US2166517A - Signal transmitting system - Google Patents

Description

INPUT OUTPUT INF UT OUTPUT BEST AVAILABLE com,

S. J. BEGUN SIGNAL TRANSMITTING SYSTEM Filed March 26, 1957 5 Sheets-Sheet 1 INVENTOR. Begun mixi Jul 18, 1939.

s. .1. BE GUN SIGNAL TRANSMITTING SYSTEM Filed larch 26,

5 Sheets-Sheet 2 INVENTOR.

A QRNEYS.

July 18, 1939. s, E M 2,166,517

smrm. TRANSMITTING sY's'rEl Filed larch 26, 1937 5 Sheets-Sheet 5 INVENT OR.

Semi Begun BY I ATTORNEY.

5 Sheets-Sheet 4 S. J. BEGUN Filed larch 26, 1937 SIGNAL TRANSMITTING SYSTEI July 18, 1939.

I) l'lnlllllil? Ill bl INVENTOR ATTORNEYS iii ' July 18, 1939. s. J. BEGUN 2,166,517

SIGNAL TRANSMITTING SYSTEM Filed March 26, 1937 5 Sheets-Sheet 5 7 SMICF I a *35 1 I INVENTOR. V Semi I B an 'I'TORNEYS .7 TFL-EPHONY.

Patented July 18, 1939 UNITED STATES Exams-e" 2,166,517 PATENT OFFICE 2,166,517 SIGNAL TRANSMITTING SYSTEM Semi J. Begun, New York, N. Y., minor, by mesne assignments, to Carl] Tucker, New York.

Application March 26. 1937, Serial No. 133,144

34 Claims.

This invention relates to improvements in electrical signal transmitting systems.

The basic object of this invention is to provide improved forms of transmission circuits between transmitting and receiving apparatus to insure a maximum of dependability of such systems.

A further object of the invention is to provide a transmission system of this nature in which the signal energy level is not reduced to impractical and inoperative values upon the development of a short circuit or an open circuit on the transmission line.

These and many more detailed and specific objects of the invention will become apparent to those skilled in the art from the following description when taken in connection with the attached drawings.

This invention resides substantially in the combination, construction, arrangement and relative location of parts, all in accordance with the following disclosure.

In the accompanying drawings:

Figure 1 is a diagrammatic illustration of one form of the invention employing conductive coupling between the transmission line and the transmitting and receiving apparatus;

Fig. 2 is a diagrammatic illustration of a modified form of system employing inductive coup Fig. 3 is a diagrammatic illustration of a modified form of the circuit of Fig, 2 including signaling means for indicating open circuits and short circuits on the transmission line;

Fig. 4 is a diagrammatic illustration of an inductively coupled system as modified for use with a plurality of signal responsive devices supplied from a single transmitting source;

Fig. 5 is a diagrammatic illustration of a further modified form of the invention illustrating the use of double conducting loops;

Fig. 6 is a diagrammatic illustration of an extended form of the system of Fig. 5 employing two sets of conductive loops; v

Fig. '7 is a diagrammatic illustration of a modification of the system of Fig. 6; and

Fig. 8 is .a diagrammatic illustration of another method of coupling a plurality of loops to a single transmitter to accomplish the objects of this invention. V

A further object of this invention is to provide improved forms of electrical signal energy transmission circuits which are highly dependable in that short circuits and open circuits on the transmission line do not have the effect of reducing the signal energy level in the transmission line to a point where the signal responsive apparatus is rendered inoperative. There are many fields of use for transmission systems having such desirable characteristics. For example,

such a system is of great value on shipboard where even under the normal operating conditions it is extremely diflicult to keep the transmission lines for signaling apparatus in good physical condition. Furthermore, under emergency conditions such transmission systems are often subjected to physical disturbances even to the extent of interruption, thereby rendering the very apparatus which is so vital in emergencies inoperative. Any improvement in such signaling systems whereby the dependability thereof is increased is of major importance in this field of use.

It will be apparent from the following disclosure that the invention herein disclosed is of course not limited to use on shipboard but may be employed in any place where it is desired to effect communication between spaced points.

For the eflicient transmission of signal energy in an electrical communication system and especially where the system is used as a safety device, it is not satisfactory to employ a transmission circuit comprising one conductor and ground or two conductors between the transmitter and receiver. The operability of such a system depends directly upon the physical condition of the transmission line and a short circuit of this conductor to ground in the first instance, or a short circuit between both conductors in the second instance, or an open circuit in both instances would render the system inoperative. bility of such disturbances of the physical condition of transmission lines, especially under emergency conditions, renders these forms of transmission circuits unavailable as part of a safety system.

Where a closed grounded loop transmission line is employed, so long as only one open circuit occurs the signal energy will reach the receiver since the signal is transmitted thereto over both legs of the loop. However, a loop circuit of this type is no longer satisfactory when one point thereof is grounded.

