, the secondary winding of the transformer 36 for such voltages during operation. of the impulsing device 20.- This path, which is normally open, comprises a capacitance element 47! of large capacity and is arranged to be completed in response to the operation of the impulsing device 20 through closure of the shunt contact springs 30. In order to prevent local electrical disturbances picked up by the line i 2 from being reproduced by the auxiliary sound reproducing unit when this unit is conditioned for operation, the key or switch is is equipped with springs for disconnecting the substation circuit from its associated line I2 when the substation apparatus is not in use. The contact springs 68 and 49 of the key l3 are also arranged to complete the path comprising the capacitance element 1? for efifectively short-circuiting the secondary winding 33 of the transformer 34 when the substation apparatus is disconnected from the line I 2.

As indicated in the drawing, the substation B is of the local battery type, a battery 56 being provided for producing voice frequency currents in responseto the operation of the transmitter i8 when this transmitter, the inductance element 39, and the battery 56 are connected, through operation of the key l3 to its off-normal position, to form a closed transmitting loop.

In order to give a visual indication that the substation B is connected to its associated line H2, or that the key i3 is operated to its ofl-normal position, there is provided a signal lamp 5'! which is arranged to be energized when the contacts 5d and 55 of the key [3 are closed.

Referring now to the operation of the system, and assuming, for example, that a call is initiated at the substation A and routed by way of the automatic switching equipment provided in the exchange i6 and the line l2 to the substation B at a time when the last-mentioned substation is idle, when the line 52 is seized by one of the connector switches provided in the exchange IG and tests idle, ringing current is projected over the line to actuate the ringing device i l, thereby to give an audible indication that the substation B is being called. The call is answered by operating the key It! to its off-normal position, thereby to interrupt, at the springs it and it, the above mentioned path for effec tively short-circuiting the secondary winding 33 of the transformer at, and to complete, at the springs 54 and the above-mentioned transmitting loop including the transmitter 68, the battery and the inductance element 39. When the key it is operated to its off-normal position, an obvious circuit is completed at the springs 56- and as for energizing the signal lamp 5?, and a direct current bridge is placed across the line conductors it and H of the line l2. This bridge may be traced from the conductor 56 by way of the springs 5B, 5! and 28, the resistor 53, the inductance elements 35 and 38, and the switch springs 52 and 53 to the opposite line conductor H. The completion of this bridge results in the operation of the connector switch to arrest the ringing operation and to complete a talking connection between the calling and called substations in the usual manner.

The answering party has the option of employing the receiver I9 or the auxiliary sound reproducing unit for translating incoming audio frequency currents into sound energy. If the answering party elects to employ the receiver H) for this purpose, this receiver is removed from its supporting member 22 in the usual manner. The hook switch 25 responds to this operation by opening its contact springs 25 and 21, closing its springs 23 and 2t, and closing its springs 25 and 26. Following the operation of the hook switch 2i to its off-normal position, the receiver is is conditioned to reproduce incoming audio frequency currents as sound energy, and the transmitter 55 is conditioned to convert sound energy into corresponding audio frequency currents for transmission over the line l2 to the calling substation A. Specifically, the path traversed by incoming voice frequency currents extends irom the line conductor it, by way of the switch springs 53 and St, the impulsing springs 28, the receiver 58, the switch springs 26 and 25, the inductance element 33 of the anti-side tone impedance network 3i, and the switch springs 5?. and 55, to the opposite line conductor i1.

When sound waves impinge upon the diaphragm of the transmitter l8, undulating audio frequency currents corresponding to the sound waves are set up in and circulate through the closed loop circuit comprising the transmitter 18, the inductance element 39 and the battery 56. The alternating component of this current causes an induced voltage of corresponding character to be developed across the terminals of the series connected inductance elements 36 and 38. This veloped across the inductance element induced voltage causes audio frequency current to be projected over the switch train in the exchange it, and over the line it to the receiver at the calling substation A. The path of this current may be partially traced as extending by way or the line conductor ll, the switch springs E53 and 52, and the inductance element 38 where it divides, one branch extending by way of the impedance element 36, the resistor the impulsing springs 28, and the springs 5! and 551 to the opposite line conductor l6; and the other branch extending by way of the springs and 2b, the receiver E9, the impulsing springs 3, and the springs 5i and 58 to the opposite line conductor i5. Due to the voltage induced in the inductance element 36, a cirulating current is set up in the closed circuit comprising this element, the resistor 40, the receiver 59, and the switch springs as and 26. By proportioning the turns of the two elements 35 and 38so that the voltage developed across the inductance element at bears the correct relation to that de- 38, the circulating current noted can be made equal and opposite to that flowing through the receiver id as a consequence of the voltage induced in the inductance element 38. Thus, the current flowing through the receiver l5! during operation of the transmitter 48 may be reduced substantially to zero, so that the well-known anti-side tone effect is realized.

