US2034703A - Transmission control in signaling systems - Google Patents

Description

' 24, 1936. F. w. METZGER l 2,034,703

TRANSMISSION CCNTROL IN SIGNALING SYSTEMS Filed Aug. 4, 1934 2 Sheets-Sheet l l y um@ CAS-FILLE ATTO/wrI March 24, 1936. F. w. METZGER TRANSMISSION CONTROL IN SIGNALING SYSTEMS Filed Aug. 4, 1934 2 Sheets-Sheet 2 /NI/ENTOR f. n/.METZGER BV j l vow.

A 7' TORNE Y Patented Mar. 24, 1.936

TED STATES PATENT TRANSMISSION CONTROL IN SIGNALING SYSTEMS Application August 4, 1934, Serial No. 738,415

6 Claims. (Cl. 179-170) OFFICE The invention relates to two-way signal transmission systems and particularly to circuits for directionally controlling transmission in such systems.

An object of the invention is to improve the cpcration of two-way repeaters in signal transmission systems.

It has been frequently found desirable to insert repeating or amplifying circuits between two-Way transmission lines in a two-way signaling system,

to compensate for .attenuation in the signals transmitted in opposite directions thereover. In the prior art one form of repeating circuit comprises two oppositely-directed one-way repeating paths which, to enable amplification of the signals for both directions of transmission, are coupled to each other and to the two-way transmission lines by three-winding transformers or hybrid coiis in such a manner as to form a Wheatstone bridge circuit. As is well known, the balsneed condiiton of such a bridge circuit is atained by providing a balancing network in one Jrm thereof to closely simulate the impedance of ne associated transmission line in another arm. niess a high degree of balance is maintained by ie balancing networks so that the repeating aths are substantially conjugate, there is a critiamount or" amplification which cannot be eX- ceeded without setting up a local circulation of energy in the form of `a sustained tone known as singing. In another form of circuit in the prior art, repeating of the signals in opposite directions Without necessitating close balancing of the impedances or" the transmission lines to .avoid singing is attained by utilizing switching means respcnsive to the transmission of voice currents or other signals in either direction to render operative the repeating path for that direction only. In certain of such circuits this may be accomplished by making the switching apparatus responsive to the signals to remove effectively a loss (attenuation) from the signaling or talking path, to switch a loss into the other path, or to do both.

In accordance with. the present invention, in a system ci the last mentioned type, one or more loss elements having .a non-linear resistance-direct current voltage characteristic, such as copper-oxide rectiiiers, are connected in the repeating paths, and signal-controlled-means are pro'- vided for applying suitable direct current voltages to these elements to so control the losses inserted thereby in the repeating paths as to provide eiiicient transmission of signals in one repeating path While effectively blocking the other path.

In one embodiment of the invention the nonlinear resistance elements in the networks are connected in series in the repeating paths and are normally biased so as to provide a high resistance to the signals, and the resistances of the nonlinear resistance elements in either path are changed to a low value by the application of suitable direct current voltages in response to transmission of signals in that path.

In a second embodiment of the invention, the non-linear resistance elements in both repeating paths are connected in series therewith and are normally biased in such a manner that the elements in one path have a high resistance while the elements in the oppositely-directed path have a low resistance. In response to transmission of signals in either path, suitable direct current voltages are supplied to the elements therein which change their resistances to a low value if they normally have a high resistance, and, simultaneously change the resistance of the elements in the opposite repeating path to a high value so as to allow eiiicient transmission of signals in the first path only.

The objects and advantages of the invention will be better understood from the following detailed description thereof when read in connection with the accompanying drawings in which Figs. 1 and 2 show schematically different modifications of the invention embodied in a two-way telephone repeater,

The two-way telephone repeater circuit of Fig. l comprises a transmission path EA including the loss networks or pads l and 2 and the one-way amplifying device 3, for repeating telephone signals in the direction from west to east between the west two-way line section Lw and the east two-way line section LE, 4and a transmission path WA including the loss networks or pads and 5 and the one-way amplifying device '6 for repeating signals in the direction from east to west between the line section LE and the line section Lw. The oppositely-directed one-way repeating paths EA and WA are connected in conjugate relation with each other and in energy transmitting relation with the line sections Lw and LE by the hybrid coil transformers H1 and H2 and associated balancing networks N1 and N2 in Well known manner.

Connected to the output of the one-Way amplifier 3 in the repeating path EA is the input of a control circuit comprising in order a wave amplifier l, a wave rectifier 8 and a relay 9, the winding of which is connected to the output of rectier 8. Similarly connected to the output circuit of the amplifier 6 in the path WA is the input of a control circuit comprising in order a wave amplifier l0, a wave rectiiier I I and a relay I2, the winding of which is connected to the output of rectifier II. In rectiers 8 and II, respectively, the rectifying tubes I3 and I4 are preferably three-element tubes of the hot-cathode, gas-lled type which break down and become conducting when the potential on the grid or control electrode therein is raised sufficiently above a critical value. In addition to the elements mentioned, the control circuits respectively contain two other three-element tubes I9 and 2|] of the cold-cathode, gas-filled type which break down and become conducting when certain potential conditions are applied to their electrodes.

