US1536907A - Carrier-current system - Google Patents

Description

May 5, 1925.

J. MILLS CARRIER CURRENT SYSTEM Filed Feb. 27, 1920 In venfor John M/'//s Arry Patented May 5, 1925.

UNITED STATES. PATENT OFFICE.

JOHN MILLS, OF WYOMING, NEW JERSEY, ASSIGNOR T0 WESTERN ELECTRIC COM- PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

CARRIER-CURRENT SYSTEM.

. Application filed February 27', 1920. Serial No.'361,911.

To all whom it may concern:

Be it known that I, JoHNMILLs, acitizen of the United States, residing at Wyoming, in the county of Essex, State of New Jersey, have invented certain new and useful Improvements in Carrier-Current Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to transmission systems and more particularly to duplex or multiplex systems of the carrier current. type for duplex communication between a plurality of pairs of stations.

The invention is illustrated in connection with a multiplex carrier current system comprising a number of duplex channels, each channel connecting a pair of telephone substations between which transmission is to be carried on. The duplex channels of the system disclosed have in common a high frequency four-wire circuit of which one pair of conductors serves to transmit all the messages in one direction and of which another pair serves to transmit all the me; sages in the other direction.

Circuits of this type frequently rely upon a condition of balance between the real line and an artificial net-work of impedance elements. The currents which are transmitted in one direction are prevented by this balanced arrangement from being transmitted back to the sending end through the oppositely directed repeater and the other part of the four-wire. circuit. Due to changes in weather conditions or other causes, it is sometimes difficult or impracticable to maintain this condition or balance, and as aresult there are heard echoes which lag slightly behind the original voice sounds.

' It is one object of the invention to provide means for preventing such echoes.

In the form of the invention disclosed, a pair of normally opened switches are introduced into a circuit connected to the o tgoing and return portions espectively of each du lex channel. Upon being closed. thcse switches short-circuit the conductor to which they are connected. Each switch is so arrang so; as to be closed by a relay asso- :iatcd with the other branch of the duplex chmmeh The current, to operate the rolavs may consist of or be derived from the high frequency modulated currents or in the case of a terminal modulating station may be of low frequency.

T he mvention therefore contemplates the provision of means such as a line balancing net-work designed to prevent reflection currents in the repeater circuit and additional means to prevent their How in case the first means is inadequate. Conversely, if the additional means should become inoperative, the circuit is not rendered inoperative since, as stated above, the switch contactsaie normally opened.

An important feature of the invention consists in means whereby in a duplex-multiplex system, the transmission of current in one direction through one duplex channel serves to temporarily render the return channel inoperative or greatly reduce its efiiciency without interfering with either the going or return paths of any of the other duplex channels. Since in particular installations reasons other than the prevention of echoing or round trip singing may exist for making it desirable to accomplish this result, the invention is'not limited to this purpose alone but may be advantage ously utilized wherever it is desired that onehalf of a duplex channel act at certa times upon the half of the channel which transmits in the opposite direction without adversely affecting the other half of the channel or t other channels or impairing their transmitting etiiciency. While -ow frequency hybrid coils are herein described as the elements causing reflection currents itshould be understood it is not contemplated tlr. the invention is limited to the prevention of reflection currents produced by such elements. Such reflection currents, as is well known may be produced by line trans formers, by repeater elements, by termina apparatus, by abnormally irregular iine loading, or by connection of line sections of different impedance characteristics to each other-. Furthermore. as stated above, it is not contemplated that. the invention is limited to the prevention be utilized for oth r purposes.

From another a. wet. the imrr-minn (mnot echoing z ltn'iay i prises a repeater having several pairs of one-way channels, one or both of the channels of a pair being so related to the other that the existence of a certain condition in one of the channels produces a variation from the normal condition in the other channel without affecting the condition of any other channel of the remaining pairs of channels.

In the preferred form means are included whereby current of a particular range of frequencies only is allowed to act upon the devices for rendering inoperative a given channel, currents of other frequencies being excluded.