In the event the answering party elects to employ the auxiliary sound reproducing unit as the receiving means, the amplifier on-oii switch, not shown, is operated to condition the amplifier 3 for operation, and the receiver is is not removed from its supporting member 22. With the hook switch 2% in its normal position as indicated in the drawing, and with the answer key it operated to its off-normal position, the primary winding 35 is substituted for the receiver it in the substation circuit. More particrdarly, the path of the signal currents incoming to the substation B may be partially traced as extending by way of the line conductor ii, the switch springs 53 and 52, theinductance element 33, the cable conductor M, the primary winding 35, the cable conductor the switch springs 2t and 2?, the impulsing springs 28, and the switch springs 5i and iii to the opposite line conductor it. Since the primary winding 35 is literally substituted for the receiver is in the substation circuit, it will be understood that the anti-side tone impedance network 31 functions to prevent voice frequency energy generated by operation of the transmitter l8 from being delivered to and reproduced by,

the auxiliary sound reproducing unit. On the other hand, incoming audio frequency currents traversing the primary Winding over the circuit just traced are amplified by the amplifier 3i and delivered to the loudspeaker 32 for reproducton. The path of audio frequency currents generated by operation of. the transmitter la is substantially the same as that traced above for the case when the receiver i9 is included in the circuit.

When the conversation is terminated and the connection is released, the key 53 is restored to its normal position to recomplete, at the springs l-$3 and it, the above-mentioned path for effectively short-circuiting the seconddary Winding 33 of the transformer If the answering party fails to restore the hey E3, the energized condition of the lamp El is a visual reminder that the substation B is still connected to the line line 52, through the l2. Obviously, when the key I3 is restored to normal, the circuit for energizing this lamp and the closed transmitting loop are interrupted at the springs 54 and 55. If the auxiliary sound reproducing unit utilized as the receiving means, the amplifier 3! is deenergized when the on-oif switch associated therewith is restored to its oil position. On the other hand, if the re-- ceiver I9 is utilized as a receiving means, this receiver is restored to its supporting member in the usual manner, to return the hook switch 2| to its normal position. It will be apparent from the foregoing description that the auxiliary sound reproducing unit and the receiver l9 may alternately be used as the receiving means during a single conversation by the simple expedient of restoring or removing the receiver 69 from its supporting member 22, thereby to actuate the hook switch 2| between its two operating positions.

