US1586821A - Receiving system for telegraphic signals - Google Patents

Description

June 1 1926;

R. c. MATHES RECEIVING SYSTEM FOR TELEGRAPHIC SIGNALS IIAAAAAIA 4 Sheets-Sheet 1 n 1 I yl II n //7 l//7/'0/.' Rain f C. Ma/h 5 Original Filed June 19 1918 R. c. MATHES RECEIVING SYSTEM FOR TELEGRAPHIC SIGNALS June 1 1926.

4 Sheets-Sheet 2 Original Filed June 19 9 Time R. C. MATHES RECEIVING SYSTEM FOR TELEGRAPHIC SIGNALS June 1,1926. 1,586,821

Original Filed June l9 1918 4 Sheets-Shet 5 Fig. 6. 7- m/w E v 7; L 5 L C by W Jun 1 1926.

R. C. MATHES RECEIVING SYSTEM FOR TELEGRAPHIC SIGNALS Original Filed June l9 1918 4 Sheets-Sheet 4 Patented June 1, 1926.

UNITED STATES 1,586,821 PATENT OFFICE.

ROBERT C. MATHES, OF WYOMING, NEW JERSEY, ASSIGNOR T0 WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A'CORPORATION OF NEW YORK.

RECEIVING SYSTEM FOR TELEGRARHIC SIGNALS.

Application filed June 19, 1918, Serial No. 240,792. Renewed March 27, 1925.

This invention relates to wave shaping or correcting means for systems. having transmission characteristics which dlstort the form of waves transmitted thereover,

. and has for an object to correct at least partially for such distortion, or to compensate subject to serious distortion, which distortion increases with the speed of signaling.

The purpose of this invention is to correct this distortion so that transmission may be carried on at a higher speed, or so that the wave form and power of the received signals may be made suitablefor operating devices which would not otherwise respond properly. n

One feature of the invention consists in inserting between the cable terminal and the responsive device to be actuated a connecting line in the form of a network, or series of networks, made up of resistance, inductance and capacity, the values of which are so chosen and the arrangement of which relative to one another is such that there are added to the received signal wave derivatives thereof in such proportion that the summation current produced has a wave form closely approximating the original transmitted wave.

In other words, where the transmitted wave'is of the customary square-top form, it becomes possible by employing this 1nvention to differentiate the received 1mpul ses as adually as the cable integrated the impu ses originally transmitted, and thus to reproduce for the actuation of the receiving mechanism an arrival wave having the desired sharp-head, fiat-top and long, gradual tail.

Such a. rocess of differentiation necessarily invo vesfcdnsiderable diminution in the power value of the signals, and in certain cases it therefore becomes necessary to provide, and by this invention there is provided, an amplifier or system of amplifiers for increasing the power of the signals to thedegree required fon efiective reception atthe cable terminal, "or for retransmission over a land line or another cable.

Such amplification should be accompllshed without the introduction of any add1t1onal distortion, and it is therefore preferable to employ for this purpose vacuum tube amplifiers of the thermionic type.

The distortion correction or differentiation may take placeand be completed prior to amplification, or, as in the preferred embodlment of the invention, such a diflerentiat1on and amplification may take place in alternate, successive steps. The latter arrangement has certain advantages, especially where vacuum tube amplifiers of the therm1on1c type are employed, for the reason that due the unilateral conductivity of such amplifiers, any reaction of one correctmg network on the preceding network is ehmmated, and, it is possible to effect the correction with greater exactness.

It w1ll, of course, be evident that in some instances where the cable distortion is not serious, but where the attenuation is lar e, amplifiers alone may be used without 't e correctmg network, and conversely, where d1stortion is great but the attenuation is relatively small, the correcting networks may be used without amplifiers.

In employing amplifiers of the vacuum tube type in telegraph systems, particularly where such systems are worked on the duplex principle, special precautions must be taken to protect the amplifiers against unbalanced potentials, due to the operation of the local sending mechanism. This is partlcularly the case where the amplifier employed is of the vacuum tube type, and is unsymmetrlcal as to its exposure to ground.

