US1728247A - Echo suppressor - Google Patents

Description

Sept. 17, 1929. D. MITCHELL ECHO SUPPRESSOR Filed March 13, 1928 1 ATTORNEY Patented Sept. 17, 1929 UNITED STATES PATENT OFFICE DOREN MITCHELL, OF NEW YORK, N. Y., ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, CORPORATION OF NEW YORK I ECHO SUPPRESSOR Application filed March 13, 1928. Serial No. 261,327.

This invention relates to echo suppressors, and, more particularly, to echo suppressors adapted for use in connection with two-wire telephone circuits.

In two-wire telephone circuits employing repeaters of the so-called 22-type,.it has been the practice to suppress the principal, echo currents in the system by associating with each side of one of the 22-type repeaters of 1n the circuit an echo suppressor unit to disable the repeater path transmitting in the opposite direction. With such an arrangement, it has been found that false operation occurs due to echoes having little or no delay in transmission. For example, a current passing over one side of the QQ-repeater and open ating the suppressor unit associated with that side would be transmitted through the hybrid coil and back over the path in the opposite direction, thereby energizing the suppressor unit associated withthe second path before the first echo suppressor unit would have time to disable the second path.

It has heretofore been proposed ,to over- 5 come this difficulty by inter osing a delay circuit between the input 0 a suppressor unit associated with one side of the circuit and the input of the suppressor associated with the other side of the circuit, thereby delaying the transmission of the impulse around the circuit until the first echo suppressor unit has had time to operate. The use of such delay circuits, however, involves a considerable additional expense over and above the echo suppressor units proper.

Another scheme that has been proposed is to make the hang-over effect of the disabling relay-of each echo suppressor unit dependent, to some extent, upon the length and amplitude of theoperating impulse. With such an arrangement, a voice wave passing over one side of the repeater and setting the one suppressor unit into operationwould, after passing into the return path to start the second suppressor unit into operation, be abruptly terminated by the operation of the first suppressor unit. Therefore, the resultant short impulse which might thus operate the second suppressor unit would not suflice to hold it operated for any length of time, and

would not cause objectionable lockout of the speech. Experience has shown, however, that such an arrangement, while effective to reduce false operation to a considerable extent, accomplishes this result at the expense of the quality of the speech transmitted, since some distortion is introduced.

In accordance with the present invention, it is proposed to dispense with the use of delay circuits and still retain the fundamental relay arrangement by arranging the echo suppressor units to exercise an electrically interlocking (or opposing) control over the disabling equipment associated with the two sides of the circuit. In order to accomplish this result, the operating winding of t e detector relay of the echo suppressor unit associated with each side of the circuit is connected in series with a winding of the detector relay of the opposite suppressor unit. The latter winding is connected in a reverse direction so that when either suppressor unit operates, it increases the biasing efl'ect on the relay of the other side by an amount depending upon the magnitude of the impulse and the number of turns in the reverse winding. Thus, if one echo suppressor unit is operated, it makes operation of the detector relay of the other echo suppressor unit very difficult, due to the increased bias.- Experience has shown that this interlcoking relay arrange- Inent gives substantially the same operation as would be obtained by the use of a delay circuit. Due to the fact that the initial voice wave operates one relay and simultaneousl checks the operation of the other, very quic echoes are prevented from falsely operating the apparatus before the first relay can operate, and hence a delay circuit is not needed.

The invention will now be more fully understood from the followin description when read in connection wit the accompanying drawing, Figures 1 and 2 of which show two different circuit arrangements embodying the principles of the invention.

Referring to. Fig. 1, there'is shown a 22- repeater arrangement comprising the path LE including an amplifier AE for transmitting in one direction, and a path LW including an amplifier AW for transmitting in the The echo suppressor equipment associated with the path LE comprises an amplifier-detector arrangement DE of well-known type, the plate circuit of the detector of said arrangement being connected to the battery B through the operating winding a of a detector relay RE. The circuit of the operating winding a also includes a winding 1; associated with the detector relay RW of the echo suppressor unit. associated with the path LW.- Said last mentioned echo suppressor unit also includes an amplifier-detector arrangement DW, similar in all replate circuit of the detector of the arrangement DW connected to the B battery through the operating winding a of the detector relay RW. The winding 6 of the detector relay RE is also included in series in the last described circuit. The Z) windings of-the two relays RE and RW are poled oppositely with respect to the a or operating "wii1dings associated with each relay. Consequently, if

an o erating current flows from the amplifieretector through the operating winding of the associated detector relay, a current flows at the same time through the b winding ofthe opposite detector relay to bias the latter and prevent its response to impulses transmitted over one path of the repeater through'the hybrid coil to the other path Eachdetector relay is also biased by means of a 'windin c suppliedwith a biasing current from a attery B through suitable resistance. biasing winding 0 is such as to normally oppose the action of current through winding 0.,