In order to initiate a call at the substation B intended for one of the other automatic substations, such, for example, as the substation A, the calling party first actuates the cail and answer key l3 to its off-normal position to per-- form the functions described above; and then actuates the impulsing device 29 in accordance with the directory number designating the called substation. It will be noted that, when the key I3 is operated to its oif-normal position, the direct current bridge, traced above, is connected across the line conductors l6 and l'e" and the line i2, thereby to cause an associated or assigned non-numerical switch in the exchange l0 to respond in the usual manner. During operation of the impulsing device 25, the impulsing springs 28 are alternately opened and closed in the usual manner, thereby to transmit impulses by way of the line 12 to the automatic switching equipment in the exchange 60. This equipment responds to the impulses in the usual manner to cause the connection to be routed by way thereof to the called line H. During each operation of the impulsing device 263 or, more particularly, during each digit dialed at the substation B, the shunt springs 29 and the shunt springs 35 are closed. At the springs 29 a path is completed for excluding the primary winding 35, the resistor 4B and the inductance element 35 from the impulsing circuit. Thus, when the springs 29 are closed, and with the hook switch 2| in its normal position as indicated in the drawing, the primary winding 35 is short-circuited over a short-circuiting path extending from its upper terminal by Way of the cable conductor $3, the switch springs and 2?, the shuntsprings 29, and the cable conductor 44 to the lower terminal of the winding 35. The completion of this path effectively reduces the possibility of transient voltages occasioned by operation of the impulsing device from being impressed on the input circuit of the amplifier 3!. There may be, however, a certain amount of inductive, capacitive or resistive coupling between the cable 2 and the other circuit elements, such that small transient voltages are developed across the terminals of the winding 35 during operation of the impulsing device. When amplified by the transformer 3 and the amplifier 3!, these small voltages may produce objectionable noise in the form of clicks reproduced by the loud speaker 32. In order to obviate this possibility, the shunt springs 38 are arranged to complete the above-mentioned path for efiectively short-circuiting the input circuit to the amplifier 3! or, more particularly the secondary winding 33 of the transformer 34 for transient or alternating voltages during operation of the impulsing device 20. This last-mentioned short-circuiting path extends from the upper terminal of the winding 33 by way of the capacitor 47, the cable conductor 46, the shunt springs 38 and the cable conductor 45 to the lower terminal of the transformer winding 33. The capacitance value of the capacitance element 6-7 is chosen of a large value so that the impedance of the above-traced path to transient or low frequency audio currents is substantially zero, and thus, even though substantial currents are developed in the secondary winding 33 during operation of the impulsing device 20, the potential difierence between the terminals of this winding is held at an exceedingly low value.

When the operation of the impulsing device 20 is ended, the shunt springs 29 and 30 are opened, in the usual manner, to interrupt the above-traced short-circuiting paths, and thereby to condition the substation circuit for voice frequency current transmission and reception. In this connection it will be apparent that, if the selected called line II is tested and found busy, busy tone current is returned over the calling loop circuit to traverse the primary winding 35 of the auxiliary sound reproducing unit and, as a consequence, is reproduced by the loud speaker to indicate that the desired connection cannot immediately be obtained. If, on the other hand, the called line is idle and ringing current is projected thereover to signal the called substation, ring-back tone current is conducted back over the calling line and through the primary winding 35 of the transformer 34 to energize the auxiliary sound reproducing unit and thus indicate that the called substation is being rung. When the called subscriber answers the call, the desired conversational connection is completed in the usual manner.

In view of the foregoing description, it will be apparent that the receiver l9 may be utilized by the calling party as the receiving means and, further, that this receiver may be removed from its supporting member 22 either before or after the dialing operation is performed. If the receiver is removed from its supporting member before the impulsing device is actuated, the shunt springs 29 serve to short-circuit the receiver in an obvious manner. Also, with the receiver removed from its supporting member, the above-traced path for short-circuiting the winding 33 of the transformer 34 is completed at the springs 23 and 2 of the hook switch 2| independently of the shunt springs 20, and is held completed so long as the receiver I9 is withheld from its supporting member. As a consequence of this arrangement, the auxiliary sound reproducing unit is substantially prevented from reproducing any audio 'frequency energy incidentally picked up by virtue of stray coupling between its input circuit and the other elements of the substation circuit, even though it is conditioned for operation. Further to preclude the possibility of voice frequency currents being delivered to the auxiliary sound reproducing unit when the receiver i9 is operatively included in the substation circuit, the circuit for energizing the primary winding 35 of the transformer 34 is held open at the springs 26 and 2'! of the hook switch 26. In this case, as well as in the case where the substation B is the called substation, the receiver l9 and the auxiliary sound reproducing unit may be interchanged at will in the substation circuit through the simple expedient of operating the hook switch 21 between its two operating positions.