Such loop systems may however be adapted to the purposes of this invention as illustrated for example in Figure 1. The system here illustrated is in connection with a so-called talk-back arrangement, that is to a two-way communication system which makes it possible to talk to each end of the line from the other.

as a loud speaker. which can also be used as is known, as a transmitter, connected to ground at one terminal and at the other terminal to the mid-point of a pair of resistances 9 and ill. The other ends of these resistances are connected by the conductors 5 and 6 to the ends of a second pair of resistors l and 8, which in turn are connected together. At 4 is diagrammatically illustrated an amplifier having input and output The possi- As shown, the sysr tem comprises a signal responsive device I, such terminals as indicated. A pair of double-pole double-throw switches are provided and arranged for-simultaneous operation by means of a single operating member 3, as diagrammatically illustrated. In the normal position of this switch,

at which time the signal responsive device 1 acts a as a transmitter, the input of the amplifier is connected between ground and the common terminal of the resistances l and 3. At the same time the terminals of the device 2 are connected to the output of the amplifier as shown. By means of the operating member 3 the switches may be moved to their other position to reverse the connections in an apparent manner, so that the transmitter l becomes a-receiver or signal responsive device, and the device 2 becomes a transmitter and is connected between ground and the input of the amplifier as is apparent from the figure. At the same time the transmission line is connected between ground and the output of the amplifier. The amplifier of course is designed to provide the necessary energy gain to effect efficient operation of the apparatus. It is desirable of course that the resistances I, 8 and 9, Ill be of equal value. By the proper selection of the value of the resistances l, 8, 9 and ID, the drop in energy level upon the occurrence of an open circuit or a short circuit to ground on either conductors 5 and '8 will not result in such a reduction in the energy level as to render the system inoperative. However, such an arrangement is not as satisfactory as it is possible to attain. To emphasize this, it is noted that if the assumption is made that the resistances 1, 8, 9 and ID are zero or very low in value, the result is the same as in the ordinary loop transmission system, and a short circuit would render the system inoperative. If, on the other hand. the value of these resistances is made very high. or even infinite, it is apparent that the energy losses would be so great as to render the system impractical. However, if the impedance of the receiver and transmitter compared with the impedance of the resistors is relatively low. an open circuit or a short circuit while diminishing the signal level an undesirable amount, would not render the system inoperative for some uses.

A much more effective system employing a double conductor or loop system is illustrated in Fig. 2. In this case the device I (used either as a transmitter or receiver) is connected in series to what may be termed for the moment the secondaries of a pair of transformers 9 and 10. The primaries are connected in series to the conductors 5 and 5 and have their common terminal grounded. The other ends of the conductors 5 and 6 are connected to what for the moment may be termed the secondaries of the transformers 1 and 8', the common terminal of which is grounded. shunted across the secondaries of transformers 1' and 8' are the resistances II and I2 and similarly the resistances l3 and I4 are shunted across the primaries of transformer 9' and [0. As before an amplifier which it may be noted can be of the vacuum tube multi-stage type, is diagrammatically illustrated at 4, and having the input and output terminals as shown. As before, a pair of double-pole, double-throw switches with a common operating member 3 are employed, and the device 2 (which may be used either as a transmitter or a receiver) is connected when the switches are in the position shown to the output of the amplifier. The primaries of transformers 'I' and 8 are connected in series by means of the switch 3 in the position 8' and the secondaries of transformers 9' and i 0' be connected so that the conductors 5 and 6 are at the same potential and of the same polarity.

To fully appreciate the operation of this system some characteristics of an ideal transformer should be reviewed. If the primary of such a transformer is considered as a load in any circuit while the secondary is open, it is well known that the primary has the characteristic of a pure reactance. If the secondary is short circuited and the coupling between the primary and secondary is close, this short circuit reflects back to the primary and the primary can therefore be considered as being short circuited. Advantage is taken of this characteristic of a transformer in the system of this invention.

To understand the operation of this system it will be first assumed that the resistances ll, l2,

I3 and II are not employed. If conductor 5 is grounded the windings of transformers 1' and 9' connected thereto are short circuited and as a result the other windings thereof are in effect short circuited. By properly matching the impedance of the transmitter and receiver this would produce no noticeable loss in transmission. A similar result occurs if conductor 6 is grounded. However, if conductor 6 for any reason is open circuited the windings of transformer 8' and I0 connected thereto will not be loaded and the other windings of these transformers will have considerable impedance, resulting in a consider- .able loss of energy transmitted over the other conductor through the transformers 8' and i0.

However, if the resistances H, I2, I3 and H are connected in circuit as shown in Fig. 2, the above described difficulty in connection with open circuit on either conductor disappears. If, for example, conductor 5 is "open circuited, the resistances II and I3 across the windings of transformers 1 and 9 connected to conductor 5, provide loads thereon so that the other windings thereof are not in effect open circuited, and there is not such a noticeable loss in energy. A similar result occurs if conductor 6 is open circuited. While it is true that the use of these resistances results in some loss in transmission, the advantage gained under the circumstances described above overweigh the disadvantages of these losses. By employing resistances of the proper value it is possible to keep the amplitude of the current in the network being fed to the receiver between extremely narrow limits.

