US2254205A - Signal transmission system - Google Patents

Description

PL 1941- J. H. BQLLMAN 2,254,205

SIGNAL TRANSMISSION SYSTEM Filed April 3, 1940 2 Sheets-Sheet l BULGE NETWORK NETWORK SLOPE NETWORK NETWORK b l/WEA/TOR By J. H. BOLLMAN N A TTORNEV Sept. 2, 1941. J. H. BOL LMAN S IGNAL TRANSMIS S I ON SYSTEM Filed April '3, 1940 2 Sheets-Sheet 2 lAl VV lX/VE/V TOR 1 h. BOLLMAN A r TORNFY Patented Sept. 2, 1941 SIGNAL TRANSMISSION SYSTEM John H. Bollman, Rutherford, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application April 3, 1940, Serial No. 327,574

11 Claims.

This invention relates to signal transmission systems and particularly to signal transmission systems having control circuits for governing the loss on transmission lines.

One object of the invention is to provide a signal transmission system composed of a number of transmission lines each having carrier and pilot channels thereon that shall control the flat ain and the attenuation characteristic on each transmission line according to the strengths of pilot currents on the respective lines and that shall control the fiat gain and the attenuation characteristic on a transmission line according to the strengths of pilot currents on other lines in case of failure of the pilot current control associated therewith.

Another object of the invention is to provide control circuits for a signal transmission system composed of a number of transmission lines each having signal and pilot channels and an amplifier and bulge and slope networks thereon that shall control the amplifier and the bulge and slope networks on each transmission line according to the strengths of pilot currents on the respective lines and that shall control the amplifier and the bulge and slope networks on a transmission line according to the strengths of pilot currents on other lines in case of failure of the pilot current control associated therewith.

A further object of the invention is to provide control circuits for a signal transmission system composed of a number of transmission lines each having carrier and pilot channels and an amplifier and bulge and slope networks thereon that shall control low frequency circuits to govcm the amplifier and the bulge and slope networks on each transmission line according to the strengths of pilot currents on the respective lines and that shall control the low frequency circuits governing the amplifier and bulge and slope networks on a transmission line according to the strengths of pilot currents on other lines in case of failure of the low frequency circuits associated therewith.

Transmission systems, for example carrier cable systems, are provided with fiat gain and twist pilot wire regulators which are located at intervals along the cable. 'It has been found that certain over-all losses occur on the pairs of conductors making up a cable which are not corrected for by the distributed fiat gain and twist regulators. 1

According-to the invention disclosed in the patent to H. K. Krist, No. 2,246,307, issued June are controlled by pilot currents, are provided to compensate for the over-all losses. tion regulators not only adjust the fiat gain but also the slope and bulge of the line attenuation characteristic. In the invention disclosed in the H. K. Krist patent, No. 2,246,307, a gain control amplifier, a slope network and a bulge network are placed on each pair of conductors in a cable at the terminal or deviation station. Each pair of conductors in the cable is not only provided with carrier channels but also with pilot channels. The pilot currents on a pair of conductors respectively control the amplifier, the slope network and the bulge network on the associated pair of conductors.

According to the present invention, provision is made for governing the amplifier, the slope network or the bulge network on a pair of conductors according to the strengths of pilot currents on other pairs of conductors in case of failure of the pilot current control means associated with the pair of conductors. Thus, in case of failure of the pilot current regulating circuits associated with one pair of conductors the amplifier and the bulge and slope networks Will be operated approximately to correct operating positions by regulating circuits associated with other pairs of conductors.

