US2347079A - Communication system - Google Patents

Description

4 Shets-Sheet 1 R. H. CAMPBELL COMMUNICATION SYSTEM Filed sept. 7, 1942 pril 18, 1944.

April 18, 1944. R. H. CAMPBELL COMMUNICATION SYSTEM Filed Sept. 7, 1942 4 Sheets-Sheet 2 MHK (flipar Q @ZZ g4 i fj/.Ld-l/'rl April 18, 1944. R. H. CAMPBELL COMMUNICATION SYSTEM Filed Sept. 7, 1942 4 Sheets-Sheet 5 April 1s, 1944.

R. H. CAMPBELL COMMUNICATION SYSTEM Filed Sept. '7, 1942 4 Sheets-Sheet 4 umm,

Patented pr. 18, 1944 2,347,079 COMMUNICATION SYSTEM Richard H. Campbell, Racine, Webster Electric Company, poration o! Delaware Application September 7, 1942, Serial No. 457,549

65 Claims.

The present invention relates to intercommunicating systems and particularly to the provision oi' new and improved circuit arrangements enabling an operator at one station to indicate to an operator at another station that he is desirous of interrupting or breaking in" on the operator at another station when the latter is talking to the former. The invention also relates to the provision oi new and improved circuit arrangements for enabling an operator at one station to signal an operator at another that it is desired to communicate with him.

In intercommunicating systems and particularly intercommunicating systems of the loudspeaker type, there has-been developed a type of system wherein a talk-listen s witch is utilized to condition a station either for transmission or reception. In some systems, alternate operation of switches at two stations between their talk and listen positions is required in order for communication to be carried on between the two stations. In other systems, the direction of communication is controlled by the operation of a switch at one station between its two positions. In systems of these types, it may happen that the operator at a station conditioned for reception desires to interrupt transmission by the station conditioned for transmission. Heretofore, this has not been possible and it is, therefore, one of the primary objects of the present invention to provide an arrangement whereby a station conditioned for reception may signal a station conditioned for transmission that it is desired to interrupt or break in on the latter.

Another of the primary objects of the present invention is to provide communication systems with signaling arrangements whereby onestation can signal another that it is desired to communicate therewith and wherein the called station is given a first distinctive signal that another station desires to communicate therewith in the event the called station is not busy and given another and diierent distinctive signal in the event the called station is busy.

A further object of the present invention is to provide communication systems with signaling arrangements whereby the calling station is given distinctive signals of the character aforesaid as to whether or not the called station is busy or not busy.

A further object of the present inventionis to provide a communicating system with signaling arrangements of the character aforesaid in which the distinctive signals given in the called and calling stations in response to the busy or not busy condition of a called station may be reversed.

A further object of the present invention is to provide improved signal supply voltage arrangements..

Wis., assignor to Racine, Wis.. a coricl. 17a-37) Another object of the present invention is to provide an improved ampliier for use with intercommunicating systems of theloudspeaker type. Other objects and advantages of the present invention will become apparent from the ensuing description in the course of which reference is had to the accompanying drawings in which:

Fig. 1 is a schematic representation ofone station of an intercommunicating system provided with apparatus constructed and arranged in accordance with the present invention;

Fig. 2 is a similar representation o1' a further portion of the system, this portion including two additional stations provided with the same equipment as station illustrated in Fig. 1;

Fig. 3 is a schematic representation of the power pack for supplying power to the ampliiier located at station I; l

Fig. 4 is a schematic representation of a voltage supply arrangement for supplying the signaling voltages utilized to provide distinctive signals at the called and calling stations dependent upon whether or not the called station is busy or not busy;

Fig. 5 is a schematic representation of a modied form of circuit arrangement for enabling one station to signal another that it is desired to break in on transmission from the other station; and

Fig. 6 is a view similar to Fig. 5 of a further modiiication.

Referring now to the drawings and more particularly to Figs. 1, 2, 3, and 4, it may be well perhaps to mention that these four figures illustrate a complete three-station communication system embodying the present invention. Space requirements prevent disclosure of the system on a single sheet of drawings, but the system as a whole may be conveniently noted if Fig. 2 is placed to the right oi.Fig. 1 and Figs. 3 and 4 below Fig. 1.

The system has been illustrated as including three stations although additional stations could be readily added to the system in a manner that will become apparent after the system has been described in detail. The three stations of the system' have been indicated by reference characters I, 2, and 3. Each of the stations is provided with translating devices capable of being utilized both as microphones and loudspeakers such as the loudspeakers II and I2 and I3 which may be of the well known permanent magnet type. The stations are also provided with amplifiers Il, I5, and I6, communication direction control switches I1, I8, and I9, and station selector switches indicated generally by reference characters 2|, 22, and 23, all respectively.

The amplifiers are all of identical construction and therefore only the amplifier I4 at `station I has been illustrated in detail. While the amplifiers may be of any well known type, the ampliers illustrated are of the negative feedback type and are constructed and arranged in accordance with one of the features of this invention to give an output that is considerably above the output obtained with conventional amplifiers.

The amplifier I4 includes input transformer 24 to the primary winding of which are connected the amplifier input conductors 25. The secondary winding of transformer 24 is connected to the tubes 26 and 21 (of the 6SJ7 type) which are arranged in parallel so that in the event one of the tubes fails for any reason whatever, the

amplifier will remain operative. The output of the tubes 26 and 21 is supplied to tubes 23 and 29 (of the 6J5 type) which 'are also connected in parallel. The output of tubes 28 and 25 is supplied to the primary winding of an interstage coupling transformer 30, the secondary of which comprises two windings 3I and 32 connected in push-pull arrangement with the power tubes 33 and 34 (of the 6V6GT type). The anodes of the two tubes are connected to the primary winding 35 of an output transformer 36 and the midpoint of the primary winding is connected by a conductor 31 to a conductor 38 through which the supply of B voltage is led to the amplifier. It may be well to note at this point that the heaters of the various amplifier tubes are continuously supplied with power but that B or plate voltage is not supplied to them except when the communication control switch I1 is in its lowermost or talk position as will be described in greater detail hereinafter.

The output transformer 36 includes a rst secondary winding 4I to the terminals of which are connected a pair of output conductors 42. The transformer also includes a second secondary winding 43, the midpoint of which is grounded to the chassis of the amplifier by a conductor 44 and the opposite terminals of which are connected by conductors 45 and 46 to adjacent terminals of windings 3l and 32 of the interstate coupling transformer 30. The other terminals of the latter are connected by conductors 41 and 43 to the grids of tubes 33 and 34, respectively.

- The grids of the two tubes are connected through a condenser 49. the purpose of which will now be described.A

The output transformer secondary winding d3 is utilized as a source of negative feedback for the push-pull connected power output stage of the amplifier. As frequencies of about 15,000 cycles may be shifted in phase enough to cause a positive instead of negative feedback and thus produce an undesirable oscillation, the condenser 49 is used to bypass or reduce these higher frequencies enough to prevent excessive positive feedback which might otherwise produce oscillation. When the condenser is usedl the amplifier can be adjusted to operate as a Class AB-2 amplifier. The amplifier thus draws grid current at high volume, that is, when the audio signal voltage applied to the grids of tubes 33 and 34 exceeds the normal grid bias voltage. The grid return circuit including conductors 45 and 45 is of low resistance and, consequently, the power output obtainable from the amplifier output stage is considerably increased. A further advantage of 'the amplifier circuit arrangement is to balance the grid current iiowing through the secondary winding 43 so that it does not deleteriously affect the nature of the amplifier output.

The amplifier also includes a volume indicator in the nature of a neon tube I connected across the primary winding 35 in series with the high -value (50,000 to 100,000 ohms) resistors 52 and 53, which prevent direct shorting lof the ampliner B supply in the event the tube or socket should ground to the chassis. Should such grounding take place, one of the resistors would probably be destroyed but the power transformer and rectifier tube saved.

The amplifier is supplied with power through a power pack indicated` generally by reference character 54 and illustrated in Fig. 3. The power pack includes a transformer 55, the primary winding 5B of which is connected to a suitable source of alternating current through conductors 51. A pilot light in the form of a neon tube 55 is connected across conductors 41 through the resistors 59 and 60. The transformer is provided with three secondary windings, the first 5I of which is utilized as a source ofpower for the cathode heaters of the amplier tubes. A secondary winding 62 is used as a source of filament heating current for the rectifier tubes 63 and 64, and a third winding 65 is utilized as a source of anode voltage for the rectifier tubes, which, it may be noted, are connected in conventional manner for full wave rectification. The B supply line 38 is connected to the filaments of the tubes 63 and 54 in customary manner. Each of the amplifiers I5 and I6 has a similar power pack associated with it and indicated in each case by the reference character 54.

The communication control switches I1, I5, and I9 are operable' between a listen position, in which they are indicated, to a talk position which is a lower position. The switches are preferably biased from their talk to their listen positions by springs 61. In the listen positions of the switches, the loudspeakers at the respective stations are connected to an interstation conductor individual thereto and in the talk positions the loudspeakers are connected to the inputs of the amplifiers and the outputs of the amplifiers are connected to the selector switches and thence through operated selector switches to the interstation circuits individual to other stations.