Since a communication system of this type depends, in order to afford a high degree of safety, upon the physical condition of the transmission line, it would be normally desirable and even nec-v essary to keep their condition under constant check. Therefore, in accordance with this invention special means have been provided which will immediately indicate if an open or a short circuit occurs anywhere on the line. In the arrangement of Fig. 3 there is shown a system which not only immediately indicates an open or short circuit on either transmission line 5 or 6, but if an open circuit occurs on either line it immediately grounds the windings of the transformers connected thereto. Thus in addition to signaling the condition of the lines, the arrangement of Fig. 3 has the advantage that the windings on open circuit may be loaded, while during normal operation they are not shunted byresistances, and hence the losses due to them are not present. In the system of Fig. 3 only those windings of transformers 1', 6', 3' and ID are shown as are directly connected to the conductors and 6, since the other portions of the system remain the same as that shown for example in Fig. 2. The relays l2, I3 and II are connected in series with the conductors 5 and 6 through battery IS. The switches I6, |1, 2| and 22 operated by the relays H, |2, Hi and I4 respectively are operated under normal conditions of the network so that switches l6 and H are closed and switches 2| and 22 are open. To get this result the switches I6 and I1 are manually closed thereby energizing all of these relays, resulting in the holding of switches l6 and H closed and switches 2| and 22 open. Connected between ground and the midpoint of battery I5 is a relay l8 which controls a switch IS in series with a grounded signal lamp and a grounded battery. Under normal conditions when there are no short circuits on the conductors 5 and 6 this relay I8 is not energized. When a short circuit occurs on either conductor to ground, relay I8 is energized. For example, if conductor 5 becomes grounded current flows from it through switch l1, relay I2, right hand portion of battery l5, and relay |8 to ground. This closes switch I9 and completes a circuit for the signal lamp 20which remains energized until the short circuit is removed.

During the time that relays H and I2 are energized switch 23 is open. This switch involves a pair of contacts as shown, each respectively connected to one terminal of each of relays 25 and 26 respectively, which in turn are connected at their other terminals to the lines 5 and 6. Relay |3 in addition to controlling switch 2|, controls switches 30 and 33 which are respectively open and closed when this relay is energized as it normally is. In the same way relay I4, in addition to controlling switch 22, controls switchcs 29 and .34 which are respectively closed and open when the relay I4 is energized as it normally is. Relay 25 controls the switches 28, 3| and 35 and relay 26 controls the switches 21, 32 and 36, all of which switches are in the position shown since the relays 25 and 26 are de-energized as they normally are. If conductor 5 should become open circuited, relays II and I2 will be deenergized, so that switch 23 closes connecting the battery 24 to relay 26 through ground over conductor 6, relay l4 and switch 2|. Relay 25 will not operate. however. since conductor 5 is open circuited. The operation of relay 26 will close switch 21, open switch 32, and close switch 36. The closing of switch 21 will be a short circuit across the winding of transformer 1' connected to conductor 5 through the closed switch 28. The closing of switch 36 will connect the signal lamp 31 through the battery to ground, energizing this device and signaling the presence of an open circuit. At the time that the open circuit occurred on conductor 5, relays l3 and (4 were de-e'nergized so that switches 2| and 22 closed. The de-energization of relay |3 causes switch 33 to open and switch 30 to close. Switches 29 and 30 being closed, put a short circuit on the winding of transformer 9' connected to conductor 5. Thus there is substantially no diminution in the energy going over conductor 6 because the shown windings of transformers 1' and 9' are short circuit through ground, reflecting this short circuit back to their associated windings. The signal lamp 31 remains energized until the open circuit of conductor 5 is eliminated. The condensers 36, 33, 40 and 4| LAU-ILHJ are employed as blocking condensers to prevent the flow of the D. C. current of these signal and control circuits from passingthrough the windings of the transformers. With this system it will be seen that under normal operating conditions there is no direct current flowing to ground which is especially important on shipboard in order to avoid the difliculties of electrolysis.

As will be apparent to those skilled in the art, a quite similar operation of the system occurs through the other sets of contacts and relays when an open circuit occurs on conductor 6. In this case the signal light 31 is energized as before, and short circuits are put across the shown windings of transformers 8' and In.

It will be apparent to those skilled in the art that different relay arrangements may be employed for accomplishing the same results. The important advantage of this arrangement is that it eliminates the necessity for load resistances constantly connected across the transformer windings, as is required by the system of Fig. 2. It is to be noted that this arrangement is capable of two-way communication in accordance with the disclosure in Fig. 2, since the amplifier, switch mechanism, transmitters and/or receivers may be connected to the other windings of the transformers in the manner shown in Fig. 2. It is important to note that all of the various connections to the relays and control devices, as well as the devices themselves may be all enclosed in a single compact unit so that the danger of injury to the control circuits is minimized. These units would be concentrated at the transmitting and receiving stations, and would not. as appears from Fig. 3. have physical lengths comparable to the lengths of the conductors 5 and 6.