The loss networks or pads I, 2, 4, and 5 each comprises one or more copper-oxide rectifying units shunted by a resistance element in series.

with a condenser. The copper-oxide rectii'ying unit I5 in the pad I is connected in series with the upper conductor of the path EA, the unit I6 in pad 2 in series with the lower conductor of the path EA, the unit I'I in pad 4 in series with the lower conductor of the path WA and the unit I8 in pad 5 in series with the upper conductor of the path WA. Each copper-oxide rectifying unit is so poled in the conductor in which it is connected that when biased by a direct current voltage in the manner which will be described below, it oiers a resistance of high value to the signal currents transmitted in the direction opposite to the direction in which the arrow head of the unit points and, when unbiased or biased by a direct current voltage of opposite polarity, it offers a resistance of very low value to signal currents transmitted in the direction opposite to that in which the arrow head points. The value of the resistance elements in shunt with the copper-oxide rectifying elements in the pads in each path determines the amount of loss inserted in the path when the associated copper-oxide rectifying units are biased. The values of the resistance elements would be selected so that the losses inserted in the paths in which they are connected would be suiicient to block the transmission of signals thereover for the latter condition. Each resistance element is short-circuited by the low resistance path through the associated copper-oxide rectifying units when the latter are unbiased so that for the latter condition, the pad is effectively removed from the transmission path as regards any appreciable effect on the transmission of signals thereover. The condenser in series with each resistance element in each pad is provided to prevent transmission of direct current therethrough when the associated copperoxide rectifying unit is biased with the direct current voltage. In some cases the condensers may be omitted without deleteriously affecting the operation of the system. Any other elements having similar non-linear resistance-direct current voltage characteristics may be substituted for the copper-oxide rectifying units in each pad.

The nature and functions of the other apparatus and circuits illustrated in the system of Fig. 1 will be described in connection with the following complete description of operation of the system.

The positive potential impressed on the anode of tube IS by the battery 25 through resistance 26 is such that tube I9 is normally ionized and in the conducting condition and current flows therethrough over a circuit which may be traced from the positive terminal of battery 25 through resistance 26 to the anode of tube I9 and through the discharge path to both cathodes of the tube and from the cathodes through potentiometer resistances 28 and 29, the negative to the positive terminal of battery 21 to ground to the negative terminal of battery 25.

The contact arm of potentiometer 29 is connected to the mid-point of the secondary winding of the output transformer 2| for amplifier 3 in the path EA, and is adjusted so that the potential of that mid-point is approximately 5 volts above ground potential. The sides of the copper-oxide rectifying units I 5 and I6 connected through the conductors of the path EA and the upper and lower halves, respectively, of the secondary winding of transformer 2I to said mid-point, are therefore also at 5 volts above ground potential. The other sides of the elements I5, I6 are connected to ground through the outgoing conductors of the path EA and the windings of the hybrid coil transformer H1. With these potential conditions the bias on each copper-oxide rectifying element I5 and I5 is such that its resistance is of very high value due to the non-linear resistance-voltage characteristics as pointed out above. Thus, the resistance elements in parallel with the copperoxide rectifying elements in the two pads I and 2 are normally eective to insert such a high loss in the path EA as effectively to block that path as regards transmitting signals from the output of amplifier 3 to the line section LE.

Similarly, the biasing potential produced on the anode of tube 2E! by battery 38 through resistance 3l is such that tube 20 is normally ionized and in the conducting condition and current I ows therethrough over a circuit which may be traced from the positive terminal of battery 3l! through resistance 3l, the anode to the two cathodes of tube 2i), through potentiometer resistances 33 and 34, negative to positive terminal of battery 32 to ground to the negative terminal of battery 30. v

The contact arm of the potentiometer 34 is connected to the mid-point of the secondary winding of output transformer 35 for amplifier 6 in the path WA. It is adjusted so that the potential of that mid-point is approximately 5 volts above ground potential. The sides of each copper-oxide rectifying element Il and I8 in the pads 4 and 5 connected through the conducto-rs of the path WA and the upper and lower halves of the secondary winding of transformer 35 to the mid-point of that winding therefore are also 5 volts above ground potential. The other sides of the elements I'I and I8 are connected to ground through the outgoing conductors of the path EA and the windings of hybrid coil transformer H2. Thus, the copper-oxide rectifying elements I 'I and I8 are biased due to these potential conditions to provide a very high resistance in both sides of the path WA and they resistance elements in shunt with said copper-oxide rectifying elements are normally effective to insert their loss Value in the path WA so that the path is effectively blocked for transmission of signals.