Referring now to Fig. 1 and station I, it may be noted that the communication control switch I1 includes a pair of switch blades 1I connected directly through the pair of conductors 12 to the voice coil of loudspeaker I i. In the indicated position of the switch I1, the loudspeaker is connected to an interstation circuit individual to vstation I andy including a pair of conductors 'I3 through the switch blades 1I, through an adjustable volume vcontrol 14 and a transformer 15. The primary winding 16 of the transformer has two terminals connected tothe conductors 13. One terminal of the secondary winding 11 of the transformer is connected by conductor 18 to a contact associated with the lowermost switch blade 1 i, while the movable contact 14 of the volume cont'rol is connected by conductor 19 to a contact associated with the other of switch blades 1 I. Volume control is effected by moving the contact 14 to vary the effective portion of the secondary winding 11.

In the indicated position of switch I1, the amplier output conductors 42 are open circuited by the pair of switch blades 8| to which they are connected.

In the lowermost position of the communication control switch, the loudspeaker II is connected to the amplifier input through the switch blades 1I in their lowermost positions and the input conductors 25. At this time, the amplifier switch blades 8| (in their lowermost positions) to` an output circuit 82 leading to the station selector switches 2| through which the amplifier output may be supplied to interstation circuits individual to the other stations of the system. In the system herein illustrated, there are but two other s uch stations and therefore two station selector switches have been illustrated. These are the switches 83 and 84 individual to stations 2 and 3, respectively.

When it is desired to communicate with station 2, station selector switch 83 is operated from its indicated lowermost position to a displaced position wherein the output circuit 82 is connected to an interstation circuit 85 individual to station 2, this connection being made through switch blades 86. When it is desired to communicate with station 3, the station selector switch 84 is operated so that the switch blades 81 thereof connect the output circuit 82 to the interstation circuit 88 individual to station 3. The station selector switches have also associated therewith additional circuits controlled thereby for signaling called stations, and also station I, in a distinctive manner dependent upon whether or not the called station is busy or not busy, as will be described in detail hereinafter.

The communication control switch I1 includes an additional switch blade 89 operable into a circuit closing position to supply B voltage to the amplifier. The switch blade 89 breaks the B supply line 38 when the switch I1 is in its uppermost or listen position and completes the circuit when it is in its lowermost or talk position.

Referring now to Fig. 2 and station 2, it may be noted that the communication control switch |8 includes a pair of switch blades 9| connected through conductors 92 to the voice coil of loudspeaker |2. In the indicated position of switch I8, the loudspeaker is connected to interstation circuit 85 individual to station 2 through a volume control 93 and transformer 94. iAt this time, the switch blades 95 of switch I1 open circuit the amplifier output to which they are connected through conductors 96. In the lowermost position of the communication control switch, loudspeaker I2 is connected to the amplifier input through switch blades 9| and the conductors 91. The amplifier output conductors 96 are at the same time connected to an output circuit 98 leading to a station selector switch 99 individual to station I and a station selector switch individual to station 3. When the station selector switch 99 is closed, the output circuit 98 is connected through switch blades I0| to the interstation circuit 'I3 individual to station and when station selector switch |00 is closed, the output circuit is connected through switch blades |02 to interstation circuit 88 individual to station 3.

The communication control switch includes also a switch blade |03 adapted when switch I8 is iny In the lowermost position of the communication control switch, loudspeaker I3 is connected to the amplifier input through switch blades |03 and input conductors ||0. The amplifier output conductors |09 are at the same timeconnected to an output circuit |I| leading to a station selector switch |I2 individual to station I and a station selector switch ||3 individual to station 2. When station selector switch I I2 is closed, the output circuit I I0 is connected through switch blades I I4 to interstation circuit 13 individual to station I and when switch ||3 is closed, circuit is connected through switch blades II5 to interstation circuit 85 individual to station 2. The switch I8 also includes a switch blade ||5 adapted to complete the B supply connection to the amplifier in the talk position of the switch.

Communication between any two stations of the system is carried on by alternate operation of the communication control switches at the two stations between their indicated and lowermost positions, i. e., between their listen and talk positions, provided of course that the station selector switches at the two stations have been closed to complete the interstation circuits between them. Suppose. for instance, that station I is communicating with station 2 (station selector switches 83 and 99 having been closed), and that the operator at station I is talking to the operator at station 2, then if the operator at station 2 desires to break-in on the operator at station I, he can` not do so even though he operates the communication control switch I8 thereat to its talk position. The reason for this is that under these conditions the loudspeakers at both stations would be connected to the inputs of the amplifiers thereat and no loudspeakers would be connected to the outputs of the amplifiers.

One of the important features of the present invention is to provide a signaling arrangement whereby under the conditions mentioned above. an indication is given at a station conditioned for talking that the listening station desires to interrupt or breakin. It is preferred that the signal be given as by the lighting of a lamp and consequently the various stations have been provided with signaling means consisting of neon tubes that are adapted to be lighted to indicate the break-in. These neon tubes are indicated by the reference characters ||6, ||1, and ||8 (of the type NE17 manufactured by the General Electric Company), at stations I', 2, and 3, respectively. The tube |I6 has one terminal connected through a voltage limiting resistor ||9 and conductor |20 to a source of direct current voltage which may be the conductor |2| through which vplate voltage is supplied to tubes 26 and 21 of the amplien The other terminal of tube 6 is connected by a conductor |22 to the midpoint of the primary winding 16 of transformer 15. The tube is shunted by a resistor |23 having a value of about 100,000 ohms and the purpose of which is to decrease the voltage across the tube terminals so that it will not be lit as a result of resistance leakage and capacity between the interstation line 13 and ground, to which the negative side of the B voltage is connected.

In similar manner, one terminal of tube |I1 at station 2 is connected through resistor |24 and conductor |25 to a source of direct current voltage while the other terminal is connected by conductor |26 to the midpoint of the primary winding'of transformer 94. Tube ||1 is bridged by the resistor |21.

The tube ||8 at station 3 is likewise connected through resistor |28 and conductor |29 to a source of direct current voltageand by conductor |80 to the midpoint of the primary winding of transformer'jli. The tube Ill'is also'bridged"` by the resistor I3|.`

I, the ground connection l|34 is made to the midpoint of a pair of resistors |35 and |35 connected across the amplier output conductors 42. At station`2, the groundconnection |31 is made at the midpoint of resistors |38 and |39 connected across-the amplifier output conductors 98. At station 3, the ground connection |40 is made at the midpoint of resistors |4| and |42 connected across the amplifier output conductors The arrangement of the neo n tube break-in signals is such that when the talk-listen switches at two stations in communication with each other are both in their listen positions, or that at one station is in its listen position and that at the other in its talk position, the neon tubes are not lit. However, when both the switches are in their talk positions, thus indicating that the station conditioned for reception desires to interrupt or break in on the station conditioned for transmission, then the tubes at both stations are lit.

When the talk-listen switches are in their listen or indicated positions, then the neon tubes are not supplied with voltage since no plate voltage is supplied-to the amplifiers as the plate supply controlling switch blades 89, |03, and |55 at the three stations are in circuit opening positions. When the talk-listen switch at one station is in its tall'. position (for instance, switch I1 at station I) and the talk-listen switch at another station (for instance, switch I8 at station 2) is in its listen position then, while the B supply voltage is connected to tube I I5 at stationw-I, there is no complete energizing circuit for this'tube because the switch blades 95 at station 2, through which the energizirg circuit for the tube is completed to ground, are in circuit opening position.

When both of the switches |1 and |8 are in their talk positions, which positions they would occupy when the operator at station 2 desires to interrupt the operator at station I, then the tubes ||5 and I I1 at stations and 2 are both lit. The energizing circuit for tube ||5 extends from the B supply conductor 38 at station I, conductors |2I, |20 and resistor ||9 to one terminal of tube IIB. The other terminal of the tube is connected to ground through conductor |22, primary winding of transformer 15 at station l, interstation circuit 13, the station selector switch blades IUI at station 2, switch blades 95, conductors 96, resistors |38 and |39 and the ground connection |31 at station 2. The various-ground connections at the stations may be connected to a single conductor or to shielding around a multiple conductor cable. The energizing circuit for tube ||1 at station 2 extends from the B supply at that station through conductor |25 and resistor |24 to one terminal of the tube, and the other terminal of the tube is connected to ground through conductor |25, the midpoint of the primary winding of transformer 94 at station 2, interstation circuit 85, switch blades 85, switch blades 8|, resistors |35 and |35,'and the ground connection |34 at station The operator at station is thereupon advised by the lighting of tube ||5 that the operator at station 2 desires to break in.

In the event station 2 had been transmitting to station and the operator at the latter desired to break in,v then both of the talk-listen switches would again be operated to their talk positions, with the results described above. namely, that both tubes ||5 and ||1 at the two stations-would be lit. j

Inasmuch as the apparatus at station 3 corresponds to that at stations and 2, the desire to break in is indicated'in the same way if station 3 is communicating with either one of the other stations.

One of the advantages of the described signaling arrangement is that it does not require any additional interstation conductors other than those utilized in the communication system. Furthermore, the connection of the tubes to the midpoints of the transformers and of the ground connections to the midpoints of resistors in the amplifier output circuits provides a balanced circuit arrangement to eliminate undesirable consequences that might otherwise result from the use of the communication circuits for signaling purposes.

Another of the important features of the present invention resides in the provision of signaling arrangements whereby a signal of a first distinctive character is actuated at both the calling and called stations upon the selection of a station that is not busy and a signal of another characteristic is actuated at both stations in the event the selected station is busy. In the instant embodiment, the rst of the signalsof distinctive characteristic is a flashing signal light and the second is a, steady light.

