Transmission system

Oct. 30, 1934. η. w. Dudley 1,979,101

TRANSMISSION SYSTEM

Filed Feb. 6, 1929 2 Sheets-Sheet 1

Fig. Z

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Fig. 2.

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ATTORNEY

Oct. 30, 1934.

1,979,101

Sheets-Sheet 2

H. W. DUDLEY

TRANSMISSION SYSTEM Filed Feb. 6, 1929

I I

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I I INVENTOR

H. PV Dudley

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attorney

Patented Oct. 30, 1934

1,979,101

UNITED STATES PATENT OFFICE

1,979,101

TRANSMISSION SYSTEM

Homer W. Dudley, Teaneck, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York

Application February 6, 1929, Serial No. 337,810

Claims. (Cl. 179—170)

This invention relates to transmission circuits and more particularly to those employing neon or similar gas disruptive discharge tubes as a means of controlling the transmission there5 through.

An object of the invention is to control transmission through a circuit by means of the signals being transmitted thereover; that is, to change it from a non-conductive to a conductive con19 dition or vice-versa.

A further object of the invention is to increase the speed of signal transmission in a two-way repeater equipped with echo suppressing and singing prevention devices above that which is 15 obtained in similar circuits using electromechanical elements, such as relays which require appreciable time to operate.

Another object of the invention is the elimination of distortion which results during the tran£0 sition from a transmission to a non-transmission condition of a repeater thus equipped.

Still another object of the invention is to eliminate noise and other disturbances which may occur in circuits of this type due to relay contacts £5 which may cause chattering or become of high resistance.

Another object-of the invention is to provide a margin against interfering voltages which tend to prevent proper operation of the repeater sys30 tem.

A feature of the invention resides in utilizing neon or other flashing tubes for controlling the operation of a two-way repeater to prevent singing and to eliminate interference in the trans35 mitted signals from echoes or reflection voltages which tend to be transmitted back through the oppositely directed branch of the circuit. In general, tubes having a critical voltage which must be applied before transmission occurs and 40 which thereafter have substantially linear transmission characteristics may be used. In accordance with the invention, tubes of this type are connected in both branches^ of a two-way repeater and are provided with a steady biasing 45 component to place them in the necessary state of conduction for proper operation of the circuit. A further biasing voltage, under the control of the speech being transmitted through one of the paths, is impressed upon the tubes;

the polarity of said voltage being such that the conduction through the speech transmitting path is increased, while, that through the oppositely directed path is prevented. .

A better understanding of the invention may be 55 had from the following description together with the accompanying drawings of which Figs. 1 to 3 show various types of loss circuits which may be used in accordance with this invention in a repeater circuit; Fig. 4 shows the transmission characteristic of the most suitable type of tube; 60 and Fig. 5 shows an application of one of the loss elements in a repeater circuit.

The loss circuits illustrated in Figs. 1 to 3 all employ neon or other gas disruptive discharge tubes, the impedance conditions of which are 65 regulated to determine the loss condition of the circuit. The transmission characteristic of the nedn tube, which is the most desirable type for use in this invention, is shown in Fig. 4. These tubes are non-conductive or opaque to currents 70 until a critical voltage is impressed on their electrodes which iodizes the gas causing it to become conductive. This critical break-down voltage is shown in Fig. 4 as Ei. When the tube has once become conductive the voltage upon its electrodes 75 must fall to E2 before it is extinguished. In the loss circuits of this invention it may be desired to bias the tubes so that they are either normally conductive or normally extinguished; A control voltage, derived from the signal current in the 80 associated circuit, is then impressed upon the tubes; the polarity of said control voltage having been selected with respect to the fixed biasing voltage so as to reverse the transmission conditions of the tubes. A margin against interfer- 85 ing voltages in the circuit may be provided by propierly selecting the value of the steady biasing voltage.