Let it be assumed that telephone signals are being received over the west line section Lw and that no signals are being simultaneously received from the east line section LE. The incoming signals are impressed on path EA by hybrid coil transformer H2 Vand are amplied by the oneway amplifier 3 in that path. A portion of the amplified signals will be diverted from output transformer 2| into the associated control circuit and after amplification by the tube 23 in amplifier 'I therein will be impressed by transformer 24 on the grid electrode of tube I3 of rectier 8. In response to the impressed potential, the gaslled tube I3 ionizes and becomes conducting. Normally, that is when tube I3 is in the deionized condition, the condenser 3l in the plate circuit of the tube is charged from battery 25 through resistances 23 and 36 and the winding of relay 9. When tube I3 becomes conducting, it completes a circuit from ground over its cathode-anode circuit to one side of the condenser 31 through resistance 35 and also to the positive terminal of battery 25 through the winding of relay 9 and resistance 26. Now condenser 3T partially discharges through tube I3, thereby immediately lowering the potential on the anode of the normally ionized, cold-cathode, gas-lled tube I9 to a point where tube I9 de-ionizes and becomes non-conducting. Since no current now flows through tube I9, the positive 5 volt potential normally maintained on one side of the rectifying elements I5 and I5 in pads I and 2 in the path EA through potentiometer 29 is removed. A negative potential of 24 vo-lts is now applied to elements I5 and I6 over a circuit extending from the neg-ative terminal of the 24 volt battery 21 through potentiometer 29, the two halves of the secondary winding of transformer 2I and the conductors of the path EA. This reversal of potential causes direct current from battery 2l to ow through the rectifying elements I5 and 5 reducing the resistance of these elements to a low value and thereby short-circuiting the resistances in pads I and 2 through these elements. This effectively removes the normal loss from the two conductors of path EA and the signals incoming from the west line section LE after amplication by the one-way amplifier 3 will be transmitted With little attenuatio-n through the elements I5 and I6 to the output of the path EA where they will be impressed on the east line section LE by hybrid coil transformer H1.

Also, when tube I3 ionizes in response to the applied signals, current is transmitted from battery 25 through resistance 23, the winding of relay 9 and tube I3. The current through the winding of relay 9 causes operation of that relay to connect ground through its armature and front contact to the anode of tube I9, and to one side of the relay winding, thereby short-circuiting the battery 25 through resistance 25 and the relay contacts. Condenser 31 now completely discharges and, since both the cathode and anode of tube I3 are now at ground potential, tube I3 de-ionizes. Relay 9 also then releases and removes the short circuit around battery 25 and resistance 26. Tube I9 does not immediately reionize after the ground is removed from its anode by the release of relay 9 since condenser 31 must first be charged by battery 25 to -a point where the potential on the anode of tube I9 is suicient to cause ionization to take place. Tube I3 does not ionize immediately upon the closure of its anode circuit, even though signals are being impressed on its grid, since the anode potential does not reach the ionization value until condenser 37 is charged to a certain point. This delay interval in the re-ionization time of tubes I3 and I9 is controlled by the charging time of condenser 3l and is therefore dependent upon the values of resistances 26 and 35 and on the capacitance of condenser 3l. This delay interval is provided to prevent a continuous cycle of ionization and de-ionization of the tube I9 which would result in the repeated raising and lowering of the resistance value of the rectifying elements I5 and I 9 in path EA during a train of signals from the west line section Lw. By controlling the charging time of condenser 31 so as to insure that tube I9 does not re-ionize in the interval between syllables, the mutilation of the syllables of speech which is known as clipping may be guarded against.

The devices 38, 49, 43, and 45 in the system of Fig. l are illustrated as copper-oxide rectifying elements, similar to the elements I5, I5, Il, and I8, but may consist of any other elements having similar non-linear resistance-direct current Voltage characteristics. The rectifying element 38 in series with a 9 volt battery 39 is connected across the secondary winding of the transformer 24 coupling the amplifier tube 23 to the rectier tube I3. Element 33 is so connected with respect to its polarity that when the grid or control electrode of tube I3 goes positive in response to the impressed signals incoming over the west line section Lw, the element tends to become of low resistance. If the potential induced in the secondary winding of transformer 24 is less than 9 volts, element 33 will have a high resistance since the induced potential is insuflicient to overcome the xed bias of 9 volts maintained on the element by battery 39. Regardless of the level of the incoming signals, the maximum potential which can develop across the secondary winding of transformer 24 and on the grid of tube I3 is, therefore, 9 volts. The grid of tube I3 is normally negatively biased by battery 32 over a circuit extending from battery 32 through potentiometer 33, ccpper-oxide rectifying element 45 and the secondary winding of transformer 24 to the grid of tube I3. Since tube 29 is normally ionized and in the conducting condition, current is flowing through the tube and through potentiometers 33 and 34 as previously set forth. The Contact arm of potentiometer 33 is so adjusted that the negative bias on the grid of tube I3 is of such a value that an impressed positive potential of 8 volts thereon is necessary to cause that tube to ionize.