Each of the stations is provided with a light source, preferably a neon tube (preferably of the same type as the tubes |I8 to H8) for each of the stations in the system. Thus station is provided with tubes |45 and |45 corresponding to stations 2 and 3, respectively; station 2 is provided with tubes `|41 and |48 corresponding to stations and 3, respectively, and station 3 is provided with tubes |49 and |50 corresponding to stations and 2, respectively.

4Upon the selection of one station by another, the tubes corresponding to the two stations are supplied with either a periodic or steady voltage dependent upon whether or not the called station is not busy or busy. These two voltages are supplied from a centrally located signal voltage supply source |5I (see Fig. 4) which will be described in detail hereinafter. From an inspection of this Fig. 4, it will be noted that three conductors |52, |53, and |54 lead from the supply source |5I to all stations of the system. The conductor |52 is a common conductor, conductor |53 is a conductor supplying the periodic voltage, and conductor |54 is a conductorl supplying the steady signal voltage.

The station condition responsive signaling arrangement is controlled in response to the positions of the station selector switches at the various stations. Referring now first to station I, it may be noted that the station 2 selector switch 83 thereat includes switch blades |55 and |55 operable simultaneously with the switch blades 88. The neon tube |45 is connected tc switch blade |55 through a. resistor |51 and conductor |58. The other terminal of the tube is connected by a conductor |59 to the corresponding terminal of the tube |41 at station 2.

In the unactuated position of selector switch 83, switch blade |55 completes a circuit to a branch conductor |5| connected to the common conductor |52 and switch blade |55 interconnects conductors. |62 and |63. The latter is a branch conductor leading to the conductor |53 through which the periodic voltage is supplied to the system, and the former leads to a contact associated with selector switch 84, as will be described shortly.

In the actuated position of selector switch 83, the signal circuit controlling switch blades |55 and |58 are moved upwardly. In this position, switch blade |55 interconnects the aforesaid conductor |62 and a branch conductor |64 leadingto the source of steady signal voltage, that is, conductorv |54, and switch'blade |56 interconnects conductor |58 and a conductor |65 leading to both stations 2 and 3.

Station1 selector switch 84 at station includes switch blades |61 and |68 operable simultaneously with the switch blades` 81. The neon tube |46 is connected to switch blade |68 through a resistor |69 and conductor 1|. The other terminal of the tube is connected by a conductor |12 to the corresponding terminal of tube |49 at station 3. In the unactuated position of selector switch 84, switch blade |68 completes a circuit to branch conductor |6| and the common conductor |52, while switch blade |61 interconnects the lpreviously referred to conductor |62 and a conductor |13 leading to both stations 2 and 3. In the actuated position of selector switch 84, the switch blade |81 interconnects conductors |64 and |13 and switch blade |68 interconnects conductors |1| and a conductor |14 leading to both stations 2 and 3.

The signal circuit controlling arrangement at station 2 is similar to that at station I. The station selector switch 99 includes a pair of switch blades |15 and |16, operable simultaneously with the switch blades |I. The neon tube |41 is connected to switch blade |16 through resistor |11 and conductor |18. The other terminal of the tube is connected to the previously referred to conductor |59. In the unactuated position ofselector switch 99, switch blade |16 completes the circuit to a branch conductor |19 leading to the common conductor |52 and switch blade |15 interconnects conductors |8| and |82. 'I'he latter is a branch conductor leading to the flashing voltage supplying conductor |53, and the former leads to a contact associated with selector switch |00. In the actuated position of selector switch 99, the signal circuit controlling switch blades |15 and |16 are moved upwardly. In this position. switch blade |15 interconnects the conductor |8| and a branch conductor |83 leading to the steady voltage supplying conductor i 54, and switch blade |16 interconnects conductors |18 and |84, the latter of which is connected to the conductor |13, which leads to both stations and 3.

Station selector switch |00 includes the switch blades |85 and I 86, operable simultaneously with switch blades |02. through resistor |81 and conductor |88 to switch blade |86. The other terminal of the tube is connected by a conductor |89 to the corresponding terminal of tube |50 at station 3. In the unactuated position of selector switch |00, switch blade |86 completes a circuit from conductor |88 to the branch conductor |19 leading to the common conductor |52 and switch blade |85 4interconnects branch conductor |8| and a conductor I9I which is connected tothe conductor |65 leading to the other stations of the system. In the actuated position of selector switch |00, switch blades |85 and |86 are moved upwardly. In this position,

The neon tube is connected blade interconnects conductors |9| and the 75 branch conductor |83 connected to the steady voltage supply line |54 and blade |86 interconnects conductors |88 and a branch conductor |92 connected to the conductor 14.

At station 3, the station selector switch ||2 includes switch blades and |96 operable simultaneously with switch blades ||4. The neon tube |49 is connected to switch blade |96 through a resistor |91 and conductor |98. The other terminal of the tube is connected by 4conductor |22 to the corresponding terminal of tube |46 at station In the unactuated position of selector switch 2, switch blade |96 completes a circuit from conductor |98 to a branch conductor |99 leading to the common conductor |52 and switch blade |95 interconnects conductors 20| and 202, the latter of which is a branch conductor leading to the periodic voltage supplying conductor |53, and the former of which leads to selector switch H3.. In the actuated position of selector switch I2, switch blades |95 and |96 are moved upwardly to a position wherein blade |95 interconnects conductor 20| and the branch conductor 203 leading to the steady Voltage supplying line |54 and blade |96 interconnects conductors |13 and 98.

The station selector switch ||3 at station 3 includes the switch blades 205 and 206 operable simultaneously with switch blades I |5. The neon' tube |50 is connected to switch blade 206 through a resistor 201 and conductor 208 and its other terminal is connected to the conductor |89 con nected to the corresponding terminal of tube |48 at station 2. In the unactuated position of selector switch H3, switch blade 206 completes the circuit from conductor 208 to the branch conductor |99 connected to the common conductor |52 and switch blade 205 interconnects conductors |14 and 20|. In the actuated position of selector switch ||3, switch blades 205 andv 206 are moved upwardly to positions wherein the former interconnects conductors |14 and 203 and the latter interconnects conductors 208 and |65.

In order to prevent excessive voltage drop across the neon tubes when signal voltage is applied thereto, due to the capacity between the wires of the signaling arrangement, each of the tubes is bridged by a resistor 2|0. These resistors may have a value of about 100,000 ohms, whereas the resistors |61, |69, etc., in series with the tubes, may have a value of about 10,000 ohms. The resistors 2|0 also enable radio frequency voltages, which may be induced in the wires because of high power radios utilized on ships, to leak out. If this were not done, these induced voltages might be suicient to light the tubes and give erroneous signals.

The signal voltage supply means |5| illustrated in Fig. 4, to which reference is now had, includes a transformer 2 having a primary. winding 2|2 4and three secondary windings 2|3, 2|4A and 2|4B. The primary winding may be connected to a suitable source of alternating current voltage. Secondary winding 2I3 is connected to the plates of a pair of rectifier tubes 2|5 and 2|6 arranged for full wave rectication and the Illaments of which are independently connected to the secondary windings 2|4A and 2|4B. The output of tube 2|5 is supplied to the steady voltage conductor |54, across'which and the common conductor is connected a condenser 2|1. The output of the other tube 2|6 is supplied to a conductor 2|8, across which and the common conductor is connected a condenser 2|9, and the conductor 2|3 is periodically connected to the conductor |53.

'I'he periodic voltage is supplied to conductor |53 by a novel arrangement including a relay 220 having a condenser 22|i connected in shunt thereto. A pair oi resistors 222 and 223 are connected in series with the parallel connected relay and condenser. This series-parallel circuit is in turn shunted by a condenser 224. The relay 220 operates a two-position switch blade 225 adapted in its indicated position (to which'it is suitably blasedl to connect conductor 2 I8 to the relay cil-,cuit through a resistor 226. When the relay winding is energized sufllciently, the switch blade 225 is actuated to connect conductor 2|8 yto the conductor |53 through which, it may be remembered, a periodic voltage is supplied to the signal circuit.

A neon pilot light 221 is connected across conductors |53 and |52 in series with resistors 228 and 229 to give an indication that the voltage supply means is operating.

When the switch blade 225 occupies its indicated position, a steady direct current voltage obtained from conductorl I8 is utilized to charge condensers 22| and 224 and to energize relay 220. The condenser 224 ischarged to a, higher voltage than condenser 22| by reason of the resistors 222 and 223 being located in circuit with condenser 22|. As the condensers are charged, an increasing voltage is supplied to the relay winding 220 until it becomes energized suieiently to move switch blade 225 to disconnect conductor |54 from the relay circuit and to connect it t conductor |53. When this occurs, the relay winding remains energized and continues to pull switch blade 225 downwardly because of the discharge of condensers 22| and 224 through the winding. Condenser 22| discharges rapidly, but condenser 224, which is charged to a higher voltage, discharges more slowly because of the series resistors 222 and 223. Consequently, switch blade 225 is held in its lowermost position until the bias applied thereto overcomes the diminishing force applied to it by the decreased current ilowing through the winding.

The described arrangement is very advantageous in that the ratio of the time voltage is supplied to conductor |53 to the time that no voltage is supplied to the conductor is relatively independent of the power required to move switch blade 225 because the energization of the relay is increased to effect operation of the switch blade in the event the latter tends to stick. If the blade tends to stick, then the condensers 22| and 224 are charged for a slightly longer time and consequently the energization of the relay is increased sothat more power is available for movement of the switch blade. the ratio is independent of the load (the number oi neon tubes energized) as condensers 22| and 224 are entirely disconnected from the load circuit When the switch blade-225 is moved from its indicated position, and the discharge is through the relay winding and not through the load which may be variable.

in order to vary the ratio of the lengths of time that the switch blade remains in its two operated positions, the circuit constants of the elements in circuit with the relay winding as well as the resistance of the relay winding itself may be varied. To increase the length of time that the switch blade remains in its actuated position, the condenser capacities may be increased so of time. In addition. the resistances of resistors 222 and 223 or oi the relay winding itself may be increased.

