US2246307A - Signal transmission line - Google Patents

Description

June 17, 1941.

H. K. KRIST SIGNAL TRANSMISSION LINE Filed April 3, 1940 nun N :i v

A T TORNEV Paten'ted June 17, 1941 UNITED ES, PATENT -OFFICE SIGNAL TRANSMISSION LINE Henry K. Krist, Madison, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application April 3, 1940, Serial No. 327,581

7 Claims.

This invention relates to signal transmission lines and particularly to signal transmission lines having control circuits for automatically compensating for any change in loss on the transmission lines.

One object of the invention is to provide a signal transmission line having carrier and pilot,

channels thereon that shall control the iiat gain on the line according to the strength of one pilot current on the transmission line and control the line attenuation characteristic according to the strength of another pilot current on the transmission line.

Another object of the invention is to provide a signal transmission line having carrier and pilot channels, a fiat gain ampliiier, a bulge network and a slope network thereon that shall govern the amplifier, the bulge network and the slope network separately according to the strengths of three pilot currents on the transmission line.

Another object of the invention is to provide a signal transmission line having carrier and pilot channels thereon that shall control the fiat gain on the line according to the strength of one pilot current, that shall control the slope of the line attenuation characteristic according to the strength of another pilotl current on the line and that shall control the bulge of the line attenuation characteristic according to the strength of a third pilot current on the line.

A further object of the invention is to provide a signal transmission line having carrier and pilot channels thereon that shall govern three low frequency control circuits respectively according to the strengths of three pilot currents on the line and that shall control the flat gain on the line, the slope of the line attenuation characteristic and the bulge of the line attenuation characteristic by said low frequency circuits.

Long transmission systems such, for example, as carrier cable systems are generally provided with flat gain and twist pilot wire regulators which are located at intervals along the cable. These pilot wire regulators may be of the type disclosed in the F. A. Brooks Patent 2,075,975, April 6, 1937. However, it is found that certain over-all losses occur on the pairs of conductors making up a cable for which compensation is not effected.

According to the present invention, terminal or deviation regulators, which are controlled by pilot currents, are provided to compensate for over-al1 losses that are not corrected for by the ilat gain and twist regulators. The deviation regulators not only adjust the flat gain but also the slope and bulge of the line attenuation characteristic. Y

In the carrier cable system employed to describe the invention, a gain control amplier, a slope network and a bulge network are placed on each pair of conductors in the cable at the terminal station. Each pair of conductors in the cable is not only provided with carrier channels but also with three pilot channels. The pilot currents on a pair of conductors respectively control the amplier, the slope network and the bulge network on the associated pair of conductors.

A filter which selects the three pilot currents is connected to the transmission line at a point beyond the flat gain ampliiier and the slope'and bulge networks. The transmission line may be a pair of conductors in a carrier cable system. 'Ihe three pilot currents selected by the filter are amplied and supplied to three auxiliary filters which respectively select the three pilot currents. The auxiliary iilter which selects the pilot current controlling the flat gain ampliiier is connected to a voltage doubler rectifier. The output from the voltage doubler rectifier is opposed by a constant potential for impressing a negative bias on the control grid of a control amplifier. The output from the voltage doubler rectier is opposed by a constant potential in order to effect a more proportional change for any variation in the strength in the pilot current.

The plate of the control vamplifier is supplied not only with direct potential but also with a low frequency alternating current preferably a cycle power current. The output from the control amplier governs a thermistor connected across the negative feedback circuit of the flat gain amplifier. An increase in the strength of the pilot current on the transmission line which governs the at gain amplifier increasesr the negative bias on the control amplifier. An increase in the strength of the negative bias on the control amplifier lowers the heating current supplied to the thermistor in the negative feedback circuit of the fiat gain ampliiier to increase the feedback and accordingly lower the gain of the amplier. An opposite effect takes place in case the strength of the pilot current on the transmission line is lowered.