In order to release the connection as established in the above-described manner after the conversation is terminated, it is only necessary for the calling party to actuate the key iii to its normal position to interrupt the loop circuit extending to the operated switch train in the exchange it. When the key it is restored to normal the other functions enumerated above are performed, that is, the transmitting loop is interrupted, the lamp 51 is deenergized, and the above-traced path for effectively short-circuiting the winding 33 of the transformer 34 is completed. When the calling loop circuit is interrupted through the operation of the key id to its normal position, the operated switch train is released in the usual manner. Obviously, if the receiver is is used as the sound reproducing device, this element is restored to its supporting member 22 at the end of the conversation. On the other hand, if the auxiliary sound reproducing unit is utilized, this unit is deenergized by returning the on-oif switch to its off position.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein, and it is intended in the appended claims to cover all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A telephone substation adapted to be connected to a telephone line for conversation over said line and comprising, in combination, a transmitter, a receiver and an anti-side tone impedance network arranged to be interconnected to form a substation circuit, said anti-side tone impedance network being operative to prevent audio frequency energy generated by operation of said transmitter from being delivered. to said receiver, an auxiliary sound reproducing device, and switching means for substituting said auxiliary sound reproducing unit for said receiver in said substation circuit, said switching means, said network and said auxiliary sound reproducing unit being so connected and arranged that said network is operative to prevent audio frequency energy generated by operation of said transmitter from being delivered to said auxiliary sound reproducing unit when said auxiliary sound reproducing unit is operatively included in said substation circuit.

2. A telephone substation adapted to be connected to a telephone line for conversation over said line and comprising, in combination, a

transmitter, a receiver and an anti-side tone im-' pedance network arranged to be interconnected to form a substation circuit, said anti-side tone impedance network being operative to prevent audio frequency energy generated by operation of said transmitter from being delivered to said receiver, an auxiliary sound reproducing unit including an amplifier and a loud speaker connected in tandem in the order named, and switching means for substituting said auxiliary sound reproducing unit for said receiver in said substation circuit, said switching means, said network and said amplifier being so connected and arranged that said network is operative to prevent audio frequency energy generated by operation of said transmitter from being delivered to said amplifier when said amplifier is operatively included in said substation circuit.

3. A telephone substation adapted to be connected to a, telephone line for conversation over said line and comprising, in combination, a transmitter, a receiver and an anti-side tone impedance network arranged to be interconnected to form a substation circuit, said impedance network including three co-upledinductance elements, two of said elements being connected in series, one of said elements being arranged to be connected in shunt with said transmitter, said receiver being arranged to be connected in shunt with a secend of said elements, whereby substantially no audio frequency voltage is developed across said receiver during operation of said transmitter, an auxiliary sound reproducing unit including an input circuit, and switching means for eifectiveiy disconnecting said receiver from said second inductance element and for coupling said input circuit to said second inductance element,

hereby substantially no audio frequency voltage is developed across said input circuit during operation of said transmitter.

4. A telephone substation adapted to be connected to a telephone line for conversation over said line and comprising, in combination, a transmitter, a receiver and an anti-side tone impedance network arranged to be interconnected to form a substation circuit, said impedance network including three coupled inductance elements, two of said elements being connected in series, one of said elements being arranged tobe connected in shunt with said transmitter, said receiver being arranged to be connected in shunt with a second of said elements, whereby substantially no audio frequency voltage is developed across said receiver during operation of said transmitter, an auxiliary sound reproducing unit including an amplifier and a loud speaker connected in tandem in the order named, said amplifier including an input circuit, and switching means for effectively disconnecting said receiver from said second inductance element and for coupling said input circuit to said second inductance element. whereby substantially no aurfio frequency voltage is developed across said input circuit during operation of said transmitter.

5. A telephone substation adapted to be connected to a telephone line for conversation thereover and comprising, in comhbination, a transmitter, a receiver, and an anti-side tone impedance network arranged to be interconnected to form a substation circuit, a member for supporting said receiver when not in use, switching means operative in response to the removal of said receiver from said supporting member for operatively including said receiver in said circuit, said anti-side tone impedance network being operative to prevent audio frequency energy generated by operation of said transmitter from being delivered to said receiver when said receiver is operatively included in said circuit, and an auxiliary sound reproducing unit, said switching means being operative to exclude said receiver from said circuit and operativelyl to include said auxiliary sound reproducing unit in said circuit when said receiver is supported by said supporting member, and said switching means, said network and said auxiliary sound reproducing unit being so connected and arranged that said network is operative to prevent audio frequency energy generated by operation of said transmitter from being delivered to said auxiliary sound reproducing unit when said auxiliary sound reproducing unit is opera tively included in said circuit.