Similarly, rectifying element 43 in series with a 9 volt battery 44 is connected across the secondary Winding of transformer 45 coupling the amplifier tube 45 in amplifier 10 to the rectifier tube I4 in rectifier II. nected with respect to its polarity that when the grid of tube I4 goes positive in response to the impressed signals incoming from the east line section LE, the element 43 tends to become of low resistance. If the potential induced in the secondary winding of transformer 46 is less than 9 volts, element 43 will have a high resistance since the induced potential is not suiiicient to overcome the fixed bias of 9 volts maintained on the element by battery 44. A maximum potential of 9 volts, therefore, is all that can develop across the secondary winding of transformer 45 on the grid of tube I4. The grid of tube I4 is normally negatively biased by battery 2l over a circuit extending from the battery through potentiometer 28, copper-oxide rectifying element 49 and the secondary winding of transformer 49 to the grid. Since tube I9 is normally ionized and conducting, current is flowing through the tube and through potentiome-ters 28 and 29 as previously set forth. The contact arm of potentiometer 29 is so adjusted that the potential placed on the grid of tube I4 is of such Element 43 is so cona value that an impressed positive potential of 8 volts is necessary on the grid of the tube to cause that tube to ionize.

When tube I3 ionizes in response to a signal incoming from the west line section Lw and deionizes tube |9, as previously described, current ceases to fiow through tube |9 and potentiometer 28 thereby removing the normal biasing potential on the grid of tube |4. The negative terminal of the 24 volt battery 21 is now connected to the grid of tube |4 in a circuit extending through potentiometer 28, rectifying element 40 and secondary of transformer 46. With this negative 24 Volt bias, a swing of 18 volts on its grid is now necessary to cause tube |4 to ionize. Since the maximum potential of 9 volts is al1 that can develop across the secondary winding of transformer 46, rectifier tube I4 cannot ionize to become conducting as long as signals are continuously incoming from the west line section Lw. Since tube I4 cannot ionize, tube 20 remains ionized thereby maintaining the proper potential conditions on rectifier elements |1 and |8 to keep these elements at a high resistance value which means that the full value of the shunting resistances in the pads 4 and 5 are effective in the path WA. Thus the east to west transmission path WA is maintained blocked as long as the west-to-east signals are being received from the west line section Lw substantially continuously.

In a manner similar to that just described for the elements of the control circuit connected with the path EA in the case where signals are first applied to the repeating circuit from the West line section LW, the corresponding elements of the control circuit connected to the path WA operate when signals are first impressed upon the repeating circuit from the line section LE to change the bias of the rectifying elements |1 and |8 in the pads 4 and 5 in the path WA so that they provide a very low resistance in that path and thus allow efficient transmission of the signals from the line section LE to the line section Lw. Also, the elements in the control circuit connected to the path WA operate in response to the signals received from the line section LE to maintain the proper potential conditions on the rectifying elements I5 and I6 in the pads I and 2 in the path EA to hold that path blocked during the substantially continuous transmission of the east to west signals from the line section LE in a manner similar to that described for the corresponding elements in the control circuit connected to the path EA described above.

Referring now to the modification of the invention shown in Fig. 2, the two-way telephone repeater circuit shown therein comprises a transmission path EA including the loss networks |0| and |82 and the one-way amplifying device |03 for repeating telephonie signals in the direct-ion from west to east between the west twoway line section Lw and the east two-way line section La, and a transmission path WA including the loss networks |04 and |05 and the oneway amplifying device |05, for repeating signals in the direction from east to west between the line section LE and the line section Lw. The oppositely-directed one-way repeating paths EA and WA are connected in conjugate relation with each other and in energy transmitting relation with the west line section Lw and the east line section LE by the hybrid coil transformers H3 and H4 and associated balancing networks Ns and N4 in Well known manner.

The loss networks or pads |0|, |02, |04, and |05 each comprises one or more copper-oxide rectifying units shunted by resistances. The copper-oxide rectifying unit ||3 in the pad |0| is connected in series with one side of a portion of the path EA located between the transformers |35 and |36 in front of the amplifying device |03 and the copper-oxide rectifying unit ||4 in the pad |02 is connected in series with the other side of the portion of the path EA located between the transformers I 35 and |36 in front of the amplifying device |03. The copper-oxide rectifying unit 5 is connected in series with one side of the portion of the path WA located between the transformers |31 and |38 in front of the amplifying device |06, and the copperoxide rectifying unit I6 is connected in series with the other side of the portion of the path WA located between the transformers |31 and |38 in front of the amplifying device |06. Each copper-oxide rectifying unit is so poled in the side of the repeating path in which it is connected that when biased by a direct current voltage in the manner which will be described below it offers a resistance of high value to signal currents transmitted in the direction opposite to the direction in which the arrow head points and when unbiased or biased by a direct current voltage of opposite polarity it offers a resistance of very low Value to signal currents transmitted in the direction opposite to which the arrow head points.