There is shown in Fig. 4 one way communication system employing the principles of this invention. At 42 is a microphone connected to the input of the amplifier 43. The output terminals of this amplifier are connected to the primary windings of the transformers 44 and 45. The

secondaries of these transformers have a common In each case the secondaries are connected in series to the signal responsive devices 56, 51 and 58. It is first to be noted that by reason of the connections between the windings of the transformers so that conductors are all of the same potential with respect to ground, a short circuit will produce little or no effect. If either conductor 5 or 6 is open circuited the load resistances 46, 41, 46 and 49 will prevent a complete open circuit on the primary windings of the transformers, so that substantially the same amplitude of energy will travel to the loud speakers over the other conductor. With this system the only way that a loud speaker can be completely out out is to have an open circuit on the branch conductor extending to the associated transformers from either conductor 5 or 6. With both ends of the feeding lines shunted with the resistance bridges as shown, the load due to these resistances will be relatively smaller the more speakers there are connected in circuit. In other words, the resistances employed may be of the same order of value as the resistances employed for example in the circuit of Fig 2 with only one speaker, regardless of the number of loud speakers employed in the system of Fig. 4. This represents the minimization of losses due to the presence of the resistors. If these resistors were duplicated for each loud speaker a considerable loss would result. This connection of resistances results in the fact that their value depends only upon how much volume reduction is permissible for the speaker unit most effective for an open circuit of either conductor between the last unit of the resistance bridge and the one preceding it. Thus this system is capable of operation at high efficiency and it is not necessary to provide special means to ground the conductors when they are open circuited as in the case of the two-way communication system of Fig. 3.

It is highly desirable in all of the systems disclosed herein to place the conductors 5 and 8 as far apart as possible, for example on shipboard these conductors can be run on opposite sides of the ship. However, in many cases it is not possible or desirable to physically space these conductors, but it is preferable to have them close together, as for example in the same cable. Under these conditions the manner of reversely connecting the windings of the transformers as shown in Fig. 4 is of practical value because these conductors are then at the same potential. Being at the same potential a short circuit therebetween will not affect in any way the transmission of signal energy.

The system of Fig. 5 shows the application of the principle of this invention to a pair of feeding loops used for transmitting the signal energy. The amplifier diagrammatically illustrated at BI is provided with the output transformers of which the secondaries 62 and 83 are shown connected in series and grounded at the common point. Their other terminals are connected respectively to the loops 5 and 8' at the common terminal of the blocking condensers 88, 81, 68 and 88. The primaries 62 and 88 are again connected so that the two loops are at the same potential. These loops are interconnected as shown by means of an impedance 18. The loud speakers 1| are connected to the secondaries of transformers l2 and 18 which secondaries are connected in series as shown. The primaries of these transformers are connected in series between the network through blocking condensers l4 and I5 and have their common terminal grounded as shown. As many of these speaker units may be applied between the loops as desired. At 16 and 11 are a pair of relays connected in series through a battery I8 across the loops in the manner shown. The midpoint of the battery is connected to ground through the winding of relay l8. Relay 18 controls switch 88 and relay 11 controls switch 8|. The fixed contacts of these switches are connected together and to ground through the signal device 82. The movable contacts of these switches are connected together and to ground through will not interfere with the operation of the loud speakers for the reasons pointed out in connection with the system of Fig. 2 for example where in this respect the transformer connections to the conductors are the same. The short circuit on one conductor will result in the flow of current over the other conductor to the connected primaries of the speaker transformers with substantially no diminution.

The occurrence of an open circuit on either or both of the loops will likewise not interfere with the operation of the loud speaker devices because the current flows to their transformers over each loop in both directions. Obviously, therefore, an open circuit will not interfere with the arrival of current at the transformers. Signal devices are provided, however, to indicate the occurrence of short circuits or open circuits. Under normal operating conditions relays l6 and H are continuously energized from battery 18 through the loops and the choke coil 88. This choke coil is proportioned to prevent the interfiow of signal current. Thus switches and 8| are open and signal device 82 is deenergized. Switch 84 is also open since the relay I8 is energized. Upon the occurrence of an open circuit on either conductor the relays l6 and 11 will be de-energized, closing switches 88 and 8| and connecting the signal devices 82 through the battery 83 to ground. Thus the presence of the open circuit is indicated. If a short circuit to ground occurs on either conductor, current will flow from ground through the short circuited loop, through either relay 16 or 11, depending upon which is connected to the short circuited loop, through the battery l4 and to ground through the relay 18. The result is that switch 84 will close and the signal loop 85 will be connected through the battery 83 to ground. Thus a short circuit on either loop to ground is indicated. The two relays l6 and 11 can obviously be replaced by a single relay in series with an impedance of equal value to maintain the A. C. balance of the loops.