- In the system of this invention there is pro- Fig; 3 shows an arrival curve for submarine.

no i

- signals with the first, second, third and fourth derivatives of such curve; Fig. 4: illustrates various forms of derived curves; and Figs. 5 to 13 inclusive show various modifications of the correcting networks.

Referring to Fig. 1, submarine cable 5 terminates in a duplex circuit comprising the two inductive ratio arms 6 and 7, the variable induct-ances 8 and 9 and the potentiometer resistance 10 to which the customary local transmitter 11 is connected. The usual artificial line 12 is provided for balancing the cable impedance. Connected across the ratio arms in the position of the usual receiving apparatus is the distortion correctting line, made up of a plurality of series elements 13, and shunt elements 14. The actual design of such networks is capable of a variety of modifications, depending upon the extent to which the signals have been distorted by the cable and upon the wave form ultimately desired.

For example, in many cases a very simple network such as that shown in Fig. 5 may be employed, in which the shunt element consists of an inductance L having a prede' termined finite resistance, or having an extra resistance 1' of the proper value in series with it, and in which the series element consists of a capacity C. The capacity C may be shunted by a resistance T as in Fig. 6, or by a combination of resistance r, and inductance I as in Fig. 7. Similarly, the resistance 7' in the shunt cir cuit may be shunted by a capacity 0 as in Fig. 7, or the resistance 1' and inductance L may together be shunted by the capacity C as in Fig. 9.

Other. resistances 9', may be added to both the shuht and series elements, as in Figs. 8 and 9, both as a protection against free oscillations and as a means for proportioning the amounts of the different derivatives to be combined in the final wave.

In extending the system further by adding more elements or sections to the correcting network, the respective amount of differentiation introduced by series and shunt elements may be proportioned in any relative value. of one or the other may, in the latter networks, be eliminated by reducing the network to one of the forms of Figs. 10, 11, 12 and 13. The advantage of the forms shown in Figs. 12 and 13 is that there is no danger of free oscillations, as neither contains both capacity and inductance. to be met in the design of such a correcting system is that the combined attenuation for steady state frequencies for the cable and correcting system together shall be fairly uniform within the range of signaling frequencies, or expressed in other words, the product of the attenuation in the cable by the attenuation in the correcting system shall In fact, the differentiating action The requirement be substantially a constant within the signaling range. When'this requirement is met or approached, by using any of the types of networks disclosed by applicant, the correcting network will give a restored wave of a shape approaching that of the transmitted wave, so that not only will the amplitudes of the different frequency components have been restored but the phases of the various components will also have been in a measure restored. That is, the propagation constant of the corrective network is reciprocal in nature to that of the line, and counteracts the distortion of the line as regards both the amplitude and the phase of the waves transmitted through it. Restoring the phase relations of the frequency components to the relations'existing in the waves as transmitted involves providing a higher rate of propagation in the correcting net work for those components of the waves which were less rapidly propagated by the line or cable, and vice versa.

The action of these various series and shunt elements in effecting the change of wave form may best be considered in connection with 3. In this figure, assume that A represents the wave form of the arrival current passing from cable through the ratio arms 6, 8, 10, 9, 7 to earth, caused by the application of a steady potential to thesending end of the cable. Such a current will develop between the terminals 16 and 17 a voltage which is roughly the first derivative B of curve A. Ifthe impedance of the path through the ratio arms is small compared to the cable impedance, and if there were no resistance in series with it, this first derivative would be very closely approximated. On applying this voltage to the first series element, the current through that element, if it be a condenser only with impedance high compared to the impedance of the ratio arms, will be the second derivative C of-the arrival curve A. Similarly, 'the voltage across the first shunt element will be the third derivative D, and the current through the second series element will be the fourth derivative E. However,

