US1642499A - Transmission regulation - Google Patents

Description

Sept. 13.1927 J. s. JAMMER- TRANSMISSION REGULATION ASQ.. .n QSG wx 5:3 f A w m a ma d o?. MM@ w @Wag g t T .Nw Lm# g E mi N IP Q ma.. E E u l m u\ M d s m F lwivu E N?. Nn E nll ,E m.. se,... w *b5 E E a... 1 H [Umzug a HQE E .E

'Patented sept. 13, 1927.

,UNITED STATESI lPivrizNT oFFlcE.

JACOB S. JAMMER, OF NEW YORK, N. Y., ASSIGNOR TO WESTERN ELECTRIC COMPANY,

' INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TRANSMISSION .REGULATION.

application med marcan, 1924. semina. 698,355.

\ This invention relates to transmission regdilation and is particularly adapted for use in multiplex si naling systems.

An object o the invention is to stabilize the transmission characteristics in two-way signaling systems.

' A related object of the invention is lto facilitate' the construction, installation and maintenance of a transmission regulating system.

Another object of the invention is to centralize the control of a transmission regulating system at one terminal thereof..

v .Another object of the invention is to provide'a method and means for indicating changes of` line equivalent in either direction in a two-way transmission system. f

It is well known that in radio and carrier .signaling systems employing fairly high frequencies the transmission characteristics of the transmission line or other medium are subject to variations which render it diiiilcult to maintain satisfactory signaling conditions. y

Changes inthe attenuation of the transmission medium of a system of the above type4 produce corresponding variations in the over-all transmission equivalentof the' system, and result in large iuctuations in the volume of a telephone o r other message being transmitted. Various `means have been proposed for overcoming the eect of these variations. Some systems provide means for automatically recording such variations as theyl occur, thus enabling the attendants at the stations throughout the system to adjust the elements'of the circuit accordingly. In other systems the adjusting or compensating means are operated automatically by the control or recording mechanisms.

Briefly, this invention provides a system of transmission regulation in which one channel of the system is set aside as a control or pilot channel. Over this channel,

- current is transmitted for the purpose of indicating the condition of the transmission medium over which the telephone or other signals are transmitted. 'The pilot current may operate a recordingdevice or an automatic compensator, or, if desired, may operate both recording and compensating devices. In order to simplify the descri tion of the invention only the means for in icating the chan s in line equivalent are shown and describe It will be evident, however, as the description proceeds, that automatic compensatingmeans may also be employed Without departing fromvt-heinvention.

According to a feature ofthe invention,

Aall of the transmission regulating mechanisms are located at a-common point in the system. More speciicallv, the pilot current' is impressed upon the e at one station which may be called the control station for transmission to a second station geographically remote therefrom. At the remote sta- -tion the received pilot current is impressed upon the line for transmission back to the controlstation. The incomin pilot current at the control station is ampli ed and passed through a detector. also included in the output `of the pilot transmission circuit atthe same station, and potentials derived Afrom these detectors are` balanced against each other in a differential galvanometer. If a change in line equivalent occurs the Y incoming pilot current changes and thus produces an unbalance of potential acrossthe alvanometer. The resulting deiiection of t e galvanometer causes the adjustment of a potentiometer in the pilot receiving channel at the control station and adjusts the input of this\circuit to balance the current in the two detectors. At the same' timethe deflection of the galvanometer operates a recordin device to give an indication of the linee ange.

The system outlined above is arranged to automatically compensate for variations in the output of the pilot current generator. If the output of this 'generator changes this results in a change in the potential across the detector in circuit therewith, but since a corresponding change is produced inthe receiving detector, the galvanometer does not change its position.

The present' invention effects a consider-J able saving in apparatus over systems employing separate apparatus to indicate changes in the opposite directions. Furthermore, since changes in the transmission A similar detector is efliciency of the line affect the pilot current ceiving circuit. This system also simplifies' the testing of the pilot channel without interfering with the transmission of signals.

Other features and advantages of the inventon will appear from the following description taken in connection with the accompanying drawing, in which:

Fig. 1 is a diagrammatic illustration of a carrier signaling system embodying the invention.

Eig. 2 shows curves illustrating the operation of the system of Eig. 1.

