US2083645A - Transmission system - Google Patents

Description

June 15, 1937. R. D. FRAcAssl 2,083,645

I TRANSMISSION SYSTEM Filed Oct. 12, 19:54 2 Sheets-Sheet 1 l INVENTOR AvAvA'A i J me w ATTORNEY June 15, 1937. R. D. FRACASSI I 2,033,645

TRANSMISSION SYSTEM Filed Oct. 12, 1934 2 Sheets-Sheet 2 INVENTOR ATTORNEY Patented June 15, 1937 UNITED STATES PATENT OFFICE TRANSMISSION SYSTEM Renato Dario Fracassi, Jackson Heights, N. Y., assignor to American Telephone and Telegraph Company, a corporation of New York This invention relates to transmission lines, and more particularly to transmission lines having repeaters included therein.

In transmission lines having included therein 5 repeaters of the type, for example, comprising two one-way line sections with vacuum tube amplifiers therein for transmission in opposite directions and having these line sections interconnected through hybrid coils, there may be a tend- 10 ency for the repeater to sing. This might be due to a circulation of energy taking place from one line section through one hybrid coil to the other line section and then through the other hybrid coil back to the first line section. Under certain 5 conditions this circulation of energy will cause singing which will interfere with transmission as is well known in the art.

The arrangements of the present invention are such that when no speech currents are present 20 on the line a loss is introduced in the transmission path of the repeater. This will tend to prevent singing. When speech currents are present on the line, the arrangements of the invention remove the loss in the direction of transmission and also suppress transmission in the opposite direction so as to prevent the occurrence of singing and to prevent echo currents from returning to the talker. Thus the arrangements of the invention will improve the singing margin when no speech currents are present. When speech currents are present the arrangement W111 permlt the introduction of additional gain in the direction of transmission and at the same time its echo suppressor action will prevent singing from occurring and echo currents from returning/to the talker. Other objects and features of the invention will appear more fully from the detailed description thereof hereinafter given.

The invention may be more fully understood 40 from the following description together with the accompanying drawings in the Figures 1, 2, 3, and 4 of which the invention is illustrated. Fig. 1 is a circuit diagram showing a preferred embodiment of the invention as applied at a repeater 45 station. Fig. 2 is a modification of Fig. 1. Fig. 3 is a circuit diagram showing the arrangements of the invention as applied to a multi-way connection, and Fig. 4 is a circuit diagram showing a further modification of the invention. The ar- 50 rangements shown by Figs. 1, 2, and 4 may also be used with multi-way connections. Similar reference characters have been used to denote like parts in all of the figures.

In Fig. 1, the invention is shown as applied to a repeater interconnecting the line sections L1 and L2. The repeater comprises the usual hybrid coils I and 2 and balancing networks'Ni and N2. Two circuits 3 and 4 are provided, each having amplifying devices such as 5 and 6. Associated with the hybrid coil I is a circuit 7 having in- 5 eluded therein an impedance 9. This serves to introduce a loss in the transmission of currents through the hybrid coil I. Similarly, a circuit 8 is associated with the hybrid coil 2 and includes an impedance I0. This serves to introduce a loss 10 in the transmission of currents through the hybrid coil 2. When speech currents are not transmitted over either of the line sections L1 or L2, these losses are inserted in the system and act to prevent singing due to a circulation of energy through the repeater.