6. A telephone substaton adapted to be connected to a telephone line for conversation there over and comprising, in combination, a transmitter, a receiver, and an anti-side tone impedance network arranged to be interconnected to form a substation circuit said impedance network including three coupled inductance elements, two of said elements being connected in series, one of said elements being arranged to be connected in shunt with said transmitter, a member for supporting said receiver when not in use, switching means operative in response to the removal of said receiver from said supporting member for connecting said receiver in shunt with a second of said elements, whereby substantially no audio frequency voltage is developed across said receiver during operation of said transmitter, and an auxiliary} sound reproducing unit including an input circuit, said switching means being operative effectively to disconnect said receiver from said second inductance element and to couple said input circuit to said second inductance element when said receiver is supported by said member, whereby substantially no audio frequency voltage is developed across said input circuit during operation of said transmitter when said input circuit is coupled to said second inductance element.

'7. A telephone substation adapted to be connected to a telephone line for conversation over said line and comprising, in combination, a transmitter, a receiver and an anti-side tone impedance network arranged to be interconnected to form a substation circuit, said anti-side tone impedance network being operative to prevent audio frequency energy generated by operation of said transmitter from being delivered to said receiver, an auxiliary sound reproducing unit including an input circuit, switching means for substituting the input circuit of said auxiliary sound reproducing device for said receiver in said substation circuit, said switching means, said network and the input circuit of said sound reproducing unit being so connected and arranged that said network is operative to prevent audio frequency energy generated by the operation of said transmitter from being delivered to said input circuit when said input circuit is operatively included in said substation circuit, an impulsing device for transmitting impulses over said line and including a pair of normally open contacts, said contacts being arranged to be closed during the operation of said device, and switching means for connecting said pair of contacts to short-circuit said receiver when said receiver is operatively included in said substation circuit and to short-circuit said input circuit when said input circuit is operatively included in said substation circuit.

8. A telephone substation adapted to be connected to a telephone line for conversation over said line and comprising, in combination, a transmitter, a receiver and an anti-side tone impedance network arranged to be interconnected to form a substation circuit, said impedance net''' work including three coupled inductance elements, two of said elements being connected in series, one of said elements being arranged to be connected in shunt with said transmitter, said receiver being arranged to be connected in shunt with a second of said elements, whereby substantially no audio frequency voltage is developed across said receiver during operation of said transmitter, an auxiliary sound reproducing unit including an input circuit, switching means for effectively disconnecting said receiver from said second inductance element and for coupling said input circuit to said second element, whereby substantially no audio frequency voltage is developed across said input circuit during operation of said transmitter when said input circuit is operatively included in said circuit, an impulsing device for transmitting impulses over said line and including a pair of normally open contacts, said contacts being arranged to be closed during operation of said impulsing device, and switching means for connecting said contacts to shortcircuit said receiver when said receiver is operatively included in said substation circuit and to short-circuit said input circuit when said input circuit is operatively included in said substation circuit.

9. A telephone substation adapted to be connected to a telephone line for conversation thereover and comprising, in combination, a. transmitter, a receiver, and an anti-side tone impedance network arranged to be interconnected to form a substation circuit, a member for supporting said receiver when not in use, switching means operative in response to the removal of said receiver from said supporting member for operatively including said receiver in said circuit, said anti-side tone impedance network being operative to prevent audio frequency energy generated by operation of said transmitter from being delivered to said receiver when said receiver is operatively included in said circuit, an auxiliary sound reproducing unit, said switching means being operative to exclude said reis supported by said supporting member, said switching means,

normally open contacts arranged to be closed during operation of said device, said switching means including contacts for connecting said first-mentioned pair of contacts to short-circuit said receiver during operation of said impulsing device and when said receiver is operatively included in said substation circuit and for connecting said first-mentioned pair of contacts to short-circuit the input circuit to said auxiliary sound during operation of said impulsing device and when said auxiliary sound reproducing unit is operatively included in said substation circuit.

