US1504406A

US1504406A - Signaling system

Info

Publication number: US1504406A
Application number: US466932A
Authority: US
Inventors: White Charles
Original assignee: Western Electric Co Inc
Current assignee: AT&T Corp
Priority date: 1921-05-05
Filing date: 1921-05-05
Publication date: 1924-08-12
Anticipated expiration: 1941-08-12

Description

mlg., y C. VVHKTE SIGNALING SYSTEM Filed May 5. 1921 2 mmm-Smm 1 ABE Lwm@

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AC3. WHIITE SIGNALING SYSTEM .2 Emma-www 2 Filed' May 5. 192k Patented .it-tug. i2, i924.

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CHARLES WHITE, OF EAST ORANGE, NEVI JERSEY, .[iSSG-NOR TO /VES'IERN ELEOTBJIC COMPANY, INCORPORATED, F NEVI YORK, N. Y., A COR'QRATION OF NEWT YRK.

SIGNALNG- SYSTEM.

Application filed May 5,

To all whom t may concern:

Be it known that l, CHAnLns VVrIr'rn, a citizen of the United States, residingiatltast Grange, in the county of Essex and State of New Jersey, have invented certain new and useful Improvements in Signaling Systems, of which the following is ar full, clear, concise, and exact description.

This invention relates to signaling systems having separate transmission circuits for oppositely directed signals, commonly known as four-wire systems, and more particularly to such systems wherein means are provided at an intermediate station for the operator or attendant to listen-in and to conmiunicate thereover, if desired.

ln ordinary telephone systems and in carrierv wave signaling systems which terminate in two-wire low frequency telephone lines, it has been customary to provide means for the operator or attendant to listenin and, if need be, to communicate over the systems. For the purpose of listening-in on those systems a. telephone receiver with suitable apparatus is connected across the. low frequency line by means of a monitoring key. For communication purposes a micro-phone circuit can be connected to the low frequency line in any suitable way, preferably by means of a patching cord.

3y this invention means is provide wheren by an operator or attendant may listen in on a four-wire telephone line, or on a fourivire low frequency termination of a carrier wave signaling system. Means is also provided whereby the operator or attendant may communicate over the system if desired.

@ne object of the invention is to provideJ means for listening-in and communie-ating over a four-wire low frequency telephone line. Another object is to provide means of this kind at a four-wire termination of a carrier wave signaling system. Still another object is to provide monitoring system wherein the operator or attendant can listen-in on both pairs of the four-wire line simultaneously. Ar feature of the invention is the use of a conjugate transformer Vto accomplish the above results. An other feature is the .provision of a relay arrangement for automatically associating the microphone with lthe proper pair of' the four-wire line 1921. Serial No. 456,932.

for talking and the receiver with the proper pair, for receiving when communicating` over the system. Still another feature is the provision of a system which can be used for communicating either over a fonrsvire system or a. two-wire system.

in one embodiment of the invention a carrier wave signaling system terminates in a four-wire low frequency telephone line. By means of a hey, a conjugate transformer or hybrid coil and a plug and jack arrangement, a tele-phone receiver and a microphone are adapted to be connected to the low frequency line. The arrangement is such that an operator or attendant may listen-in on bot-h pairs of conductors simultaneously without causing interference therebetween or he may communicate either over the carrier system or over the four-wire low fre quency line. Aln order to insure that his receiver and microphone will each be connected to the proper pair of conductors, an automatic relay switching system is provided. Further provision is made for using the same system in connection with a twoway carrier channel and its associated low frequency line.

rthe invention will now be described more in detail with reference to the accompanying drawings. Fig. l shows the preferred form of the invention as embodied in a four-wire carrier wave terminal station. Fig. la illustrates a two-way carrier terminal with twoe wire low frequency termination located at the station of F l with which the arrangement of l is adapted to be used. Fig. 2 shows another embodiment also adapted for use in a. four-wire system. it is to be understood that th-e detailed description does not limit the invention to the precise embodiments illustrated. Y

Referring now to Fig. l of the drawing, a. four-wire low frequency telephone line, comprising one pair of conductors 5 and another pair G, is connected by means of a. carrier wave terminal station to a common transmission line l/iL, rEhe conductors 5 terminate in a pair of jacks 7. The transmitting circuit TC of the carrier terminal station terminates, on the low frequency side, in jacks 8 and, on the high frequency side, at the bridge connections of balanced transformer 9. A balancing network HFPL to balance the main line ML, is also connected to the balanced transformer 9 in a well-known manner. Jacks 7 and 8 are connected'together in such a way as normally to furnish a continuous circuit between conductors and transmitting circuit TC. Conductors 6 terminate in acks 10. Receiver circuit RC is connected, on the low frequency side, to jacks 11 and on the high frequency side to the series'winding of the balanced transformer 9. Jacks and 11 are so connected together that normally a continuous thej dotted lines 17. Y

vchannel Vis shown, but any number may be circuit is provided between conductors 6 and the receiver circuit RC.

