Title:
Signal transmission system
United States Patent 2208617


Abstract:
538,807. Automatic volume control. STANDARD TELEPHONES & CABLES, Ltd. (Western Electric Co., Inc.). Feb. 27, 1940, No. 3622. [Class 40 (iv)] In a carrier transmission system, a pilot current received at a main repeater station controls the strength of a second pilot current sent back to control the gain at the preceding repeaters. The second pilot current may also control the gain at the main station itself and at subsequent stations. In all cases gain is controlled by varying the heating of a substance having a high and preferably negative temperature co-efficient of resistance, e.g. silver sulphide or boron, in the beta circuit of the amplifier concerned. In one arrangement, Figs. 4 to 6 (not shown), the second pilot is controlled by the combined effect of two pilots received over separate lines and controls the gain of repeaters in a number of lines at each station. In a modification, Figs. 7 to 9, pilot current received over the uppermost line in the main station 5 is filtered out and rectified and control the amount of commercial frequency current supplied by a generator 71 to be passed on via an adjusting network 67 and hybrid coil to a control circuit 69 for the local amplifiers and via a network 83 and a further hybrid coil to a control circuit 85 which is coupled via a phantom circuit on the upper two pairs to the control circuit of the amplifiers at the preceding station 6. These control circuits are also fed with an adjustable amount of commercial frequency current via networks 68, 88 to determine the normal gain. The second pilot is also fed via a circuit 86 and a phantom circuit formed by the lower two pairs to similar adjusting networks and hybrid coils at the repeater station 8 for the control of gain there and at repeater station 7. At each station the ignition circuit of a three electrode cold-cathode discharge tube is fed with current direct from the commercial frequency source and with current from the gain-control circuit in opposition. Normally the tube remains inert but if the pilot current fails the tube breaks down and provides a circuit whereby the gain controlling elements are heated to an average extent. The circuit 87 may involve a phantom circuit on additional signalling pairs.



Inventors:
Wilson, Ira G.
Application Number:
US25581239A
Publication Date:
07/23/1940
Filing Date:
02/11/1939
Assignee:
BELL TELEPHONE LABOR INC
Primary Class:
Other Classes:
330/52, 330/86, 330/124R, 333/15
International Classes:
H04B3/12
View Patent Images:



Description:

This invention relates to signal transmission systems and particularly to pilot channels for carrier current systems.

One object of the invention is to provide a sig6 nal transmission line having pilot and carrier channels thereon and a main station with auxiliary stations on each side thereof that shall control amplifiers at said stations according to the pilot current at the main station to maintain the signal level constant at the main station and to maintain the signal level at the auxiliary stations beyond the main station approximately constant.

Another object of the invention is to provide 1a cable comprising a number of pairs of conductors having pilot and carrier channels thereon and a main station with auxiliary stations on each side of the main station that shall control amplifiers at said stations on each pair of conductors according to the pilot currents on a number of pilot channels at the main station to maintain the signal level on the pairs of conductors constant at the main station and to maintain the signal level on pairs of conductors at auxiliary stations beyond the main station approximately constant.

A further object of the invention is to provide a signal transmission line having pilot and carrier channels thereon and a main station with auxiliary stations on each side thereof that shall control a low frequency current according to the pilot current on a pilot channel at the main station and that shall control amplifiers at the stations by said low frequency current to main3s tain the signal level constant at the main station and to maintain the signal level at the auxiliary stations beyond the main station approximately constant.

In a signal transmission line having pilot and carrier channels it is necessary to provide repeater stations at intervals along the line to maintain the energy level of the signals. The gain effected at the repeater stations must be governed according to the losses on the line in order to maintain the energy level of the signals constant.

In one form of the invention a signal transmission line carrying pilot and carrier channels has a main station and auxiliary stations located 60 on each side of the main station. Amplifiers of the feedback type are located at each of the stations.

The amplifiers are each controlled by an element having a high negative temperature coefficient of resistance, for example, silver sulphide inserted in gt Ahe beta circuit. At the main station pilot current on the pilot channel is filtered off and employed for controlling a low frequency source of current. The low frequency current which is controlled according to the energy level of the pilot current is employed to energize heating coils associated with the resistance elements in the beta circuits of the various amplifiers.

The auxiliary stations on the transmission line before the main station are controlled by a backward acting circuit and will insure a constant energy level for the signals at the main station.