Excellent results have been obtained with an arrangement wherein the conductor 2|-8 has a voltage of about 200 volts, the relay winding 220 has resistance of about 5,000 ohms, and resistors 222, 223, and 22| have resistances of about 5,000 ohms, and the condensers 22| and 224 a capacity oi about 4 microfarads. When thus arranged, the neon tubes, when supplied with the periodic voltage, iiashabout 4 times per second and the ratio oi' the period of illumination to the period of darkness is about 60 to 40.

If it is .desired to reverse the character of the distinctive signals given at the various stations upon the selection of a busy or a not busy station; a reversing switch 230 (see Fig. 1) may be provided whereby the connection of conductors' conductor |54 is periodically supplied with volt-l age.

Another advantage of the arrangement is that the steady voltage applied to conductor |54 from rectifier tube 2|5 is substantially independent of the load connected across the periodic voltage supply conductor |53. Thus, a change in load in either circuit is reflected into the other circuit only by a slight voltage drop across the transformer itself. This would not :be the case if the steady voltage was taken from the same rectiiier as the periodic voltage.

In operation oi' the system, it is contemplated that the amplifiers of the various stations will be conditioned for immediate operation as by the connection of the power pack transformers 55 to suitable source of alternating current. When thus connected, the operators at the various stations will be apprised of the operative condition oi the ampliiiers by the glowing of the neon tubes 5B. The signal voltage supplying means |5| also has its transformer 2li connected to a suitable source of alternating current so that the steady and periodic signaling voltages will fbe at all times supplied to the conductors |54 and |53. The neon tube 221 which is connected to the periodic voltage supplying conductor |53 thus ashes periodically to indicate that the voltage supplying means is operating.

Furthermore,

Under normal conditions, i. e., when none of the stations in the system is in us'e, the communi cation control switches Il, i8, and i9 are in theiil uppermost indicated positions so that the loud?- speakers il, i2, and I3 are connected through their associated volume controls and transformers to the interstation circuits 13, 35, and 08 individu; ai to the three/stations. The amplifier output circuits are opened by the communication control switches and no plate voltage is supplied to the ampliers although the heaters of the various amplier tubes are supplied with current to make the ampliers ready for instantaneous operation.

The break-in signaling tubes H6, H1, and ||8 at the stations are deenergized. The various station selector switches are also in their unactuated positions and the signaling tubes |45 to |50 are deenergized, the pairs of tubes |45 and |4'|l |46 and |43, and |48 and |50, each being connected in series to the common conductor |52. The tubes that the condensers discharge for a longer period |45 and |41 are connected in series to the comcalling station and the called station 2.

mon conductor through a circuit including the branch conductor |6| at station I, switch blade |51, conductor |58, resistor |51, the tube |45, interstation conductor |59, the tube |41 at station 2, resistor I 11, conductor |18, switch blade |16, and the .branch conductor |19 at station 2 which is also connected to conductor |52. Tubes |46 and |49 are similarly connected to the common conductor through a circuit including the branch conductor |6| at station I, switch blade |68, conductor |1I, resistor |69, the tube |46, interstation conductor |12, the tube |49 at station 3, resistor |91, conductor I 98, switch blade |96, and branch conductor |99 at station 3. Tubes |48 and |50 are connected to the common conductor through the circuit including branch conductor |19 at station 2 switch blade |86, conductor |88, resistor |81, and the tube |48 at station 2, interstation conductor |89, the tube |50 at station 3, resistor 201, conductor 208, switch blade 206, and the branch conductor |99.

Assuming rst that the operator at station I desires to communicate with the operator at station 2 and that the latter station is not busy, then the operator at station I actuates selector switch 83 and a flashing signal is produced at both tige T e operator at, station I is thereupon advised that station 2 is not busy and the operator at the latter station is apprised by the hashing signal light that another station desires to communicate therewith. A flashing signal is supplied at both' stations by the connection of the tubes |45 and |41 at stations I and 2, respectively, to the conductor |53 which, it may be remembered, is supplied with a periodic or intermittent voltage. The energizing circuit for the two tubes is as follows: conductor |52 at station 2, branch conductor |19, switch blade |16 (which is in its indicated position as selector switch 99 has not yet been actuated) conductor |18, resistor |11, tube |41, interstation conductor |59, tube |45 at station I, resistor |51, conductorv |58, switch blade |56 in its uppermost position, interstation conductor |65, conductor |9| at station 2, switch blade |85 in its unactuated position, conductor IBI, switch blade |15 in its unactuated position, and branch conductor |83 which is connected to conductor |53 ion 2. atl'isittmthis time, the operator at station 2 isapprised of a call by the ashing of a signal light and if the operator at station I desires, .he can also call the operator at station 2 by using. the intercommunicating apparatus. In doing this, it is necessary for the operator at station I simply to ,operate the communication control switch I1 thereat to its lowermost or talk position. When this is done, the loudspeaker IIA at station I is connected to the input of the ampliner I4 and the output of the amplier is connected to loudspeaker |2 at station 2 through the switch blades 8| of switch I1 at station I, the actuated station selector switch blades 86 and the interstation circuit 85 individual to station 2 and to which loudspeaker I2 is normally connected through its associated volume control 93 and transformer 94. Thus if the operator at station 2 hears the call, he can respond thereto, but if he is not where he can hear the call, the station selector switch at station I can be left in its actuated position so that the signal light at station I will flash periodically until the operator at station 2 responds.

In order for the operator at station 2 to reply former rst to actuate selector switch 99. When the station selector switches 83 and 99 at stations and 2 have both been actuated, the tubes |45 and |41 are both deenergized. The tubes are connected in series to the steady voltage supplying conductor |54, but there is no circuit to the common conductor, and the tubes are deenergized. 'I'he circuit connections of the two tubes at this time are as follows: conductor |54 at station 2, conductor |83, switch blade |15 in its uppermost position, conductor I8I, switch blade |85 in its unactuated position, conductor |9|, interstation conductor |65, switch blade |56 at station 2 in its uppermost position, conductor |58, resistor |51, tube |45, interstation conductor |59, tube |41 at station 2, resistor |11, conductor |18, switch blade |16 in its uppermost position, conductor |84, interstation conductor I 13,. switch blade |61 at station I in its unactuated position, conductor |62, switch blade |55 in its uppermost position, 'and branch conductor |64 leading to conductor |54 at station I.

After the station selector switches at stations I and 2 have been operated as described above, then communication between the two stations may be carried on by the alternate operation of the communication control switches I1 and I8 between their talk and listen positions. In theY event one of the stations is conditioned for transmitting to the other by the operation of its switch to its talk position and the operator at the other station desires to break in on the one, then all that is necessary is for the operator a't the other station to actuate the switch thereat to its talk position. Both the switches are thereupon operated into their talk positions with the result that the break-in signal tubes II6 and II1 at the two stations are energized in a manner heretofore t0 a call from station I, it ls necessary for the 75 described in detail.

It will now be assumed that stations I and 2 are in communication with each other as described above and that station 3 selects one of the two stations, for instance, station 2. To select station 2, the operator at station 3 actuates station selector switch I`I3, whereupon tubes |48 and I 50 at stations 2 and 3 are supplied with a steady voltage and thus glow steadily to indicate to the operator at station 3 that station 2 is busy and to indicate to the operator at station 2 that station 3 desires to communicate therewith. At this time, tubes |48 and |50 are connected in series acrossconductors |52 and |54, the circuit being as follows: conductor |52 at station 2, branch conductor |19, switch blade |86 in its unactuated position, conductor |88, resistor |81, tube |48, interstation conductor |89, tube |50 at station 3, resistor 201, conductor 208, switch blade 206 in its actuated position, interstation conductor |65, conductor |9| at station 2, switch blade |85 in its unactuated position, conductor I8I, switch blade |15 in its uppermost position, and conductor |83 which is connected to the -steady voltage supply-l ing conductor |54.

At this time, the operator at station 2 has the option of continuing to communicate with station I or to communicate with station 3. Should theoperator at station 2 decide to communicate with station 3 for any reason whatever, as such, for instance, as a belief that the call from station 3 is of an urgent or emergency character, then the operator at station 2 can return to its unactuated position the number I station selector switch 83, and operate the station 3 selector switch 84. If this is done, the tubes |48 and |50 at stations 2 and 3 are extinguished, whereas tubes |45 and |41 at stations I and 2 will be supplied with a steady voltage and glow continuously. 'Ihus the loperator at station I is advised of the changeover in the status of station 2', namely, that this station has selected some other station for communication. The tubes |48 and |50 at stations 2 and 3 are connected to the: steady voltage supplying conductor |54 but not to the common conductor and are consequently deenergized. This circuit connection is as follows: conductor. |54 at station 2, conductor |83, switch blade |85 in its uppermost position, conductor |8I, interstation conductor |85, switch blade 205 at station 3 in its uppermost position, conductor 208, resistor 201, tube |50, interstation conductor |88, tube |48 at station 2, resistor |81, conductor |88, switch blade |86 in its uppermost position, conductor |92, interstation conductor |14. switch blade 205 at station 3 in its uppermost position, and conductor 203 which is connected to'conductor |54.