10. A telephone substation adapted to be connected to a telephone line for conversation thereover and comprising, in combination, a transmitter, a receiver, and an anti-side tone impedance network arranged to be interconnected to form a substation circuit, said impedance network including three coupled inductance elements, two of said elements being connected in series, one of said elements being arranged to be connected in shunt with said transmitter, a member for supporting said receiver when not in use, switching means operative in response to the removal of said receiver from said supporting member for connecting said receiver in shunt with a second of said elements, whereby substantially no audio frequency voltage is developed across said receiver during operation of said transmitter, an auxiliary sound reproducing unit including an input circuit, said switching means being operative efiectively to disconnect said receiver from said second inductance element and to couple said input circuit to said second inductance element when said receiver is supported by said member, whereby substantially no audio frequency voltage is developed across said input circuit during operation of said transmitter when said input circuit is coupled to said second inductance element, and an impulsing device for transmitting impulses over said line, said impulsing device including a pair of normally open contacts arranged to be closed during operation of said device, said switching means including contacts for connecting said first-mentioned pair of contacts to short-circuit said receiver during operation of said device and when said receiver is removed from said supporting member and for connecting said first-mentioned pair of contacts to short-circuit the input circuit of said auxiliary sound reproducing unit during operation of said impulsing device and when said receiver is supported by said member.

11. A telephone substation adapted to be connected to a telephone line for conversation over said line and comprising, in combination, a sound reproducing unit, an input circuit for said unit, an input transformer including a primary winding and a secondary winding, said secondary winding being included in said input circuit, an impulsing device for transmitting impulses over said line, means for effectively short-circuiting said secondary winding during operation of said device, thereby to prevent said sound reproducing device from responding to current flowing through said secondary winding during operation of said device, and means for at least partially short-circuiting said primary winding during the operation of said impulsing device.

12. A telephone substation adapted to be connected to a telephone line for conversation over said line and comprising, in combination, a sound reproducing unit, an input circuit for said unit, an input transformer including a primary winding and a secondary winding, said secondary winding being included in said input circuit, an impulsing device for transmitting impulses over said line, a normally incomplete path for effectively short-circuiting said secondary winding for alternating or transient voltages developed thereacross, said path including a capacitance element, and means for completing said path during operation of said device, thereby to prevent said sound reproducing device from responding to alternating or transient voltages developed across said secondary winding during operation of said device.

13. A telephone substation adapted to be connected to a telephone line for conversation over said line and comprising, in combination, a sound reproducing unit including a vacuum tube ampliher and a translating device connected in tandem in the order named, an input circuit for said amplifier, a voltage amplifying transformer comprising a primary winding and a secondary winding, said secondary winding being included in said input circuit, an impulsing device for transmitting impulses over said line, a normally incomplete path for effectively short-circuiting said secondary winding for alternating or transient voltages developed thereacross, said path including a capacitance element, and means responsive to the operation of said impulsing device for completing said path thereby to prevent said sound reproducing means from responding to alternating or transient voltages developed across said secondary winding during operation of said impulsing device.

14. A telephone substation adapted to be connected to a telephone line for conversation-over said line and comprising, in combination, a sound reproducing unit including a vacuum tube amplifier and a translating device connected in tandem in the order named, an input circuit for said amplifier, a voltage amplifying transformer comprising a primary winding and a secondary winding, said secondary winding being included in said input circuit, an impulsing device for transmitting impulses over said line, a normally incomplete path for effectively short-circuiting said secondary winding for alternating or transient voltages developed thereacross, said path including a capacitance element, means responsive to the operation of said impulsing device for completing said path thereby to prevent said sound reproducing means from responding to alternating or transient voltages developed across said secondary winding during operation of said impulsing device, and means responsive to the operation of said impulsing device for at least partially short-circuiting said primary winding, thereby substantially to minimize the development of transient or alternating voltages across said secondary Winding during operation of said impulsing device.

