US2154579A - Telephone conference circuit - Google Patents

Description

Apl18,1939. J A.PARROTT TELEPHONE CONFERENCE C IRCUIT Filed Nov. 2o, 1937 wmv l .r BS@ Tv M LAEQ

Patented Apr. 18, 1 939 TELEPHONE CONFERENCE CIRCUIT John Angell Parrott, BMlyll, N. Y., asltnor to American Telephone and Telegraph Company. a corporation of New York Application November 20, 1937, Serial No. 175,105

10 Claims. (CL 179-42) This invention relates to telephones systems. More particularly, this invention relates to circuits for holding conferences between a plurality of parties. Still more particularly, this invention relates to private branch exchange telephone systems, otherwise known as P. B. X systems, and it relates to arrangements for increasing the number of parties which may be engaged in simultaneous conversation over such systems.

One of the objects of this invention is to increase the number of parties at a P. B. X system which can participate in a conversation or con ference. Y i

Another of the objects of this invention is to increase the number of parties to a telephone conference all of which are served by the P. B. X system and at the same time include at least one party to the conference who is not served from the P. B. X system. Y v

This invention will be better understood from the detailed description hereinafter following when read in connection with the accompanying drawing showing one embodiment of the invention merely for the purpose or illustration.

In the drawing the reterencecharacters I. 2. 3,

4 and 5 represent a hybrid coilnetwork and the reference characters 6, 1, 8, 9 and I0 represent a similar hybrid coil network, both of the networks being of well known type and construction. The coil 5 of one of the networks is connected to the terminals common to the equal coils B and 'l and 8 and 9 of the other hybrid coil network through a one-way amplifier II. The coil I0 of the second hybrid coil network is connected to the terminals common to the equal coils I and 2 and 3 and i of the first-mentioned hybrid coil network through an oppositely directed one-way amplier I2. These amplifiers II and I2 may be of any well known' construction.

The terminals at the right of coils 2 and l are connected to a step-down transformer I3, the coil of fewer turns of which is connected to a plurality of jacks I 4, I5, etc. of any well known type. Only two jacks I4 and I5 are shown at this point for illustration, but it will be clear that four or more jacks may be paralleled to the two just refered to. The terminals at the left ofcoils I and 3 are similarly connected to a step-down transformer 23, the coil of fewer turns of this transformer being connected to a plurality of jacks, two of which are shown merely for the purpose of illustration; although it will be obvious that four or more jacks may be added to the circuit and these would ordinarily be paralleled to jacks 24 and 25 in setting up the circuit oi' this invention.

The jacks il, I5, 2l. 2l, etc. are bridged by fixed networks i6, I1, Zi. 21. respectively, and these extend to a common bus. Each of these networks comprises an arrangement ofelenients of inductance, capacitance and resistance interconnected in such a way as to simulate the irnpedance of a telephone subscriber's average extension set and circuit. The various subscribers telephone sets are designated II, 52. 63. 54 etc. and they may be connected by plugs Il, l2, 4,3, M, etc., respectively, to the jacks Il, I5, 2|, 25. etc.

As any jack, such as M, is connected by an ap propriete cord circuit to an extensionv set, such as Si, the corresponding network. in this case network I6, will be disconnected from the circuit of transformer I3 upon the insertion of the plug 4I of the ,extension'set circuit into the jack Il. In other words. either a subscribers set or a network simulating its average impedance will always be connected to the system at any one of the various positions. Such an arrangement has for its object the maintenance of substahtially constant impedance relationships at all times. The impedance conditions during varied operations will be maintained substantially constant whether the maximum number of telephone ex? tensions are being used or not.

The terminals at the right oi' coils 1 and 9 extend to a jack l0. This jackis employed, as in ordinary P. B. X systems. for connecting the circuits shown in the drawing to a common circuit 29 which leads to a central ofllce or other point.

, At the central oilice the modiiled P. B. X system maybe switchedeither manually or automatically from one subscriber-'S line to another subscriber's line in any manner well known in the art. The trunk line circuit 29 extending `from the central ofiice to jack lil may also be used for the transmission of ringing and other super7 visory signals in any manner known to the art and this feature forms no part of thisinvention.