as the shunt inductances have resistance in series, and the series condensers have shunt resistances, the final result is not a. derivative curve of any one degree but the sum of the original arrival curve and certain amounts of each of the other derivative curves, which amounts will depend upon the impedances in series with the shunting inductances, and upon the impedances shunting the condensers. There will thus be produced at the ,terminals of the last section of the correcting network a current wave having-approximately the form of curve H, Fig. 4, the characteristic feature of which is the steep front and. relatively flat top. When the time if, required to reach the maxtortion, but by proper design this distortion can be controlled so that it will not sensibly interfere with the proper recording-of signals. For example, in translating the corrected arrival curve H of Fig. 4 to the amplifier system, an ordinary transformer would distort the curve to the form corresponding to curve J, whereas a properly desi ned transformer such as that provided by t is invention will prolong the curve as shown in curve I.

The criterion for such a. properly designed transformer is that the ratio of in- (luct-ance in .henries to resistance in ohms in the primary or cable side of the transformer shall be greater than the time in seconds which may be covered by the maximum probable number of consecutive impulses of the same polarity in the tele graphic'code employed.

The amplifying system is shown in Fig. 1

as a three-stage amplifier employing vac-' uum tube elements of the well-known ther-v mionic type. emitting cathodes 1-9 of these amplifiers are connected serially in circuit with a source of heating current 20. Resistances 21 are inserted in this heating circuit for the purpose of maintaining the respective input electrodes 22 negative with respect to the filaments 19. The output electrodes or anodes 24 are maintained positive with respect to the filaments 19, by means of a direct current source 25 which is connected The filaments or electron;

- to the several anodes 24, in multiple, through the impedances 26.

The operation of such a system is now so well understood as to need only casual reference here. Suffice it to say that changes in potential are developed across the termiacts on the input circuit of the second amplifier to produce in its output-circuit a varying current, and therefore to set up across the terminals of "the resistance 29 a potential variation which in turn controls the current in the output circuit of the third, and in this case, the last amplifier.

The receiving device '30 to be actuated may have resistal'ice-condenser coupling to the last output'circuit, as shown in Fig. 1, or a transformer coupling, or the output circuit may be connected to a second transmission line, either a cable or a land line, the receiving device to be actuated being located at the other end of such cable or land line. 7

Inasmuch as such amplifying systems are customarily grounded, as at 31, the operation of the transmitting apparatus 11 would, if steps were not taken to prevent it, cause a fluctuation in the potential of the terminal 32 of transformer 18 with respect to ground.

Such a fluctuation would, of course, be amplified in the amplifying system, and might cause serious difliculty in the'reception of signals simultaneous-with such local transmlssion. By inserting between the primary and secondary windings of the transformer 18 a grounded shield 33, the secondary winding is effectively shielded from such fluctuating potentials, and this difliculty is done away with. In practice it is furthermore found desirable, owing to the extreme sensitiveness of the amplifier apparatus, to shield the complete amplifier system from extraneous disturbances, such as stray fields, by enclosing the apparatus'in an iron box, preferably lined with copper. Suclr a shield is indicated by the dotted line in Fig. 1.

In the arrangement of Fig. 2 the distortion correction or differentiation of the received signals and their amplification are each effected in alternate succeeding stages. Here the shielded transformer 18 is preferably connected so that its primary winding comprises the two fixed ratio arms 6 and 7, the secondary winding being directly connected to the input circuit of the first amplifier. Under certain conditions it Will be preferable to connect shunt elements 14 across the terminals of each ofthe windings 6, 7. Between the first and second amplifiers are -in serted the two. shunt networks 14 and the series network 13. One of the shunt networks 14 may also serve the purpose of the impedances 26 of Fig. 1, and is so illustrated. A second set of correcting networks is inserted between the second and third amplifiers, whileother correcting networks may be inserted between other ampl' yinmstages, if desired. The main advantage (i he arrangement of Fig. 2 is that the' amplifiers are unilaterally conductive and thus act as an effective barrier to any reactionby the second correcting stage on the first and by the third on the second. This makes it possible to design each correcting stage independently without reference to the stage which is to precede it in the system. It will be obvious that the system is by no means limited to three-stage amplification, that any number of amplifying stages may be employed, and that the amplifying and distortion correction stage may be combined in any arrangement, the primary requirement being that there is produced at the terminals of the receiving device 30 a Wave of such shape as most effectively to operate such" receiving device, and of suflicient amplitude to cause its positive response.

