US1545541A - Tandem-operated echo suppressor - Google Patents

Description

July 14, 1925.

INVENTOR J13.- M Wfit Airmen/51 S. B.- WRIGHT TANDEM OPERATED ECHO SUPPRESSOR Flled July 2 1924 I mi .4,

Patented July 14, 1925.

. SUMNER B. WRIGHT, OF EAST f 1,545,541 ur OFFICE."

ORANGE, NEW" JERSEY, ASSIGNOR TO AMERICAN TELE- PHQNE AND TELEGRAPH COMPANY. A CORPORATION OF NEW YORK.

TANDEM-OPERATED new; i

Application filed July 2,

'1'0 all "whom it may concern:

rcsiding at East Orange, in the county of Essex and State of New Jersey, have invented certain Improvements in- '.l:nidem-()perated Echo Suppressors, of which tlie tollowing is a specification.

This invention relates to transmission 'circuits, and more particularly to transmission circuits employing echo suppressors.

One of the objects of the invention is to provide an arrangement whereby two or more circuits, each equipped with echo sup pressors, may be operated intandem. The problem presented when two or more circuits, each having an echo suppressor, are switched together, is to prevent the cir cuits getting into such a condition that, when two subscribers at the ends begin to talk at about the same timc,.neithcr subscriber will be able to hear the other. i

The nature ol. the trouble will be evident if we imagine the two circuits, each containing an echo.suppressor, are connectial togethcr. It the subscriber at end A bcgins to talk, the voice currents generated will cause the suppressor near his end to operate in such a wayas to short-circuit the transmission path coming from the subscribcr at the end B. If, before the voice currents from the subscriber at end A reach the second suppressor near the end it, the subscriber at end B has already started to talk and the voice currents generated at his station have caused the suppressor near his end to operate, it will be evident that the voice of the subscriber atA will be blocked by the the voice of the subscriber at 15 will be blocked by the suppressor'near the A cnd. Talking under these conditions would be dillicult because part or" the time both subscribers might be talking with neither one hearing the other. I

.In accordance with the present invention it is proposed to overcome this dilliculty by a ranging two transmission circuits adapted tandem in such a manner Be it known that I, SUMNER BiHnunrr,

to be connected in that when a tandem connection is established. the echo suppressor uiiitffor shorten-coil ing the path transmitting west will be disablcd in the case of the one circuit. and the echo suppressor unit for short-circuiJ ing the path transmitting east will be disabled in thc rasc of the other transmission circuit. Under 'oll' transmission suppressor near end it while 7 SUPPRESSOR.

1924. Serial No. 723,802.

one echo suppressor for transmission in a it will not be possible I provided with echo suppressors of the ordinary type and arranged to be connected in tandem, while Fig. 2 illustrates'a similar pair of tour-wire repeater circuitsprovided with means for disabling certailrof the echo suppressor units in accordance with the present in vention; 4

Referring to Fig. 1, a four-wire circuit is schematically shown, said circuit being equipped with the usual one-way repeaters and an echo su ipress'or-between stations A and l5, while a similar circuit is shown between stations l3 and G. ncctiims'over either circuit, each individual echo suppressor tunctions in its normal man nor, that. is, when transmission takes place from. A to B the A--l3 suppressor operates and slmrt-cirmaits the opposite branch of the tour-wire circuit, suppressing echoes from I5, and vice versa. If these two circuits gcthcr in tandem and a person at A began talking to a person at l, the A-li supprcssor would operate and cut olt transmission .lrom C, while a short time later the l-----(. supprcssor would also o}.)crate*and cut from (3. ll", however, during the interval between the operation of the A-l5 and l-C suppressors, waves from the party at C should arrive .at the suppressor C-l3, these waves would operate the GB suppressor, thus cutting'o'tt' transmission from Fnrthern orc, since the AB suppressor would alreac'ty'be operated, the transmission l'rom the subscriber at C could not get through to A aiul p artics at both A and (i might talk for some time without either hearing the other. A Fig. 2 shows. schematically. an arrangement for obviating this dilliculty by making one-half of each sup'prcssor inoperative wbcn tlre'two circuits are coniuwted together in landcm. In this ligurc, an operators through tollcortl circuit is shown at ll betwccn the two l'iiuravirc circuits. This toll-I cord is arrangcd'so that when all four of its vFor terminal conill) plugs are inserted in the line and network 13Cks by which the four-wire circuits are terminated at station B, the line terminals of the four-wire .circuits as Well as the network terminals will be directly connected together. By means of this connection it will be apparent that an almost perfect condition of balance will obtain at each hybrid coil by reason of the fact that the circuit connected to the line jack is identical electrically with the circuit connected to the network jack. In short, there is practically no unbalance at the B terminalsof either four-wire circuit, so that the effect is practically the same as though the individual lines of the two four-wire circuits were directly connected together at station B.

