US1394190A - Testing system for four-wire circuits - Google Patents

Description

C. S. .DEMAREST. TESTING svsrsm roa FOUR-WIRE cmcuns.

APPLICATION FILED JULY 24 I920 1,394,190, Patented Oct. 18, 1921. 4 SHEETS-SHEET l- I INVENTOR v afianamsl ATTORNEY C. S. DEMAREST. TESTING SYSTEM FOR FOUR-WIRE CIRCUITS. APPLICATION- FILED my 24, I920.

Patented Oct. 18, 1921.

. 4 SHEETS-SHEET 2- INVENTOR 6: J: fiend/at BY ATTORNEY C. S. DEMAREST.

TESTING SYSTEM FOR FOUR-WIRE CIRCUITS. APPLICATION FILED JULY 24, 1920.

1,394,190, Patented 061:. 18, 1921.

4 SHEETSSHEET 3.

INVENTOR 653911022216 BY ATTORNEY 0. s. DEMAREST. TESTING SYSTEM FOR FOUR-WIRE CIRCUITS. APPLICATION FILED JULY 24; I920.

Patented Oct. 18, 1921.

4 SHEETS-SHET 4.

INVENTOR 63 Jim;

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ATTORNEY UNITED STATES,

PATENT OFFICE.

CHARLES S. DEMAREST, OF RIDGEWOOD, NEW JERSEY, ASSIGNOR TO AMERICAN TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

TESTING SYSTEM FOR FOUR-WIRE CIRCUITS.

Specification of Letters Patent.

Original application filed February 24, 1919, Serial No. 278,945. Divided and this application filed July 24, 1920. Serial No. 398,657.

To all whom it may concern:

Be it known that I, CHARLES S. DEMAREST, residing at Ridgewood, in the county of Bergen and Stateof New Jersey, have invented certain Improvements in Testing Systems for Four-Wire Circuits, of which the following is a specification.

This invention relates to telephone transmission systems and more particularly to means for controlling the connection of telephone repeaters to a four-wire telephone transmission circuit, and for testing the efliciency of such type of circuit.

This application is a division of my copending application, Serial No. 278,945, filed February 24, 1919.

Heretofore it has been customary to connect the repeaters into the four-wire repeater circuit, and to maintain such connection permanently, regardless of the nature of the circuit that may be connected with each end of the said four-wire circuit. The telephone repeaters connected with a four-wire circuit are usually designed and operated to give an amplification that will compensate notv only for the loss in the four-wire circuit itself, but also for the losses in the telephone trunk lines that may ordinarily be connected with the said four wire circuit. lVhen such a circuit is completely connected from subscriber to subscriber, the repeater is balanced and will operate satisfactorily, that is, without singing. It has been found that whenever an operator connects her telephone set with such circuit for the purpose of supervising such connection, an unbalanced condition is created and the repeaters begin to sing, thereby impairing the transmission over the circuit.

It is the object of this invention to provide a testing circuitthe function of which is to determine whether the repeaters are operating properly so as to produce the desired transmission gain.

This invention will'be better understood from the following description, when read in connection with the attached drawing of which Figure 1 shows a cord circuit at, for example, a toll oflice to connect the incoming trunk circuit with the four-wire repeater trunk shown in Fig. 2, which for purpose of description, is assumed to extend between two toll oflices; Fig. 3 shows a cord circuit at the other of said toll ofiices to connect said repeater trunk with circuits of the type with whlch the repeater circuit is designed to cooperate. Fig. 4 shows a testing circuit by means of which the repeaters shown in Fig. 2 may be tested. The complete circuit may be clearly seen by arranging all the Figs. 1, 2 and 3 so that the bottom edge of Figs. 2 and 8 coincide respectively with the top edge of Figs. 1 and 2. Fig. 4 should be arranged symmetrically below Fig. 2.

Fig. 1 shows a cord circuit at the toll board E terminating in a plug P adapted to beinserted in the jack J 8 of the testing circult shown in Fig. 4 and also in a plug P, adapted forinsertion in either jack J 4 or jack J of the toll circuit shown in Fig. 2.