' The other end of the four-wire low frequency line 5 6 terminates in a two-Wire ordinary telephone exchange or subscribers stat-ion'A. The conductors 5 and 6 are conjugately connected to station A through the balanced transformer 12 with its low frequency balancing network LFN. This is a well-known arrangement and needs no further descriptio-n.

In the transmitting circuit TC is a modulator M, an oscillator O, a modulator band filter MBF, and an input transformer 15. The oscillator O functions as a source of carrier Waves for this channel. VThe receiver circuit comprises a detector band -filter DBF, a detector D, a detector amplifier DA, a low pass filter LPF yand a transformer 16. f

The modulator M, the oscillator C, the detector D and the detector amplifier DA. may be of any suitable design, but preferably comprise three electrode thermionic vacuum discharge devices. The modulator band filter MBF Iand detector band filter DBF are broad band-pass filters of the general type described in Patents Nos. 1,227,113 and 1,227,114 to G. A. Campbell, May 22, 1917. These filters are adapted to .pass a band of frequencies equal to the quency and of all lower frequencies,

Connections for additional transmitting channels are indicated by the dotted lines 16, and additional receiving channels by Only one additional inserted in a. similar manner.

In the operation of this system `a terminal Vstation similar to the one illustrated is located at the distant end of the common line ML.V The receiving circuit of that station is adapted to cooperate with the transmitting circuit of the terminal illustrated, while the transmitting circuit of the distant station is adapted to cooperate with the receiving circuit of Fig. 1.

A message may be transmitted from the station A to the distant cooperating station as follows:

Voice currents originating at station A are transmitted by the balanced transformer 12 and conductors 5 through normally closed contacts of jacks 7 and 8 and the transformer 15 to the modulator M. In the modulator M carrier waves from the oscillator C are modulated by the incoming voice current-s and transmitted from the modulator through the modulator band filter MBF and the balanced transformer 9 to the main lin@ ML. Assuming now for purposes of description that the station of Fig( 1 is `the cooperating distant station, the modulated carrier waves from the common line ML are transmitted to the receiving` circuit RC by the balanced transformer 9 through the detector band filter DBF to the detector D. In the system illustrated both the modulated and unmodulated currents are transmitted to the common line ML and received therefrom. In the detector D the modulated and unmodulated currents are combined to produce the original voice currents which are amplified in the detector amplifier DA and transmitted through the low pass filter LPF, transformer 16, normally closed contacts of jacks 11 and 10, conductors 6 and the balanced transformer 12 to the station A.

In order to provide for 'monitoring or listening-in by the operator or attendant at the carrier termin-al station, a monitoring key K and a conjugate transformer or hybrid coil 2O are used to associate a telephone receiver 26 with the low frequency conductors of each of the transmitting` circuit TC and the receiving circuit RC. When key K is operated, conductors 2l bridged across the transmitting circuit TC are connected through the upper closed contacts (normally open) of key K and the transformer 22 to the series winding of hybrid coil 20. Conductors 2B which are bridged across the receiving circuit RC are connected through the lower closed contacts (normally open) of key K and the transformer 24 to the bridge terminals of hybrid coil 20. Ilelay 25 is operated by the operation of key K due to the closing of the energizing circuit of relay 25 at the lowest closed contact (normally open) of key K. This circuit may be traced from the ground side of battery 27, through battery 27, winding of relay 25, lowest closed contact (normally open) of lrcy K to ground. The operation of relay 25 connects receiver 26 with the line terminals of hybrid coil 20 at the closed front contacts (normally open) of relay 25. Across the opposite line terminals of hybrid coil 2O is connected an impedance 23 which balances the impedance oliE receiver 26. With the key K in its normal position, receiver 26 and hybrid coil 2O are disconnected from the carrier terminal apparatus.