Figs. 6 and 7 disclose systems employing two different independent double loops to feed a number of receiving units. Each loop has an independent control arrangement to indicate open circuits or a grounded condition of one or the other conductors of the loop pairs. The relay arrangement illustrated for each pair of loops is the same as that described in full detail in Fig. 5. The loud speakers are connected to the loops in the same way. For this reason the control arrangements and the speaker operation will not be described since each pair of loops operates in the same way as the arrangement of Fig. 5.

The feature of the system of Fig. 6 is in the manner in which the amplifier is coupled to the two loops so that if by chance both channels of one pair of loops becomes grounded this will have no effect upon the operation of the other pair of loops. The output of the amplifier is connected to the primaries of four transformers 80, 8|, 82 and 83. The primaries of transformers 80 and 8| are connected in series through the resistances 84 and 85 to the output of the amplifier and in parallel with the primaries of transformers 82 and 83, which are connected in series with the resistances 88 and 81. The primaries are connected as indicated so that the potentials of both leads of each pair are the same. The secondaries of transformers 80 and 8| are connected in series with each other and with the resistances 88 and 88 across the two loops 8' and 5' of one pair. In a similar way the secondaries of transformers 82 and 93 are connected in series with resistances I and IN across the two loops "and 5" of the other pair. The common terminal of each pair of secondaries is grounded as shown.

The resistances are all selected to have a value so that if both loops of one pair should become grounded the impedance unbalance thus caused will not be reflected back into the output of the amplifier to such an extent as to prevent useful transmission of energy over the loops of the other pair.

It is of course apparent that the number of pairs of loops may be increased by duplication and by connecting them in parallel to the output of the amplifier. Thus a short circuit to ground on both loops of any pair is not reflected back in any substantial manner to interfere with the operation of the loops of all the other pairs.

Since resistances or impedances as described in the arrangement of Fig. 6 involve a constant energy loss which it is desirable to eliminate, the system of Fig. '7 has been developed. In this arrangement as before, the two pairs of loops, the manner of connecting the loud speakers thereto, and the signaling circuits for indicating open circuits and short circuits are the same. The system of this figure differs in that a different method is illustrated for connecting the output of the amplifier with the pairs of loops without employing impedances to prevent the reflection back to the amplifier of short circuits of both loops of a pair to ground. In this case the output terminals of the amplifier I are connected to the primaries in series of a pair of transformers I02 and I03. The secondaries of these transformers are connected in series with the primaries of the four transformers I04, I05, I06 and I 01. The secondaries of these four transformers are connected in pairs in series to the loops 5 and I5 and 5" and I5", respectively as shown. The common point of these secondaries is grounded. If both loops for example 5" and 6" of one pair should be accidentally grounded. the secondary space of the transformers I06 and I0! can be considered as short circuited. This short circuit will reflect back to transformer I03, which is properly matched in impedance to the output impedance of the amplifier so that the output energy of the amplifier will be transferred to the transformer I02 and onto the other pair of loops. With this arrangement the energy level in the other pair of loops will be higher than the normal energy level when both loops are operated.

The advantage of this system over that of Fig. 6 is that there is no energy loss due to the presence of impedances corresponding to the impedances 94 to WI inclusive. This transformer arrangement of Fig. 7 can be used for more than two pairs of loops by simply paralleling the additional pairs to the output of the amplifier.

The control apparatus for operating the signal lights 82 and 85 is the same as that shown in Figs. 5 and 6. and therefore has been indicated in Fig. 7 diagrammatically by a square and the symbol It is again worthwhile noting that with systems of this type. especially when used on shipboard the different types of loops may be spacially distributed over different parts of a ship so that any physical damage to one pair is less likely to simultaneously occur on the other pairs.

Fig. 8 illustrates another transformer arrangement for coupling the output of the amplifier to three or more output circuits such as the pairs of loops previously discussed, In this case the primaries 202, 203 and 204 of three transformers are connected in series to the output of the amplifler I. The secondaries thereof are connected respectively in series with the primaries of the pairs of transformers 205 and 206, 201 and 208, and 209 and 2 I 0. The secondaries of these transformers are connected in series in pairs with their common terminal grounded. Their remaining terminals are respectively connected to the output circuits, the remainder of which may be of any form such as that shown for example in Fig. 5. The short circuit to ground of both loops of each pair connected to the independent pairs of secondaries of the arrangement of Fig. 8 will not be reflected back to the output of the amplifier to interfere with the operation of the other loops.

The arrangement of Fig. 8 lends itself to selective operation of a plurality of transmitting loops. Thus, for example if pairs of loops are connected to the leads of each of the pairs of secondaries in accordance with the system of Fig. 5. and double contact grounding switches SM, 302 and 330 are connected across the loop supply leads, then it is possible by closure of one or more of these switches to intentionally ground the loop associated wherewith as distinguished from accidental grounding. Thus, for example. if switch 30I is closed both of the leads of the secondaries of the associated transformers are directly grounded, with the result that that transmitting loop connected thereto is short-circuited and none of the signal responsive devices connected to that loop are operated. All the signal energy. however, is then distributed as explained in the case of accidental ground to the other loops through the other transformers. This simple arrangement provides a safe and dependable method of selected operation of a plurality of loops from a single signal source. An advantage of this ai rangement is that if anything goes wrong with the short circuiting switches, as for example if the contacts thereof are guarded, the worst that could happen is that the signal responsive devices of the connected loop will continue to operate. which of course is not as serious as a failure involving inoperativeness of the equipment;

It is of course apparent to those skilled in the art that instead of using manually operated grounding switches that remotely controlled mechanical or electromagnetic switches or relays may be employed.