Fig. 2 shows a four-wire repeater trunk circuit extending between two toll ofiices, designated-E and F, and terminating at each of these offices in two jacks. The four-wire circuit is of the usual type, having two twowire branches which are electrically related by means of the hybrid repeating coils X and Y. Associated with coil X are two networks N and N the former. being adapted to balance the circuit connected with jack J and the latter being designed to control the transmission gain when the repeater is connected through the jack J with a circuit having a lower transmission equivalent than that connectedwith the jack J When a circuit is connected with jack J both networks are connected into the repeater circuit. In a similar manner coil Y has associated with it two networks N and N N being adapted to balance the circuit connected with jack J and N, functioning as a gain control network for a circuit connected with jack J Each group of jacks at either end of the four-wire circuit has associated with it a group of relays controlled by the circuits connected with said jacks and adapted to control relays 25 and 26 of the repeater circuit which, in turn control the connection of the repeaters to the branches of the fourwire circuit, and the connection of the heater batteries with the filaments.

Fig. 3 shows a cord circuit located at the toll ofiice F terminating in two plugs P and P P being adapted for insertion in jacks J and J of the four-wire trunk circuit and plug 1? being adapted for insertion injack J 9 of the testing circuit shown in Fig. 4.

'ofiice F and likewise plugs Fig. 4 shows the repeater testing equipment which is preferably though not necessarily located inithe same office in which the repeatershown in F ig. 2 is located and is connected by means or ring-down trunks 67 and 68 with the switchboards at the toll oflices E and F terminating therein in jacks J and J respectively;

known type, has the same transmission equivalent as the four-wire circuit has when the repeaters are disconnected. A swltch 74 is provided for connecting the oscillator 70 with either end of the repeater circuit or'of the artificial line 72. A switch 75 is provided to connect the oscillator and the receiver alternately with the transmission circuit and with the artificial line;

In order to'test the repeater, plug P is inserted in j ack J and plug P in jack J Plug P is inserted in jack J 8 at toll oflice E and plug'P is inserted in iack J, at toll 4 and P are inserted in jacks J and 5 respectively. Relay 12 of the'cord circuit at ofiice E and relay 37 or" the cord circuit at ofiice F will be operated,and if thekeys in both cord circuits are normal the repeaters 59 and 60 will be energized in the manner shown clearly in my'copending application, Serial No. 278,945, filed February 24, 1919. If key 74 of the testing circuit is operated in the left hand direction an alternating electromotive force will be applied over contacts of keys 74 and f 7 6, tip and ring contacts of plug P and jack J trunk 67, over the tip and ring conductors of the cord circuit at oifice E,through branch 77 of the four-wire repeater circuit including the repeater 59, over the con- 7 ductors of the cord circuit at ofiice F andthe conductors of trunk 68, tip and ring contacts of jack J and plug P right hand normals contacts of switches 76 and 74,

through receiver shunt 73 to the receiver 71.

Switch 75 is'now operated, thereby causing the operation of relays 79 and 80, which disconnects the" source of tone 70 and the receiver' 71 from the trunk circuits 67 and 68, respectively, and connects said source of tone toone end ofthe artificial line 72, and the receiver 71 to the other end of said artificial line. o.

e The receiver shunt 73 is gradually varied o until the volume of tone received in the receiver 71; when the receiver is connected across the artificial line IS the same as when and the plug it is connected across the trunk leading to one end of the four-wire repeater circuit.

If the switch 74' is thrown "in. the right hand direction the source 'of alternating of jack J and plug P left hand contacts of switches 76 and 74, receiver shunt 73 to receiver 71. By operating switch 75 in the manner heretofore described thevibrator 70 and thereceiver and receiver shunt are alternately connected with the four-wire circuit and with the artificial line, and shunt 73 is varied until the volume of tone in the receiver 71' when the receiver is connected with the artificial line is the same as when connected with the four-wire repeater circuit. The reading upon the scale of the receiver shunt represents the transmission gain due 'to the presence of repeater 60 in the circuit.