For a detailed description, reference will be had to the accompanying diagram wherein Fig. 1 shows the features of the invention applied to a multiplex system adapted to allow communication between several pairs of low frequency stations over the same four-wire circuit; and Fig. 2 is a circuit diagram showing the arrangement of parts at one end only of the high frequency line in a modified form of the invention.

\Vhere? the expression band of frequencies.-or range of frequencies is used herein, it is meant to include a range which may be limited to a single frequency as well as a band comprising a plurality of frequencies.

Referring to Fig. l, the circuits of the system will be traced through in one direction from a substation S to a substation S which will serve equally for tracing the circuits in the opposite direction, the parts occurring in the same order, having the same functions, and being designated by identical reference characters. Beginning with substation S, this station is connected to the hybrid coil HC, through the low' frequency line L1). The line LL may include one or more telephone exchanges or repeater stations if desired and is intended to indicate any line through which low frequency signal currents may be propagated but in the present instance is considered as a telephone line. The line LL is balanced by the network LN. From hybrid coil HP to the modulator M connection is made through a circuit 8. The modulator is supplied with carrier frequency current by a suitable generator G or other suitable source. The modulator which may be of any known type of carrier suppression modulator functions to modulate the current supplied by G in accordance with the signaling currents transmitted through conductor 8. The modulated currents are amplified by amplifier A and pass through filter F, for impression upon the line it) of a four-wire circuit ll. Modulated currents of other carrier frequencies from other low frequency lines are also impressed upon the line 10 through a series of other filters of which F only is shown.

At a repeater station, the incoming currents are amplified by amplifier A and impressed upon band filters BF BF etc. These filters are each adapted to'transmit only the band of frequencies corresponding to one modulated high frequency current. The filter BF for example, transmits the current whose base frequency corresponds to that of the generator G. After passing the filter BF a small portion of the current is utilized in actuating the thermionic amplifying relay TR whose input circuit includes the high resistance r in shunt to the line and whose output circuit contains an alternating currentelectromagnetic relay R which is adapted to close the switch S. The thermionic relay however, may be con nected to the line in other ways. The switch S is located in a circuit 12 which is in shunt to the return channel of the repeater station which is adapted to transmit messages from the station S to station S. lVhen the switch S is closed, this return channel is short-circuited and rendered inoperative. The principal part of the high frequency current after passing filter BF passes through a similar band filter B1 and continues on through the line 10 to the detector station where the desired frequency is selected from the other modulated waves by the filter F detected by detector 1) and amplitied by the amplifier A. The detected currents pass through the conductor 9 to the hybrid coil HC and the line LL to the station S.

Associated with the other channel at the repeater station is a modified form of apparatus connected between the band filters BF and BF which are designedto selectively transmit other modulated currents, as for example, those passing through the filter F Tn this form a relay is included directly in the line and actuatcs the switch S to close the circuit 12. Any form of apparatus other than the two shown herein may be designed to accomplish the same function.

() wrafion.

\Ylicn messages are transmitted from station S to station S, there will sometimes be a reflection or transmission of energy through the return channel owing to an unbalance 0t theline LL and its network LN adjacent to station S. These currents being reverscly transmitted would ordinarily 'be repeated and, amplified by the various apparatus along the line, heard by the operator at S as echoes. \Vhcn the improvements herein described are used howercr, the return channel will be shortcircuitcd so that this echoing will not occur. The relay lt may have a time lag approximately equal to but preferal ily somewhat less than the time of transmission of a wave from the repeater station to the reflection point and back again. This CH- cumstancc may be utilized in designing the relays. The time lag may be as much less than this amount as desired. Since, however, it is desired that: the return channel be restored to normal condition as quickly as possible, it is advantageous that these relays be of the quick release type. It should be noted that in this system the modulators M are of the carrier suppression type which cause the transmission of modulated current only during the time the low frequency waves are acting thereon. The principles of the invention are applicable to other systems in which carrier suppression modulators are not used.