The detector relay RE controls a hang-over rela RE which performs the dual function of ort-circuiting (and thereby disabling) the path LW, and of introducing a hangover efl'ect by which the armature of the hang-over relay maintains the short circuit for a predetermined hang-over period after the impulse which startedthe operation has ceased. The ban -over relay RE comprises an operating win ing c, a hang-over winding a, anda bias: ing winding b. The operating windin 0 is energized when the armature of relay is removed from its back ,contact, thereby removing a short circuit from the winding 0 so that current can flow from the battery B". The biasing current for the winding b is sup- 66 plied by the battery B and is regulated by the spects to the arrangement DE, with the The normal current through theresistance 1', so that, under normal conditions, this biasing current is just suificient to hold the armature of the hang-over relay RE firmly in its nonoperated condition. The hang-over effect introduced by the winding a is controlled by the charge and discharge of the condenser CE in a manner which will be described in more detail later.

The detector relay RW associated with the amplifier-detector arrangement DW controls a hang-over relay RW', similar to RE. This hang-over relay also includes an operating winding 0, a hang-over winding a and a biasing winding 6. The operation of the hangover winding 'a is also controlled by the charge and discharge of the condenser CW. Likewise, the armature of the hang-over relay RW controls the application of a short circuit to the path LE.

The operation is as follows: A voice wave incoming from the line L passes into the path LE and throughthe amplifier AE to the line L Part of the Voice energy passing over-the path LE enters the amplifier-detector arrangement DE, thereby producing a unidirectional current in the plate circuit of the latter. This current passes through the winding a of the detector relay RE and also through the opposing winding 1) of the detector relay RlV. Both relays RE and RW are normally biased by means of the current through their windings a so as to hold their armatures in the non-operated condition, as shown in the diagram. The current through the winding a of the relay RE produces an effect of such magnitude as to overcome the normal bias due 'to the winding 0 and toshift the armature of the relay from its nonoperated to its operated contact. The current through the winding 1) of the relay RW produces a pull in the same direction as the normal bias due to the current in the winding 0, and, consequently, the armature of the relay RW will be held in'its non-operated posi-- tion notwithstanding the fact that some of the voice energy flowing over the path LE may pass from the hybrid coil into the path LWV to operate the amplifier-detector arrangement DW before relay RE- is operated, and thereby energize the winding 0, of the detector relay RW. Obviously, this prevents any false operation of the'echo suppressor unit associated with the path LVV.

Returning to the detector relay RE, as soon as its armature is shifted from its non-operated contact, it opens the short circuit to ground, which normally prevents the energization of the winding dot the hang-over relay RE, and said winding is at once energized to shift the armature of relay RE to its operated contact and thereby apply a short circult to the. path LW and to the input of the amplifier-detector DW. iransniisison from the line L to the line L is thereby'prevented', so that echoes passing over the circuit in the direction from the listening subscriber tothe talking subscriber are blocked.

The armature of the detector relay RE, upon reaching its operated position, provides a discharge path through the resistance r, to ground for the condenser CE, said condenser being previously charged by the battery B through the hang-over windlng a and the resistance 1-,.

When the voice wave passing over the path LE ceases, winding a of relay RE is .no longer energized, and the'pull due to the biasing winding 0 of said relay restores the armature to its non-operated position. The additional bias introduced into the relay RW due to the current flow through the winding b of the relay RW also ceases, so that the relay RW is in a condition to res 0nd to voice waves passing over the circuit W.

As soon as the armature of the relay RE leaves its operated position upon being restored to normal, the discharge path to ground'for the condenser CE is opened, and current flows from the battery B through the winding a and resistance r, to charge the condenser vCE. .This charging current passes through the .Winding a in such a direction as to tend to hold the armature of the hang-over relay'RE in-its operated position and thereby maintain the-shortcircuit closed. As the con- 7 denser OE charges up, the current through the winding a decreases in accordance with the exponential law until the pull due to the biasing winding 1) is sufficient to overcome the pull due to the winding a, whereupon the ar- "mature of the hang-over relay RE is restored to its non-operated position and the short circuit is removed from the line LW. This hang-over period can be made sufliciently long to insure that any echo currents returning from east to west will have arrived at the foregoing point before the short circuit is removed.

It will, of course, be obvious that for voice currents transmitted from the line L over the path LW to the line L,, the operation of the other half ofv the a" paratus including the amplifier-detector D the detector relay RW and the hang-over relay RW, will be similar to that already described. In this case, of course, the unidirectional current from DW' energizes the winding (1 of the relay RW to shift its contact. At the same,

time, the current passes throughthe op osing winding 6 of the relay RE to increase t e has of the latter, tending to hold thearmature against its back contact.