Remembering now that station selector switch 88 at station 2 has been returned to its indicated position, then the circuit whereby tubes |45 and |41 at stations I and 2 are supplied with a steady voltage upon station 2 giving precedence to station 3 over station I, is as follows: conductor |52 at station 2, conductor |18, switch blade |15 in its lowermost position, conductor |18, resistor |11, tube |41, interstation conductor |59, tube |45 'at station I, resistor |51, conductor |58, switch blade |58 in its uppermost position, interstation conductor |85, conductor |8| at station 2, switch blade |85 in its uppermost position, and conductor |83 which is connected to conductor l54at station 2.

.In the event two stations of the system select a third at approximately the: sarne time, and prior to the third having responded to a call from one of the two, then both neon tubes at the third station and the tubes corresponding to the third station at the two other stations are all supplied with periodic voltage to give flashing signals. Tubes |45 and |41 at stations I and 2 are connected in series across the common conductor |52 and the periodic Voltage supplying conductor |53 in the manner heretofore described in conjunction with the selection of station2 by station I. The tubes |58 and |50 at stations 2 and 3 are connected across the common conductor and conductor |53 through a circuit that is as follows: conductor |52 at station 2, conductor |19, switch blade |88 in its unactuated position, conductor |88, resistor |81, tube |48, interstation conductor |88, tube |50 at station 3, resistor 201, conductor 208, switch blade 205 in its uppermost position,

' interstation conductor |65, conductor IBI at station 2, switch blade |85 in its unactuatedposition, conductor |8I, switch blade: |15 in its unactuated position, and conductor |82 which is connected to conductor |53.

Under the above circumstances, the called station (station 2) has the option of communicating with either one of stations l or 2. Assuming, rst, that station 2 selects station by the operation of selector switch 99, then tubes |45 and |41 at stations I and 2 are extinguished and tubes |48 and |50 are connected across the common conductor and the steady voltage supplying conductor |54 so that the latter tubes glow continuously. The circuit connections existing at this time are the same as those heretofore described in conjunction with the conditions existing at the time stations and 2 are communicating with each other and station 3 selects station 2.

Assuming, now, that station 2 selects station 3 and not station I, then tubes |48 and |50 at stations 2 and 3 are extinguished while tubes |45 and |41 at stations I and 2 glow continuously. The circuit conditions existing at this time are the same as those previously described in conjunction with the situation wherein stations I and 2 were communicating, station 3 called station 2 and station 2 gave precedence to station 3 over station I.

A conference between all of the stations of the system may also be arranged. In this event, the station desiring to arrange the conference can call the other stations of the system and the operators at the other stations can then operate all the station selector switches thereat to connect the communication circuits for conference purposes.

Assuming that station I desires to arrange the conference, then the operator at station I operates the station selector switches 83 and 84 corresponding to stations 2 and 3. Tubes |45 and |48 at station i and also tube |41 at station 2 and tube |49 at station 3 are thereupon supplied with periodic voltage in a manner heretofore described, and the enumerated tubes thus flash on and off. The operators at stations 2 and 3 then first operate selector switches 99 and I|2 conditioning the respective stations for communication with station I. The operator at station then operates the communication control switch I1 thereat to its talk position and informs the operators at stations 2 and 3 of the desire to arrange a conference. The operators at the called stations thereupon operate selector switches |00 and II3, respectively, with the net result that all the station selector switches in the system are closed. At this time, the tubes |45 to |50 are all extinguished inasmuch as the tubes are all disconnected from the common conductor |52. After the circuits have been arranged for the conference, the stations can individually transmit to the other stations by operation of the communication control switches thereat to their talk positions, the communication control switches at the other stations being in their listen positions.

In a system comprising more than three stations, if less than all of the 'stations are arranged for a conference, any other station selecting one of the conferring stations will be given a signal that the called station is busy in the same manner that the third station of the specific embodiment illustrated is given a signal upon the selection of a busy station.

In Fig. 5 there is illustrated a modified circuit arrangement for enabling one station to signal another of a desire to break in upon the transmission from the other station to said one station. The circuit arrangement of this figure corresponds closely to that previously described except for the connections of the break-in signal tubes I I6 and I I1 at stations I and 2, and like elements in this gure have been indicated by the reference characters previously used. The tube ||8 at station I is connected directly to the B supply conductor 38 through resistor ||9 and to the midpoint of the output transformer secondary winding 4I of amplifier I4 by a conductor 240. The tube I I1 at station 2 is similarly connected to the B supply conductor 38 at that station through resistor I 24 and to the midpoint of the secondary winding of the output transformer of ampliler I5 by conductor 24|. The energizing circuit for tube II1 at station 2 is completed at station I through a conductor 242 leading from the midpoint oi' the primary winding 15 of transformer 15 to a contact associated with a switch blade 243 forming part of and operable with the remaining switch blades of the communication control switch I1. The switch blade is grounded by a conductor 244'. The energizing circuit for tube ||5 at station I is completed through a similar circuit arrangement at station 2 including a 'conductor 245 leading from the midpoint of the primary winding of transformer 84 to a contact associated with switch blade 245 forming part of and operable simultaneously with the remaining switch blades of communication control switch I5. The switch blade is grounded by conductor 241.

The operation o1' the arrangement illustrated in Fig. 5 is the same as that of the previous embodiment. When the communication control switches at the two stations are in their uppermost or listen positions. the tubes |I5 and II1 are both deenergized. When the two -stations have been placed in communicating relationship with each other by the closure of the station selector switches 83 and 58, then the tubes remain deenergized when the communication control switch at one station is in its listen position and the communication control switch at the other is in its talk position. When both switches are in their talk positions, as is the case when a station conditioned for reception desires to interrupt a station conditioned for transmission, then the energizing circuits for the two tubes are completed simultaneously. The energizing circuit for tube I|5 at station I is completed across the B supply at that station. the circuit extending from the B supply conductorV 38 through resistor IIS to the tube II5 and thence to ground through conductor 240, the midpoint of secondary winding 4I of amplier I4, the output conductors 42, switch blades 8| of switch I1, the output circuit 52, switch blades 85 in their closed positions, interstation circuit 85, the midpoint of the primary winding of transformer 84 at station 2, conductor 245, switch blade 245 in its lowermost position, and the ground connection 241. The energizing circuit for tube II1 at station- 2 is similarly completed from the B supply conductor 35 at that station to ground as follows: conductor |24, tube II1, conductor 24|, midpoint of the secondary winding of the output transformer of amplitler I5, output conductors 86, switch blades 85, the output circuit 85, switch blades IIII, interstation circuit 13, midpoint of primary winding at station I, conductor 242, switch blade 243 in its lowermost position, and the ground connection 244.

The modification of the invention illustrated in Fig. 6 differs somewhat from those previously described in that the neon tube at a station conditioned for reception from another station conditioned for transmission is energized while the tube at the station conditioned for transmission is not energized until the station conditioned for reception operates the Vcommunication control switch thereat to condition it for transmission.

Referring now to Fig. 6, in which elements corresponding to those previously described are indicated by like reference characters, it may be noted that the tube I|5 at station I is connected to the midpoint of the primary winding of the transformer 15 through conductor 25| and resistor 252 and to ground by a conductor 253. In like manner, the tube II1 at station 2 is connected to the midpoint of the primary winding of transformer 84 by conductor 254 and resistor 255 and to ground by a conductor 255. .The e'nergizing circuit for tube ||5 at station I is completed through a circuit at station 2 including a conductor 251 leading from the midpoint oi' secondary winding of the output transformer of ampliiier I5 to a switch blade 255 through a resistor 255. Ihe switch blade 255 forms part of the communication control switch I5 and is adapted when the latter is in its talk position to complete a circuit to the B supply conductor 35 through a branch conductor 258. 'I'he energizing circuit for tube II1 at station 2 is similarly completed at station I through a conductor 25| leading from the midpoint of the secondary winding 4| oi' ampliiier I5 to switch blade 252 through a resistor 255. The switch blade 252 forms part of the communication control switch I1 and is adapted to complete a circuit to the B supply line 35 when the switch I1 is in its talk position through a branch conductor 254.

After stations I and 2 have been placed in communication with each other by the closure of the station selector switches 53 and l88, then with both the communication control switches I1 and I5 in their listen positions, both tubes II5 and II1 are deenergized. When the switch I1 at station I is in its talk position and switch I8 at station 2 is in its listen position, tube II1 at station 2 is energized through a circuit including the interstation conductors 84 individual' to station 2 and the switch blade 252 in its circuit closing position wherein it connects the B supply line 35 to the interstation circuit. When the switch I 1 is in its listen position and switch I8 in its talk position. tube II6 at station I is. energized through a similar circuit including the interstation circuit 13 individual to station I and switch lblade 255 in circuit closing position.

When one of the stations desires to interrupt the other station conditioned for transmission, it is necessary only to operate the communication control switch thereat toits talk position. When this is done, the neon tube at the station originally conditioned for transmission is energized to give an indication to the operator thereat that the other station desires to interrupt or break in on the transmission.