The auxiliary stations on the transmission line beyond the main station are controlled by a forward acting circuit. A forward acting control circuit in a pilot channel system will not be able to exactly maintain the energy level of the signals constant at the controlled stations. However, it is possible to maintain the energy level of the signals approximately constant and relieve the work required at the next main station. It is apparent that the next main station will hold the energy level of the signals substantially constant.

In a pilot channel arrangement constructed as above indicated it is apparent that a saving will be.effected in the amount of apparatus required and that the signal level will be held close to the level required. At the terminal of the transmission line means will be provided by mop-up circuits to maintain the energy level of the signals constant. In the mop-up circuits no forward acting control circuits will be employed.

In a cable carrier system constructed in accordance with the invention the pairs of conductors in the cable will have not only carrier channels but also pilot channels. A main station on the cable will have a number of auxiliary stations located on each side thereof. An amplifier is provided at each station for each pair of conductors. The amplifiers are preferably of the feedback type controlled by a resistance element having a high negative temperature coefficient of resistance. The resistance elements which are located in the beta circuits of the amplifiers are controlled by heater coils. A number of the pilot currents on the pilot channels are selected at the main station and combined for governing a low frequency control current. A number of pilot currents are employed in order to insure against failure of the gain control apparatus in case of failure of one pilot current. The controlled low frequency current is employed to govern the amplifiers on the stations before the main station by means of backward acting circuits and to control the amplifiers at the stations beyond the main station c by forward acting circuits. The energy level of 2 the signals on the different pairs of conductors a will be maintained substantially constant at the t main station. At the auxiliary stations beyond f the main station the energy level of the signals a can be maintained only approximately constant.

In the accompanying drawings, 3 Figs. 1, 2 and 3 taken together disclose a gain c control circuit constructed in accordance with the invention. In assembling the drawings, Fig. 2 is attached to the left side of Fig. 1 and Fig. 3 is attached to the left side of Fig. 2; Figs. 4, 5 and 6 taken together disclose a carrier cable system constructed in accordance with the invention. In completing the circuit shown in Figs. 4, 5 and 6, Fig. 5 is attached to the left side of Fig. 4 and Fig. 6 is attached to the-left side of Fig. 5.

Referring to Figs. 1, 2 and 3 a carrier current transmission system.is illustrated .comprising .wo conductors I nd d 2. A main station 3 and four auxiliary stations 4, 5, 6 and ,7 are connected to the transmission line comprising conductors I and 2. The auxiliary stations 4 and 5 are positioned at one side of the main station 3 and the auxiliary stations 6 and 7 are positioned on the other side of. the main station 3.

An amplifier 8 in the transmission line at the main station 3 is controlled by a beta circuit having a resistance element 9 therein. The resistance element 9 has a high negative temperature coefficient of resistance and preferably is composed of silver sulphide. The resistance element is controlled by heater coil 10. Amplifiers 11 and 12 are respectively placed in the transmission line at the auxiliary stations 5 and 4.

The amplifiers II and 12 have beta circuits which are respectively controlled by resistance elements 13 and 14. Resistance elements 13 and 14 are of similar construction to the resistance elements 9 at station 3. Heater coils 15 and 16 are respectively provided for controlling the resistance elements 13 and 14.

.45 Amplifiers 17 and 18 are positioned in the transmission line at stations 6 and 7. The amplifiers l7 and 18 are provided with beta circuits respectively controlled by resistance elements 19 and 20. Resistance elements 19 and 20 have high negative temperature coefficients of resistance and preferably are composed of silver sulphide.

Heater coils 21 and 22 are respectively provided for controlling the resistance elements 19 and 20.

The transmission line comprising conductors I and 2 not only has a number of carrier chan.els thereon for signal purposes but has a pilot channel supplied with pilot current by means of a suitable source 23. The carrier currents and the pilot current may have relatively high frequencies. At the main station 3 a filter 24 is provided for selecting the pilot current transmitted over the line from the source 23. The pilot current selected by the filter 24 is amplified by amplifier 25 and rectified by a rectifier dou-65 bler 26. The rectified pilot current supplied by the rectifier doubler 26 is supplied to a control tube-27. The plate circuit of the tube 27 is connected to a source 28 of relatively low frequency current so that the low frequency current from the source 28 is controlled in accordance with the amplitude of the pilot current on the transmission line at station 3. The controlled low frequency current from the control tube 27 is amplified by tube 29 and supplied to two low fret6 quency control conductors 30 and 31. In-the ircuit shown in Fig. 2 of the drawings the filter 4 is connected to the amplifier 25 by means of ,transformer 32. The amplifier 25 is connected o the rectifier doubler 26 by means of a transormer 33. The control tube 27 is connected to implifier tube 29 by means of transformer 34.