The bulge network on the transmission line is controlled in a similarrmanner to that of the flat gain amplier by another pilot current on the transmission line. The auxiliary filter which selects the pilot current governing the bulge network is connected to a voltage doubler rectiiier which controls the negative bias on a control ampliiier. The control amplifier governs the heating of a thermistor having a negative coefficient of resistance which is included in the bulge network. An increase in the strength of the pilot current on the transmission line which controls the bulge network increases the negative bias onthe control grid of the control amplifier. A reduction in the output from the control amplifier lowers the heating of the thermistor in the bulge network to increase the resistance thereon. An increase in the resistance of the thermistoiin the slope network increasesy the loss eected by the bulge network. An opposite effect is produced in the operation orf-the bulge network in case the strength of the pilot current of the transmission line is lowered.

The auxiliary filter which selects the pilot current for controlling the slope network is connected to a voltage doubler rectifier which. impresses a negative bias on the grid of a control amplifier. The control amplifier governs a thermistor having anegative coefcient of resistance in the slope network to control the operation of the network. The control ampliers employed for governing the slope and the bulge networks are each supplied with low frequency alternating current the same as the control ampliiier em- .ployed to govern the flat gain amplilier so that the thermistors governing the slope and bulge networks are each controlled by circuits having low. frequency currents impressed thereon. 'Ilie thermistors associated with the iiat gain amplifier and the bulge and slope networks may be located at any desired distances away from the control amplifiers. The thermistor included in the slope network is governed in the same manner as the thermistor included in the bulge network. The thermistors may be of the type disclosed in the E. F. Dearborn application Serial No. 280,692, filed June 23,1939.

The single figure in the accompanying drawing is a diagrammatic View of a transmission system constructed in accordance with the invention.

Referring to the drawing, a terminal or deviation gain control station I is shown connected to a transmission line having input conductors 2 and 3 and output conductors 4 and 5. The input conductors 2 and 3 are connected by a transformer 6 to a iiat gain amplifier 1 having a negative feedback circuit 8. The negative feedback circuit 8 includes series resistance elements 9 and I and a shunt connected resistance element II. The resistance element l l has negative temperature coeicient of resistance and is controlled by a heater coil I2. The amplifier 1 is connected to a slope network or equalizer I3 which in turn is connected to a bulge network or equalizer I4. A resistance element I having a negative temperature cceliicient of resistance is included in the network 3 for control purposes. lThe resistance element I5 is controlled by a heater coil I6. The bulge network I4 is provided with a resistance element l1 having a negative temperature coefficient of resistance which is controlled A by a heater coil I8. The resistance elements II, I5 and I1 may be of the type disclosed in application or E. F. Dearborn, Serial No. 230,692. The bulge network is connected to an ampliiier I9 which in turn is connected by a transformer to the output conductors 4 and 5.

The transmission line is not only provided with a number of carrier channels but also with three pilot channels. The three pilot currents on the transmission line are selected by a main filter 2I which is connected to the transmission line beyond the amplifier i9. The filter 2| which selects the three pilot currents comprises two transformers 22 and 23, a crystal 24, a condenser 25 and a resistance 2S shunted across the secondary winding of the transformer 23. The main lter 2l is connected to the input circuit of an amplifier tube 21 which is preferably of the pentode type. The amplifier 21 is provided with a control grid 28, an anode 29 and a cathode 30. The anode 2S is connected to a battery 3l by a circuit including a resistance element 32 and three auX- iliary filters 33, 34 and 35. Negative bias for the control grid 2t of the tube 21 is supplied by the potential drop across a resistance element 31.

rlhe three auxiliary lters 33, 34 and 35 in the output circuit of the amplifier tube 21 select the pilot currents respectively controlling the flat gain amplifier 1, the slope network i3 and the bulge network I4. The slope network I3 in the transmission line may be of the type disclosed in the patent to H. W. Bode 2,096,027, October 19, 1937., or th'e patent to E. L. Norton, 2,019,624, November 5, 1935. The bulge network I4 may be of the typedisclosed in the S. Darlington Patent2,l53,743, April 11, 1939. The circuit from the battery 3l to the tube 21 may be completed to ground through the resistance element 31. The alternating current circuit for the tube 21 may be completed through the condenser 33.