By means ot the monitoring[circuit just described an operator listening in at the receiver 26A can hear what is going on on either the transmitting circuit TC or the receiving circuit RC, but dueto the conjugacy of hybrid coil 20, current in conductors 2l has no effect upon conductors 23 and vice versa. Consequently, a monitoring system is provided for a tour-wire low frequency telephone circuit whereby an operator muy listen-in simultaneously on each pair ot conductors without causing interference between the pairs ot conductors.

.ln order to provide tor communication over the system by the operator or attendant, the aplaratus now to be described is provided. y

For receiving` purposes, receiver 26 is connected to jacks 3l through the normally closed back contacts ot relay 25, normally closed contacts ot key KT and the normally closed haci( contacts ot relay 32. AFor talking purposes, microphone is associated with jacks 34 through an induction coil normally closed contacts of ringing vkey RK and normally closed back contacts ot relay 36. ln order to provide for call signaling by the operator, a source ot ringing current 37 is adapted to be impressed upon `the system hy means of ringing key RK. A twoconductor cord 3S, terminating in plugs 39 and 40 is adapted to patch the circuits terminating' in jacks 3l to those terminating` in either jacks 7 or 8. The three-conductor cord 4l, terminating in plugs 42 and 43 is adapted to patch the circuits terminating in jacks 34 to those terminating in either jacks l0 or ll.

Relays 32 and 36 Aare provided to automatically interchange jacks 31 and 34 with respect to the receiver 26 and the micro phone 33. ln the normal position ot' relays 32 and 36, receiver 26 is connected to jacks 31, and `microphone 33 to jacks 34 over' the circuits hereinhetore traced. lWhen relays `32 and 36 are actuated, receiver 26 is connected to jack 34 through the normally closed hack contacts of relay 25, normally closcd contacts ot key KT and the closed itront contacts (normally open) of relay 32, while the microphone 33 is connected to jacks 3l through the induction coil 35, the normally closed contacts of ringing key RK and the closed front contacts (normally open) ot relay 36.

The operation of communi-eating Jfrom the carrier terminal station to the station A will. now be described. Jacks 3l and 7 arr patched together loy means et cord 38 hy the insertion of pings 39 into jacks 'i' and plugs 40 into jacks 31. Jacks l0 and 34 are patched together by means ot cord 41 by the insertion off plugs 43 into jacks 16 and plugs 42 into jacks 34. it message originating at station fi. is transmitted to receiver 26 through the conjugate transformer l2, conductors 5, tip connections of jacks 7 and plugs 39, conductors ot cord 33, tip connections of plugs 40 and jacks 3l, normally closed back contacts of relay normally closed contacts of key KT and normally closed back contacts ot relay A. message originating at the carrie-r terminal station in microphone is transmitted to station A through the induction coil 35, normally closed contacts of ringing key ltli, normally closed back contacts ot relay tip connections oit jacks 34 and plugs 42., tip conductors of cord 4l, tip connections of plugs 43 and jacks l0, conductors 6 and bridge connections ot conjugate transformer l2. The insertion of plugs 39 in jacks T and plugs 43 in jacks lO, disconnects the conductors 5 and 6 trom the carrier transmitting circuit TC and receiving circuit it@ respectively at the open contacts (normally closed) ot jacks and 10.

In the event that the opera-tor a t vthe carrier station wishes to communicate by means of carrier wave transmission over the main line ML instead of with the station plugs 39 are withdrawn from jacls 7 and inserted in jacks' 3 and plugs 43 are withdrawn from jacks l() and inserted in jacks il. The insertion of plugs 43 in jacks ll causes the operation of relays 32 and 36 so that re ceiver 26 is now connected to the receiver circuit RC and the microphone 33, to the carrier transmitting circuit TC. The energizing circuits' ot relays 32 and 36 entend from the ground side of batteries 44 and 45 respectively, through those batteries, wind ings of relays 32 and 36 in parallel to the normally closed left-hand contact ot' key KT, through the sleeve contacts ot jacks 34 and plugs 42, through the sleeve conductor of cord 41, the sleeve contacts ot plugs 43 and jacks 1]., and the resistance 46 to ground.

The message circuit between the carrier terminal station and a distant cooperating station may he traced as follows:

A, message originating in the microphone 33, after passing through the induction coil 35, normally closed contacts oit ringing key RK, closed front contacts (normally open) oft relay 36, tip connections ot' jacks and plugs 40, conductors ot cord 33, tip connections of plugs 39 and jacks 8 and trans ltormer 15, modulates the carrier current `trom oscillator From the modulator M it passes through the band filter li/BF and the conjugate transformer 9 as modulated llO energy to the main line ML. Modulated energy incoming from the main line ML passes through the conjugate transformer 9 and detector band filter DBF to the de tector D, where the originating voice currents are detected. vafter amplification by the detector amplifier DA, they pass through the low pass filter LPF, transformer 16, tip connections of jacks 11 and plugs 43, tip conductorsy of cord Ll1, tip connections of plugs 42 and jacks 84e, closed front contacts (normally open) of relay 32, normally closed right-hand contacts of key KT, and normally closed back conta-cts of relay 25 to the receiver 26.