nhe amplifier 29 is connected to the conductors 10 and 31 by means of a transformer 35. The 5onductors 30 and 31 supply low frequency control current to each of the stations on the trans- ii nission line for controlling the gain by the various amplifiers.

The heater coil 10 for controlling the resistance element 9 at station 3 is connected to the control conductors 30 and 31 by means of a transformer 36. Adjustable resistance elements 37 and 38 are provided in the connections between the heater coil 0 and the tranhe trsformer 36 for adjusting not only the rate of gain but the flat gain effected by the amplifier 8. In the transmission line under consideration it is assumed that the various sections of the transmission line are subjected to substantially the same temperature conditions so that the flat gain effected at a station may be adjusted as above set forth. ,25 Heater coils 15 and 16 at stations 5 and 4 are respectively connected to the control conductors 30 and 31 by means of transformers 39 and 40.

Adjustable resistance elements 41 and 42 are provided in the connection between the heater coil ,3 15 and the transformer 39. Adjustable resistance elements 43 and 44 are provided in connection between the heater coil 16 and the transformer 40. The adjustable elements 41 and 42 at station 5 and adjustable resistance elements p35 43 and 44 at station 4 serve to adjust the rate of gain and the flat gain at the stations 5 and 4.

The heater coils 21 and 20 at stations 6 and 7 are respectively connected to the control conductors 30 and 31 by means of transformers 45 and a 46. Adjustable resistance elements 47 and 48 . are provided in the connections between the heater coil 21 and the transformer 45 and adjustable resistance elements 49 and 50 are provided in the connections between the heater coil 22 and the transformer 46. Resistance elements' 47 to 50, inclusive, at stations 6 and 1 serve to adjust the rate of gain and the flat gain effected by the amplifiers 17 and 18 at stations 6 and 7.

The pilot current supply from a source 23 is,50 selected by the filter 24 for governing the operation of the amplifiers at the stations 3, 4, 5, 6, and 7. The selected pilot current is amplified by the amplifier tube 25, rectified by the rectifier doubler 26 and supplied to control tube 2 for governing the low frequency current from the source 28. The controlled low frequency current is amplified by the amplifier 29 and supplied to the control conductors 30 and 31. The control current is fed back for controlling stations 4 and 5 and is fed forward for controlling stations 6 i" and 7. The heater coils 15, 16 and 10 at stations 5, 4 and 3 are controlled by the low frequency current on the conductors 30 and 31 to maintain the energy level of the signals on transmission , line at station 3 substantially constant. :' At stations 6 and 1 the energy level of the signals can only be held approximately constant.

By means of a forward acting circuit the amplifiers at stations 6 and 7 can be controlled to approximate closely the level of the signals re- quired at these stations. However, at the next main station the energy level of the signals will be held constant. Moreover, by reason of providing the two forward acting stations, 6 and 7 it is possible to relieve the load carried by the 1ý5 next main station. It should be noted in thi system shown in Pigs. 1, 2 and 3 only one filte: is connected to the transmission line and th only connection between the various auxiliarl stations and the main station is a circuit carry. ing the low frequency control current. The ap. paratus for adjusting the low frequency curreni according to the energy level of the pilot curreni is only necessary at the main station. In a systern constructed as above set forth it may be noted the distance through which the control currents are transmitted is reduced by one-half, This greatly reduces the line loss bythe control currents and therefore the voltage required by Sthe control currents.

Referring to Figs. 4, 5 and 6, a carrier cable system is illustrated comprising a number of pairs of conductors having not only carrier channels but also pilot channels. In Figs. 4, 5, and 6 five g0 pairs of conductors 51, 52, 53, 54 and 55 are illustrated. It is to be understood, however, that the cablee may be provided with any desired number of similar pairs. of conductors.