The system shown in Eig. 1 is represented as comprising two terminal stations W and E, respectively, interconnected by the multiplex line ML. Cne or more repeater stations may be connected to the line ML intermediate the terminal stations.

Low frequency lines L1, L2 and L2, which may be telephone lines or other signaling lines, are arranged for simultaneous and independent communication over the line ll/lL with corresponding similar lines L11, L12, and L12 at station E. Similar low frequency lines L11, L1 and L1G at station E are arranged for communication over the line LED with corresponding similar lines Lt, L and La at station W. rlhe low frequency lines L1 and L1q L2 and L, and L3 and L at station W are associated through the usual hybrid coil circuits, not shown, to form groups of two-way communication channels. A similar arrangement is employed at station E.

Carrier currents are utilized for transmission over the line 11H1 and are grouped according to their frequencies, the lower frequencies, as a group, being used for transmission from station W to station E, and the higher frequencies as a group being used for transmission from station E to station Low pass grouping filters LP1 and LP2 at the respective terminal stations are each aired with a high pass filter HP1 and HP2. hese filters serve to separate the directional groups of carrier waves to the respective terminal transmitting and receiving circuits. These filters and each of the other filters shown throughout the system may be constructed and designed in accordancewith the principles laid down in the United States patent to Campbell No. 1,227 ,113, issued May 22, 1917.

For the pur ose of the present description, a low pass filter may be taken to be an filter which transmits freely currentsof a l frequencies between zero and a preassigned limiting frequency and suppresses the transmission of currents of all frequencies higher than said limiting frequency. Conversely, a high pass filter may be taken to be any filter which freely transmits currents of all freuencies higher than a pre-assigned limiting requency and suppresses currents of all freuencies lower than said limitin frequenc pecific types of both of 'these inds of manana ters are shown, 'for example, in Fig. 11 of the above mentioned Cam bell patent.

Each of the low fiiequency lines L1, L2 and L2 is connected to one of the transmitting circuits SG1, SC2 and SC3, respectively, which comprise the usual oscillator, modulator and transmitting lter. The low frequency lines L11, L15 and L1 are connected to similar transmitting circuits correspondingly lettered but with subscripts affixed thereto. The low frequency lines L4, L, L and L11, L12 and L1s are connected to corresponding receiving circuits RC1, RC2, etc. each comprising the usual receiving filter, demodulator and amplifier. A transmission system of this general character is shown in Eig. i9 of a paper entitled Carrier current telephony and telegraphy b E. H, Colpitts and C. E. Blackwell, pu lished in the lransactions of the American Institute of Electrical Engineers, volume 40, 1921.

'lhe repeater E, which forms no part of the present invention, may be of any suitable type such as that disclosed in the United States patent to liaibourn, No. 1,413,357, issued April 18, 1922. Each of the repeater channels includes an input filter, an amplifier andan output filter, for further details of which reference may be made to the Raibourn patent.

lln addition to the signaling channels indicated, a control or pilot channel is also connected with the line ML employing a frequency different from that of any of the signalin channels and including band pass filters P 1 and PE2 at station W and filters PE11 and PF12 at station E for the pilot fre uency. The pilot channel associated wit filter PF1 at station W includes a transmitting oscillator 5 of any suitable type, an adjustable current regulator 6 and an ampli fier 7. The output of the amplifier 7 is coupled to the filter PF1 by means of a transformer 8. A thermocouple 9 is inserted in circuit with the secondary of the transformer 8. The-thermocouple 9 may be of any well known type comprising a filamentary element which is heated by the alternating current passing between its two terminals in the pilot channel, this filament being arranged to heat a junction of two dissimilar metals so that a direct current E. M. F. is produced between the terminals of these metals, this E. M. F. being proportional to a function of the amplitude of the alternating current flowing through the filament. A va-f4 riable resistance element 10 is included between the terminals of the two dissimilar metals of the the-rmocouple for a purpose hereinafter to be described. In place of the thermocouple it will be obvious to use a suitable rectifying detector or other quantitative indicator. 1

The receiving pilot channel associated with the filter PE2 at station Wkincludes a pair of variableV rheostats 12 and 13 the contact arms of which are mounted on a common control shaft 11. The contact arms of the variable rheostats 12 and 13 are connected iny series with the primary of a transformer 14 the secondary of which is connected to the input of an amplifier which `5 able resistance element 20 similar to the ele-` may comprise a pair of three-element electric discharge tubes 15 and 16. The output l10 of this amplifier is coupled by means of a transformer 17 to the heating element of a thermocouple 18 in series with an adjustable current regulator 19. The thermocouple 18'is identical to thermocouple 9, a variment 10 being connected across the terminals 'of its two dissimilar metals.