By insertin the plug. P, in the jack J 5 in the jack J it; will be noted that there has been included in the four-wire transmission circuit the networks N and N and consequently the artificial line 72must have the same impedance as the four-wire circuit including the said networks but having the repeaters disconnected. If, however, the said plugs'are inserted in jacks J and J respectively, the networks are not included in the said four-wire circuit (as has been shown in my copending application, Serial No. 278,945,- filed' February 24, 1919) and consequently the artificial line 72 must be adjustedso as to have the same characteristic impedance as the four-wire circuit without the networks N and N and with the repeaters disconnected;

From the foregoing description'of the apparatus in which this invention is embodied and of its mode of operation, it will be seen that this invention provides a simple and eificient'method' for'determining the im provement in transmission due to the connection of the repeaters 1n the four-wlre transmlsslon clrcult. Although th1s invenelectromotive force will be applied to the tion is shown as embodied in the single form, it is apparent that itis capable of em bodiment in other andvaried forms without departing from the spirit and scope of the appended claims. 7 7

'l/Vhat is claimedis: V

1. In a telephone system, the combination ofa four-wire repeater trunkcircuit,-having telephonic repeaters associated therewith but normally disconnected therefrom, a testing circuit comprising an artificial line having a transmission equivalent equal to that of the repeater trunk circuit when the said repeaters are disconnected, and link circuits for connecting said repeater circuit with said testing circuit, the said testing circuit being adapted to apply an alternating electromoti-ve force or" telephonic frequency alternately to one end of said circuit and to one end of said artificial line, a receiver and a measuring device adapted to be alternately connected with the other end of said repeater trunk circuit and with said artificial line, whereby the tones received in said re ceiver may be compared as to magnitude.

2. In a telephone system, the combination with a four-wire transmission circuit having repeaters associated therewith but normally disconnected therefrom, a testing circuit, link circuits having a plurality of keys associated therewith arranged to connect the said four-wire circuits with the said testing circuit, and switching means for effectively connecting the said repeaters with the said four-wire circuit when the said link circuits are connected with their respective associated circuits and all but one of said keys are in their unoperated positions.

3. In a telephone system, the combination with a four-wire repeater circuit of testing trunk circuits, link circuits for connecting each end of the said repeater circuit with its corresponding testing trunk circuit, an artificial line having the same transmission efiiciency as the said four-wire circuit when the repeaters are disconnected therefrom, a source of testing potential, a measuring device and means to connect both the said source and the said device alternately with the said testing trunks and with the said artificial line.

, 4. In a telephone system, the combination with a four-wire repeater circuit having a plurality of repeaters associated therewith but normally disconnected therefrom, of a gain testing circuit and a plurality of link circuits for connecting the said repeater circuit with the said testing circuit, the link circuits having means associated therewith for controlling the connection of the said repeaters with the said four-wire circuit.

5. In a telephone system, the combination with a four-wire repeater circuit having line balancing networks and gain control networks assoeiated with each end thereof, the said four-wire circuit terminating in a plurality of jacks at each end, of a testing circuit having an artificial line of adjustable impedance associated therewith, link circuits adapted to connect the said testing circuit with the said four-wire circuit, and to control the connection of the said gain control networks with the said four-wire circuit.

6. In a telephone system, the combination with a four-wire repeater circuit having a plurality of repeaters associated therewith but normally disconnected therefrom and also line balancing networks and gain control networks associated therewith, of a testing circuit having an artificial line whose impedance may be Varied, and also a source of electromotive force and a gain measuring device associated therewith, and link circuits for connecting the said four-wire circuit with the said testing circuit and adapted to control the connection of the said repeaters and also of the said gain control networks with the said four-wire circuit.

In testimony whereof, I have signed my name to this specification this twenty-first day of July, 1920.

CHARLES S. DEMAREST.

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