One main station 56 and four auxiliary stations 5 57, 58, 59, and 60 are positioned on the pairs of conductors 51 to 55, inclusive. The stations 57 and 58 are positioned on one side of the station 56 and the stations 59 and 60 are positioned on the other side of the main station 56. Amplip3 fiers 61 are provided on the pairs of conductors 51 to 55, inclusive, at the main station 56. The amplifiers 61 each have a beta circuit controlled by a resistance element 62. The resistance elements 62 are cont are trolled by heater coils 63. Am5 plifiers 64 are provided at station 57 for the pairs of conductors 51 to 55, inclusive. Beta circuits for the amplifiers 64 are controlled by means of resistance elements 655. Resistance elements 65 as also the resistance elements- 62 have a high negative temperature coefficient of resistance and preferably are composed of silver sulphide. The resistance elements 65 are controlled by heater coils 66.

Amplifiers 67 are provided at station 58 for the pairs of conductors 51 to 55, inclusive. The amplifiers 67 are provided with beta circuits controlled by resistance elements 68. Reistance elements 68 have a high negative temperature coefficient of resistance and may be composed of 'o silver sulphide. The resistance elements 68 are controlled by heater coils 69. Amplifiers 70 are provided at station 59 for the pairs of conductors 51 to 55, inclusive. Beta circuits for the amplifier 70 are controlled by resistance elements 71.

5 Resistance elements 71 in turn are controlled by heater coils 72. Amplifiers 73 at station 60 are provided for the pairs of conductors 51 to 55, inclusive. The amplifiers 73 are provided with beta circuits under control of resistance elements 10 74. Resistance elements 74, the same as resistance elements 71, have a high negative temperature coefficient of resistance and may be composed of silver sulphide. The resistance elements 74 are controlled by heater coils 75.

A pilot filter 76 is connected to the pair of conductors 54 at station 56 to select a pilot current supplied by a source 77. A pilot filter 78 connected to the pair of conductors 55 selects the pilot current supplied to the conductors 55 by means of a source 79. The filter 76 is connected to an amplifier 80 by means of the transformer 81 and the output of the amplifier 80 is connected by the transformer 82 to a rectifier doubler 83. The filter 78 is connected by a trans76 former 84 to an amplifier 85. The output of the e amplifier 85 is connected by a transformer 86 r to the rectifier doubler 83. The rectifier doubler e 83 is connected to a control tube 87. A source y of low frequency current 88 is connected to the - output circuit of the tube 87. The tube 87 is connected by transformer 89 to an amplifier 90 and the amplifier 90 is connected by transformer S91 to a pair of control conductors 92 and 93.

S The two pilot currents selected from the pairs i of conductors 54, and 55 jointly control the rectifier doubler 83. The rectified pilot currents Sgovern the control tube 81 to 'control the low Sfrequency current from the source 88 according to the amplitudes of the pilot currents on the pairs of conductors 55 and 54. The controlled current is amplified and supplied to the control circuit comprising the conductors 92 and 93.

The heater coils 66, 69, 63, 72 and 75 at the stations 57, 58, 56, 59 and 60 are connected in parallel to the control circuit comprising con- 90 ductors 92 and 93. The heater coils 66 and 69 at stations 57 and 58 are controlled by a backward acting circuit whereas heater coils 72 and 75 at stations 58 and 60 are controlled by a forward acting circuit. Adjustable resistance ele- S2 ments 94 are associated with the heater coil 86 for controlling the rate of gain and the flat gain of the amplifiers 64. Adjustable resistance elements 95 are associated with the heater coil 69 for controlling the rate of gain and the fiat 00 gain of the amplifiers 67. Adjustable resistance elements 96 are associated with the heater coil 63 for controlling the rate of gain and the flat gain of the amplifiers 61. Adjustable re.i:cnstan elements 97 and 98 are respectively associated '3 with the heater coils 72 and 75 for controlling the rate of gain and the flat gain of the amplifiers 70 and 73.

The control current on the conductors 92 and 93 which is governed in accordance with the pilot currents on the pairs of conductors 54 and 55 control the amplifiers at the stations 57, 58 and 56 to maintain the energy level of the signals at the main station 56 substantially constant.

The control current on the conductors 92 and 4t 93 governs amplifiers at stations 59 and 60 to maintain the energy level of the signals at these stations substantially constant.

Modifications in the systems and in the arrangement and location of parts may be made within the spirit and scope of the invention and such modifications are intended to be covered by the appended claims.