It will be apparent to those skilled in the art that with the loop arrangement as disclosed. the pairs of loops may be multiplied so as to reduce the number of loud speaker or receiver units connected to each pair, thereby minimizing the number of speakers or receivers which are disabled if one pair of loops go out of service, with the gen eral result of greatly increasing the overall safety of the system.

It is noted in connection with these systems, and especially by reference to Fig. 4. that it is desirable to wind the secondaries of the transformers 50 and 5|, 52 and 53, and 54 and 55 to have a direct current resistance of about 4 ohms when the A. C. impedance of the voice coil, for example, of the loud speakers is 12 ohms. With this arrangement a direct short circuit of the voice coil to any one speaker will not be reflected back to the conductors 5 and 8 to interfere with the operation of the other loud speakers in any manner.

It is hardly necessary to note that in some installations instead of actually connecting the socalled grounded terminals to ground, they may all be interconnected by a conductor of the proper electrical characteristics.

From the above description it will be apparent to those skilled in the art that the principles of this invention may be applied in a practical sense in a wide variety of arrangements. I do not, therefore, desire to be strictly limited to this disclosure as given for purposes of illustration, but rather to the scope of the appended claims.

What is claimed is:

l. A talk-back signaling system comprising an amplifier, a pair of combined transmitter-receivers, a transmission line comprising a pair of conductors, impedances connecting the conductors together at their respective ends, means connecting one of said transmitter-receivers to the impedance at one end of the line, and switching means for connecting the impedance at the outer end of the line to the output or input of the amplifier and the other transmitter-receiver to the input or the output of the amplifier.

2. In a signaling system the combination comprising a source of signal energy, a signal responsive device, a transmission line comprising a pair of conductors, two pairs of transformers, one set of responsive windings of each pair being connected in series across the respective ends of the conductors, means for grounding the common terminal of each pair of windings, an impedance shunted across each of said windings, the other set windings of each pair of transformers being respectively connected in series, one set to the signal source and one set to the signal responsive device.

3. In a talk-back signal transmission system the combination comprising an amplifier, a pair of transmitter-receivers, a transmission line comprising a pair of conductors, a pair of transformers, the respective windings of each pair being connected in series across the respective ends of the conductors, the common terminal of each pair of windings being grounded, impedances shunted across each of said windings, the other winding of one pair of transformers being connected in series to one transmitter-receiver, and means for connecting the other pair of windings of the other pair of transformers alternately to the output and input of the amplifier and the other transmitter-receiver alternately to the input and output of the amplifier.

4. In a signaling system the combination comprising a source of signal energy, a signal responsive device, a transmission line comprising a pair of conductors, two pairs of transformers, one set of respective windings of each pair being connected in series across the respective ends of the conductors, means for grounding the common terminal of each pair of windings, a resistance shunted across each of said wind ngs, the other set windings of each pair of transformers being respectively connected in series, one set to the signal source and one set to the signal responsive device.

5. In a talk-back signal transmission system the combination comprising an amplifier, a pair of transmitter-receivers, a transmission line comprising a pair of conductors, a pair of transformers, the respective windings of each pair being connected in series across the respective ends of the conductors, the common terminal of each pair of windings being grounded, resistances shunted across each of said windings, the other winding of one pair of transformers being connected in series to one transmission-receiver, and means for connecting the other pair of windings of the other pair of transformers alternately to the output and input of the amplifier and the other transmitter-receiver alternately to the input and output of the amplifier.

6. In a signaling system the combination comprising a source of signal energy, a signal responsive device, a transmission line comprising a pair of conductors. means for coupling the signal source and the receiver to the respective ends of both conductors, said means comprising pairs of transformers at the respective ends of the transmission line having the respective windings of the pairs connected to the ends of the conductors, impedances shunting said windings, and a common grounding connection for the impedance and associated winding.

7. In a signaling system the combination including a transmission line comprising a pair of conductors, impedances shunted across the respective ends of the conductors, said impedances having an intermediate point grounded, a signal source coupled to the impedance at one end of the line, a signal responsive device coupled to the impedances at the other end of the line, and means connected to said conductors for signaling the grounding of either conductor or the open circuiting of either conductor.

8. In a signaling system the combination including a transmission line comprising a pair of conductors, impedances shunted across the respective ends of the conductors, said impedances having an intermediate point grounded, a signal source coupled to the impedances at one end of the line, a signal responsive device coupled to the impedances at the other end of the line, and means for connecting a resistance across the portions of the impedances connected to a conductor when it is open circuited.