In the arrangement employed to describe the invention, two pairs of conductors in a carrier cable system are provided with an amplifier and slope and bulge networks. Each pair of conductors is provided not only with carrier channels but also with three pilot channels. The three pilot currents on each pair of conductors respectively govern the flat grain amplifier, the slope network or equalizer, and the bulge network or equalizer. A'pilot filter which selects the three pilot currents on the pair of conductors is connected'to the conductors at a point beyond the amplifier and the bulge and slope networks. The selected pilot currents are amplified and then supplied to three auxiliary filters which separate the three pilot currents that govern the operation of the fiat gain amplifier, the slope network and the bulge network. 1

The pilot current which is selected by the auxiliary filter for operating the flat gain amplifier is supplied to a bridge in the form of' a voltage doubler rectifier. The output from the voltage doubler rectifier, opposed by a constant potential, supplies negative bias for operating a control space discharge device. The control space discharge device'is energized by a direct-current .17, 1941, terminal or deviation regulators, which source and a source of alternating current. The

The deviacontrol space discharge device governs the operation of a heater coil for controlling a resistance connected across the negative feedback circuit in the fiat gain amplifier. The resistance element controlled by the heater coil has a negative temperature coefficient of resistance and preferably is of the type disclosed in the E. F. Dearborn application, Serial No. 280,692, filed June 23, 1939. The resistance element in the feedback circuit of the flat gain amplifier is so controlled as to oppose any change in the strength of the pilot current from normal value. If the pilot current tends to increase in strength, the gain of the feedback amplifier is reduced to bring the strength of the pilot current back to normal value.

The output from the control space discharge device is not only connected to the heater coil for governing the resistance in the feedback circuit of the flat gain amplifier but is also connected through 'esistance elements to equalizing bus conductors. Other control space discharge devices for governing the heater coils to govern other flat gain amplifiers in other pairs of conductors are also connected to the equalizing bus conductors by resistance elements. Thus, in case of,failure of the circuit governing the heater coil for governing a flat gain amplifier on a pair of conductors, current will be supplied from the equalizing bus conductors for operating the heating coil to an approximate value for main taining the strength of the pilot current on the pair of conductors at approximately correct strength.

The auxiliary filter which selects the pilot A current for operating the slope network is connected to a voltage doubler rectifier for controlling the operation of a control space discharge device. The output from the voltage doubler rectifier is opposed by a standard potential source to effect a more than proportional change for any change in the strength of the pilot frequency current. The control space discharge device is energized not only by direct current but also by a low frequency power current. The output from the control space discharge device is connected to a heater coil for governing a resistance in the slope network. The resistance in the slope network controlled by the heater coil has a negative temperature coeiicient of resistance and may be of the same type as that employed for controlling the feedback circuit of the fiat gain amplifier. The control space discharge device is not only connected to the heater coil for governing the operation of the slope network but is also connected through resistance elements to equalizing bus conductors. The equalizing bus conductors are connected similarly to other control space discharge devices associated with other pairs of conductors so that in case of failure of the control for one slope network the control may be taken over by the equalizing bus conductors.

The auxiliary filter which selects the pilot current for operating the bulge network is connected to a voltage doubler rectifier which in turn controls the negative bias impressed on the grid of a control space discharge device. The output from the voltage doubler rectifier is opposed by a constant potential source to effect a more than proportional change in the operation of the control space discharge device than the changes in strength on the pilot current. The control space discharge device'is energized by a direct-current source and by a source of alternating current which, if so desired, may be a commercial source of power. The output circuit of the control space discharge device is connected to a heater coil for operating a resistance element having a negative temperature coefficient of resistance. The resistance element is included in the bulge network on the pair of conductors. This resistance element having a negative temperature coefficient of resistance may be of the same type as that employed in controlling the feedback circuit of the fiat gain amplifier. The output circuit of the control space discharge device is not only connected to the heater coil for governing the bulge network but is also connected through resistance elements to equalizing bus conductors. The equalizing bus conductors are connected through resistance elements to other control space discharge devices associated with the bulge networks on other pairs of conductors. Thus in case of failure of the control circuits for operating a bulge network on one pair of conductors, the control of this network may be taken over by the equalizing bus conductors connected to the heater coil which governs the operation of the network.

In the accompanying drawings, Fig. 1 when placed above Fig. 2 discloses a system constructed in accordance with the invention.