15. A telephone substation adapted to be connected to a telephone line for conversation over said line and comprising, in combination, a sound reproducing unit including a vacuum tube amplifier and a translating device connected in tandem in the order named, an input circuit for said amplifier, a voltage amplifying transformer comprising a primary Winding and a secondary winding, said secondary winding being included in said input circuit, an impulsing device for transmitting impulses over said line, a normally incomplete path for effectively short-circuiting said secondary winding for alternating or transient voltages developed thereacross, said path including a capacitance element, means responsive to the operation of said impulsing device for compieting said path thereby to prevent said sound reproducing means from responding to alternating or transient voltages developed across said secondary winding during operationv of said impulsing device, means responsive to the operation of said impulsing device for at least partially short-circuiting said primary winding, thereby substantially to minimize the development-of transient or alternating voltages across said secondary winding during operation of said impulsing device, switching means for connecting said substation to said line, and contacts included in said switching means for completing said path when said substation is disconnected from said line.

16. A telephone substation adapted to be connected to a telephone line for conversation over said line and comprising, combination, a transmitter, a receiver and an anti-side tone impedance network arranged to be interconnected to form a substation circuit, a member for supporting said receiver when not in use, switching means operative in response to the removal of said receiver from said supporting member for operatively including said receiver in said circuit, said anti-side tone impedance network being operative to prevent audio frequency energy generated by operation of said transmitter from being delivered to said receiver when said receiver is operatively included in said circuit, an auxiliary sound reproducing unit including a vacuum tube amplifier and a translating device connected in tandem in the order named, an input circuit for said amplifier, a voltage am plifying transformer including a primary winding and a secondary winding, said secondary winding being included in said input circuit, said switching means being operative to exclude said receiver from said substation circuit and operatively to include said primary winding in said substation circuit when said receiver is supported by said supporting member, said switching means, said network and said primary winding being so connected and arranged that said network is operative to prevent audio frequency energy developed by operation of said transmitter from being delivered to said input circuit when said primary winding is operatively included in said substation circuit, an impulsing device for transmitting impulses over said line, means responsive to operation of said impulsing device for short-circuiting said receiver when said receiver is operatively included in said substation circuit and for efiectively shcrt-circuiting said primary winding when said primary Winding is operatively includedin said substation circuit, a normally incomplete path for effectively shortcircuiting said secondary winding for transient or alternating voltages, said path including a capacitance element, means responsive to the operation of said impulsing device for completing said path, and contacts included in said switching means for completing said path when said receiver is removed from said supporting member.

17. A telephone substation adapted to be connected to a telephone line for conversation over said line and ficomprisin g, in combination, a transmitter, a receiver and an anti-side tone impedance network arranged to be interconnected to form a substation circuit, a member for supporting said receiver when not in use, switching means operative in response to the removal of said receiver from said supporting member for operatively including said receiver in said circuit, said anti-side tone impedance network being operative to prevent audio ire-- quency energy generated by the operation of said transmitter from being delivered to said receive when said receiver is operatively included in said circuit, an auxiliary sound reproducing unit in cluding a vacuum tube amplifier and a translating device connected in tandem in the order named, an input circuit for said amplifier, a voltage amplifying transformer including a. primary winding and a secondary winding, said secondary winding being included in said input circuit, said switching means being operative to exclude said receiver from said substation circuit and operatively to include said primary winding in said substation circuit when said receiver is supported by said supporting member, said switching means, said network and said primary winding being so connected and arranged that said network is operativeto prevent audio frequency energy developed by operation of said transmitter from being delivered to said input circuit when said primary winding is operatively included in said substation circuit, an impulsing device for transmitting impulses over said line, means responsive to the operation of said impulsing device'forshort-circuiting said receiver when said receiver is operatively included in said substation circuit and for efiectively short-circuiting said primary winding when said primary winding is operatively included in said substation circuit, a normally incomplete path for effectively short-circuiting said secondary winding for transient or alternating voltages, said path including a capacitance element, means responsive to the operation of said impulsing device for completing said path, contacts included in said switching means for completing said path when said receiver is removed rom said supporting member, switching means for connecting said substation to said line, and contacts included in said switching means for completing said path when said substation is disconnected from said line.