It may be well again to note that While only a comparatively few stations have been illustrated in the description of the various embodiments of the invention, it should be understood that the number of stations may be increased as required by the needs of the particular installation. While the invention has been disclosed in conjunction with the specic details of preferred embodiments thereof, it should be understood that such details are not intended to be limitative of the invention except in so far as set forth in the accompanying claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. In an intercommunicating system of the type comprising a station having a communication direction control switch operable to condition the station for reception or transmission and a second station, the combination including, break in signal means at the first station, and means including signal means control circuits and a, switch at the second station controlling said circuits so constructed and arranged that the signal means at the iirst station can be operated from the second station when the first is conditioned for transmission and the second for reception for providing a signal at the station conditioned for transmission that it is desired to break in on the transmission from the station.

2. In an intercommunicatng system oi the type comprising a first station having a communication direction control switch operable to condition the station for reception or transmission and a second station, the combination including, break in signal means at the rst station, and means including a switch at the second station i'or operating said signal means when the communication direction control switch at the i'lrst station conditions that station for transmission, thereby to indicate a desire to break in on the transmission from the first station.

3. In an intercommnicating system of the type comprising a ilrststation having a communication direction control switch operable to condition the station for reception or transmission, a second station and a communication circuit between the stations, the combination including, signal means at the nrst station, and means including said communication circuit and a switch at the second station for operating said signal means when the communication direction control switch at the first station conditions that station for transmission, thereby to indicate a desire to break in on the transmission from the iirst station.

4. In an intercommunicatingsystem oi the type including a. rst station having a communication direction control switch operable to condition the station for reception or transmission and a second station, the combination including, signal means at said iirst station, signal controlling means at said iirst station for conditioning said signal means for operation when said communication direction control switch conditions said station ior transmission, and means including signal `controlling means at the second station for operating said signal means when said first station is conditioned for transmission. A

'including a first station having a communication direction control switch operable to condition the station for reception or transmission and a second station, the combination including, signal means at said first station, switch means at said iirst station' operable simultaneously with said communication direction control switch for conditioning said signal means for operation when said communication direction control switch is operated to condition said station for transmission, and means including switch means at the second station for operating said signal means when said iirst station is conditioned for transmission.

6. In an intercommunicating system oi' the type including a first station having a communication direction control switch operable to condition the station for reception or transmission and a second station, the combination including, a signal light at said rst station, a source of power for said light, switch means at said rst station operable simultaneously with said communicationl direction control switch for partlycompleting the connection of said light to said source of power when said communication direction control switch is operated to condition said station for transmission, and means including switch means at the second station for completing the connection of said light to' said source of power when said first station is conditioned for transmission.

7. In an intercommunicatng system oi the type Comprising a Pair f stations each having a communication direction control switch operable to condition the station for reception or transmission, the combination including, break in signal means at each station, and means including .a switch at each station for operating the signal means at another when the communication direction control switch at said other station conditions said other station tor transmission, thereby to indicate a vdesire to break in on the transmission from said other station.

8. In an intercommunicatng system of the type comprising a pair of stations -each having a communication direction control switch operable to condition the station for reception and transmission, the combination including, signal means at each station, signal controlling means at each station for conditioning the signal means at that station i'or operation when the communication control switch thereat conditions the station for transmission, and signal controlling means at each station operable when the station is conditioned for transmission for operating the signal means at the other station when the signal means at the other station is conditioned for operation.

9. In an intercommunicatng system oi the type comprising a pair oi' stations each having a communication direction control switch operable to condition the station for reception and transmission, the combination including, signal means at each station, signal controlling means at each station operable simultaneously with the communication direction control switch thereat for conditioning the signal means at that station ior operation when the communication control switch thereat conditions the station for transmission, and signal controlling means at each station operable simultaneously with the communication direction control switch thereat and operable when the station is conditioned for transmission for operating the signal means at the other station when the signal means at the other station is conditioned for operation.

l0. In an intercommunicatng system of the type comprising a pair of interconnected stations having communication direction control switches alternately operable to condition the stations for reception and transmission, the combination including, signal means at each station, and means including signal means control circuits and switch means operable simultaneously with the ,communication direction control switches controlling said circuits so constructed and arranged that the signal means at a station conditioned for transmission can be operated from a station conditioned for reception upon operation of the communication direction control switch at the latter station to condition it for transmission for providing a signal that it is desired to break in on the transmission from the station.

11. In an intercommunicatng system of the type comprising a pair of stations having com munication direction control switches alternately operable between talk and listen positions for providing two way communication between the stations, the combination including signal means at each station, and signal controlling means at each station operable simultaneously with the communication control switch thereat so constructed and arranged that the signal means at a station conditionedfor transmission is operated when the communication direction control switch at the other station is operated to 76 tionithe other station for transmission.

condi- 12. In an intercommunicating system of the type comprising a pair of stations interconnected by a pair of interstation circuits and having communication direction control switches alternately operable between talk and listen positions for providing alternate two way communication between the stations in opposite directions over said interstation circuits, the combination including. signal means at one station associated with one of said circuits, signal means at the other station associated with the other of said circuits, and signal controlling means at each station operable simultaneously with the communication control switch thereat so constructed and arranged that thesignal means at a station conditioned for transmission is operated when the communication direction control switch at the other station is operate-d to condition the other station for transmission. i

13. In an intercommunicating system of the type comprising a pair of stations having communication direction control switches alternately operable between talk and listen positions for providing two way communication between the stations, the combination including, a signal light at each station, a source of power at each station, and signal controlling means at each station operable simultaneously with the communication control switch thereat so constructed and arranged that the light at a station conditioned for transmission is connected to a source of power and energized when the communication direction control switch at the other station is operated to condition the other station for transmission.

14, In'an intercommunicating system of the type comprising a pair of stations interconnected by a communication circuit and having communication direction control switches alternately operable between talk and listen positions for providing two way communication between the stations, the combination including, signal means at each station connected to said communication circuit in balanced manner, and signal controlling means at each station connected in balanced manner to said communication circuit and operable simultaneously with the communication control switch thereat so constructed and arranged that the signal means at a station conditioned for transmission is operated through said communication circuit when the communication direction control switch at the other station is operated to condition the other station for transmission.

15. In an intercommunicating system of the type comprising a pair of stations interconnected by a pair of interstation circuits and having communication direction control switches alternately operable between talk and listen positions for providing alternate two way com- -munication between the stations in opposite directions over said interstation circuits, the combination including, a signal light at each station connected in balanced manner to one of said circuits, a source of power at each station, and signal controlling means at each. station operable simultaneously with the communication control switch thereat for conditioning the signal light at the station for connection to a source of power when the communication direction con, trol switch conditions the station for transmission, and means including signal controlling means at each 'station connectedl in balanced manner to a communication circuit and operable simultaneously with the communication direction control switch thereat for completing the connection of the light at the other station to a source of power.

16. In an intercommunicating system of the type comprising two or more stations adapted to be connected by a pair of interstation circuits and a common conductor and each having an ampliiier, a loudspeaker utilizable both as a receiver and a transmitter, station selector -means, and a communication direction control switch operable to condition the station for reception over one of said circuits by connection of the loudspeaker thereto or for transmission over the other by connection oi' the loudspeaker to the input of the amplifier and of the output thereto through the station selector means, whereby two way communication can be carried on between two stations by alternate operation of the switches thereat, including in combination, a transformer in the reception circuit at each station having a primary winding connected to said one circuit thereat and a secondary winding adapted to be connected to the loudspeaker through said communication direction control switch when the latter conditions the station for reception, a signal light ateach station having one terminal connected to the mid point of the primary winding of the transformer at that station, a source of power at each station, switch ymeans operable with the communication direction control switch at each station for partly completing the connection of the light at the station to the source of power thereat by connecting the other terminal of the light to the source when the communication direction control switch conditions the station for transmission, a pair of resistors connected across the amplifier output at each station, a connection from between the resistors i-o said common conductor, and other switch means forming part of and operable with the communication direction control switch at each station for completing the connection of the light at the other station to the source of power at the other station through said common conductor and transmission circuit when the communication direction control switch conditions the station for transmission, whereby the signals at both stations are connected to their respective sources of power when both stations are conditioned for transmission.

17. In an intercommunicating system of the type comprising two or more stations adapted to be connected by a pair of interstation circuits and each having a communication direction control switch operable to condition the station for reception over one of said circuits or for transmission over the other, whereby two way communication can be carried on between two stations by alternate operation of the switches thereat, including in combination, a signal light at each station connected to the reception circuit for that station. a source of power at each station, switch means operable with the communication direction control switch atveach station for partly completing the connection of the light at the station to the source of power thereat when the communication direction control switch conditions the station for transmission, and other switch means operable with the communication direction control switch at each station for completing the connection of the light at the other station to the source of power at the other station through said transmission circuit when the communication direction contml switch conditions the station for transmission, whereby the signals at both stations are connected to their respective sources of power when both' stations are conditioned for transmission.

18. In an intercommunicating system of the type comprising two or more stations adapted to be connected by a pair of interstation circuits and a common conductor and each having a communication direction control switch operable to condition the station for rec ption over one of said circuits or for transm ssion over the other, whereby two way communication can be carried on between two stations by alternate operation of the switches thereat, including in combination, a transformer in the reception circuit at each station, a signal light at eachi station connected to the mid point of the primary winding of the transformer at that station, a source of power at each station, switch means operable with the communication direction control switch at each station for partly completing the connection of the light at the station to the source of power thereat when the communication direction control switch conditions the station for transmission, a pair of resistors connected across the transmission circuit at each station, a connection from between the resistors to said common conductor, and other switch means forming part of and operable with the communication direction control switch at each station for completing the connection of the light at the other station to the source of power at the other station through said common conductor when the communication direction control switch conditions the station for transmission, whereby the lights at both stations are connected to their respective sources of power when both stations are conditioned Afor transmission.