If desired, the generators G which supply the out-going and incoming carrier frequencies of a single duplex channel, may generate the same or different frequencies. same frequency is employed in both direc tions the filters F, may be identical or they may be so designed that one filter passes the lower side band p-s and the other the upper side band [7+8 where represents the carrier frequency in cycles per second and 3 represents the signaling frequency. In the latter case, the frequencies will preferably be staggered, that is, the frequencies of one side band transmitted in one direction will be intermediate to other bands transmitted in the opposite direction. Inthe case where the generators have different -trequcimies, staggering may also be used; thus from one endhot' the line. transmission may be carried on upon carrier waves having frequencies of 10,000, 20,000, etc., and in other directions. upon waves having carrier frequencies of 15,000, 25,000, etc.

Referring to Fig. 2 there will beseen at the station S the line LL. the. hybrid coil HC, circuit 8, generator modulator M, amplifier A, and the filters F,, F, and F arranged in a manner similar to that in Fig. 1. To the circuit 8, however, is connected in any suitable manner a relay circuit 12 containing any suitable device such as relayH' arranged, upon actuation, to close a switch S, and thereby short-circuit the return channel leading to the input side of the detector D. At the modulating and detecting station at the remote .end of the line (not shown), which is preferably identical with that described, another relay R and switch S, are provided. They are preferably to be. con nected, however, so that the relay will be actuated by currents traversing the system,

in the opposite'direction to those actuating 'relay S, and will render inoperative the return path corresponding thereto. The switch S, may be connected to the output circuit of the detector or in any other way to the return path so as-to render it inoperative. It will be understood that the filters F and F, will each be connected to another hybrid coil HC and low frequency line LL, and the filters F5 and F will likewise be connected If the to still another ybrid coil, etc. The operation of this syst am will be fully understood by comparison with the description of the operation of no system shown in Fig. l.

The subject-matter of this specification may be regarded as an improvement in some respects upon that described in United States Patent No. Lat-34,790, issued Xovember 7, 1922, Serial No. 322,154 filed September 0, 1919.

lVhile certain complete systems embodying the invention are described herein, the invention is not limited to a particular embodiment but may be embodied in other constructions. Certain features may be utilized in other systems. The novel features which are believed to be inherent in the invention are defined in the appended claims.

- What is claimed is:

1. A system for duplex-multiplex transmission comprising pairs of stations, means for accomplishing a plurality of two-way transmissions on different frequency-selective. channels between pairs of communicating stations, and means associate .l-with said system whereby one-way transmission between one of said pairs of stations renders transmission in the opposite direction impossible, said last mentioned means functioning without interfering with transmission between others of said pairs of stations.

2. A system of duplex-multiplex signaling having aplurality of channels, each of which has separate outgoing and incoming paths, an echo preventing means in each path of a plurality of said channels operlira able under the influence of waves trans,

mitted in onedirection by one of said paths to render the cooperating oppositely-conducting path incapable of efficient transmisslon.

3. A telephone system comprising means for simultaneously connecting several pairs of stations, said means comprising common conductive line sections, reflection produc ing means in said system, and means controlled by signal currents for reventing reflection currents due to signa s passing between one of said pairs of stations from retraversing the line, said means functioning without destroying the transmitting efficiency of said system asto other pairs of stations.

4. A carrier current system comprising a tour-wire circuit, means for transmitting several highfrequency modulated currents ineach direction over said circuit, reflection causing means in said circuit, and means operable by one of .said modulated currents passing through said circuit to rendersaid circuit incapable of transmitting reflection currents due to said modulated current.

v5.'A duplex four-wire circuit, means for transmitting a plurality of high frequency modulated currents through said circuit, and means whereby transmission in one direction of said currents renders said system incapable of transmitting in the-"other direction until the cessation of transmission.

6. A repeater circuit comprising several sets of selective circuits for the transmission of selected bands of frequencies in each direction, means operable by a small fraction of the energy being transmitted through any one of a plurality of said circuits to render another of said circuits temporarily inoperative for transmission in the opposite direction.