One of several types.of loss circuits which may be used in a repeater circuit in accordance with 90 this invention employs series elements as shown in Fig. 1. The circuit is connected in the line by means of the transformers 3 and 4. In series with the transformer windings are the neon tubes 1 and 2; the biasing battery 5; and the 95 resistance 6 across which the control voltage is ’ impressed through the leads 8, said control voltage being derived from the current transmitted over the circuit in a manner hereinafter described in connection with Fig. 5. One tube is 100 connected in each line; and the battery 5 and resistance 6 at the midpoint of the transformer windings give the circuit symmetry. A condenser 7 is connected in shunt to the resistance 6 to provide a path of low impedance for al- 105 ternating currents. _a

When the tubes 1 and 2 are extinguished the loss circuit presents infinite impedance to alternating currents and when in the break-down condition small impedance thereto. If the circuit 110

1,079,101 conditions require that the loss circuit be opaque when no control voltage is applied across the resistance 6, a biasing voltage from the battery 5 slightly smaller than E2 is impressed upon the 5 tube. This value is selected in order to insure extinguishing the tube when the control voltage falls to zero. The control voltage applied across the resistance 6 is poled to aid the battery 5 and when sufficiently large causes break-down and 10 conduction through the tube. If the circuit conditions require that the loss circuit be transparent when no control voltage is applied, the voltage of battery 5 is initially in excess of the break-down voltage Ei and the control voltage 15 when applied opposes this to extinguish the tube. , The biasing voltages may be somewhat larger or smaller than Ei or E2 as the case may be, as for instance E« or Eo to provide a margin against interfering voltages.

Fig. 2 is another type of series loss element which permits a grounded biasing battery 10 to be employed. In this circuit, the control voltage, which is derived similar to that of Fig. 1, is impressed across the resistance 11 through the 25 leads 8; and branch resistances 12 and 13 are provided around the condenser 7 so that the conduction through one tube does not unduly limit the voltage across the other tube and prevent it from conducting. Here again the control volt30 &amp;ge across the resistance 11 may be additive or subtractive in accordance with circuit requirements. The remaining circuit elements are similarly numbered and function the same as the correspondingly numbered elements of Fig. 1.

A shunt type of loss circuit is illustrated in Fig. 3. The circuit is connected in the repeater or transmission path by means of the transformers 3 and 4 as in the case of the series loss circuits and a neon tube 15, or similar flashing 40 tube, is shunted across the conducting paths.

A biasing voltage is applied to the tube by means of the grounded battery 16. A resistance 17 is connected in series with the battery 16, across which is applied a control biasing voltage through 45 the leads 8, said control voltage being derived from the current in the transmission path, as hereinafter described in connection with Fig. 5. The resistance 18, which is equal in value to resistance 17, serves to balance the circuit. Con50 densers 7 and 14 are inserted at the midpoint of the secondary and primary winding of the transformers 3 and 4 respectively to prevent short circuiting of the biasing battery 16 and at the same time to present a symmetrical path of 55 low impedance to alternating or signal currents.

When the tube 15 is extinguished it presents infinite impedance to alternating currents and the loss circuit as a whole is transparent or readily transmits current.

60, When sufficient bias is applied to produce break-down the tube 15 presents a short-circuit path of small impedance to alternating current, and the loss circuit as a whole is opaque or of high impedance to the signal current.

The tube 15 operates similarly to that described in connection with the series circuit. If . the circuit conditions‘require that the loss circuit be opaque when no control voltage is applied across the resistance 17, the biasing voltage * 70 16 must be in excess of the tube break-down voltage to insure a conducting path through the tube. As can be seen by referring to Fig. 4, this biasing voltage must be in excess of Ei. When the' control voltage across the resistance 17 is 75 poled to oppose the biasing voltage 16 in order to reduce it sufficiently to extinguish the tube when the transparent condition of the loss circuit is desired.

If circuit conditions require that the loss circuit be transparent when no control voltage is 80 applied across the resistance 17, the biasing voltage 16 is small enough so that the tube is normally extinguished (slightly smaller than E2 Fig. 4) . To produce the opaque condition of the loss circuit, a control voltage^- is applied across the 85 resistance 17 through the leads 8, said control voltage being derived from the current in the line in a manner described in connection with Fig. 5. This voltage is poled to increase the value of the tube biasing voltage above the value 90 at which break-down occurs.

