US1567209A - Subscriber s equipment for program transmission - Google Patents

Description

Dec. 29,1925- 1,567,209

J. F. TOOMEY SUBSCRIBERS EQUIPMENT FOR PROGRAM TRANSIIISSION Filed Dec. 1. 1923 '&w a& aim l umw -Janmw 129mm m.hwJ J IN VEN TOR Patented Dec. 29, 1925.

UNITED STATES PATENT OFFICE.

JOHN F. TOOMEY, OF NEN YORK, N. Y., ASSIGNOR T0 AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

SUBSGRIBERS EQUIPMENT FOR PROGRAM TRANSMISSION.

Application filed December 1, 1923. Serial No. 677,992.

To all whom it may concern:

Be it known that 1, JOHN F. TOOMEY, residing at New York, in the county of New York and State of New York, have invented certain Improvements in Subscribers Equipment for Program Transmlssion, of which the following is a specification.

This invention relates to program trans mission over wires and particularly'to systems in which a program channel, employing audio frequencies, is superposed upon an ordinary subscribers telephone line.

It has been proposed to use ordinary subscribers telephone lines for program purposes by transmitting program currents over the lines at voice frequencles dur ng such times as the telephone line is not belng used for ordinary telephonic purposes. Under such circumstances, it is desirable that the program system be so superposed on the telephone line that the program apparatus will be disconnected either when a call comes in to the subscribers line or when the sub scriber desires to send out a call.

It is one of the objects of the present invention to so arrange the subscribers apparatus that a low impedance loud speaker may be used at the subscribers station for program purposes and may be disconnected 0 automatically as soon as the operator plugs into the subscribers line. The disconnection actually takes place before the l1ne 1s disconnected from the program equipment at the central office and connected to the calling jacks. This is a particularly desirable feature where machine ringing 1s employed, as the ringing current flowing through the low impedance loudspeaker might trip the machine ringing apparatus if the. loud speaker were not disconnected. Another object of the invention is to so arrange the subscribers circuit that the loud speaker will be disconnected at once upon taking the receiver from the switchhook of the telephone set. Other and further objects of the invention will appear more fully hereinafter; I

The invention may now be understood from the following description when read in connection with the accompanying drawings, Figures 1, 2 and 3 of which illustrate different modifications of the invention.

Referring to Fig. 1, L designates an ordinary telephone subscribers line terminating at the subscribers substation in the usual substation set 10. At the central oflice the subscrlbers line is connected over the contacts of the cut-off relay CO to the primary of a transformer 11, the secondary of which is 111 circuit with a trunk T leading to a program station. The line relay LR is connected 1n circuit with the primary winding of the transformer 11, as shown, and the usual line lamp 12 is controlled by the line relay. The cut-off relay CO is so arranged that when operated in response to the insertlon of a plug in jacks such as J and J the line L will be disconnected from the program circuit and connected to the switchmg jacks.

At the subscribers station the loud speaker 13 is arranged to be bridged across the subscribers line L over a contact of the swltchhook 14: and over a contact controlled by a high resistance relay R. The relay R is also bridged across the subscribers line upon the actuation of the contact 15 of a nonlocklng key K, the relay R being locked up when once actuated and thereby maintaining the loud speaker in connection with the subscribers line. The circuit of the high resistance relay R is arranged so that it will be opened immediately upon inserting a plug in a calling jack at the central office and before the cut-off relay has had time to operate and connect the subscribers line to the calling jacks. The high resistance relay is therefore immediately unlocked and'deenergized to open the loud speaker circuit. The relay R will also be unlocked in a similar manner by taking the receiver ed the switchhook to initiate a telephone call at the subscribers station or by actuating the contact 16 of the non-locking key at the end of the transmission of the program.

The operation is as follows: If the subscriber desires to receive program trans mission he momentarily actuates the nonlocking key to close the contact 15. This completes a circuit for the high resistance relay It from battery at the central oiiice over the back contact of the relay S, through the right-hand winding of the line relay LR, over the lower back contact of cut-ofi relay CO, ring side of the line L, over switchhook contact 1 1, normally closed contact 16 of key K, momentarily closed contact 15 of key K, through the winding of the relay R, over the tip side of the line L, upper back contact of cut-01f relay CO and through the IOU right-hand winding of the line relay LR to ground. The relay R is actuated over the circuit above traced but the resistance of said relay is so high that it does not permlt the line relay LR to be actuated. The relay R- is locked up over its inner front contact independently of the contact 15, wh1ch is opened as soon as the key K is released. At its outer front contact relay R closes a bridge circuit 17 through the loud speaker 13 and over the contact 14: of the switchhook.

In order to prevent the low impedance loud speaker 1.3 from actuating the line relafy LR, a condenser 18 is inserted in series therewith. The subscribers line is normally connected over the back contact of the cut-off relay CO and through the transformer 11 to the trunk T leading to the program source and consequently the circuit is now in condition to receive the program transmission.

If, while the line is being used for program purposes, a call comes in for the subscribers station the operator inserts a plug in one of the multiple jacks J or J, thereby closing a circuit over the sleeve of the jack for the relay S. The relay S, upon being energized, attracts its armature and disconnects battery from the ring side of the line L so that the relay R is at once released and unlocked, at the same time opening the circuit of the loud speaker 13. The relay S, at its front contact, closes a circuit for the cutoff relay CO, which disconnects the line L from the trunk T and connects it to'conducto'rs leading to the multiple jacks J and J. Battery is now supplied over the ring side of the line through the cord circuit but as the relay R has been unlocked it will not be again actuated 'since the contact 15 of the non-locking key K is open.-

It will be seen that the relay R is released to open the circuit of loud speaker '13 before the line L is actually connected to the answering jacks and consequently there is no possibility that ringing current will pass through the loud speaker 13.