\Vhen the toll cord establishes the connection between the two four-wire circuits in tandem, a ground is connected to thesleeve conductor of the line jack of the four-wire circuit extending from station A to station B, thereby causing current to flow through .a control wire (which may be a simplex or composite circuit of any well-known type, if desired) to operate a relay X atthe fourwire repeater station at which the echo suppressor A-B is applied. This relay renders the AB half 'of the echo suppressor inoperative by opening the shortcircuit controlled by the AB half of the sup-- pressor, the B-A half of the suppressor, however, remaining in its normal condition.

7 Similarly, the C-B half of the echo suppressor on the circuit between B and C is rendered inoperative when the other end of I l the toll cord is inserted in the line jack at B by means of a ground applied to another similar control wire to operate the relay Y. The B-C half of the suppressor is not disabled, however, as the relay W remains normal because the sleeve at C j is not grounded.

The resulting effect is, therefore, that of a four-wire circuit equipped with a single 'eeliosuppressor arrangement, the two halves of which are located not near the center of the circuit but one near the receiving en for each direction. Consequently, when the subscriber at'A talks to the subscriber at C, the voice currents will ,be transmitted through station over the upper lines of wire ciicii mils west,

each four-wire circuit, and upon arriving at the point where the echo suppressor B-C is applied, ..the latter suppressor. will be opcrated'to' short-circuit the line of the fourit between B. and C which trans- This prevents C to A so that echo currents transmitted through the, hybrid coil at C cannot be propagated back to station Theline trainsn'i'itiing w cstbelwccn stations A and B is, of cm'u'se, not disabled so that anyrclm currents which pass through the hybrid coil of the four-wire circuit bet een A and B at station ever, may

transmission fromrents transmitted in.

B will be transmitted back to the subscriber at A. As already pointed out, however, the balance at this. point will be almost perfect as it does not depend upon the simulation of a real line by a network. Therefore, the echo currents which will be returned'to station A from this point'will be so small in volume that they may be disregarded. The echo currents transmitted through the hybrid coil at station C, howhave considerable magnitude because the balance at that point depends up on the simulation of a real line bya compromise network so that the unbalance may be considerable. Echoes transmitted to A from this point. are prevented, however, by means of the echo suppressor unit B-O.

The method above described is applicable to circuits built up of more than two fourwire repeater circuits equipped with individual echo suppressors. For example, it will be apparent that if a connection be C to a third four-wire circuit established at by means of a toll cord connection similar to that shown at -B,.the relay W would be operated to disable the suppressor unit'B C and its place would be taken by half of another suppressor located at a point beyond Similarly, if a connection is established at A to another four-wire circuit, the relay Z *"ill be operated to disable the suppressor nit BA, its place in turn being taken by one-half of a suppressor unit located beyond A. It will be understood, of course, that where connections are to be. established at either A or O to other four-wire circuits, the network N .will be disconnected and connections established to network jacks, as shown at station B. It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely difi'erent from those illustrated without departing from the spirit oftheinvention as defined in the following claims.

What is claimed is:

i1. In a transmission system, a plurality of transmission circuits adapted to be connect ed in tandem, a pair of echo suppressor units associated with each circuit, one being responsive to currentstransmitted in one direction for disablingthecircuit for transmission in the opposite direction, being responsive to currents transmitted in the opposite direction for disabling thecircuit for transmission in the'first direction, and means operating upon the connection of said circuits in tandem to render all of said echo suppressor units ineffective except-one pair, of which one will be responsive to ourother responsive to currentstransmitted in the opposite direction.

2. In a transmission one direction and the system, a plurality of transmission circuits adapted tobe connectlllll the other V I sponsive to currents transmitted in one direction-Ior disabling the circuit for transmission in theopposite direction, the other being responsive to currents transmitted in the opposite direction for disabling the circuit for transmission in the first direction,

means for connectin said transmission circults-1n tandem, an circuits controlled by said means for rendering all of said echo suppressor units ineffective except one pair,

of which one unit will be responsive to ourrents transmitted in one direction and the other unit will be responsive to. "currents transmitted 'in the opposite direction.

3. In a transmission system, a plurality of transmission circuits adapted to be connected in tandem, a'pairof echo suppressor units associated with each circuit, one being re sponsive to currents transmitted in one direction for disabling the circuit-for transmission in the opposite direction, the other being responsive to currents transmitted in the opposite direction for disabling the circuit for transmission in the first direction,

and means operative when said circuits are connected 111 tandem to render all of said echo suppressor'units inefiective except one unit associated with one of said circuits and res 'onsi've to transmission 1n one direction an I another unit associated with another of said circuits and responsive to currents transmitted in the opposite direction.

4. In a transmission system, a plurality of transmission circuits adapted to be connected in tandem a pair of echo suppressor units associated wlth each circuit, one being responsive to currents transmitted in one direction for disabling the circuit for transmission in the opposite direction, the other being responsive to currents transmitted in the opposite direction for disabling the circuit for transmission in the first direction, means to connect said transmission circuits in tandem, and circuits controlled by said with one of said transmission circuits and responsive to currents transmitted in one direction and another unit associated with another of said transmission circuits and responsive to currents transmitted in the oppositedirection.

In testimony whereof, I have signed my name to, this specification this 1st day, of

July, 192%.

, SUMNER B. WRIGHT.

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