In the arr ement above described," relaysRE, RE, W and RW' may all be ex actly alike, the differences in operation being due to the different circuit arrangements by which they are connected. A modified arrangemen't is ossible, however, as shown in Fig. 2, in whic the function of the opposing winding b and the biasing winding, 0 may be that plate current from a given amplifier-detector flows through the operatin Winding of its associated relay and the win ing be of the opposite relay. Consequently, when one relay, as, for example, RE, is operated by its winding a in response to voice currents, the biasing current throu h the winding be of the opposite relay R\ is increased, thereby preventing operation of the latter. The circuits of the hang-over relays RE and RW' are identical with and are operated in the same manner as those of Fig. 1.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely difierent from those illustrated without de arting from the spirit of the invention as de ned in the following claims.

What is claimed is:

1. In a two-way communication system, a

directions, an echo suppressor unit associated with each path comprising a detector anda relay operated therehy,.each relay controlling means for disahling the opposite path, and an opposing winding for each relay energized under the control of the detector which operates the opposite relay, whereby when one relay is energized for operation the ther relay is prevented from operating.

2. In a two-way communication system, a pair of paths adapted to transmit in opposite directions, an echo suppressor unit associated with each path comprisin a detector and a relay operated thereby, eac relay controlling means .for disabling the opposite path, and a winding for each relay connected in opposition to its normal windinggand energized by current supplied by the detector which operates the opposite relay, whereby when one relay is energized for operation the other relay is prevented from operation.

3. In a two-way communication system, a pair of paths adapted to transmit in opposite directions, an echo suppressor unit associated with each path comprising a detector and a relay operated thereb ,each relay controlling means for disabling t e opposite path, an op erating winding-and an opposing winding for relay being in circuit with lay is prevented from operation.

4. In a-two-way communication system, a

pair of paths adapted to transmit in opposite pair of paths adapted totransmit in opposite directions, an echo suppressor unit associated with each path comprising a detector and a relay operated thereby, each relay controlling means for disabling the opposite path, an operating winding and an opposing winding for each relay, the operating winding of one relay and the opposing winding of the other relay being connected to be supplied with current from one detector, and the operating winding of the latter relay and opposing winding of the first relay being supplied with current from the other detector, whereby when one relay is energized for operation, the

. other relay is prevented from operation.

5. In a two-way communication system, a pair of paths adapted to transmit in opposite directions, an echo suppressor unit associated with each path comprising a detector and a relay operated thereby, an opposing winding for each relay energized under the control of the detector which operates the opposite relay, whereby when one relay is energized for operation, the other relay is prevented from operation, means controlled. by each relay for disabling the opposite path, and means for maintaining the path disabled a predetermined time after the transmission wave passing over the other path has ceased.

- 6. In a two-way communication system, a pair of paths adapted to transmit in opposite directions, an echo suppressor unit associated with each path comprising a detector and a relay operated thereby, an opposing winding for each relay energized by current supplied by the detector which operates the opposite relay, whereby when one relay is energized for operation, the other relay is prevented from operation, means controlled by each relay for disabling the opposite path, and means for maintaining the path disabled'a predetermined time after the transmission wave passing over the other path has ceased.

posing winding of the other relay being connected to be supplied with current from one detector, and the operating winding of the latter relay and opposing winding of the first relay being supplied with current from the other detector, whereby when one relay is energized for operation, the other relay is prevented from operation, means controlled by each relay for disabling the opposite path, and means for maintaining the path disabled a predetermined time after the transmission wave passing over the other path has ceased.

9. In a two-way communication system, a pair of paths adapted to transmit in opposite directions, an echo suppressor unit associated with each path comprising a detector and a relay operated thereby, each relay controlling means for disabling tne opposite pat-h, an opposing winding for each relay, and means whereby when one relay is operated the opposing winding of the other relay is simultaneously energized to prevent the operation of said other relay and thereby suppress quick echoes.

In testimony whereof, I have signed my name to this specification this 12th day of March, 1928.

DOREN MITCHELL.

7. In a two-Way communication system, a

- pair of paths adapted to transmit in opposite directions, an echo suppressor unit associated with each path comprising a detector and a relay operated thereby, an operating winding and an opposing winding for each relay, the said opposing winding of each relay being in circuit with the operating winding of the other relay, whereby when one relay is energized for operation, the other relay is prevented from operation, means controlled by each relayfor disablin the opposite path, and means for maintaining the path disabled a predetermined time after the transmission wave passing over the other path has ceased.

8. Ina two-way communication system, a pair of paths adapted to transmit in opposite directions, an echo suppressor unit associated with each pathcomprising a detector and a relay operated thereby, an operating winding and an opposing winding for each relay, the operating winding for one relay and the op-

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