The auxiliary filter 33 which selects the pilot current governing the fiat gain amplifier 1 comprises a transformer 3S and an adjustable condenser 40. Preferably in the circuit under consideration, this `filter selects a frequency of 12 kilocycles. The auxiliary filter 34 which selects ie pilot current for controlling the slope network !3 comprises a transformer 4I vand an adjustable condenser 42. The filter 34 preferably in the circuit under consideration selects a frequency of 56 kilocycles. The auxiliary filter 35 which selects the pilot current for governing the bulge network I4 comprises a transformer 43 and an adjustable condenser 44. The filter 35 in the circuit under consideration selects a frequency of 28 kilocycles. The frequencies of the three pilot currents for governing the fiat gain amplifier 1, the slope network I3 and the bulge network I4 are selected lin va manner to prevent interference between the control of the Various pieces of apparatus. Interference between the controls effected by the various pilot currents is prevented by the construction of the networks land 'the spacing of the pilot currents.

The secondary winding of the transformer 39 is connected to two opposite vertices of a bridge 45 in the vform of a voltage doubler rectifier. Voltage doubler rectifiers of this type are disclosed in the patent to D. M. Terry 2,084,115, June 15, 1937. The bridge 45 comprises two condensers 46 and 41 and two rectiiiers 48 and 49 which are preferably in the form of copper oxide elements. The output vertices of the bridge 45` are connected across a resistance element 50 which supplies a negative bias for governing a control space discharge deviceV 5I. The control space discharge device 5I is preferably in the form of a pentode tube. The two copper oxide elements 4S and 49 in the bridge 45 are oppositely connected so as to effect rectication of each half wave of a current supplied thereto.

The control space discharge device 5I comprises anode 52, a contrbl grid 53 and a cathode 54.V Current is not only supplied to the anode 52 .power current.

` the gain desired.

from the battery 3| Vbut also alternatingV current from a low frequency source 55. The source 55 may,'if so desired, be a local 60-cycle source of The circuit vfrorn'the battery 3| through the device 5| may be traced from one `5 terminal of the battery 3| through a choke coil 56, secondary winding of a transformer 5l, primary windingof a transformer 58, anode 52 and cathode 54 to the other terminal .of the battery 3|. The low frequency source 55 is connected to the device 5I by means of the transformer 51. A condenser 59 is provided for completing the alternating currentV circuit through the device 5|. The potential across the resistance element 5B supplied by the voltage doubler for impressing a negative bias on the grid 53 ofthe device 5| is opposed by the potential drop across a portion of the resistance element 6I). The potential drop across theresistance element 65 is provided by a battery 5| which is connected to the resistance B0 :2D in series With the resistance element 62. The potential drop across the resistance element 53 is opposed by the potential drop across the portion of the resistance element in order to ob.- tain a more than proportional change for any change in strength of the pilot current selected Vby the auxiliary filter 33.