A voice controlled repeater circuit in which the invention may be used is shown in Fig. 5. This is a two-way repeater having separate paths for repeating signals in opposite directions. The line 95 L is terminated in the balancing network 51 and the hybrid coil 52 which aids in separating the waves received from and impressed upon the line L. The line Li is similarly terminated by the network 53 and the hybrid coil 54. Amplifiers 55 100 and 56 of the usual type are connected respectively in the oppositely directed paths for amplifying, respectively, the west to east and the east to west signals. The west to east and the east to west paths are equipped, respectively, with the voice 105 controlled loss circuits 60 and 70 and 80 and 90 which are similar to the series loss element circuit described in Fig. 2, although any of the other loss circuits heretofore described or which may be equivalent thereto may be employed. The im- 110 pedance which these circuits present to the signals traversing their respective paths is dependent upon the Condition of conductivity of the tubes 61, 62, 71, 72, 81, 82, 91 and 92. Conductivity of tubes 61 and 62 and 81 and 82 is controlled 115 by the amplifier-rectifier 57 which rectifies a portion of the signal current traversing the west. to east path, while that of the tubes 91 and 92 and 71 and 72 is controlled by the corresponding amplifier-rectifier 58 when transmission is 120 through the opposite path.

It has previously been stated that the purpose of the invention is to prevent singing of the repeater and to suppress echo effects which may be produced. For example, if some of the am- 125 plified energy from one path should get into the oppositely directed path due to poor balancing of networks against lines or other impedance irregularities, the loss circuits 60 and 90 would be in the high loss condition being non-conductive 133 to signaling energy during periods of non-transmission over their respective paths and the loss circuits 70 and 80 would be in the low loss condition.

However, when energy to be amplified is im- 135 pressed upon either path, a portion of said energy is rectified and applied to the loss circuits of both paths to render the one in the signaling path, which is normally opaque to signals, transparent and that in the other path, which is normally transparent to signals, opaque.

Thus, for example, when signals from the line L are,impressed upon the west to east path, a portion of their energy is rectified by the rectifier 57 and applied to the resistances 63 and 83. This 115 produces a biasing voltage for the tubes 61 and 62, making them conductive so that signals are readily repeated to the line Li.

At the same time the voltage drop across the resistance 83 is poled so as to extinguish the tubes 150

1,979,101 the amplifier 56, and impressed upon the line L through the hybrid coil 52 thereby producing undesirable echo effects and possibly also causing singing of the repeater. These contingencies can be obviated by the use of the loss circuits in ac- 80 cordance with the invention, because the lower branch of the repeater in Fig. 5, amplifying in the direction of the signals, is rendered transparent and the upper branch, repeating ώ the opposite direction, is made opaque to these signals thus 85 eliminating the undesired effects above mentioned.

During periods of non-transmission in either direction, the loss circuits 70 and 80 are in the break-down or transmission condition, and the 90 loss circuits 60 and 90 are extinguished or in the opaque condition. When signals are transmitted from the line L over the west to east branch of the repeater, a portion of the energy is rectified by the amplifier-rectifier 57 and applied across the 95 resistances 63 and 83. The voltage drop across the resistance 63 augments the biasing voltage from battery 64 upon the tubes 61 and 62 sufficiently to place them in the break-down condition in which the resistance offered to speech 100 signals is small, and readily permits transmission of the signals to line L. The voltage drop across the resistance 83 opposes the biasing voltage of battery 84 and decreases the bias upon the tubes 81 and 82, heretofore in the break-down condi- 105 tion, sufficiently to extinguish them. In this condition they present infinite impedance to any energy of the west to east signals which may tend to be transmitted back in the reverse direction.

The loss circuits 90 and 70 operate in a similar no manner when signals are being repeated in the east to west direction.

Although but one circuit has been shown in which the various types of loss circuits may be utilized, the invention is not to be restricted there- 115 to, but is to be limited only by the scope of the appended claims.