Tf the operator should by any chance interchange plugs 89 and 48 by inserting plugs 89 in jacks 11 and plugs 48 in jacks 8, relays 32 and 36 would not be operated since there would be no ground connection from the sleeve of jacks 8. Still the message cirrcuit would be correct since the microphone 83 would be connected to the carrier transmitting circuit TC and the receiver 26 would be connected to the carrier receiver circuit RC. The transmitting circuit, under this condition, may be traced from the microphone 38, through the induction coil 35, the normallyl closed contacts of ringing key RK, normally closed back contacts of relay 3G, the tip connections of jacks 811- and plugs 42, tip conductors of cord 4:1, tip connections of plugs 113 and jacks 8, which jacks constitute the terminal of' the transmitting circuit TC. The receiving circuit may be traced from the receiver 26 through the normally closed back contacts of relay 25, vthe normally closed right-hand contacts of key KT, the normally closed back contacts of relay 82, tip connections of jacks 31 and plugs 40', conductors of cord 38, tip connections of plugs 89' and jacks 117 which jacks constitute the termination of the receiving circuit RC.

ln order to provide for communication from the carrier terminal station over a two-wire low `frequency line or over a twoxvay carrier channel terminating on the low frequency side in a twoiwireV line, key KT provided. lts use will be described hereinafter 'in connection with Fig. l?.

In Fig. 2, a modified system is provided whereby an operator or attendant at a carrier terminal station mayvcommunicate in either direction over the four-wire system of Fig, 1. Like reference characters in all of the figures are used to designate like elements.

The connections of relays 32 and 36to jacks 31 and 34 in Fig. 2, are identical with the connections of these elements in Fig. 1. Instead of connecting lthe receiver directly to the armature contacts of relay 82 and the transmitter directly to the armature contacts of relay 35, an operators subset comprising a microphone 51, a receiver 52 and an induction coil 53 are associated with the armature conta-cts of relays 32 and 3G through the conjugate transformer 50. The operators subset is connected to one set of line terminals of the transformer 50 and is balanced by a network CN connected to the opposite pair of terminals. rlhe direction in which transmission takes place through this circuit arrangementis shown by arrows.

lVhen the arrangement of Fig. 2 is used with the transmission system of Fig. 1, jacks 31 and 34C are patched to jacks and 10 or 8 and 11 in exactly the same manner as hereinbefore described and the results accomplished are entirely similar. .Further detailed description of the connections and the operation of the system is therefore not required.

ln Fig. 1a is shown a two-way carrier wave transmission system terminating in a two-wire low frequency line whereby conversation may be carried on between an ordinary telephone subscribers subset or telephone exchange B and a distant cooperating station over a common transmission line ML. The lines ML are separate physi ca` lines which terminate at the same station where the carrier apparatus of Figs. 1 and 1 are located. The station B is connected to the carrier terminal station by a line 54: terminatingl in jacks 55. The low frequency terminals of the transmitting circuit T C and receiver circuit RC are conjugately connected by means of the conjugate transformer 5G to the two-wire circuit terminating in jacks 57. Normally a continuous circuit is provided from the conjugatc transformer 56 to the low frequency line 5e through the normally closed contacts of jacks 57 and 55. A low7 frequency network LFN to balance the/low frequency line 54 is normally connected to the conjugate transformer 56 through the normally closed back contacts of relay 58. The eh ments in the carrier transmitting circuit TC and in the receiver circuit RC may be identical with those described iu connection with Fig. 1 and are connected to the main line ML in an identical manner.