The rectifying unit |3 in the pad |0| is shunted by the equal resistances |1 and ||8 in series, the rectifying unit ||4 in the pad |02 is shunted by the equal resistances H9 and |20 in series, the rectifying unit ||5 in the pad |04 is shunted by the equal resistances |2| and |22 in series, and the rectifying unit ||6 in the pad |05 is shunted by the equal resistances |23 and |24 in series. The values of the resistance elements ||1, ||8 in pad |0|; ||9, |20 in pad |02; |2I, |22 in pad |04; and |23, |24 in pad |05 determine the amount of loss inserted in the transmission path in which they are connected when the copper-oxide rectifying units in the pads are unbiased or are biased so as to offer a resistance of high value in the signal transmitting direction in the path. The values of the resistances would be so selected that the loss inserted in the repeating paths would be sufficient to block transmission of signals or echoes therein for the latter condition. The series resistance elements in each pad are short-circuited by the low resistance paths through the associated copper-oxide rectifying units when the latter are biased to offer a low loss in the repeating path in which connected in the signal transmitting direction so that for the latter condition the pad is effectively removed from the transmission path as regards any effect on the transmitted signals. Any other elements having similar non-linear resistance-direct current voltage characteristic may be substituted for the copper-oxide rectified elements in the loss networks or pads.

' Connected across the loss networks |0| and |02 in the repeating path EA, between the mid-point of resistances ||1 and ||8 and the mid-point of resistances ||9 and |20 is the input of a control circuit comprising in order an amplifier |01, a rectifier |08 and a gas-filled discharge tube I 09. Similarly connected across the loss networks |04 and |05 in the repeating path WA between the mid-point of resistances |23 and |24 and the mid-point of resistances |2| and |22 is the input of a control circuit comprising in order an amplifier ||0, a rectifier and a gas-filled discharge tube H2.

The amplifiers |03, |00, |01, and ||0 may be of any of the well known types, for example, of the type employing three-electrode vacuum tubes. The rectiers |03 and may be of any of the well known types but are preferably all of the type employing copper-oxide rectifying elements. The gas-lled discharge tubes |09 and ||2 are preferably three-element tubes of the hot-catho'de gas-filled type which break down and become conducting when the potential on the grid or control electrode therein is raised suii'ciently above a critical value.

The rectifier |08 comprises two oppositely poled copper-oxide rectifying units in series shunted by two condensers in series, the output of the control amplifier |01 being coupled by transformer i 39 across the junction point between the two copper-oxide rectifying units and the junction point between the two condensers in rectier |08. Similarly, the rectifier comprises two oppositely poled copper-oxide rectifying units in series shunted by two condensers in series, the output of the control amplifier ||0 being coupled by transformer l0 across the junction point between the two copper-oxide rectifying units and the junction point between the two condensers in rectifier A resistance is connected across the output of rectifier |08, that is, acro'ss the two rectifying units therein in series, and an equal resistance |21 is connected across the output of rectifier that is, across the two rectifying units therein in series. The two resistances |25 and |21 are connected in series and are shunted across the two resistances |20 and |28 in series, respectively, in the individual portions of the input circuits of the gas-filled discharge tubes |09 and ||2.

The input and output circuits of the gas-filled rectifier tubes |09 and ||2 are respectively connected in push-pull relation. The anode-cathode circuit of the rectifier tube |09 includes in series the plate battery and the series resistance |3| and |32, and the anode-cathode circuit of rectifier tube ||2 includes in series plate battery |30 and resistances |33 and |34. The gridcathode circuit of gas-filled tube |09 comprises in series grid battery |29 and the series resistances |20` and Ml, and the grid-cathode circuit of the gas-filled tube ||2 comprises in series the grid battery |29 and the series resistances |28 and |42'.

The junction point between the series resistances |3| and |32 in the output circuit of the gas-filled tube |03 is connected to the mid-point of the secondary winding of transformer in the path EA, and thus to one side of each copperoxide rectifying element |3 and Il@ in the pads |0| and |02, respectively, through the respective halves of said secondary winding. Similarly, the junction point between the series resistances |33 and |34 in the plate circuit of gas-filled tube ||2 is connected to the mid-point of the secondary winding of the transformer |38 in the path WA and thus to one side of each copper-oxide rectifying element |5 and I3 in pads |00 and |05, respectively, through the two halves of said Secondary winding.

By the connections detailed above, the input circuits of the gas-filled discharge tubes |09 and ||2 and the output circuits of the rectiers |08 and are connected together in a differential circuit in such manner that the output of the rectiers determines the voltages in the differential circuit. As will be explained below in connection with the operation of the system of Fig. 2, the voltages in the differential circuit control the ionization of tubes |09 and H2, which, in turn control the potential conditions on the copper-oxide rectifying elements H3, ||f| in loss networks |0| and |02, and on copper-oxide rectifying elements ||5, llt` in the loss networks |04 and |05.

The nature and functions of the other apparatus and circuits illustrated in the system of Fig. 2 will be described in connection with the following complete description of the operation of that system.

With the filaments or cathodes of tubes |09 and ||2 energized by an individual or a common battery (not shown), either tube |09 or tube ||2 is ionized and in the conducting condition depending upon the direction of the last previous signal impressed upon the repeater. If these previous signals were in the direction from east to west having been applied to the repeater from the east line section LE, the conditions disclosed in the differential circuit comprising the output circuits of rectiers |08 and and the input circuits of gas-filled discharge tubes |09 and ||2 will be such as to put the tube I2 in the ionized condition and the tube |09 in the de-ionized condition. On the other hand, if the previous signals were in the direction from west to east having been applied to the repeater from the west line section Lw, the tube |09 is ionized and the tube ||2 is de-ionized.