9. In a signaling system the combination including a transmission line comprising a pair of conductors, impedances shunted across the respective ends of the conductors, said impedances having an intermediate point grounded, a signal source coupled to the impedances at one end of the line, a signal responsive device coupled to the impedances at the other end of the line, means for connecting a resistance across the portions of the impedances connected to a conductor when it is open circuited, and means for signaling the grounding or open circuiting of either conductor.

10. In a signaling system the combination including a transmission line comprising a pair of conductors, a pair of impedances shunted, in

series across the respective ends of the conductors, the common terminal of each pair of irnpedances being grounded, a source of signal energy coupled to the impedances at one end of the line, a signal responsive device coupled to the impedances at the other end of the line, and signaling means interconnecting the conductors for indicating the grounding of either conductor.

11. In a signaling system the combination in cluding a transmission line comprising a pair of conductors, a pair of impedances shunted in series across the respective ends of the conductors, thecommon terminal of each pair of impedances being grounded, a source of signal energy coupled to the impedances at one end of the line, a signal responsive device coupled to the impedances at the other end of the line, and signaling means interconnecting the conductors for indicating the open circuiting of either conductor.

79. TFLEPHDNY- 12. In a signaling system the combination including a transmission line comprising a pair of conductors, a pair of impedances shunted in series across the respective ends of the conductors, the common terminal of each pair of impedances being grounded, a source of signal energy coupled to the impedances at one end of the line, a signal responsive device coupled to the impedances at the other end of the line, and signaling means interconnecting the conductors for indicating the grounding of either conductor.

13. In a signaling system the combination including a transmission line comprising a pair of conductors, a pair of impedances shunted in series across the respective ends of the conductors, the common terminal of each pair of impedances being grounded, a source of signal energy coupled to the impedances at one end of the line, a signal responsive device coupled to the impedances at the other end of the line, and means connected between said conductors for placing a short circuit across the portions of said impedances connected to a conductor when it is open circuited.

14. In a signaling system the combination including a transmission line comprising a pair of conductors, a pair of impedances shunted in series across the respective ends of the conductors. the common terminal of each pair of impedances being grounded, a source of signal energy coupled to the impedances at one end of the line, a signal responsive device coupled to the impedances at the other end of the line means connected between said conductors for placing a short circuit across the portions of said impedances connected to a conductor when it is open circuited, and means connected between said conductors for indicating the grounding of either conductor.

15. In a signaling system the combination including a transmission line comprising a pair of conductors, a pair of impedances shunted in series across the respective ends of the conductors. the common terminal of each pair of impedances being grounded, a source of signal energy coupled to the impedances at one end of the line, a signal responsive device coupled to the impedances at the other end of the line, means connected between said conductors for placing a short circuit across the portions of said impedances connected to a conductor when it is open circuited. and means connected between said conductors for indicating the open circuiting of either conductor.

16. In a signaling system the combination including a transmission line comprising a pair of conductors, a pair of impedances shunted in series across the respective ends of the conductors, the common terminal of each pair of impedances being grounded, a source of signal energy coupled to the impedances at one end of the line, a signal responsive device coupled to the impedances at the other end of the line, means connected between said conductors for placing a short circuit across the portions of said impedances connected to a conductor when it is open circuited, and means connected between said conductors for indicating the grounding of either conductor.

1'7. In a signaling system the combination comprising a source of signal energy, a transmission line comprising a pair of conductors, a pair of transformers having their respective windings connected in series, one pair being con- Examiner nected to the output of the signal source and ends of said conductors, the common terminal of said last windings being grounded, a pair of impedances shunted across said conductors by spaced points and grounded intermediate the ends thereof, a plurality of signal responsive devices and transformers for coupling each of said devices to the conductors between said impedances, one pair of windings of each transformer being connected in series to the associated signal responsive device and the other pair of windings of each transformer being connected in series between the conductors and having their common point grounded.

18. In a signaling system the combination comprising a source of signal energy, a transmission line comprising a pair of conductors, a pair of transformers having their respective windings connected in series, one pair being connected to the output of the signal source and the other pair being connected to the respective ends of said conductors, the common terminal of said last windings being grounded, a pair of impedances shunted across said conductors by spaced points and grounded intermediate the ends thereof, a plurality of signal responsive devices and transformers for coupling each of said devices to the conductors between said impedances, one pair of windings of each transformer being connected in series to the associated signal responsive device and the other pair of windings of each transformer being connected in series between the conductors and having their common point grounded, the direct current impedance of the windings connected to the signal responsive devices being substantially equal to the impedance of the signal responsive devices.

19. In a signaling system the combination comprising a plurality of independent transmitting networks, a source of signal energy, a plurality of transformers having their primaries connected in series with the output of the signal source, the secondaries of each transformer being connected in series with the primaries of a pair of transformers, the secondaries of each pair of transformers being connected in series and to the network.