What is claimed is: 1. In combination, a signal transmission line having pilot and carrier channels thereon, said channels carrying pilot and carrier currents, a main station and a plurality of auxiliary stations on said line, said auxiliary stations being located on each side of said main station, an amplifier for said channels at each of said stations, and means controlled by pilot current at the main station for simultaneously governing each of said amplifiers to maintain the level of the currents on the channels constant at the main station 6 and at the auxiliary stations before said main station and to maintain the level of the current at the auxiliary stations beyond said main station approximately constant.

2. In combination, a signal transmission line having a pilot channel and a number of carrier channels thereon, a main station and a plurality of auxiliary stations on said line, said auxiliary stations being located on each side of said main station, an amplifier for said channels at each of said stations, and means controlled by the pilot current at the main station for simultaneously governing each of said amplifiers to maintain the signal level constant at the main station and at the auxiliary stations before said main station and to maintain the signal level at the auxiliary stations beyond said main station approximately constant.

3. In combination, a transmission line having 0l pilot channels and carrier channels thereon, a main station and a plurality of auxiliary stations on said line, said auxiliary stations being located on each side of said main station, a source of relatively low frequency current at said main station, an amplifier for said channels at each of said stations, means for combining said pilot currents to control the current from said low frequency source, and means for simultaneously controlling said amplifiers by said controlled low .A frequency current to maintain the signal level constant at the main station and at the auxiliary stations before said main station and to maintain the level of the signals at the auxiliary stations beyond said main station approximately g correct.

4. In combination, a cable having a plurality of pairs of conductors, a pilot channel and carrier channels on said pairs of conductors, a main station and a plurality of auxiliary stations, on S0 said cable, an amplifier for the channels on each. of said pairs of conductors at each station, and means controlled by the pilot current on the pilot channel at the main station for simultaneously governing each of said amplifiers to maintain 8 the signal level constant at the main station and at the auxiliary stations before said main station and to maintain the level of the signals at the auxiliary stations beyond said main station approximately constant.

S5. In combination, a cable having a plurality of pairs of conductors, pilot channels and carrier channels on said pairs of conductors, an amplifier for the channels on each of said pairs of conductors, means for picking a number of pilot currents from the pilot channels and means for combining said pilot currents and for controlling said amplifiers according to the strength .of said pilot currents.

6. In combination, a plurality of pairs of con0 ductors, pilot channels and carrier channels on said pairs of conductors, a station having amplifiers respectively associated with said pairs of conductors, means for filtering off the pilot currents from two pilot channels, and means for combining- said pilot currents and for controlling the amplifiers: at the station by said pilot currents.

7. In combination, a plurality of pairs of conductors, pilot channels and carrier channels on said.pairs of conductors, a station having ampliers respectively associated with said pairs of conductors, a source of relatively low frequency current at said station means for filtering off the 1i0 pilot, currents from a number of pilot channels, means for combining said pilot currents to control the current from said low frequency source and means for simultaneously controlling said amplifiers by said low frequency current. 8. In combination, a cable having a plurality of pairs of conductors, pilot channels and carrier channels on said pairs of conductors, a main station and auxiliary stations for said cable, said auxiliary stations being located on each side of g0 said main station, means for picking two pilot currents from the pilot channels at the main station and means for combining said two pilot currents and for simultaneously controlling said amplifiers according to the strength of said pilot -5 currents to maintain the carrier current level" constant on the different pairs of conductors at the main station and at the auxiliary stations before the main station and to maintain the level of the carrier currents approximately con- Xo stant at the auxiliary stations beyond said main station.

9. In combination, a plurality of pairs of conductors, pilot channels and carrier channels on said pairs of conductors, a main station and 5 auxiliary stations for said pairs of conductors, said auxiliary stations being located on each side of said main station, an amplifier for said channels on each of said pairs of conductors at each of said stations, a source of relatively low frequency current at said main station, means for picking off two pilot currents from the pilot channels at the main station, means for combining said pilot currents to control the current from' said low frequency source and means for simultaneously controlling said amplifiers by said controlled low frequency current to maintain the signal level constant on the pairs of conductors at the main station and at the auxiliary stations before the main station and to maintain the level of the signals at the auxiliary stations beyond the main station approximately constant.

IRA G. WILSON.