The variable rheostats 12 and 13 serve the purpose of automatically adjusting the in- 20 put of the thermionic amplifying tubes 15 balance of which determines the .direction and 16 in accordance with variations in the transmitted and received pilot current. The thermocouples 9 and 18 form part of a control circuit the condition of balance or unadjusting mechanism comprising the rheonu) stats 12 and 13 is secured through the medium of an automatic controlling apparatus generally indicated at 22.

The controlling apparatus 22 by itself forms nojpart of the present invention and lhas not been illustrated in detail, since it may comprise any suitable or well known arrangement by which the control `shaft 11 'is held stationary while the galvaneuneter 2I`is in its `zero or mid-positiomand is autof matically rotated in one direction or the other dependent upon the direction of deflection 'of the galvanometer. Such rotation persists, continuously or by steps, untilu the `galvanometer is again brought to its zero position. vThe control apparatus 22 is also preferably of the type having a recording chart and associated mechanisms for. making a permanent record of the variations ,i produced by the defiection of the galvanometer 21.y One specific system for accomplishing this resultis shown and described in the United States patent to Brewer, No. 1,356,804, issued October 26, 1920.

The lpilot current generated by the oscillator 5 is continuously transmitted from station W to station E and thence back to station W, this current, as pointed out above,

being of a frequency .different from thatof any of the signaling channels. At station E since the system herein shownand detion.

scribed is operated on a groupfrequency basis, the incoming pilot current is passed through a frequency converter or amplifiermodulator 23 where it is amplified and combined With the current generated by a source of alternating current 24, and is then impressed upon the line ML for transmission back to station W. This frequency conversion is necessary to enable the pilot current to pass through the repeater directional filters EIF and EOF and the grouping filters HP1 and HP2 'which are high pass filters and hence sup-press current of the original pilot frequency which isa low frequency designed to pass through the lov7 pass repeater directional filters WIF and WOF and the grouping filters LP1 and LP2.

The transmission of the pilot current is illustrated graphically in Fig. 2 in which attenuation is plotted against frequency.

The curve F, indicates the attenuation of the lower frequency grouping filters LP1 and LP2 and the repeater directional filters WIF and \VOF, and the curve F2 indicates the attenuation of the higher frequency grouping filters HP1 andi-IP2a and the repeater directional filters EIF and EOF.

The pilot frequency generated by the oscillator 5 and transmitted from station W to station E is represented bythe letter A, while the pilot frequency transmitted from station E to station W is represented by the letter B. It will ybe seen that durrents of the frequency of pilot current A are transmitted with substantially negligible attenuation by the low pass grouping and repeater .directional filters, but that currents of this frequency are greatly attenuated by the high pass grouping and repeater directional filters. The pilot frequency A may be located nearthe frequency limit above ters begins to increase, as shown in 2, and similarly the frequency B maybe near the lower limit of the high pass filters.v If

the separation between the oppositely directed pilot frequenciesis say 2,000 cycles, the pilot current A may be combined with a current of 2,000 cycles frequency in the frequency converter 23 at station E and thence passed through the pilot 'filter PF,2 which may be designed to transmit only the upper side band produced by such modula- It will be seen that the modulated pilot current B will be transmitted by the grouping filters HP1 and'HP2, and the repeater directional filters EIF and EOF.