The space discharge device 5| is governed by the potential variations across the resistance element 50 for supplying low frequency heating cur- (30 rent to the heater coil I2 through the transformer 58. The heater coil I2 governs the temperature of the resistance element II to control the feedback eifected by the amplifier l. If theV pilot current on the transmission line whichconggg-5 trols the flat gain amplifier 'I increases in strength, the potential drops across the resistance element 5I) increases to increase the negative bias on the grid 53 of Vthe control space discharge device V5I. This lowers the output .i430 from the device 5I to lower the heating current supplied to the coil I2. The temperature of the resistance element II is lowered togreduce the shunt eiect thereof in the feedback circuit of the amplifier l. Accordingly, the feedback 0h45 the amplifier 'I' isincreased to lower the gainef.- fected by the amplifier and therefore to obtain In oase the strength of the pilot current on the transmission line decreases, an opposite .effect is produced to raise the gain effected by the flat gain amplifier The secondary winding of the transformer 4| in the auxiliary filter 34 is connected to two opposite vertices of a voltage doubler rectier 53 which is similar in construction and operation to the voltage doubler 45 above mentioned. The auxiliary filter 34 selects the pilot current employed for governing the operation of the slope network I3. The output vertices of the voltage doubler rectier 53 are connected across a resistance element 54 which serves to impress negative bias on the control grid 65 of a control space discharge device 66. The control space discharge device 65 is similar in construction and operation to the control space discharge device 5| and is supplied with direct current from the battery 3| and alternating current from the source 55. The potential drop across the resistance element S4 which is impressed on the grid 65 is opposed by the potential drop across the portion of the resistance element 6l. The resistance element 6l is energized by the battery 6I. The output circuit of the control space discharge device 66 is connected by a transformer 68 to the coil I6 for heating the resistance ele- 75 coil i8 b-y means of a transformer '|6.

, ment I5. The'r'esistance element I5 whichhas negative temperature coefficient resistance is included in the circuit of the network I3.

If the pilot current onV the transmission line which controls the slope network I3 increases in strength the potential drop across the resistance element 64 is increased to reduce the output from the control space discharge device 66. l This reduces the low .frequency current in the heating coil I5 to reduce the temperature of the resistance element I5. A reduction in the temperature of the resistance .element I5 increases the resistance thereof and increases the loss on the line effected by the slope network I3. In case the pilot current governing the operation of. the slope network I3 is reduced in strength; below normal value then an opposite operation to that described above takes place. y

The auxiliary filter 35 which selects the pilot current for governing the operation of the .bulge network I4 is connected to a voltage doubler rectifier circuit 69 by means of the secondary winding of the transformer 43. ,The voltage doubler rectier circuit G9 is similar in construction and operation to the voltage doubler rectifier circuit 45. The .output vertices of the bridgegin the voltage doubler rectifier 69 are connected to the terminals of the resistance element 'IIL The potential drop across the resistance element 'III controls the operation of a control space discharge device 'II which is similar in construction and operation to the controll space discharge, device 5I. The device II comprises an anode 12, a control grid 13 and a cathode 14. The negative bias. impressed on the control grid VI3 by the drop across the resistance element I0 is opposedbyra portion of the potential drop across the resistance element l5. The potential drop acrossthe i resistance element I5 is effected by a circuit connected to the battery 6|: The anode 12 of-the device '1| is supplied with alternating current from the source 55 and direct current from the battery 3| in a manner similar to that described with respect to the control device 5|. Low frequency control current from the control space discharge device II is connected to the heating The heating coil I8 governs the temperature Vof theresistance element II for governing the operation of the bulge network I4. l

If the strength of the pilot current on the transmission line which governs the operation of the bulge network I4 increases in strength the potential drop across the resistance element 1I] is increased. An` increase in the potential drop across the resistance element 'I0 decreases the low frequency current output from the control spacedischarge device II. A decrease in the output from the control space discharge device 'II lowers the current flow throughv the heating coil I8 to reduce the temperature of the resistance element I`|. A reduction in the temperature of the resistance element I`| increases the resistance thereof to increase the loss effected by the network I4.

The slope network I3 governs the slope of the attenuation characteristic of the transmission line and the bulge network I4 governs the bulge of the attenuation characteristic of the transmission line. The two networks I3 and I4 are so operated as to correct for any change in the slope or bulge of the attenuation characteristics.

Modifications in the cincuits and in the arrangement and location of parts may be made within the spirit and scope of the invention and such'modications are intended'to be covered by the appendedclairns.