Let it be assumed that the last previous signals impressed on the repeater circuit were in the east to west direction and that, therefore, tube l2 is ionized and tube |09 is de-ionized. With tube |2 ionized and in the conducting condition, current ows from the plate battery |30 through resistances |33 and |30. Due to the drop in voltage caused by the current flow through resistances |33 and |30, the junction point of the latter resistances is at a lower potential than the junction point of resistances |3| and |32 in the anode-cathode circuit of tube |09. This difference in potential results in a flow of biasing current through the copper-oxide rectifying elements ||3, H0, ||5 and H0 over a circuit which may be traced from the junction point of resistances |3| and |32 to the mid-point of the secondary winding of transformer |35, through copper-oxide rectifying elements ||3 and ||4 in parallel with the resistances ||1, ||8, ||9 and |20, respectively, each half of the primary winding of transformer |36, from the mid-point of said primary winding to the mid-point of the primary Winding of transformer |36 in the patli EA through copper-oxide rectifying elements I5 and ||0 in parallel with resistances |2|, |22 and |23, |24, respectively, each half to the mid-point of the secondary winding of transformer |38 and thence to the junction point of resistances |33 and |34. This current flows through elements ||5 and ||3 in the conducting directions causing their resistances to be reduced to low values. However, the biasing current flows through the copper-oxide rectifying elements ||3 and I0 in the direction in which their resistance is Very high. The latter elements, therefore, insert a high loss in the repeating path EA. In addition, due to the high resistance of copper-oxide rectifying elements H3 and H0, the resistances |30 through resistances I 3| and |32.

tion of that tube.

vI I1 and I I9 in parallel therewith are effective to insert their full resistance value in series with the input of amplifier |01 effectively preventing transmission subsequently of signal currents from the line section LW to the control Acircuit having its input connected across the path EA. Since the copper-oxide rectifying elements |I5 and I6 are low in resistance at this time, resistances I2| and |22 and the resistances |23 and |24 are eifectively in parallel and provide a loss in the input to amplifier I I0 which is less than the loss in the input to amplifier |01.

With the repeater in the condition hereinbefore set forth, that is, with a high loss in the path EA due to the high resistance of elements ||3 and I I4 and with a low loss in the path WA due to the low resistance of elements II5 and IIB, let it be assumed that signalsare applied to the repeater from the west line section LW, no signals being simultaneously applied thereto from the east line section LE.

The signals will be impressed on path EA by the hybrid coil transformer H4 and will be passed by transformer |35 and by--passed around the high resistance copper-oxide elements I I3 and II4 through the shunting resistance circuits. A portion of the incoming signals will be diverted at the mid-points between resistances |I1, IIB and between resistances I I9, I2 into the control circuit where it will be amplified by the amplifier |01 and then rectified by the rectifier |08, causing a direct current potential to be applied across the conductors |43 and |44.

This application of a direct potential across the conductors |43 and |44 in response to the rectified signals causes current to flow in the differential circuit comprising resistances |25, |26, |21

and |28 in the direction which lowers the negative potential on the grid of tube' |09 and increases the negative potential on the grid of tube ||2. the grid of tube |09 causes that tube to ionize and become conducting. Upon the ionization of tube |09, a circuit is completed from ground on the cathode of tube |09 through the cathode-anode circuit of the tube to one side of the condenser |41 connected between the plates of tubes |09 and H2, and to the positive terminal of battery Condenser |41 partially discharges, causing a surge of current through condenser |41 which momentarily reduces the potential on the anode of tube II2 to a value below that required to maintain ioniza- Tube II2 de-ionizes and, since its cathode-anode circuit is opened, current ceases to flow in the circuit from the positive terminal of battery |30, through resistances |34 and |33, to ground at the cathode of tubey ||2. The junction point of resistances |33 and |34 therefore assumes the full potential of battery |30.

Since tube |09 is ionized, current flows from the positive terminal of battery |30 through resistances |32 and |3| to ground over the anodecathode discharge path of tube |09. Due to the voltage drop caused by the current flow through resistances |3I and |32, the junction point of these resistances is at a lower potential than the junction point of resistances |33 and |34. The potentials at these junction points are now the reverse of those which obtained before signals were impressed on the path EA. The biasing current through the non-linear resistance elements II3, II4, II5, and IIE is therefore owing in the direction opposite to the previous cur- This decrease in the negative potential onv rent flow through these elements, being now in the conducting direction through elements II3 and II4 and in the non-conducting direction for elements I|5 and IIS. Due to this reversal of biasing current, elements II3 and II4 become low in resistance value and eiectively short circuit resistances I I1, IIB and I|9, |20, respectively, reducing the loss in path EA while elements II5 and II6 become high in resistance value so that the resistances I2I, |22 and |23, |24 in parallel therewith become effective to insert a high loss in path WA. Elements I|3 and H4, being low in resistance value, the resistances IIS and |20 are effectively placed in parallel with resistances II1 and I|9, respectively, thereby reducing the loss in the input Acircuit to the control circuit amplifier |01. Since elements ||5 and IIE are now high in resistance value, resistances |2| and |23 are removed, in effect, from in parallel with resistances |2 and |24, respectively, thereby increasing the loss in the input circuit to the control circuit amplifier ||0.