18. Telephone substation apparatus adapted to be connected to a telephone line for conversatipn thereover and comprising, in com bination, transmitting means and receiving means adapted to be interconnected to form a substation circuit, said receiving means including an amplifier and a loud speaker connected in tandem in the order named, an input circuit for said amplifier, a receiver adapted to be used in lieu oi said receiving means in communicating over said line, and means for effectively short-circuiting said amplifier input circuit when said receiver is connected for use in communicating over said line,

19. Telephone substation apparatus adapted to be connected to a telephone line for conversation thereover and comprising, in combination, transmitting means and receiving means adapted to be interconnected to form a substation circuit, said receiving means including an amplifier and a loud speaker connected in tandem in the order named, an input circuit for said amplifier, a receiver, switching means operable selectively to connect said receiving means and said-receiver ior use in communicating over said line, and means including said switching means for effectively sliort-circuiting said amplifier input circuit when said receiver is connected for use in communicating over said line.

20. Telephone substation apparatus adapted to be connected to a telephone line for conversation thereover and comprising, in combination, transmitting means and receiving means adapted to be interconnected to form a substation circuit, said receiving means including an amplifier and a loud speaker connected in tandem in the order named, an input circuit for said amplifier, a receiver, a member for supporting said receiver when not in use, switching means operative in response to removal of said receiver from said supporting member, means including said switching means for selectively connecting said receiving means and said receiver for use in communicating over said line, and means including said switching means for rendering said amplifier input circuit ineliective to deliver alternating current energy to said receiving means.

21. Telephone substation apparatus adapted to be connected to a telephone line for conversation thereover and comprising, in combination, transmitting means and receiving means adapted to be interconnected to form a substation circuit, said receiving means including an amplifier and a loud speaker connected in tandem in the order named, an input circuit for said amplifier, a receiver, a member for supporting said receiver when not in use, switching means operative in response to removal of said receiver from said supporting member, means including said switching means for selectively connecting said receiving means and said receiver for use in communicating over said line, and means including said switching means for effectively short-circuiting said amplifier input circuit when said receiver is connected for use in communicating over said line.

22. A telephone substation adapted to be connected to a telephone line for conversation thereover and comprising, in combination, a transmitter, a receiver and an anti-side tone impedance network arranged to be interconnected to form a substation circuit, said anti-side tone impedance network being operative to prevent audio frequency energy generated by operation of said transmitter from being delivered to said receiver, an auxiliary sound reproducing unit including an amplifier and a loud speaker connected in tandem in the order named, an input circuit for said amplifier, switching means for substituting said input circuit for said receiver in said substation circuit, said network and the input circuit of said amplifier being so connected and arranged that said network is operative to prevent audio freqeuncy energy generated by operation of said transmitter from being delivered to said input circuit when said input circuit is operatively included in said substation circuit, an impulsing device for transmitting impulses over said line, and means controlled by said impulsing device for preventing audio frequency energy from being delivered to said input circuit during operation of said device.

23. A telephone substation adapted to be connected to a telephone line for conversation thereover and comprising, in combination, a transmitter, a receiver and an anti-side tone impedance network arranged to'be interconnected to form a substation circuit, said anti-side tone impedance network being operative to prevent audio frequency energy generated by operation of said transmitter from being delivered to said receiver, an auxilitary sound reproducing unit including an amplifier and a loud speaker connected in tandem in the order named, an input circuit for said amplifier, switching means for substituting said input circuit for said receiver in said substation circuit, said network and the input circuit of said amplifier being so connected and arranged that said network is operative to prevent audio frequency energy generated by operation of said transmitter from being delivered to said input circuit when said input circuit is operatively included in said substation circuit, an impulsing device for transmitting impulses over said line, said device including contact springs adapted to be operated into engagement during operation of said device, and means comprising a path shunting said input circuit and completed in response toengagement of said contacts for preventing audio frequency energy from being delivered to said input circuit during operation of said device.

24. A telephone substation adapted to be connected to a telephone line for conversation over said line and comprising, in combination, a sound reproducing unit including an amplifier, an input circuit for said amplifier, switching means for connecting said substation to said line, and means controlled by said switching means for efiectively short-cirouiting said input circuit when said substation is disconnected from said line.

.25. A telephone substation adapted to be connected to a telephone line for conversation over said line and comprising, in combination, a sound reproducing unit including an amplifier, an input circuit for said amplifier, switching means for connecting said substation to said line, and a low impedance path completed by contacts included in said switching means for effectively short-circuiting said input circuit when said substation is disconnected from said line.

JOHN HENRY VOSS.

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