19..In an intercommunicating system of th type comprising two or more stations adapted to be connected by a pair of interstation circuits and each having a communication direction control switch operable to condition the station for reception over one of said circuits for transmission over the other, 'whereby two way communication can be carried on between two stations by alternate operation of the switches thereat, including in combination, a source of power at each station, a signal light at each station having one terminal connected to the source of power at that station, switch means operable with the communication direction control switch at eachvstation for connecting the other terminal of the light at the station to said other circuit when the communication direction control switch-conditions the station for transmission over said other circuit, and other switch means operable with the communication direction control switch at each station for completing the connection of the light at the other station to the source of power at the other station through said one circuit when the communication direction control switch conditions the station for transmission, whereby the signals at both stations are connected at their source of power when both stations are conditioned for transmission.

20. In an intercommunicating system of the type comprising two or more stations adapted to be connected by a pair of interstation circuits and a common conductor and each having a communication direction control switch operable to condition the station for reception over one of said circuits or for transmission over the other. whereby two way communication can be carried on between two stations by alternate operation of the switches thereat, including in combination, a source ofl power at each station, a transformer in the reception circuit at each station, a connection from the mid point of the primary winding of the transformer at each station to the communication direction control switch,lswitch means operable with the communication direction control switch at each station for connecting the common conductor to said connection when the communication direction control switch conditions the station for transmission, a signal light at each station having one terminal connected to the source of power thereat, and other switch means forming part of and operable with the communication direction control switch at each station for connecting the other terminal of the light at the station to the transmission circuit thereat and thereby completing the connection of the light at the other station to the source of power at the other station when the communication direction control switch conditions the station for transmission, whereby the lights at both stations are connected to their respective sources of power when both stations are conditioned for transmission.

21. In an intercommunicating system of the v type comprising two or more stations adapted to be connected by a pair of interstation circuits and a common conductor and each having an amplifier, a loudspeaker utilizable both as a receiver and a transmitter, station selector means, and a communication direction control switch operable to condition the station for reception over one of said circuits by connection of the loudspeaker thereto or for transmission over` the other by connection of the loudspeaker to the input of the amplifier and of the output thereto through the station selector means, whereby two way communication can be carried on between two stations by alternate operation of the switches thereat, including in combination, a transformer in the reception circuit at each station having a primary winding connected to said one circuit thereat and a secondary winding adapted to be connected to the loudspeaker through said communication direction control switch when the latter conditions the station for reception, a connection at each station from the mid point of the primary winding of the transformer at that station to the communication direction control switch, switch means operable with the communication direction control switch at each station for connecting the connection at the station to the common conductor when thevcommunication direction control switch conditions the station for transmission, a signal light at each station having one terminal connected to the source of power and its other terminal to the amplier output circuit, and other switch means forming part of and operable with the communication ldirection control switch at each station for completing the connection of the light at the other station to the source of power at the other station through said common conductor and transmission circuit when the communication direction control switch conditions the station for transmission, whereby the signals at both stations are connected to their respective sources of power when both stations are conditioned for transmission. y

22. In an intercommunicating system of the type comprising two or more stations adapted to be connected by a pair oi interstation circuits and a common conductor and each having a communication direction control switch operable to condition the station for reception over one o1'.

said circuits for transmission over the other, whereby two way communication can be carried on between two stations by alternate operation of the vswitches thereat, including in combination, a signal light at each station connected to the reception circuit for that station and to the common conductor, a source of power at each station, switch means operable with the communication direction control switch at each station for connecting the light at the other station to the source of power at the station through the transmission circuit and common conductor when the communication direction control switch conditions the station for transmission, whereby the signal light at a station conditioned for transmission may be connected to a source of power upon operation oi the communication direction control switch at a station conditioned for reception to condition the latter station for reception.

23. In an intercommunicating systemoi' the type comprising two or more stations adapted to be connected by a pair of interstation circuits and a common conductor and each having a communication direction control switch operable to condition the station for reception over one of said circuits or for transmission over the other, whereby two way communication can be carried on between two stations by alternate operation oi' the switches thereat, including in combination, a transformer in the reception circuit at each station, a signal light at each station connected to the mid point of the primary winding of the transformer at that station and to the common conductor, a source of power at each station, and switch means forming part of and operable with the communication direction control switch at each station for connecting the light at the other station to the source oi power at the station through said transmission circuit common conductor when the communication direction control switch conditions the station for transmission, whereby the signal light at a station conditioned for reception is connected to the source of power at a station conditioned for transmission and a station conditioned'for reception from one conditioned for transmission can signal the latter by conditioning the station for transmission.

24. In an intercommunicating system of the type comprising two or more stations adapted to be connected by a pair oi interstation circuits and a common conductor and each having an amplifier, a loudspeaker utilizable both as a receiver and a transmitter, station selector means, and a communication direction control'switch operable to condition the station for reception over one of said circuits by connection of the loudspeaker thereto or for transmission over the input of the amplier and of the output thereto through the station selector means, whereby two way communication can be carried on between two stations by alternate operation of the switches thereat, including in combination, a transformer in the reception circuit at each station having other by connection of the loudspeaker to the signal light at each station connected across the mid point of the primary winding of the transformer at that station and the common con-` ductor, a source of power at each station, switch means operable with the communication direction control switch at each station for connecting the source of power thereat to the transmission circuit when the communication direction control switch conditions the station for transmission, whereby the signal light at a station conditioned for reception is connected to the source of power at a station conditioned for transmission and a station conditioned for reception from one conditioned for transmission can signal the latter by conditioning the station for transmission.

25. In a multiple station intercommunicating .system of the loudspeaker type comprisinga plurality of stations. any two of which can be placed in communication with each other over two interstation circuits, each of which is utilized for communication in one direction only, and each station having a communication direction control switch operable to condition the station tor reception or transmission, the combination including, signal means at each station, and

means including switch means operable simultaneously with said communication direction control switches and circuits controlled thereby for operating the signal means at a station conditioned for transmission from a station conditioned for reception upon operation of the comoperable simultaneously with said communication direction control switches and circuits controlled thereby for operating the signal means at a station conditioned for transmission `from a station conditioned for reception upon operation of the communication direction control switch at the station conditioned for reception to condition that station for transmission.

27. In a multiple station intercommunicating system.' the combination including, signal means at each station, station selector switches at each station, means including circuits between stations controlling the signal means and controlled by the station selector switches for eiecting operation of said signal means to produce dilerent distinctive signals at both selected and selecting stations when a station selects another dependent trolling the signal means and controlled by said a primary winding connected to said one circuit switch means for eiecting operation of said signal means to produce diierent distinctive signals at the station at which switch means is operated -and the station corresponding to the operated switch means dependent upon whether or not switch means has been operated at the latter station.

29. In a multiple station intercommunicating system, the combination including, signal lights at each station corresponding to other stations in the system, switch means at each station corresponding to other stations of the system, means including circuits between stations controlling the signal lights and controlled by said switch means for selectively eiecting steady or periodic energization of said signal lights to produce different distinctive signals at thestation at which switch means is operated and the station corresponding to the operated switch means dependent upon whether or not switch means has been operated at the latter station.

30. In a multiple station intercommunicating system, the combination including, signal lights at each station corresponding to other stations in the system, station selector switches at each station corresponding to other stations of the at each station corresponding to other stations in the system, station selector switches at each station corresponding to other stations of the system, a source of steady voltage. a source oi periodic voltage, means including circuits between stations controlling the signal lights and light circuit controlling switches operable with said selector switches for selectively connecting said signal lights to said periodic or steady voltage sources to produce different distinctive signals at the station at which a selector switch is operated and the station corresponding tothe operated selector switch dependent upon whether or not a selector switch has been operated at the latter station.

32. In a multiple station intercommunicating system, the combination including, neon tubes at each station corresponding to other stations of the system, station selector switches at each station corresponding to other stations of the system, a source of steady voltage, a rst conductor leading therefrom to all stations, a source of periodic voltage, a second conductor leading therefromto all stations, a common conductor connected Ato both voltage sources and leading to all stations, and means operable conjolntly with said selector switches for producing a iiashing of tubes at both a selecting and selected station if no selector switches are operated at the selected station and a steady glow of the tubes in the event a selector switch has been operated at the selected station, said means including conductors connecting in series the tubes at each pair of stations corresponding to said stations, a pair of switches operable with each selector switch, the first of said switches being connected to a terminal of its associated tube and operable when the selector switch is not operated to connect the tube to the common conductor and when the selector switch is operated to connect the tube to a conductor leading to a second of said pair of switches asso--V ciated with the selector switches at other stations corresponding thereto, the second of said pair of switches at each station being connected in series to said last mentioned conductor and operable when the selector switch is not operated to connect said last mentioned conductor to said second conductor through other corresponding switches at the station and when the selector switch is operated to connect said last mentioned conductor to said ilrst conductor.

33. In a multiple station intercommunicating system, the combination including, signal means at each station, station selector switch means at each station individual to other stations of the system, means including circuits between stations controlling the signal means and controlled by said switch means for effecting operation of said signal means to produce a periodic signal or another signal at the station at which switch means is operated dependent upon whether or not switch means has been operated at the station corresponding to the operated switch means.