Referring to the drawings, a terminal or deviation station I is shown connected to a pair of conductors in a carrier cable system having input conductors 2 and 3 and output conductors 4 and 5. The input conductors 2 and 3 are con nected by a transformer 6 to a flat gain amplifier l of any suitable type. The fiat gain amplifier I is provided with a negative feedback circuit having series resistance elements 8 and 9 and a shunt resistance element It. The shunt resistance element I0 has a negative temperature coefficient of resistance and may be of the type disclosed in the above-mentioned application of E. F. Dearborn, Serial No. 280,692. The resistance element I0 is controlled by a heater coil H in a manner to be hereinafter described.

The amplifier I is connected to a slope equalizer or network [2 which may be of the type disclosed in the H. W. Bode Patent 2,096,027, October 19, 1937 or in the E. L. Norton Patent 2,019,624, November 5, 1935. The slope network I2 is controlled by a resistance element l3 having a negative temperature coefficient of resistance. This resistance element l3 may be of the, same type as the resistance element :0 employed to control the flat gain amplifier 1. A heater coil I4 is provided for governing the operation of the resistance element It in a manner to be hereinafter set forth.

The slope network I2 is connected to a bulge equalizer or network I5 which may be on the type disclosed in the S. Darlington Patent 2,153,743, April 11, 1939. The bulge network I5 is governed by a resistance element l0 having a negative temperature coefficient of resistance. The resistance element It may be of the same type as the resistance element It employed to control the flat gain amplifier 1. The resistance element I6 is governed by a heater coil H in a manner to be hereinafter set forth. The bulge network 15 is connected by an amplifier l8 and a transformer I9 to the output conductors i and 5.

The pair of conductors not only is provided with carrier channels but also with three pilot channels. A pilot filter 20 is connected to the pair of conductors. beyond the amplifierv 8 for selecting the three pilot currents. The pilot filter comprises two transformers 2| and 22, a crystal 23, a condenser 24 and a resistance element 25 connected across the secondary winding of the transformer 22. nected to the input circuit of an amplifier 26 in the form of a pentode tube. The amplifier 26 comprises an anode 21, a control grid 28 and a cathode 29. Negative bias for the control grid 28 is supplied by the potential drop across a resistance 30. Potential for the anode 21 is supplied from abattery 3| through a resistance element 32 and auxiliary filters 33, 34 and 35. The auxiliary filters 33, 34 and 35 respectively select the three pilot currents which are employed to control the fiat gain amplifier 1,'the slope network l2 and the bulge network l5. vThe filter 33 comprises a transformer 36 and an adjustable condenser 31. The auxiliary filter 34 comprises a transformer 38 and an adjustable condenser 39. The auxiliary filter 35 comprises a transformer 46 and an adjustable condenser 4|.

The secondary winding of the transformer 36 which forms a part of the auxiliary filter 33 is connected to two opposite vertices of a bridge circuit 42. The bridge circuit 42 is in the form of a voltage doubler rectifier of the type-disclosed in the patent to D. M. Terry, 2,084,115, June 15, 1937. The voltage doubler rectifier comprises two condensers 43 and 44 and two rectifiers 45 and 46 which are preferably of the copper oxide type. The output vertices of the voltage doubler rectifier are connected across a resistance element 41. The potential drop across the resistance element 41 is employed to govern the operation of a control space discharge device 48 in the form of a pentode tube. The device 48 comprises an anode 49, a control grid 50 and a cathode 5|.

control grid 50 is opposed by a portion of the potential drop across a resistance element 52. The resistance element 52 is connected to a battery 53 through a resistance 54. The potential drop across a portion of the resistance element 52 opposes the potential drop across the resistance element 41 to effect a more than proportional change in the operation of the control space discharge device 48 for changes in strength of the pilot current selected by the auxiliary filter 33.

The anode 49 of the device 43 is supplied with direct potential from the battery 3| by a circuit which extends from one terminal of the battery 3| through a choke coil 55, secondary winding of the transformer 56, primary winding of the transformer 51, anode 49 and cathode 5| to the other terminal of the battery 3|. A source of low frequency current 58 is connected to the plate circuit of the device 48 by means of the transformer 56. The alternating-current circuit through the device 48 is completed by a condenser 59.