Let it be assumed now that an operator or attendant at the carrier terminal of Fig. 1 wishes to connnunicatc with a party at station B. The key KT will be thrown to its operated position and jacks 84 will be patched to jacks 55 by the insertion of plugs 4-2 in jacks 3st and plugs 4?), in jacks 55. The insertion of plugs 43 in jacks 55 disconnects the carrier terminal apparatus from the line 5ft at the open contacts (normally closed) of jacks 55. The operation of key KT disconnects relays 82 and 3G from the sleeves of jacks 34. at the normall;T closed (now open) left-hand contact of key KT and connects relay 59 to the lll) Leos/ice sleeves of jacks 34. Relay 59 is not operated, however, since its energizing circuit is open at the sleeves ofjacks 55. The function of relay 59 will be hereinafter described. The operation of key KT also disconnects receiver 26 from jacks 3l at the right-hand open contacts (normally closed) and connects the receiver 26 to the bridge points of the operator-s telephone set through the normally closed back contacts of relay and the closed (normally open) right-hand contacts of key KT. l

message originating at station B reaches the receiver 26` over the line 54, tip` connections of jacks and plugs 43, tip` conductors of cord 4l', tip connections of plugs 42 and jacks 34, normally closed back contacts of relay 36, normally closed contacts of ringing key RK, normally closed back contacts of relay 59, bridge connections of the operators telephone set, righthand closed contacts (normally open) of key KT and normally closed back contacts of relay 25. A message originating at microphone reaches the station B through the induction coil 35 Vand the circuit just traced except that practically none of the current reaches the lreceiver due to the anti-side tone connection of the operators telephone set.

ln order that the operator or attendant at the carrier telephone station of Fig. l may communicate over the two-way channel of the carrier terminal station of Fig. la, plugs 43 are withdrawn from jacks 55 and inserted in jacks 57. Due to this operation,l relays 58 and 59 are operated by current in an energizing circuit which may be traced from the ground side of battery 60, through battery 60, winding of relay 59, left-hand closed contact (normally open) of key KT, sleeve contacts of jacks 34 and plugs 42, sleeve conductor of cord 41, sleeve contacts of plugs 43 and jacks 57, winding of relay 58 to ground. The operation of relay 59 has the effect of insertingl a resistancel 62 in the lower conductor of the operators telephone circuit by removing a shortcircuit about the resistance 62 at the open contact (normally closed) of relay 59 and connect-- ing a resistance element 6l across this circuit the closed front contact (normally open) of relay 59. Resistance elements 62 and 6l when so connected operate as an artificial line of a certain length depending upon thel values of the resistances 62 and 6l, The operation of relay 5S substitutes a network MN to balance the operators telephone circuit in place of the low frequency network LFN which normally balances the low frequency line 54. The function of the artificial line is to reduce the effect upon the conjugate transformer 56 of impedance changes in the microphone 33 of the operaltors telephone circuit and so to permit lof maintaining the required balance by means of a fixed network MN. By the substitution of network MN for the normally connected network LFN, a simple artici al line, such as is provided `by the resista-nces 6l and 62, may be used.

l'lxhile the invention has been described in connection with carrier current lterminal stations, it is equally applic-able to ordinary four-wire telephone circuits. lts application to such a circuit will be obvious to those skilled in the art from the descrip- Ition of its application to the low frequency four-wire termination of a carrier currenttelephone system and further description will, therefore, not be given.

'The scope of the invention is understood to be defined by the appended claims.

1iWhat is claimed is:

l. In a telephone system, a four-wire line, a telephone receiver, a conjugate transformer, means to connect said receiver to' said conjugate transformer, meansto connectsaid conjugate transformer to the fourwire line, and means to cause connection of the receiver to the conjugate transformer whenever the conjugate Itransformer is connected to the four-wire line.

2. In a telephone system, a four-wire line, a telephone receiver, a conjugate transformer, a relay to connect said receiver to said conjugate transformer, and `a key to connect the conjugate transformer to the four-wire line.

3. In a telephone system, a four-wire line, a telephone receiver, a conjugate trans former, a relay `to connect the receiver to the conjugate transformer, a key to connect the conjugate transformer tothe fourwire line, and means to cause the operation of the relay whenever the key is operated -to connect the conjugate transformer to the four-wire line.

4. ln a telephone system, a four-wire line, a telephone receiver, a conjugate coil, means to connect the receiver to the conjugate coil, means tol connect the conjugatecoil to the four-wire line, means to operate the receiver-connect-ing means whenever the. conjugate coil is connected. to the four-wire line, and an impedance connected to the conjugate coil to balance the telephone receiver. l

5. ln a telephone system. a telephone receiver, a conjugate coil, a relay to connect the receiver to the conjugate coil, a key to connect the conjugate coil to the four-wire line, and an impedance connected to the conjugate coil to balance the telephone receiver.