7. A four-wire circuit for duplex-multiplex carrier transmission, comprising reflection causing means at each terminal, a two-way repeater in said circuit, said repeater comprising individual circuits for selectively repeating different signaling waves, and a relay associated with each one-way circuit for rendering the one-way circuit for transmitting in the opposite directioninefiicient, said relay having a time lag substantially equivalent to the time of transmission. of a wave from said repeater to a reflection point and return.

8. A multiplex transmission systemhaving a channel pointed in one direction, a channel pointed in the other direction and means for rendering said system inoperative for the transmission of a certain bandof frequencies in one direction, said means comprising two filters in said channel pointed in one direction, and a device for controlling the channel pointed in the other direction operatively associated with said first named channel between said filters and shielded thereby from the portions of the system lying beyond said filters.

t). A repeater normally adapted to repeat more than two bands of frequencies, each hand reprcsenting a signaling channel, devices including relay means operative under the influence of electric currents for rendcring said repeater inoperative to repeat a certain band of frequencies, and aselective circuit for causing currents of a limited frequency range only to operate said devices.

10. A transmission system for transmitting several bands of frequencies in one direction and several bands of frequencies in the other direction, devices operative under the influence of a band individual to each device and selected from several bands transmitted in one direction to render said system inoperative to transmit a certain band of frequencies in one direction, and a selective circuit to limit the range of frequencies of currents affecting said devices.

11. A repeating station comprising means for repeating several bands of frequencies in one direction and means for repeating corresponding bands of frequencies in the other direction, and means operative by repeating any one of said bands to render the means for repeating the eorrseponding band in the other direction inoperative.

12. A repeater. system having several duplex channels and means cooperating with each duplex channel whereby the transmission of waves therethrough in one direction changes from efficient transmitting to ineflicient transmitting condition'the channel for repeating waves in the other direction.

13. A repeater system having several means each adapted to accomplish the repeating of a particular band of frequencies in one direction, several means each adapted to accomplish the repeating of a particular band of frequencies in another direction, and means whereby the transmission of any selected band of said bands of frequencies in one direction renders the system less efficient for the transmission of a selected hand of frequencies in the other direction.

14. A multiplex signaling system including channels for the transmission of messages between several pairs of substations, said channels comprising conductors in common, and means operated by message currents in one direction in one of said channels for reducing the transmitting efficiency of the return path of said channel without causing material interference with any other of said channels.

15. A multiplex repeater circuit comprising several sets of selective circuits for the transmission of selected bands of frequencies, each comprising a speech modulated carrier wave, in each direction, and means operable by a fraction of the energy being transmitted through one of said circuits to render one of said circuits adapted for transmission in the opposite direction temporarily inoperative.

16. A repeater circuit comprising several sets of selective circuits for the transmission of selected bands of frequencies in each direction, one of said bands in each direction representing a telephone message, and means operable by the transmission of one of said bands comprising telephone message energy through one of said channels in one direction to render inoperative a telephone message channel for transmission in the opposite direction.

17. A transmission system for transmitting several bands of frequencies in one direction and several bands of frequencies in the other direction, a plurality of said bands in each direction representing a cor-responding plurality of telephone messages, devices operative under the influence of transmission of one of said bands in one direction to render said system inoperative to transmit a certain band of frequencies llil) lit) in one direction, and a selective circuit to other direction, wave controlled means operative by repeating one ofsaid bands to render. the means for repeating a corresponding band in the other direction inoperative, and a band pass filter for-limiting to a definite range of frequencies the trans.- fer of currents to said wave controlled means.

19. A. telephone transmission system having several duplex telephone transmission channels, means cooperating with each duplex channel whereby the transmission of waves therethrough in one direction varies the normal condition of the channel for repeating waves in the other direction, and means preventing a corresponding variation of condition of another duplex channel.

20. A transmission system having several duplex channels, each comprising frequency-selective means for limiting the transmission therethrough to a definite range of frequencies, and means cooperating with each duplex channel whereby the transmission of waves therethrough in one direction changes from eflicient transmitting to ineflicient transmitting condition the channel for repeating waves in the other direction. I

In witness whereof, I hereunto subscribe my name this 20th day of February A. D., 1920.

JOHN MILLS.

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