The terminals at the left of coils C and '8 may be connected by means of a switch `II or permanently wired to either oi` two circuits. One of these circuits includes a network 3,2 simulating the impedance of 'the line 29 extending between the jack 30 and the central office and still an other network 33-34 which is intended to simulate the circuit or circuits at the central ofllce to which the arrangement shown in the drawing may be connected. The network 32 may include. for example. series resistive elements and shunt capacitive elements. The network IS-pl may comprise series resistive and capacitive eleF ments as shown, convenient values of which may be 600 ohms and 2 mf., respectively. The latter values are given merely by way of example and are therefore not to be considered as the only values suitable for these elements nor are they to be treated as limiting the invention in any way.

The other circuit to which the terminal at the left of windings 6 and 4- may be connected may include a cable pair 3l similar to the pair 29 connected to jack 30. The cable pair 35 may be terminated at the central office in a network 36--31 similar to the network 33-34. Either oi' the two circuits extending to switch 3| will balance the hybrid coil arrangement 3--1-4--3--Iil against the circuit extending between jack 30 and the central office.

The circuit described hereinabove differs from the ordinary P. B. X circuit in several respects: (l) It includes amplifiers II and I2.which are not found in the ordinary P. B. X system.

(2) One of the pairs of windings 'of the hybrid coil arrangement at the left, as for example, windings 2 and 4, are connected to a transformer i3 and to the telephone extension sets or equivalent networks connected to the transformer I3 instead of to an ordinary balancing network. (3) The other of the pairs of windings of the hybrid coil arrangement at the left is connected to a plurality of parallel extension y telephones or equivalent networks through a step-down transformer 23 and not to but a single telephone extension. These are some of the departures of the arrangement of this invention from the prior art P. B. X system.

Telephone currents coming in from the central ofllce over conductors 29 pass over the winding I0- to the amplifier I2. Here they` are amplifled and are then transmitted through the windings I. 2, 3 and 4. At these windings the currents divide approximately equally. half of the currents flowing through transformer I3 to the various extension telephones connected to jacks I4, I5, etc., the remaining currents flowing through transformer 23 to the telephone extension sets connected to jacks 24, 25, etc.

Outgoing telephone currents pass over winding 5, through amplifier Il to the points common to windings 6 and 1 and 8 and I and then over jack 30 and over the cable pair 29 extending to the central onice. 'Ihese currents are then transmitted to the subscrlbers set to which the central ofce circuit is switched.

The arrangement described will readily permit twelve (or more) P. B. X extension telephones to be connected simultaneously in parallel arrangement to a subscribers telephone set (or sets) reached over a trunk connection from jack 30. These circuits are then suitable for a telephone conference between all of these various parties. The grade of transmission for the twelve (or more) parties with the circuit described will be commercially satisfactory, but the transmission can be improved with better balance between the two sides 'of each hybrid coll network. This arrangement represents a substantial improvement over former circuits which provided satisfactory communication between only two stations and permitted transmission though of poorer grade when a third party was added.

The amplifiers II and I2 are inserted into the circuit for the purpose of compensating for the loss introduced by the numerous bridged extension telephones. With the arrangement illustrated and described, it will be observed that the low side of each of the transformers I3 and vdescribed hereinabove.

23 is connected to a group of the telephone extension circuits. The transformers I3 and 23 act to reduce and practically eliminate reflection losses between the amplifiers and the buses to which the extension stations are connected.

The various extension telephone sets 5I, 52, 53. 54. etc.. and the lines connecting these sets to the buses would ordinarily be of the same design and manufacture. However, if these sets differ appreciably from each other or ii' lines vary considerably in length or in other properties. these deviations may be compensated by appropriate changes in the elements of the networks I8, il, 26, 21, etc.. and by suitable traffic operating practices to assure connection of each type extension to the proper jack.

In the arrangement illustrated in the drawing, it is desirable that equal numbers of extension telephone sets, or their equivalent networks. be connected to the two bus-bars. Obviously, the latter may be accomplished by other means than For example, instead of the jacks and associated networks shown in the drawing, the bus connectedto transformer 23 might be bridged by jacks so arranged that when plugged into, contacts would close. which connect an appropriate network to the bus associated with transformer I3. This might be employed for all of the jacks or for only those jacks to be used for special extension circuits which, for example, are appreciably longer than the average or have different transmission characteristics.