Associated with the circuit v3 is a detector device II and associated with the circuit 4 is a detector device I2. When speech currents are transmitted over one of the line sections as, for example, from the line L2, these speech currents will actuate the detector device I I and cause the relay I3 to be operated. This will open the circuit 1 and remove the loss introduced thereby from the system. The operation of the relay I3 will also close a circuit I 5 which will short-circuit the circuit 4 in the manner of the wellknown echo suppressor. In like manner, when speech currents come in over the line L1, the detector device" will be operated and, in turn, will operate the relay I4. The operation of the relay I4 will open the circuit 8 and remove the loss introduced thereby from the system. The operation of relay I4 will close the circuit I6 and short-circuit the circuit 3 in the manner of the well known echo suppressor. With this arrangement, it will be seen that when no speech currents are being transmitted, a loss will be introduced in the system and will tend to prevent singing from currents other than speech currents. However, when speech currents are transmitted over the system, the loss is removed, or, in other words, additional gain is introduced in the repeater circuit without impairing the singing margin, since singing cannot occur with one circuit disabled by the short circuit. P l f- Fig. 2 is a modification of the arrangements 01' Fig. 1. The arrangements of Fig. 2 are substantially similar to those of Fig. 1 except that two additional relays such as I8 and 2| are provided. In Fig. 2, when speech currents come in over the line L2, the detector device II is actuated and operates relay It. This will open the circuit I and remove the loss introduced thereby from the system. The operation of the detector II will also, through the agency of circuit 285, actuate the relay 2| which, in turn, will close a short circuit 22 over the circuit i in the manner of the well known echo suppressor. In like manner, speech currents coming in over the line L1 will actuate the detector device l2 which will operate the relay M which, in turn, will open the circuit 8 and remove the loss introduced thereby from the system. The operation of detector i2 will, through circuit ll, operate the relay It and close a short circuit l9 across circuit 3 in the manner of the well known echo suppressor.

It will be seen that in this arrangement as in the previous arrangement, a loss is introduced in 5 the system when speech currents are not on the line and this loss is removed when the speech currents are transmitted thereover. At the same time the line in the direction opposite to that of speech transmission is disabled.

Fig. 3 shows an arrangement of the invention which may be used when multi-wave connections are established as, for example, between the line L4 and other lines, such as L6 and L3. The line L4 is connected to the line L3 through repeater apparatus A shown within the dotted lines. This repeater apparatus comprises the usual hybrid coils and 26 and the balancing networks Na and N4. It comprises two circuits 2'! and which have included therein amplifier devices 30 such as 29 and 35. Associated with the hybrid coil 25 will be a circuit having included there in an impedance 35. This will serve to intro duce a loss in transmission of currents through the hybrid coil 25. This loss will tend to prevent singing which would be caused by currents other than voice currents. When the voice currents come in from line L4, the detector device 3| will cause the relay 33 to be operated. This will open the circuit 35 and remove the loss introduced by the impedance 38. When voice currents come in over the line La, the detector device 32 will actuate the relay 34 and cause a short circuit across the circuit 2'? in the manner of the well known echo suppressor. The line L3 would be associated with a common line Ls. Bridged across this line might be other lines such as L5 and L7. These lines would be connected to apparatus similar to A, originally referred to and enclosed in the dotted lines. This apparatus would be connected to other lines such as L6 and LB.

With such an arrangement loss is introduced in only one direction of each repeater, said loss being removed when speech currents are transmitted in that direction. When speech currents are transmitted in the other direction echo suppressor action takes place which disables the side of the repeater transmitting in the direction opposite to that of speech transmission. This arrangement is particularly adapted for use on circuit arrangements where two or more such devices can be used at specified points, such as the separate points along a transmission line or in a multi-way connection as shown in Fig. 3. When properly used one of the arrangements removes loss in the direction of transmission while the remaining devices act to suppress echoes. The action of each arrangement is reversed when the direction of transmission through it is reversed.

Referring to Fig. 3 when transmission is from L4 to L3 and thence to L5, L6, L7, La, etc., the loss is removed from the path through the hybrid coil 25 but remains in all other paths associated with La, La, etc. Echo suppressor action takes place in the apparatus designated A associated with L6, L3, etc.

- In multi-repeatered two-wire circuits or in multi-way interconnecting circuits, such as represented by Fig. 3, a plurality of singing paths exists as enumerated below.

First, there are so-called local paths, that is, involving only one repeater. Referring to Fig. 3 such a path begins at L4, thence through the amplifier element 29, thence tothe hybrid coil 25,

thence to the amplifier element 38 by means of the transmission path brought about by the unbalance between 1.13 and its associated network N3 and finally back to L4 through hybrid coil 26. In the passive state (no speech currents) the loss introduced by the impedance 85 decreases the tendency to sing around this local path.

In addition to the above there are so-called combined paths, that is, paths involving a plurality of repeaters. path involving two repeaters begins at L4, thence through the amplifier 29 t the hybrid coil 25, thence to L3, thence through L9 to L5, thence through the amplifier to the hybrid coil associated with L6, thence through the unbalance between La and its associated network Ne, thence through the amplifier transmitting back toward L5, thence to the hybrid coil associated with L5, then to L5, thence to L9, thence to L3, thence to the hybrid coil 25, thence to. amplifier 3Q, thence through the hybrid coil 26 to L4.