The low frequency output current from the device 48 is connected by the transformer 51 to the heater coil The heater coil II, as before set forth, controls the temperature of the resistance element |0 which has a negative temperature coefficient of resistance. The resistance. l0 governs the feedback circuit for the fiat gain amplifier 1.

v Ifthe pilot current on the pair of conductors which controls the hat gain amplifier 1 rises above normal value, the rectified current im- The potential drop across the resistance element 41 which is impressed on the The pilot filter 29 is conpressed across the resistance 41 increases to increase the. negative .bias impressed on the control grid 59 of the device 48. The low frequency output from the device .48 is reduced to reduce the current supplied to the heater coil II. This reduces the temperature of the resistance element I0 and accordingly increases the resistance value thereof. An increase in the resistance value of the resistance element l9 decreases the gain of the fiatgain amplifier 1 to return the strength of the pilot current governing the fiat gain amplifier to normal value. If the strength of the pilot current governing the fiat gain amplifier 1 falls below normal value, an opposite operation takes place.

The control device 48 is not only connected to the heater coil H by the transformer 51 but is also connected through resistance elements 60 and BI to a pair of equalizing bus conductors 62. The equalizing bus conductors 62 are also connected in a similar manner to the control space discharge devices which govern the operation of other flat gain amplifiers on other pairs of conductors. In Fig. 1 of the drawings, the connection to another control device is indicated. A transformer 63 which is similar to the transformer 51 connects a control device, not shown, not only to a heating coil 64 for governing the feedback on an amplifier for another pair of conductors, but also through resistance elements 65 and 66 to the equalizing bus conductors 62. In case of failure of the low frequency current supplied by the transformer 51 to the heater coil H for governing the flat gain amplifier 1, it is apparent control current will be supplied to the heater coil H from the equalizing bus conductors 62 through the resistance elements 69 and 6|. Thus; in case of failure of the low frequency control circuits for the heater coil governing an amplifier, it is apparent control of the amplifier will be effected from low frequency control circuits associated with other pairs of conductors. The auxiliary filter 34 which selects the pilot current for governing the slope network I2 is connected by the transformer 38 to two vertices of a voltage doubler rectifier 61. The voltage doubler rectifier 61 is similar in construction and operation to the voltage doubler rectifier 42. The output voltage is impressed across a resistance element 68 which controls the negative grid bias impressed on a control space discharged device69. The device 69 is in'the form of a pentode tube the same as the control space discharge device 49.and comprises an anode 15, a control grid 1| and a cathode 12. The negative bias obtained by the potential drop across the resistance element 68 which is impressed on the control grid 1| is opposed by the potential drop across a portion of a resistance element 13. The

resistance element 13 is in circuit with the battery 53 in the same manner as the resistance element 52. The device 69 is energized not only by the battery 3| but also by the low frequency source of power 58.

A transformer 14 connects the output circuit of the device 69 to the heater coil l4 which controls the resistance element |3 in the slope network |2. The transformer 14 also connects the output from the device 69 through resistance elements 15 and 16 to equalizing bus conductors 11. The equalizing bus conductors 11 are also connected in the same manner to the control means for other slope networks associated with other pairs of conductors. One connectionto another slope network is indicated in Fig. 1 of the bulge of the transmission attenuation characteristic on each pair of conductors, means comprising a low frequency circuit connected to each of said slope and bulge networks for governing the operation thereof, means for respectively controlling the low frequency circuits associated with the slope network and the bulge network of a pair of conductors by two pilot currents on that pair of conductors, and means for connecting in parallel the low frequency circuits connected to all said slope networks and for connecting in parallel all the low frequency circuits connected to the bulge networks.