The increase in the loss in the input to the amplifier-rectifier associated with the path opposite to that in which signals are being repeated, serves to prevent the ionization of the gas tube controlled by the then non-repeating path in the event of an unbalanced line. For example, with signals being impressed on path EA and the repeater functioning as hereinbefore set forth, let it be assumed that the east line section LE is not in close balance. A portion of the signals in path EA, after amplication by amplier 03, are fed back into path WA through the hybrid coil transformer H3. However, since the loss in the input to amplifier I I 0 is greater than that in the input to amplier |01, the level of the waves in the output of rectifier III is lower than that of the waves in the output of rectifier |08. Having the greater output, rectifier I8 therefore maintains control of the gas tubes, keeping tube |09 ionized and preventing the ionization of tube I2.

In this manner the repeater functions properly even though one or both associated lines are not in close balance.

In the foregoing description it was assumed that tube I I2 was ionized and tube |09 de-ionized prior to the application of signals to path EA over the west line section LW. Assume, instead, that tube I 09 is ionized and tube IIZ de-ionized prior to the application of the signals to path EA. Under this condition the ow of biasing current through the copper-oxide rectifying elements is in such direction that elements ||3 and l I4 are low in resistance value, while elements and IIB are high in resistance value. When signals are now impressed on path EA over the west line section Lw, no action takes place in the signalcontrolled gaseous tube circuits other than that the output of rectier |08, under control of the incoming signals, maintains the proper potentials on the grids of tubes |09 and H2 so that tube |09 remains ionized and tube I |2 de-ionized.

Assume now that the signals incoming over the west line section Lw have ceased, and that, with tube |09 remaining ionized and tube II2 deionized, signals are impressed on path WA over the east line section LE by the hybrid coil transformer H3. These signals will be passed by the transformer |38 and a portion thereof will be diverted through resistances |22 and |24 into the associated control circuit and will be amplified by amplifier IIO therein. The amplified signals will be impressed by the transformer |40 on the rectifier III. The rectified signals in the output of rectifier III will then be applied to the differential control circuit for the gaseous tubes |99 and II2 over conductors |43 and I 44. Due to this applied potential, current flows through the differential circuit in the direction which reduces the negative potential on the grid of tube I|2 and increases the negative potential on the grid of tube |99. Tube II2 ionizes and becomes conducting in response to the lowering of the negative potential on its grid.

With tube II2 ionized, a circuit is completed from ground on its cathode through the cathodeanode circuit to one side of condenser |41, and to the positive terminal of battery |30 through resistances |33 and |36. Condenser |41 partiail discharges, causing a surge of current through the condenser which momentarily lowers the potential on the anode of tube |09 below the value required to maintain ionization, and tube IGS therefore de-ionizes. In de-ionizing, tube |59 opens the circuit from battery I 30 through resistances |32 and I 3| to ground on its cathode. Since current ceases to flow through resistances I3| and I 32, the junction point of these resistances assumes the full potential of battery |39. Tube ||2 now being ionized, current ows from the positive terminal of battery |30 through resistances |34 and |33, to ground over the anodecathode circuit of the tube. Due to this current ow, the junction point of resistances |33 and 34 is at a lower potential than the junction point of resistances I3! and |32. Due to this difference in potential, biasing current now flows through the copper-oxide rectifying elements in a circuit hereinbefore traced in connection with the description of operation for the case where signals are repeated from west to east, but in the direction opposite to that which flowed through these elements when tube |09 was ionized and tube I I2 de-ionized. This current flow is now in the conducting direction through elements II and IIG, reducing their resistance to a low value and is in the non-conducting direction through elements IIS and. H4 thereby increasing the resistance of these latter elements to a high value so as to insert a loss in path EA. Since the resistance of elements I|5 and I|6 is now low in value, resistances I2I and |23 are eiectively placed in parallel with resistances |22 and |24. This lowers the loss in the input circuit to amplier I IG. Elements I I3 and II4 being high in resistance value, resistances II8 and |20 are effectively removed from in parallel with resistances |II and I9, respectively, thereby increasing the loss in the input circuit to amplier I 91. This regulation of the input to the signal-controlled amplifier-rectiers insures the properfunctioning of the repeater circuit under unbalanced line conditions as previously set forth.

As long as signals continue to be impressed on path WA over the east line section LE, tube ||2 remains ionized and tube |09 de-ionized. Upon the cessation of the east line signals, tubes II2 and IGS remain in their foregoing respective conditions until signals are impressed on path EA over the west line section Lw, at which time tube |09 ionizes and tube II2 de-ionizes, causing the repeater circuit to function in the manner similar to that set forth in connection with the description of operation for transmission of west to east signals.