If, instead of operating the system on a group frequency basis, the signaling system employs the same frequency in bothdirections, n'o frequency conversion isnecessary at the remote station, the pilot current simply being amplified and impressed. upon the line for transmission back to the control station.

which' they attenuation of the low pass fill The operation of the system is as follows: The variable resistance elements 10 and 2O are adjusted so that equal potentials are derived from the thermocouples 9 and 18 under the desired transmission conditions of ,the line ML. After such adjustment the elements 10 and 2() may remain in their adjusted positions at all times. The pilot current A generated by the oscillator 5 is transmitted through the pilot filter PF1 and low pass grouping filter LPl to the line ML and thence through the repeater directional filters WIF and WOF and amplifier WA to the remote station E. At station E the pilot current is transmitted by the low pass grouping filter LP2 and is selected by the pilot filter PFll. The pilot current A 1s amplified and combined in the amplifierlnodulator 23 with the current generated by the alternating current source 2-1 in the manner described above to produce the return pilot current B. The pilot current B is transmitted through pilot filter PF,L and high pass grouping filter HP2 to the line ML, and thence through repeater directional filters EIF and EOF and amplifier EA to station iV. At station W the pilot current B is transmitted by the grouping filter HP1 and is selected by the pilot filter PF2 from which it is transmitted to the receiving pilot channel Where it is amplified and passed through thermocouple 1S.

If a change in line equivalent occurs anywhere in the system the incoming pilot current changes and produces a correspond1ng change in the potential derived from the thermocouple 18. When the potential derived from the thermocouple 18 varies from the potential derived from therniocouple 9 a resulting unbalance of potential 1s produced in the windings of the differential galvanometer 21. The resulting defiection of the galvanometer causes a corresponding adjustment in the automatic controller 22 which in operating rotates the shaft 11 to adjust the variable rheost'ats 12 and 13 in the input circuit of the receiving amplifier tubes 15 and 16 until the output of this amplifier is returned to normal. Vhen the amplifier output is returned to normal the galvanometer 21 likewise returns to its normal or center position. The recording mechanism associated with the controller 22 makes a permanent record of the line change which may be compensated for by adjusting electrical elements in the transmission line at the station W or at the repeater stations or at the other terminal, or partly at each of these points. If the output of the oscillator` 5 changes, this results in a change in the potential across the thermocouple 9, but since the potential across the receiving thermocouple 18 is similarly affected, the gal- Vanometer does not change its position,

If desired, the controller 22 may be em-` Lea-acne ployed to automatically control adjusting elements in the transmission circuit t0 compensate for changes of line equivalent in either direction of transmission. Various other changes mayl also obviously be made without departing from the spirit of the invention. Accordingly, the system illustrated and described in detail should be considered as merely defining one form of' the invention, but is not to be construed as limiting the invention, the scope of which is defined by the appended claims.

What is claimed is:

1. The method of transmission regulation which comprises transmitting a control wave from a control station to a remote station over a medium Whose transmission efficiency is variable under different conditions, amplifying the Wave received at the remote station, retransmitting over said medium to the control station a wave of an amplitude proportional to that of the control wave received 'at the remote station, and utilizing the transmitted wave and the retransmitted wave at theA control station to indicate variations in the transmission characteristics of said medium.

2. The method of transmission regulation which comprises transmitting a control Wave from a control station to a remote station over a medium whose transi'nission efficiency is variable under d iflerent conditions, retransniitting over said medium to the control station a wave of an amplitude proportional to that oi' the control wave received at the remote station, and utilizing potentials derived solely from the waves transmitted from the control station over said medium to the remote station and the waves retransmitted from the remote station and received at the control station to indicate variations in thel transmission characteristics of said medium.

3. The method of transmission regulation which comprises transmitting a control current between two terminals of a loop circuit whose transmission efiiciency is variable under different conditions, combining the transmitted current with another current at a point intermediate said terminals, and utilizing potentials derived from the current transmitted'at one terminal and received at the other terminal to indicate variations in the characteristics of said circuit.

4. The method of transmission regulation which comprises transmitting a cont-rol current from a control station to a remote station over a medium whose transmission efiiciency is variable under different conditions, amplifying and impressing the current received at said remote station upon said medium for transmission back to said control station, and impressing potentials, derived from the current transmitted from the control station and the current received at said control station upon a control device.