34. In a multiple station intercommunicating system, the combination including, neon tubes at each station corresponding to other stations of the system, station selector switches at each station corresponding to other stations of the system, a source of steady voltage, a iirst conductor leading therefrom to all stations, a source of periodic voltage, a second conductor leading therefrom to all stations, a commqi conductor connected to both voltage sources and leading to all stations, and means operable conjointly with said selector switches for producing a flashing of a tube at a selecting station if no selector switches are operated at the selected station and a steady glow of the tube in the event a selector switch has been operated at the selected station, said means including conductors connecting the tubes at each station to the stations corresponding thereto, a pair of switches operable with each selector switch, a first of said switches being connected to a terminal of its associated tube and operable when the selector switch is not operated to connect the tube to the common conductor and when the selector switch is operated to connect the tube to a conductor leading to a second of said pair of switches associated with the selector switches at other stations corresponding thereto, the second of said pair of switches at each station being connected in series to said last mentioned conductor and operable when the selector switch is not operated to connect said last mentioned conductor to said second conductor through other corresponding' switches at the station and when the selector switch is operated to connect said last mentioned conductor to said iirst conductor.

35. In a multiple station intercommunicating system, the combination including, signal means at each station, switch means at each station corresponding to other stations of the system, means including circuits between stations controlling the signal means and controlled by said switch means for eifecting operation of said signal means to produce a periodic signal or another signal at the station corresponding to the operated switch means dependent upon whether or not switch means has been operated at the latter station.

36. In a multiple station intercommunicating system, a source oi steady voltage, a ilrst conductor leading therefrom to all stations, a source of periodic voltage, a second conductor leading therefrom to all stations, a common conductor connected' to both voltage sources and leading to all stations, and means operable conjointly with said selector switches for producing a flashing of a tube at a selected station if no selector switches are operated at the selected station and a steady glow of the tube in the event a selector switch has been operated at the selected station, said means including a conductor connecting the tubes at each station to corresponding stations, a pair of switches operable with each selector switch, a rst of said switches being connected to a terminal of its associated tube and operable when the selector switch is not operated to connect the tube to the common conductor and when the selector'switch is operated to connect the tube to a conductor leading to a second of said pair oi switches associated with the selector switches at other stations corresponding thereto, the second of said pair-of switches at each station being connected in series to said last mentioned conductor and operable when the selector switch is not operated to connect said last mentioned conductor to said second conductor through other corresponding switches at the station and when the selector switch is operated to connect said last mentioned conductor to said first conductor.

37. In a multiple station intercommunicatlngI system, the combination including, signal means returning said signals to non-operated condition upon operation of the switch means corresponding to the rst station at said corresponding station.

38. In a multiple station intercommunicatlng system, the combination including, signal lights at each station corresponding to other stations in the system, station selector switches at-each station corresponding to other stations of the system, a source of periodic voltage, means including circuits between stations controlling the signal lights and light circuit controlling switches operable with said selector switches for selectively connecting said signal lights to said periodic voltage source to produce distinctive signals at the station at which a selector switch is operated and the station corresponding to the operated selector switch at which a selector switch has not been operated and for disconnecting said lights from said source of periodic voltage upon operation of the selector switch corresponding to said first station at said corresponding station.

39. In a multiple station intercommunicatlng system, the combination including, signalmeans at each station, switch means at each station corresponding to other stations ofthe system, means including circuits between stations controlling the signal means and controlled by said switch means for effecting operation of said signal means to produce a distinctive signal at the station at which switch means is operated and the station corresponding to the operated switch means and at which switch means has not been operated and for returning said signal means to non-operated condition upon operation of the switch means corresponding to the first station at said corresponding station, and means including said circuits and switch means for effecting operation oi the signal means to produce other system, a source of steady voltage, a source of periodic voltage, means including circuits between stations controlling the signal lights and light circuit controlling switches operable with said selector switches for connecting said signal lights to said periodic voltage source to produce distinctive signals at the station at which a selector switch is operated and the station corresponding to the operated selector switch at which a selector switch has not been operated and for disconnecting said signal lights from said periodicvoltage source upon operation of the selectorV switch corresponding to said first station at said corresponding station, and means including said circuits and light circuit controlling switches for connecting signal lights at a third station and one of said two first mentioned stations to said source of steady voltage upon operation at said third station oi a selector switch corresponding to said one station.

41. In a multiple station intercommunicating system, the combination including, signal lights at each station corresponding to other stations in the system, and means including switch means at each station corresponding to other stations in the system and controlling the signal lights at-other stations for producing flashing of the signal lights at the other station when switch means at said other stations occupy predetermined positions.v y

42. In a multiple station intercommunicating system, the combination including, signal lights at each station corresponding to' other stations in the system, and means including switch means .at each station corresponding to other stations in the system and controlling the signal lights'at other stations for producing flashing of the signal lights at the other stations in response to the operation of the switch means at the station in the event no switch means have been operated at said other stations.

43. In a multiple station intercommunicatlng system, the combination including, signal lights at each station corresponding to other stations in the system, and means including switch means at each station corresponding to other stations in the system and controllingthe signal lights at other stations for producing flashing of the signal lights at the other stations in response to the operation of the switch means at the station in the event switch means have been operated at said other stations.

44. In a multiple station intercommunicatlng system, the combination including, signal lights at each station corresponding to other stations in the system, and means including switch means at each station corresponding to other stations in the system and controlling the signal lights for producing ilashingof the signal lights at each station in response to the operation of the switch means thereat when the switch means at stations corresponding to the operated switch means occupy predetermined positions.

45. In a multiple station intercommunicating system, the combi'iation including, signal lights at each station cori sponding to'other stations in the system, and mans including switch means at each station corresponding to other stations in the system and controlling the signal lights for producing flashing of` the signal lights at each station in response to the operation of the switch means thereat when the switch means at stations corresponding to the operated switch means have been operated.

46. In a multiple station intercommunicating system, the combination including, signal lights at each station corresponding to other stations in the system, and means including switch means at each station corresponding to other stations in the system and controlling the signal lights for producing flashing of the signal ihts at each station in response to the operation of the switch means thereat when the switch means at stations corresponding to the operated switch means have not been operated.

47. In a multiple station intercommunicating system, the combination including, signal lights' at each station corresponding to other stations in the system, and means including switch means at each station for controlling signal lights at that and at other stations for producing ashing of the signal lights at that and at other stations corresponding to operated switch means when the switch means at the other stations corresponding to the operated switch means occupy predetermined positions.

48. In a multiple station intercommunicating system, the combination including, signal lights at each station corresponding to the other stations in the system, and means including switch means at each station for controlling signal lights at that and at other stations for producing ilashing of the signal lights at that and at other stations corresponding to operated switch means when the switch means at the other stations corresponding to the operated switch means have not been operated.

49. In a multiple station intercommunicating system, the combination including, signal lights at each station corresponding to other stations in the system, and means including switch means at each station for controlling signal lights at that and at other stations for producing ashing 'of the signal lights at that and at other stations corresponding to operated switch means when the switch means at the other stations corresponding to the operated switch means have been operated.

50. In a multiple station intercommunicating system, the combination including, signal means at each station, station selector switches at each station, means including circuits between stations controlling the signal means and controlled by the station selector switches for effecting operation of said signal means to produce different distinctive signals at both selected and selecting stations when a station selects another dependent upon whether or not a station selector switch has been operated at the selected station, and means for reversing the natures of the distinctive signals produced in response to the selection of a station at which a selector switch has or has not been operated.

l. In a multiple `ttation intercommunicating system, the combination including, signal lights at each station, station selector switches at each station, means including circuits between stations controlling the signal means and controlled by the station selector switches for eiecting operation of said signal means to produce steady glow or flashing of signa1 lights at both selected and selecting stations when a station selects another dependent upon whether or not a station selector switch has been operated at the selected station, and means for reversing the nature of the signals produced upon selection of a station at which a selector switch has or has not been operated.

52. A periodic voltage supply system, including in combination, a source of voltage, a, voltage output conductor, switch means operable alternately to connect said conductor to and to disconnect said .conductor from said source, and means including a relay having a winding energized from said voltage source through said switch means when the latter disconnects said output conductor'from said voltage source for periodically operating said switch means.

53. A periodic voltage supply system, including in combination, a source of voltage, a voltage output conductor, switch means operable between two positions alternately to connect said conductor to said source and to disconnect said conductor from said source, and means including a relay having a winding adapted to be energized from said voltage source through said switch means when the latter disconnects said output conductor from said voltage source for periodically operating said switch means between its two positions.

54. A periodic voltage supply system, including in combination, e. source of voltage, a voltage output conductor, a relay having a Winding, a switch blade connected to said source oi? voltage and operable in one position to connect said source to said conductor and to disconnect said relay Winding from said source and in another position to disconnect said source from said conductor and to connect said source to said relay winding, and means including a condenser associated with said relay winding for determining the lengths oi time the switch blade is in its two positions.

55. A periodic voltage supply system, including in combination, a source of voltage, a voltage output conductor, a relay having a winding, a switch blade connected to said source of voltagel operable in one position to connect said source to said conductor and disconnect said relay winding from said source and in another position to disconnect said source from said conductor and to connect said source to said relay winding, and means including a condenser in circuit with said relay winding and charged when said winding is connected to said source and discharged when said winding is disconnected from the source for determining the lengths of time the switch blade is in its two positions.

56. .A periodic voltage supply system, including in combination, a source of voltage, a voltage output conductor, a relay having a winding, a switch means operable in one position to connect said source to said conductor and to disconnect said winding from said source and in another position to disconnect said source from said conductor and to connect said source to said relay winding, and means including a condenser-resistor network in circuit with said relay winding and through which said relay winding is energized and discharging through said winding 4when the winding is disconnected from said source for determining the

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