Should the cathode circuits of tubes |09 and I I2 be opened during maintenance of the repeater or for any other reason, the tube which is ionized at that time will de-ionize. When the cathode circuits of the'tubes are again closed, both tubes may remain de-ionized. The first signal impresssed over either line section will, however,

cause the tube associated with the repeating path of that signal to ionize, after which the repeater circuit functions as previously described, one or the other of tubes |09 and I I2 remaining ionized depending upon the direction of the last repeated signal.

Many modifications of the circuits illustrated and described within the spirit and scope of the invention will be apparent to persons skilled in the art. The invention is to be limited only within the scope of the appended claims.

What is claimed is:

1. In combination, two oppositely-directed oneway circuits for transmitting alternating current signals in opposite directions between stations, a loss pad in each circuit including one or more elements having a non-linear resistance-direct current voltage characteristic which when biased by a direct current voltage of one polarity and of the proper value will condition the pad to offer a high loss to the transmitted signals in said circuit and When biased by a direct current Voltage of the opposite polarity and of the pro-per value will condition the pad to offer a low loss to the transmitted signals, means normally applying the first-mentioned voltage to said elements in each pad so that both pads are in the high loss condition, means responsive to the initiation of signal transmission in either circuit to' remove the normally-applied voltage from the elements in that circuit and to apply thereto the second-mentioned voltage to put the pad in the low loss condition, and means responsive to signals in the circuit in which they are first initiated to prevent later-initiated signals in the other circuit from causing a change in the loss conditions of the pads in either circuit during the substantially continuous signal 'transmission in the first circuit.

2. The' combination of claim 1 and in which the application of the normal biasing voltage to the elements of the pad in each circuit is controlled by a normally-ionized gas-filled discharge device, and the removal of the normal biasing voltage and the application of the proper voltage to put that pad in the low loss condition is caused by the de-ionization of said device in response to initiation of signal transmission in that circuit.

3. In combination in a signal transmission system, two oppositely-directed one-way circuits for transmitting alternating current signals in opposite directions between stations, a loss pad in each circuit including one or more elements having a non-linear resistance-direct current voltage characteristic which when biased by a direct current voltage of one polarity and of the proper value will condition the pad to provide a high loss to transmitted signals in said circuit and when biased by a direct current voltage of the opposite polarity and of the proper value will condition the pad to provide a low loss to transmitted signals in that circuit, means normally applying to the elements of the pad in one circuit the firstmentioned voltage and to the elements o-f the pad in the other circuit the second-mentioned voltage, control means responsive to the initiation of signal transmission in either circuit to so control the voltages on the elements of the pads in said circuits that the pad in the circuit in which said transmission is initiated is maintained or put in the low loss condition and the pad in the other circuit is put or maintained in the high loss condition, and means responsive to signal transmission in the circuit in which rst initiated to prevent later-initiated signals in said other circuit from changing the loss condition of the pad in either circuit during substantially continuous transmission of the rst-initiated signals in the first circuit.

4. The system of claim 3 and in which said means normally applying said first-mentioned voltage to the elements of the pad in one circuit and said second-mentioned voltage to the elements of the pad in the other circuit comprises a differential circuit including a normally ionized and a normally de-ionized gas-lled discharge device, and the means responsive to signal transmission in either circuit for so controlling the voltages on the elements of the pads in the two circuits that the pad in the circuit transmitting signals is in the low loss condition and the other pad is in the high loss condition, comprises means for rectifying a portion of the transmitted signals and for applying the rectified signals to the diierential circuit in such manner as to properly control the ionization in the two discharge devices.

5. The system of claim 3- in which the means normally applying the voltages to the elements of the pads in said one-way circuits comprises a differential circuit consisting of two electric discharge devices connected in push-pull relation, the output of which is connected across the nonlinear resistance elements in the pads in both oneway circuits, and the means responsive to the initiation of signal transmission in either one-way circuit to so control the voltages on the pads in said circuits that the pad in the circuit in which signal transmission is initiated is maintained or put in the low loss condition and the pad in the other circuit is maintained or put in the high loss condition comprises means for rectifying a portion of the transmitted signals and for applying the rectified signals to the differential circuit in such manner as to produce the proper potential conditions in its output.

6. In combination, two oppositely-directed oneway circuits for transmitting alternating current signals in opposite directions between stations, a loss pad in each circuit comprising one or more impedance elements in series therewith and of such values as to oifer a high loss to transmitted signals, one or more copper oxide rectifying vunits effectively in shunt with the series impedance elements in each paid and in series relation with said circuit, said copper oxide rectifying units being normally biased by direct current in such manner as to offer a resistance of high value in the direction of transmission of said signals, and switching means connected to each one-way circuit and responsive to initiation of signal transmission therein to change the direct current bias on the rectifying units shunting the impedance elements in the pad in that circuit so that said units offer a low resistance to the transmitted signals, and to disable the switching means connected to the other one-way circuit,

FREDERICK W. METZGER.

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