In case the subscriber should desire to initiate a call while the line is being used for program receiving he merely takes the receiver off the switchhook, thereby opening the contact 14, which causes the relay R to be released and unlocked, thus opening the circuit 17 through the loud speaker 13. The line relay LR Will be operated through the low resistance path of the subscribers set 10 and will cause the line lamp 12 to glow. The operator, in response to the line lamp, inserts an answering plug in one of the jacks J or J, with results already described.

When the subscriber is receiving program transmission and desires to be disconnected from the program station he simply presses the non-locking key K to momentarily open the contact 16, thereby releasing the relay R and unlocking the same. The relay R in turn opens the circuit of the loud speaker 13 so that the program transmission can no longer be heard.

A modification is shown in Fig. 2, in which the loud speaker circuit includes an amplifier. The amplifier comprises a vacuum tube 19 of the usual type, having its plate circuit connected through a trans former 20 to the loud speaker 19. Its grid circuit is connected through a transformer 21 to the bridge circuit 17 of the subscriber's set. In order to provide operating currents for the amplifier, a transformer is provided having a primary winding 22 connected to suitable A. G. power mains and having secondary windings 23, 21 and 25. The secondary winding steps down the voltage to a value such, for example, as six volts, suitable for operating the filament of the amplifier 19. The secondary winding 21:, on the other hand, steps the voltage to a value such, for example, as 110 volts. suitable for supplying the plate current of the amplifier 19.

In order to rectify the plate current a vacuum tube rectifier 26 is provided. The grid and plate of this tube may be connected together to form the positive electrode while the filament, as usual, constitutes the negative electrode. The discharge path of the tube is connected in series between the secondary 24 and .the plate of the tube 19. The filament of the tube 29 is supplied with current through the secondary 25. which'steps'down the voltage to a. value such, for example, as six volts, suitable for the filament supply.

In order to smooth out the rectified current supplied to the plate of the tube 19 a choke coil 27 is included in series with the plate and, if desired, a condenser 28. may be shunted across the plate circuit to by-pass the high frequency components. In order to eliminate, so far as possible, the noise of the A. G. current supplied to the filament of the tube 19, the plate of said tube is connected through a condenser 29 and the resistance 30 to the midpoint of the secondary 23.

The circuit arrangement of the remainder of the subscribers set and the circuits at the central ofiice are the same as those de scribed in connection with Fig. 1, and the operation is also the same, the only difference being that the amplifier 19 amplifies the program transmission received in the circuit 17 before impressing it upon the loud speaker 13. The operation of the amplifying equipment will be obvious from the description already given and it will be understood that when the program equipment is not in use the leads from the amplifier to the power mains will be opened by a suitable switch.

Fig. 3 illustrates a similar arrangement differing from that of Fig. 2 only in that the amplifier is supplied from direct current power mains. As in the case of the amplitier of Fig. 2, the amplifier in Fig. 3 consists of a vacuum tube 19, having its output circuit connected through a transformer 20 to a loud speaker 13 and its grid circuit con nected through a transformer 21 to the bridge circuit 17. In this case, however, the connection to the bridge circuit is made through a potentiometer 31 of well known construction. The grid or C battery may be supplied from dry cells and the same holds true for the plate current. The filament current, however, is supplied from direct current power mains through a resistance 32. The remaining apparatus, both at the central oflice and at the substation, is similar to that of Fig. 1 and operates in the same manner. As the operation of the amplifier is obvious no description of the circuit operation is necessary.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated without departing from the spirit of the invention as defined in the following claims.

\Vhat is claimed is:

1. In a program system, a telephone line having switching terminals, means to connect said telephone line to a program station, program receiving equipment associated with said telephone line, means controlled by a subscriber for connecting said receiving equipment to the line and means responsive to the establishment of a telephone connection to the switching terminals of the line for automatically disconnecting said receiving equipment and thereafter connecting the line to the switching terminals.

2. In a program system, a subscribers telephone line, means for connecting said line to a program station, program receiving equipment associated with said line, means including a relay that can be operated under the control of the subscriber for c011- necting said receiving equipment to the line, switching terminals for the line, and means responsive to the establishment of a connection to said switching terminals for releasing said relay to disconnect the receiving equipment and for thereafter connecting the line to the switching terminals.

3. In a program system, a subscribers telephone line, connections from said line to a program station, program receiving equipment associated with said line, a relay for connecting said receiving equipment to the line, means controlled by the subscriber for operating and locking up said relay, switching terminals for the line, and means responsive to the establishment of a connection to said switching terminals for momentarily disconnecting battery from the line, thereby releasing and unlocking said relay, and means for thereafter connecting the line to the switching terminals.

i. In a program system, a subscribers telephone line, a. cut-off relay, means for connecting said line over the contacts of said cut-off relay to a program station, program receiving equipment adapted to be bridged across the subscribefis line, a relay for establishing said bridge, means under the control of the subscriber for establishing a circuit through said last mentioned relay over the line conductors to a source of current at the central office, Witching terminals for said line at the central office, means responsive to the establishment of a connection to said switching terminals for disconnecting said current source from the line to release said last mentioned relay and disconnect said program receiver, and means for thereafter actuating the cut-off relay to establish a connection from the line to said switching terminals.

5. In a program system, a subscribers telephone line, means to connect said subscribers line to a program station, program receiving equipment adapted to be bridged across said line, said equipment including a loud speaking receiver and an amplifier, means to bridge said equipment across the subscribers line under the control of the subscriber, switching terminals for said line, and means responsive to the establishment of a connection to said switching terminals for opening the connection to said receiving equipment and thereafter connecting the line to said switching terminals.

In testimony whereof, I have signed my name to this specification this 30th day of November, 1923.

JOHN F. TOOMEY.

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