What is claimed is:V Y

1. In comlbination a signal transmission line 'having signal and pilot currents thereon, a control station, an amplifier and slope and bulge networks on said line at said station, and means for simultaneously and separately controlling said amplier, said slope network and said bulge network by different pilot currents .on the .transmission line to govern the iiat gain on .the line, the 'slope of the line attenuation characteristic andthe bulge of the line attenuation ycharacteristic.

In combinationa signal transmission line having carrier and pilot currents thereon, an amplier and slope and bulge networks on said line, means comprising circuits having low fre- `quency current thereon for separately governing said amplien said slope networks and said b-ulge network, and means comprising said pilot currents for separately controlling said low frevquency circuits to govern the fiat gain on the line, the slope of line attenuation lcharacteristic and the bulge of the line attenuation characteristic.

3. -In combination a signal transmission line having carrier and pilot currents thereon, a control station, a bulge network on said line at said station for controlling the bulge of the line attenuation characteristic, a slope network on said `line at said station for controlling the slope of the line attenuation characteristic, Vmeans comprising lowA frequency circuits for separately governing said networks, and means for governing one of said low frequency cincuits to control the ybulge of the line attenuation characteristic according to the strength of one pilot current. on `the line and for simultaneously governing another one `of said low frequencyV circuits to control the slope of the line attenuation characteristic according to the strength of another pilot current on said line.

4. In combination a signal transmission line having carrier currents and relatively high irequency pilot currents thereon, a contr-ol station, an amplifier on said line at said station for controlling the flat gain, a` slope network on said line at said station for controlling the slope of the line attenuation characteristic, a bulge network on said line at said station for controlling the bulge of the line attenuation characteristic, `and means simultaneously for controlling said amplier by one pilot current to govern the iat gain on the line, for [controlling the slope network by a second pilot current to govern the slope of the transmission line attenuation characteristic and for controlling the bulge network by a third pilot current to govern the bulge of the `transmission line attenuation characteristic.

5. In combination a signal transmission line having carrier currents and three relatively high "frequency'pilot currents thereon, an amplifier and slope and bulge networks on said line, means comprising low frequency circuits for separately governing said amplifier to control the flat gain on the line, for governing said slope network to control the slope of the line attenuation characteristic and for governing said bulge 'network to control the 'bulge of the line attenuation characteristic, and means controlled by said. pilot currents for respectively governing the strengths of the low frequency currents on said low frequency circuits for controlling the amplier gain, the slope network loss and the bulge network loss to maintain the energy of the different frequency currents on said line the same at any desired levels.

6. In combination a signal transmission line having carrier and pilot currents thereon, a 'control station, an amplifier on said line at said station, a slope network on said line at said station for governing the slope of the line attenuation characteristic, a bulge network on said line at said station for governing the bulge of the line attenuation characteristic, means for separating three pilot currents from the currents on the transmission line and for separating the three pilot currents, means controlled by one of said pilot [currents for governing said amplifier to control the flat gain on said line, means controlled by another one of said pilot currents for governing said slope network to adjust the slope of the transmission line attenuation characteristic, and means controlled by the third one of said pilot currents for governing the bulge network to adjust the bulge ofthe transmission line attenuation characteristic, said last three-mentioned means operating simultaneously.

F7. In combination a signal transmission line having carrier and pilot currents thereon, a control station, an amplier on` said line at said station having a feedback circuit, a first network on said line yat said station for governing the slope of the line attenuation characteristic, a second network on said line at said station for governing the bulge of the line attenuation characteristic, means for separating said pilot currents from the carrier currents at a point beyond said amplier and said networks, means for separating three of said pilot currents, means controlled by one of said pilot currents for governing the feedback circuit of said amplifier to control the flat gain of the currents on said line, means controlled by a second one of said separated Ypilot currents for governing said rst network to adjust the slope of the line attenuation ycharacteristic and means controlled by the third separated pilot current for governing the second network to adjust the bulge of the line attenua- `tion characteristic, said last three-mentioned means operating simultaneously.

HENRY K. KRST.

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