6. In a telephone system, a telephone receiver, a conjugate coil` a relay to connect the telephone receiver to the conjugate coil when the relay is energized, a key adapted when operated to connect the conjugate coil to the four-wire line, means to energize the relay effective Whenever the key is operated, and an impedance connected to the conjugate coil to balance the telephone receiver.

7. ln a telephonel system, a four-wire line comprising two pairs of conductors, a. telephone receiver, a conjugate coil, a series Winding for said conjugate "coil, a bridge connection for said coil, means to connect the series Winding to one pair of conductors, means to connect the bridge Winding to the other pair of conductors, and'means to connect thereceiver to the conjugate coil Whenever the series Winding and bridge connection of the conjugate coil are connected each to a pair of conductors of the four-Wire line.

8. In a telephone system, a four-Wire line comprising-'two pairs of conductors, a telephone receiver, a conjugate transformer, a series Winding for said transformer a bridge connection for said transformer, means to connect the receiver to the conjugate transformer, and a key adapted to, connect the series Winding to one pair and the bridge connection to another pair of said four- Wire line and to cause the connection of the telephone receiver to the conjugate transformer.

9. In a telephonesystem, a four-Wire line comprising tivo pairs of conductors, a teleT phone receiver, a conjugate transformer, a series Winding and a bridge connection for said transformer, a relay adapted to connect the receiver to the conjugate transformer, and a key adapted to connect the series Winding and the bridge connection each toa pair of conductors of the four- Wire line and to cause the energization of the relay to connect the receiver to the conj ugate coil.

10. In a telephone system, a four-Wire line comprising` two pairs of conductors., a telephone receiver, aconjugate transformer, a series Winding for said transformer, a bridge connection for said transformer, a

1elay adapted to connect the receiver to they transformer, a key adapted to connect the series Winding to one pair and the bridge connection to another painof conductors of said four-Wire line and to cause the actuation of the relay to connect the receiver to ceiving circuit, means to connect said circuits to a common line, a telephone receiver, a conjugate transformer, means to conjugately connect said transformer to said transmitting and receivingcircuits, and means to connect said receiver to said conjugate connecting means, operative whenever said conjugate connective means is actuated.

13. In a carrier current telephone system, a carrier transmitting circuit, a carrier receiving circuit. means to connect said cnrrier circuits to a common line, a telephone receiver, a `conjugate transformer, a series Winding for said conjugate transformer, a bridge connection for said transformer, means to connect the series winding with the carrier transmitting circuit, means to connect the bridge connection ivith the carrier receiving circuit, and means to connect the receiver With the conjugate transformer Whenever the series Winding and bridge connections are connected to the carrier transmitting circuit and the carrier receiving` circuit respectively.

111-. In a carrier current telephone system, a carrier transmitting circuit, a carrier receiving circuit, means to connect said circuits to a carier transmission line, a telephone receiver, a conjugate transformer, a. series windingfor said transformer, a bridge connection for said transformer, means adapted to connect the receiver to the conjugate transformer, and a kej7 adapted to connect the series Winding to the carrier transmitting circuit and the bridge connection to the carrier receiving circuit respectively and to cause the actuation of the receiver-connecting` means.

1:3. In a carrier current telephone system, a carrier transmitting circuit, a carrier receiving circuit, a telephone receiver, a conjugate transformer, a series winding for said transformer and a bridge winding for said transformer, a relay adapted upon energization to connect the telephone receiver to the conjugate transformer, and a key adapted upon actuation to connect the series winding` to the carrier transmitting circuit and the. bridge connection to the carrier receiw ing circuit and to cause the energization of said relay.

16. In a carrier current telephone system, a carrier transmitting circuit, a carrier receiving circuit, a telephone receiver, a conjugate transformer, a series winding` for said transformer and a bridge connection for said transformer, a relay adapted upon encrgization to connect the telephone receiver to the conjugate transformer, a key adapted upon actuation to connect the series Winding to the carrier transmitting circuit and the bridge Winding to the carrier receivi circuit and to cause the energization of said relay, and an impedance connected Cil to the conjugate transformer to balance the telephone receiver.

17. In a telephone system, a four-wire line, a receiving circuit and transmitting circuit at a monitoring station, means adapted to connect said receiving circuit and said transmitting circuit to the tour-wire line,

and automatic switching means to interchange the relative connection ot said transmitting and receiving circuits.