20. In a signaling system the combination comprising a plurality of independent transmitting networks, a source of signal energy, a plurality of transformers having their primaries connected in series with the output of the signal source, the secondaries of each transformer being connected in series with the primaries of a pair of transformers,thesecondariesof each pair of transformers being connected in series and to the network and having their common terminals grounded.

21. In a signaling system the combination comprising a plurality of independent transmitting networks, a source of signal energy, a plurality of transformers having their primaries connected in series with the output of the signal source. the secondaries of each transformer being connected in series with the primaries of a pair of transformers, the secondaries of each pair of transformers being connected in series and to the network and having their common terminals rounded, and grounded signal responsive devices connected to the network.

22. In a signaling system the combination comprising a source of signal energy, a pair of conductors each forming a closed loop, means for connecting the source of signal energy between each of said loops and ground, and a plurality of signal responsive devices connected between each of said loops and ground.

23. In a signaling system the combination comprising a source of signal energy, a pair of conductors each forming a closed loop, means for connecting the source of signal energy between each of said loops and ground, a plurality of signal responsive devices connected between each of said loops and ground, and means for indicating either a short circuit to ground on either loop or an open circuit on either loop.

24. In a signaling system the combination comprising a. source of signal energy including a pair of transformers, a pair of conductors each forming a closed loop, the secondaries of said transformers being connected in series and having their common point grounded, connections in the other terminals of the secondaries to the respective loops, a plurality of signal responsive devices and a pair of transformers for coupling each signal responsive device to said loops, said last pair of transformers having their primaries connected in series between the loops and their common terminal grounded, and their secondaries connected in series with the signal responsive devices.

25. In a signaling system the combination comprising a source of signal energy including a pair of transformers, a pair of conductors each forming a closed loop, the secondaries of said transformers being connected in series and having their common point grounded, connections in the other terminals of the secondaries to the respective loops, a plurality of signal responsive devices and a pair of transformers for coupling each signal responsive device to said loops, said last pair of transformers having their primaries connected in series between the loops and their common terminal grounded and their secondaries connected in series with the signal responsive devices. and means connected to the loops for indicating either a short circuit or an open circuit on either loop.

26. In a signaling system the combination comprising a source of signal energy, a pair of networks each comprising two closed conductive loops, a plurality of signal devices interconnected between each of the loops and ground, transformer means for coupling the source of signal energy between each of the pairs of loops and ground, and means for preventing the reflection of open circuits on either loop of each pair back to the signal source.

27. In a signaling system the combination comprising a source of signal energy including an amplifier, a pair of networks each comprising two closed conductive loops and transformer means for coupling the output of the amplifier with each network, said transformer means comprising a pair of transformers having their primaries connected in series with the output of the amplifier, two pairs of transformers having their primaries connected in series with the secondaries of said pair of transformers, and their secondaries connected in series across the loops of the respective pairs and having a common ground.

28. In a signaling system the combination comprising a source of signal energy including an amplifier, a pair of networks each comprising two closed conductive loops and transformer means for coupling the output of the amplifier of said pair of transformers and their secondaries connected in series across the loops of the respective pairs and having a common ground, the signal responsive devices being connected to the pairs of loops each by pairs of transformers having their primaries connected in series across the loops of the respective pairs with a common ground and their secondaries connected in series with the signal responsive devices.

29. In a system for selectively supplying energy from a signal source to a plurality of transmitting loops the combination comprising a source of signal energy, a plurality of transformers having their primaries connected in series to the signal source, a plurality of pairs of transformers each pair having their primaries connected in series with the secondary of one of the first mentioned transformers, the secondaries of each pair being interconnected and having a common grounded terminal and a pair of supply terminals for connection to the transmitting loops, and means for selectively grounding each pair of supply terminals to ground the loops connected thereto.

30. In a system for selectively supplying energy from a signal source to a plurality of transmitting loops the combination comprising a source of signal energy, a plurality of transformers having their primaries connected in series to the signal source, a plurality of pairs of transformers each pair having their primaries connected in series with the secondary of one of the first mentioned transformers, the secondaries of each pair being interconnected and having a common grounded terminal and a pair of supply terminals for connection to the transmitting loops, and means for selectively grounding each pair of supply terminals to ground the loops connected thereto, said selective means comprising a switch.

31. In a signaling system the combination comprising a grounded source of signal energy, a grounded signal responsive device and a transmission line comprising a pair of conductors connected together at each end through impedances, and means for connecting the signal source and the responsive device to the respective ends of the transmission line at substantially the midpoint of the respective impedances, the portions of each impedance being magnetically isolated from each other.

32. A communication system comprising a loop circuit, signal responsive devices, a physical connection from one terminal of each signal responsive device to said loop circuit, and a ground connection to the remaining terminal, and series impedances inserted in said circuit between said signal responsive devices as a protection against service interruption by open, shunt or ground conditions.

33. A communication system according to claim 32 in which said impedances include capacitors.

34. A communication system according to claim 32 in which said impedances include resistors.

SEMI J. BEGUN.

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