Ilm

5. The method of transmission regulation which comprises transmittingr a control current from a control station to a remote station over a medium Whose transmission et'- ticiency is variable under different conditions, modulating the current received at solely from the transmitted and received' currents upon a common control device/ v 7. The method of transmission regulation Which comprises transmitting a control ciirrent from a control station to a remote ,sta-

tion over a medium Whose transmission eiiiciency is variable under differentconditions, combinin the currentareceived at said rcmote station with another current, impressing the combined current upon said medium for transmission back to said control station, and impressing the current received at said control station upon a control device.

8. The method ofy transmission regulation which comprises transmitting a control current from a control station to a remote sta-- tion over a medium Whose transmission eiiciency, is variable under dilferent conditions,

combining the current received at said re.-

mote station 4with another current ,`,impress ing the combined current upon said medium for transmission back to said control station, and differentially impressing potentials. derived from the currents transmitted and received at said control station upon .a control` device. 7

9. A system of transmission regulationciency is variable underdiferent conditions, a control station anda remote stat-ion associated therewith, Vmeans at said' control stat-ion for impressing -a control Wave upon said medium for transmission to said remote station, means for retransmit'ting over said medium to the control station a Wave of an am# plitude proportional to that of the control wave received at the remote station, an indicatin device, and means at the control station or diierentially impressing potentials 'derived only from the Waves transmitted and received over said medium upon said device.

11. A-system of transmission regulation n comprising a medium whose transmission eficiency is variable vunder dierent conditions,means for transmitting a control current between two terminals of said medium,

-means for combining the transmitted current With another current at a point intermediate said terminals, a control device, and means for ditferentiallyimpressin the current transmitted andreceived at'sai terminals upon said device.

12. A system of transmission regulation comprising a transmission line extending between a control station and a remote station and terminating in an outgoing channel andan incoming channel at said control station,

means at said control'station for impressing a control Wave'upon said outgoing channe for transmission over said line to said remote station, means forretransmitting'over said line tothe control station, a wave of an amplitude proportional to that of the control wave received at the remote station, means at said control station for transmitting the received wave to said 'incoming channel, an indicating device, means for impressing potentials derived from said outgoing and incoming channels upon said in' dicating device, a variable circuit controlling element in said incoming channel, and means controlled by said indicating device for concomprising a medium whose transmission eiciency is variable under different conditions, a control station and a remote station associated therewith, means at said control station for impressinga control wave upon said medium for transmission to said remote station, means for amplifying the wave received at the remotel station, means for rctra'nsmitting over said medium to the control station a wave of an amplitude proportional to thatot the control wave received -at the remote station, and means controlled by the outgoing Wave and the incoming wave at the said variable element.

system for indicating variations in trollin transmission equivalent, a control station and a remote station, a loop circuit connectin said stations and terminating in a trans- `mitting and a receiving branch at said con-` control station to indicate variations in the transmission characteiisticsofl said medium. 10. A system of transmission regulation comprising a medium whose transmission ehitrol station, the transmission eiiiciency of said circuit being variable under diiierent conditions, an indicating device, thermo- 'couples in said transmittingl and receiving branches dilerentially connected to said indicating device, a variable rheostat in said receivin branch, and means controlled by said in icating device for controlling said rheostat. f

' 14. In combination,l a transmission medium, a control station ,and a remote station associated therewith, means at,y said control station for im ressing a control current'upon said medium. or transmission to said remote station, means at said remote station for impressing the received current upon said transmission medium for transmission back to said control station, and an indicating device at said control station controlled solely by the control current transmitted over said medium to the remote station and by the current retransmitted from the remote station to the control station.

15. In a'carrier Wave transmission system in which Waves comprised in a lower frequency group are transmitted in one direction throuo'h the system and Waves comprised in a higher frequency group are transmitted in the opposite direction, terminal stations for said system, means at the first mienne' station to generate and transmit a control wave of a frequency comprised in one of said groups, means at the other station to receive said Wave and to retransmit to the first station a Wave of a frequency comprised in the other respective group and of an initial amplitude proportional to that of the control Wave received at said other station, and means at the first station to receive the retransmitted wave and to utilize it to indicate variations in the transmission characteristics of the system.

In witness whereof, I hereunto subscribe my name this 7th day of March, A. D. 1924.

JACOB S. JAMMER.

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