18. In a telephone system, a tour-wire line comprising two pairs of conductors, a receiving circuit and a transmitting circuit at a monitoring station, means adapted to connect said receiving circuit to either pair of conductors, means to connect said transmitting circuit to the other pair ot said conductors, and automatic switching means to cause the receiving circuit and transmitting circuit to loe connected respectively to the same pair of conductors independently of the way in which said receiving and trans'- mittiiig connecting means are connected to said conductors.

19. ln a telephone system, la tour-wire line comprising two pairs of conductors, a receiving circuit and a transmitting circuit at a monitoring station, means to normally connect the receiving circuit to one pair of conductors and other means to normally connect the transmitting circuit to the other pair of conductors, and switching relays automatically energized to connect the receiving and transmittingcircuits respectively to the same pair or" conductors whenever the receiving and transmitting connecting means are interchanged.

20. Ina telephone system, a tour-wire line comprising two pairs ot conductors, a receiving circuit and a transmitting circuit at a monitoring station, means to normally connect the receiving circuit to one pair oit conductors and other means to connect the transmitting circuit to the other pair oi conductors, and switching relays unall'ected by the normal connection or' said transmitting and receiving` connecting means and adapted to interchange said transmitting and receiving circuits it the transmitter and receiving connecting means are reversely connected to said pairs ot conductors.

21. In a telephone system, a tour-wire line comprising tivo pairs of conductors, a receiving circuit adapted to he normally connected to one pair oi conductors and a transmitting circuit adapted to he normally connected to the other pair of conductors, a pair ot jacks normally7 connected to said transmitting circuit, another pair of jacks normally connected to said receiving circuit, means to connect said first-mentioned pair of jacks to one pair of conductors, means to connect said second pair ot jacks to the other pair of conductors, and switching means between said liacks and said receiving and transmitting circuits to interchange said jacks with respect to said transmitting and receiving circuits whenever said connecting means are reversely connected to said pairs oli conductors.

22. ln a telephone system, a :tour-wire line comprising two pairs of conductors, a receiving circuit anda transmitting circuit at a monitoring station, a pair of jacks normally connected to said receiving circuit and a pair ot jacks normally connected to said transmitting circuit, means to normally connect said receiving ack with one pair ot conductors, means to normally connect said tiansi'nitting jack with the other pair oitl conductors, and a switching relay connected between said receiving and transmitting jacks and said receiving and transmitting Ycircuits to interchange said jacks with r'- spect to said receivingand transmitting circuits it said connecting means are reversely connected to said pairs et con ductors.

23. In a telephone system, a four-wire line comprising a pair ot conductors for transmitting and a second pair of conductors for receiving, a pair ot cut-oil1 jacks in said transmitting conductors, a pair of cut-oft jacks in said receiving conductors, a receiving circuit and a transmitting circuit at a monitoring station, a pair of receivingjacls normally connected to vsaid receiving circuit, a pair of transmitting jacks normally con.- nected to said transmitting circuit, a patching cord adapted to normally connect said receiving jacks with said cut-oil jacks in the 'transmit-ting pair of conductors, another patching cord adapted to normally connect said transmitting jacks with said cut-oil' jacks in the re .eiving pair of conductors, and switching means adapted to automatically interchange said receiving and transmitting jacks if said transmitting jacks are patched to said cut-oil7 jacks in the transmitting pair of conductors.

24. in a telephone system, a ifouifwireline comprising a pair oi conductors tor transmitting and a second pair ot conductors for receiving, a pair ot cut-oil jacks in said transmittingconductors, a pair oi cut-oil jacks in said receiving conductors, a receiving circuit and a transmitting circuit at a monitoring station, a pair of receiving jacks normally connected to said receiving circuit, a pair of transmitting jacks normally connected to said transmitting circuit, a patching cord adapted to normally connect said receiving jacks with said cut-oi'f jacks in the transmitting pair ot conductors, another patching cord adapted to normally connect said transmitting jacks with said cut-olf acls in the receiving pair of conductors, and switching means adapted to automatically interchange said receiving and transmitting jacks if said jacks are revers'ely lili patched to the cut-off jacks in said transmitting and receiving pairs of conductors.

25. In a telephone system, a four-Wire line comprising a pair of conductors for transmitting and a second pair of conductors for receiving, a pair of cut-off a-cks in said transmitting conductors, a pair of cut-off jacks in said receiving conductors, a receiving circuit and a transmitting circuit at a monitoring station, a pair of receiving jacks normally connected to said receiving circuit, apair of transmitting jacks normally connected to said transn'iitting circuit, a patching cord adapted to normally connect said receiving jacks with said cut-oilz jacks in the transmitting pair of conductors, another patching cord adapted to normally connect said transmitting jacks with said cut-ott jacks in t-lie receiving pair of conductors, and relay contacts connected in circuit between said receiving and transmitting jacks and said receiving and transmitting circuits adapted to interchange said transmitting and receiving jacks with respect to said transmitting and receiving circuits if said transmitting and receiving jacks are reversely connected tov said cut-off acks in the transmitting and receiving pairs of conductors.