The hybrid coil transformers are illustrated as of the three-winding type. It will be clear that such transformers are not indispensable in carrying out the principles of this invention. Obviously any other hybrid arrangement having equivalent properties may be inserted into the system in piace of the three-winding transformers shown.

It will be understood that the two one-way amplifiers illustrated may of course be replaced by any two-way amplifier well known in the art. If desired, the amplifier may be of a type such that when amplification of telephonic or other currents flowing in one direction is taking place, the flow of currents in the opposite direction will be suppressed or prevented.

While this invention has been shown and described in certain particular arrangements merely for the purpose of illustration, it will be obvious that the invention may be applied to other and widely varied organizations without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is:

l. The combination of two groups of parallelconnected telephone sets, first and second three winding transformers, two of the windings of the rst transformer interconnecting the two groups of sets, a. one-way amplifier connecting the third winding of the transformer to the midpoints of two of the windings of the second transformer, a second oppositely directed oneway amplifier connecting the third winding of the second transformer to the midpoints of said two windings of the first transformer, a trunk circuitlconnected to said two windings of the second transformer, and a network connected to segrtwo windings of said second transformer to b nce the trunk circuit.

2.1The combination of two groups of telephf le extension sets, the sets of each group beingv connected in parallel relationship, a hybrid coil network formed of three mutually coupled windings, two transformers each having one of its windings connected to a common pair of the windings of the hybrid coil network, the

5 remaining winding of each transformer being connected to one of the groups of extension sets. a remote telephone set, said remote telephone set being connected to the midpoints of the common pair of windings of the hybrid coil network for transmitting telephone currents simultaneously to all of the extension sets, said remote telephone set being connected to the third winding of the hybrid coil network for receiving telephone currents simultaneously from all of said extension sets.

' 3. A system for providing a conference circuit between a plurality of telephone extension circuits with one or more remote telephone circuits, comprising a plurality of networks, each $0 simulating a telephone extension circuit, means for paralleling all of said extension circuits or their corresponding simulating networks into two groups. two hybrid coil transformers, the two groups of extension circuits being connected to one of said hybrid coil transformers to balance each other, a trunk circuit to which any one of the remote telephone circuits may be connected, a network simulating the trunk circuit. said latter network and said trunk circuit ben ing connected to the other of said hybrid coil tr nsformers to balance each other, and ampli ying means coupling the two hybrid coil transformers.

4. The combination of two transformers, two

u one-way oppositely directed amplifiers interconnecting said transformers, two groups of parallel connected telephone circuits connected to one of the transformers so that the groups of telephone circuits will balance each other, and a 40 telephone line connected to the other transformer, thereby permitting simultaneous twoway communication with good quality over said telephone line and over all of the telephone circuits.

45 5. A telephone conference circuit comprising two groups of parallel connected telephone circuits, a telephone line, means for coupling said line to all of said telephone circuits, said means including two transformers, one of said trans- 59 formers interconnecting the two groups of teleby the addition of a plurality of networks each corresponding to one of the telephone circuits, and means for connecting each of said networks to the parallel circuit with which it is associated upon the disconnection therefrom of the 10 corresponding telephone circuits.

7. In a telephone conference system, the combination of two substantially equal groups of telephone subscribers' circuits, a transformer coupling said two groups of circuits, a trunk 15 circuit, and means including a two-way amplifier for coupling the trunk circuit with the transformer.

8. A telephone conference system having, inv combination, a plurality of groups of two-way 2o telephone subscribers' circuits, means including a transformer for coupling all of said circuits to each other, a main circuit over which televphone currents may flow in opposite directions,

and means including an amplifier for coupling 25 said main circuit with said transformer coupling means, telephone currents flowing over the main circuit being amplified by said amplifier before being received by said subscribers circuits, telephone currents ilowing in said subscribers circuits being amplified by said amplifierl before being transmitted over said main circuit.

9. The combination set forth inclaim 8 including, in addition, a plurality of networks each simulating one of said subscribers circuits, and means responsive to the removal of .any of said subscribers circuits for substituting the corre-

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