In the passive state (no speech currents) each path involves a number of losses introduced corresponding to that introduced by the impedance 36, the number of such losses corresponding to the number of repeaters involved in the path.

In a multi-way connection as illustrated by Fig. 3 in the active state (speech currents existing) only one of the above losses is removed, said removed loss being that associated with the repeater connected to the talkers line. The removal of this loss impairs the singing margin around the local path as such but singing is assumed to be prevented by the balance between L3 and Na and also between L4 and N4. All other paths are short-circuited by the echo suppressor action taking place in the devices associated with the other repeaters.

In the arrangement shown in Fig. 4 there is illustrated a two-wire line section L1 and a fourwire line section composed of sections L2 and L2". These line sections are interconnected by repeaters 5 and 6. Repeater 6 is connected to the line section L1 by means of the hybrid coil and transformer 59. The repeater 6 is connected to the line section L2 by means of the transformer-5i. The repeater 5 is connected to line section b" by means of transformer 52 and to the line section L1 by means of transformer 53 and the hybrid coil I.

When speech currents are transmitted from the line section L1 over the hybrid coil I they act upon the detector l2 and the detected currents operate the relays M and I8. The relay M will open the circuit of its contact and remove the loss introduced by the coil which is connected in series with that contact. At the same time the operation of relay !8 will place a short-circuit about the primary winding of the transformer 52 for the purpose of echo suppressor action. The removal of the loss by the action of relay [4 will cause an increase in the level of energy transmitted through the repeater 6 and over the line section L2.

When speech currents are received from the For illustration one such line section L2" they will reach the detector II, which will act upon these currents, and the detected currents will operate relays l3 and 2|. The relay I3 will open the contact associated therewith and hence remove the loss provided by the coil which is coupled to the primary winding of the transformer 53. The operation of the relay 2| will place a short-circuit across the line connected to the primary winding of the transformer 50 for the purpose of echo suppressor action. The removal of the loss by the operation of relay I3 will cause an increase in the level of energy transmitted through repeater 5 and through the transformer 53 and the hybrid coil l to the line section L1.

Thus it is evident that the use of the arrange ments shown in any of their forms tends to improve greatly the over-all singing margin since it adds attenuation or completely removes the so-called combined singing paths, leaving at the most a single open path wherein sufiicient singing margin may be easily maintained.

While the invention has been disclosed as embodied in certain specific arrangements which are deemed desirable, it is understood that it is capable of embodiment in many and other widely varied forms without departing from the spirit of the invention as defined by the appended claims.

What is claimed is:

1. In a two-way communication system, the combination of a two-way telephone repeater having two hybrid coil networks adapted to transmit signaling currents in the two directions over different paths, means responsive to signaling currents in one path to remove loss from said path and to insert loss in the other path, one of said losses being inductively coupled to its associated hybrid coil network, said means consisting of an amplifier-detector, an impedance, shortcircuiting means and a relay, said relay removing said impedance from across one of the windings of the hybrid coil network in the path transmitting signaling currents and connecting the short-circuiting means across the bridge points of the same hybrid coil network.

2. A transmission line comprising two line sections interconnected by a repeatered transmission system, said repeatered transmission system comprising two one-way circuits having amplifiers therein and two hybrid coils for conmeeting said one-way circuits to said line sections, a pair of resistances each connected across one of the windings of said hybrid coils and inductively coupled to the respective one-way circuits, and means responsive. to the transmission of currents of a certain type over the corresponding one-way circuit for opening the circuit of the corresponding resistance and for shunting the circuit of the other one-way circuit.

3. In a two-way communication system, the combination of a two-way telephone repeater having two hybrid coil networks adapted to transmit signaling currents in two directions over different paths, means responsive to signaling currents in one path to remove loss from said path and to insert loss in the other path, said means consisting of an amplifier-detector, an impedance coupled to each hybrid coil network, shortcircuiting means, and a relay, said relay removing one of said impedances from across one of the windings of its corresponding hybrid coil network in the path transmitting signaling currents and connecting the short-circuiting means across i the bridge points of the same hybrid coil net- Work.

RENA'IO DARIO FRACASSI.

Images