26. In a carrier current telephone system, a carrier terminal station, a receiving circuit and atransmitting circuit at said terminal station, means adapted to connect said receiving and transmitting circuits to said carrier terminal station, and automatic switching means to interchange the connections of saidi transmitting andreceiving circuits.

27. In a carrier current telephone system, a carrier transmitting circuit, a carrier receiving circuit, means to connect said circuits to a carrier transmission line, a receiving circuit and a transmitting `circuit at a carrier terminal station, means to connect said receiving circuit to said carrier transmitting circuit, other means to connect said transmitting circuit to said carrier receiving circuit, and automatic switching means to interchange the connection of said receiving and transmitting circuits to said carrier transmitting and receiving circuits respec-v .means and said transmitting and receiving circuits adapted to interchange said transmitting and receiving circuits if said connecting means are reversely connected to said carrier transmitting and receiving circuits.

29. In a carrier current telephone system, a carrier terminal station, a carrier transmitting circuit, a carrier receiving circuit, a telephone transmitting circuit and a telephone receiving circuit all at said carrier terminal station, means to connect said telephone receiving circuit to said carrier transmitting circuit, other means adapted to connect said telephone transmitting circuit to said carrier receiving circuit, and switching relays adapted to interchange said transmitting and receiving circuits whenever said connecting .means are rcversely connected to said cariier transmitting and receiving circuits and operated whenever said connecting means are actuated.

30. In a carrier current telephone system, a carrier transmitting circuit, a carrier receiving circuit, a telephone receiving and a telephone transmitting circuit at the carrier terminal station, a pair of receiving jacks normally connected to said receiving circuit, a pair of transmitting jacks normally connected to said transmitting circuit, means to connect said receiving jacks to said carrier transmitting circuit, means adapted to connect said transmitting acks to said cai'- rier receiving circuit, and switching means between said jacks and said receiving` and transmitting circuits adapted to interchange said receiving and transmitting circuits whenever said connecting means are reversely connected to the carrier transmitting and receiving circuits.

3l. In a telephone system, a four-wire line, a two-wire line, a receiving circuit and a transmitting circuit at a monitoring station, means to connect said transmitting and receiving circuits to said four-wire line, means to connect said transmitting circuit to said two-wire line, and means operative upon such a connection to connect said rcceiving circuit to said transmitting circuit in operative relation with said tivo-wire line.

32. In a telephone system, a four-wire line, a two-wire line, receiving and transmitting circuits at a monitoring station, means to connect said receiving and transmitting circuits to the four-wire line, means to connect said transmitting circuit to said tivo-wire line, and a key adapted to connect said receiving circuit to said transmitting circuit in operative relation for telephone use with said two-wire line.

33. The method of signaling in a carrier wave system having a station tern'iinating in a four-Wire low frequency line, which method comprises transmitting signals over the low frequency line and listening-iii simultaneously on each pair of conductors of the low frequency line without causing interference therebetween.

34. In a signaling system, two pairs of transmission conductors, means for impressing voice frequency signals upon each pair Sil lti.)

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of conductors, and means tor listening-in simultaneously on each pair of conductors without causing interference therebetween.

35. In a signaling system, two pairs of voice current conductors, two pairs of car rier current conductors electrically connected to said first pairs of conductors respectively, means for impressing voice frequency signais upon each pair of conductors, and means for listeningin simultaneously on each pair et conductors without causing interference therebetween.

36. In a signaling system, two pairs of voice current conductors, two pairs of carrier current conductors, means electrically connecting said voice current pairs with said carrier current pairs respectively, and means for monitoring a conversation in both direc tions simultaneously without mutual inten ference between said pairs carrying oppositely directed elements of said conversation.

37. In a signaling system, a terminal station, a second station, two pairs ot voice frequency lines extending between said stations, a source of carrier current and a detecting means connected to said pairs ot' lines respectively at said second station, and means for monitoring a conversation in both directions simultaneously without mutual interference.

In witness whereof, I hereunto subscribe my name this 3rd day of May, A. D., 1921.

CHARLES WHITE.