6. In a signal system, a plurality of pairs of conductors each having carrier currents and pilot currents thereon, a network for changing the attenuation characteristic and an amplifier on each of said pairs of conductors, means comprising a low frequency circuit connected to each of said amplifiers and networks for governing the operation thereof, means for respectively controlling the low frequency circuits associated with the amplifier and network of a pair of conductors, and means for connecting in parallel the low frequency circuits connected to all said amplifiers and for connecting in parallel all the low frequency circuits connected to the networks.

7. In a signal system, a plurality of pairs of conductors having carrier currents and three pilot currents on each of said pairs of conductors, an amplifier and slope and bulge networks on each of said pairs of conductors, means comprising a low frequency circuit connected to each of said amplifiers and networks for governing the operation thereof, means for respectively controlling the three low frequency circuits associated with the amplifier and networks of a pair of conductors by the three pilot currents on that pair of conductors, and means for connecting in parallel the low frequency circuits connected to all said amplifiers for connecting in parallel all the low frequency circuits connected .to the slope networks and for connecting in parallel all the low frequency circuits connected to the bulge networks.

8. In a signal system, a plurality of pairs of signal conductors having carrier currents and three pilot currents on each of said pairs of conductors, an amplifier and slope and bulge networks on each of said pairs of conductors, a control thermistor associated with each of said amplifiers and networks, a separate low frequency circuit for controlling each of said thermistors, means controlled by the pilot currents on each pair of conductors for respectively governing the low frequency circuits connected to the thermistors of the amplifier and networks for that pair of conductors, means for connecting all the low frequency circuits associated with said amplifiers in parallel through resistance elements, for connecting all the low frequency circuits associated with said slope networks in parallel through resistance elements and for connecting all the low frequency circuits associated with said bulge networks in parallel through resistance elements.

9. A cable having a plurality of pairs of conductors, a number of said pairs of conductors having carrier currents and three relatively high frequency currents thereon, an amplifier and slope and bulge networks on each of a number of said pairs of conductors, a circuit having a low frequency current thereon for each amplifier and network on each of said number of pairs of con ductors, and means for respectively controlling the low frequency circuits associated with the amplifier and networks on each pair of conductors by the three pilot currents on each pair of conductors to respectively govern the fiat gain and slope and bulge of the attenuation characteristics of the cable pairs of conductors, and means for adjusting the amplifier, slope network or bulge network of a pair of conductors according to adjustment of similar apparatus on other pairs of conductors in case of failure of the low frequency circuit controlling the amplifier, slope network or bulge network.

10. A cable having a plurality of pairs of conductors, each of said pairs of conductors having carrier currents and three relatively highfrequency pilot currents thereon, an amplifier and slope and bulge networks on each of said pairs of conductors, means comprising circuits having low frequency current thereon for separately governing the amplifier, the slope network and the bulge network on each of said pairs of conductors to control respectively the flat gain, the slope of the attenuation characteristic and the bulge of the attenuation characteristic on each of said pairs of conductors, means controlled by the three pilot currents on a pair of conductors for respectively governing the strengths of the low frequency currents controlling the amplifier, the slope network and the bulge networks of the pair of conductors to maintain the energy levels of the different frequency currents on the pair of conductors the same at a desired level, and

means for connecting together the low frequency circuits governing the amplifiers of all pairs of conductors to insure control of an amplifier in case of failure of the low frequency current effecting control thereof for connecting together the low frequency circuits governing the slope networks of all pairs of conductors to insure control of a slope network in case of failure of the low frequency current eifecting control thereof and for connecting together the low frequency circuits governing the bulge network of all pairs of conductors to insure control of a bulge network in case of failure of the low frequency current effecting control thereof.

11. In a signal system, a plurality of pairs of signal conductors having carrier and pilot currents on each pair of conductors, a plurality of control means on each pair of conductors for respectively governing a number of different characteristics of the transmitted currents, a number of circuit means respectively controlled by the pilot currents on a pair of conductors for separately governing the control means on the pair of conductors, and means in case of failure of the control means governing a characteristic of the transmitted current on a pair of conductors for governing the control means by circuit means associated with other pairs of conductors.

JOHN H. BOLLMAN.

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