It will further be obvious that the correcting networks which have been disclosed are not limited in their operation to any particular frequency values, but that, depending on their constants, they may be applied to other frequency ranges than those employed in submarine cable telegraphy, so that the invention in its broader aspects relates to wave transmission systems generally.

What is claimed is 1. The combination with a telegraph conductor, of a responsive device, a connecting line between said conductor and said device, the electrical constants of said line being so chosen that the product of the attenuation in said conductor by the attenuation in said line shall remain substantially constant within the range of signalin frequencies transmitted over said conductor and said line.

2. The combination with a submarine cable, of an electric discharge repeater h ving a. cathode, an anode and an impedance control element for amplifying signals received from said cable, and a transformer having a primary winding connected to said cable and its secondary winding connected to the input circuit of said repeater, the ratio of inductance to resistance in said primary winding being greater than the time in seconds covered by the maximum probable number of consecutive impulses of the same polarity occurring inThe telegraphic .code employed.

3. In combination with a telegraph eonductor, an'electricdischarge repeater for amplifying signals received from said conduct-or, said repeater having a cathode, an anode and an impedance control element, a transformer having its primary winding connected to said conductor and its secondary winding connected to said repeater, and a signal correcting network bridged across the terminals of said primary winding.

4. The combination with a'telegraph conductor, of a duplex network, a transformer having a plurality of windings, two of said windings being included in the two ratio arms of said dup ex network respectively,

an amplifying and distorting system having its input circuit connected to another winding of said transformer, and a responsive device connected to the output circuit of said system.

5. The combination with a signaling conductor of a responsive device for indicating the arrival of signaling current waves from said conductor, repeaters for transmitting with substantially equal attenuation all of the'frequencies throughout a wide rangc of frequencies, means for adding to the incoming signal wave derivatives thereof in such proportions as to produce a change in the wave form of the incoming signal waves prior to impressing them on said rcpcatcrs, and a transformer coupling bctwccn said repeaters and said means.

6. The combination with a tclcgraph conductor of a responsive device. mcans intcrmediate said conductor and said dcricc for adding to the incoming wave dcrivativcs thereof in such proportions as to make available at the terminals of said l'r.-ipolll-'i\'o device a wave form substantially likc that ol' the original transmitted signal arc. and a series of directly connected thcrmioaic am plifiers for amplifying said wave prior to its: application to said responsive dcvicc.

7. The combination with a signaling transmission line which attenuates certain frequencies in the signal frequency range differently than other frequencies. of a multi-stage amplifier for amplifying said signals, and a plurality of correcting networks interposed between the various stages of said amplifier. each of which networks corrects in part for the unequal attenuation of said line.

8. The combination with a submarine cable of means for transmitting (lircrt current signaling impulses thereovcr. a plurality of wave shaping networks each of which corrects in part for the unequal attenuation of signaling frequencies by said cable, and. at least two of which perform their maximum correcting function in diil'creut parts of the signal frequency range, and means between said networks to prevent an adjust ment of one from changing the \vavc correcting action of another.

9. The combination with a signal transmission line which distorts the signals, of signal receiving apparatus therefor comprising a plurality of high impedance electric discharge relays arranged in cascade, a substantially distortionless inductive electric coupling for impressing signaling energy upon the first of said relays, and impedance means for shaping the signal wave between said relays.

10. The combination with a signal transmission line which distorts the signals, of signal receiving apparatus therefor comprising an amplifying system, a transformmary winding and additional signal 001'- recting means associated with said amplifying system. 11. The combination with three signal wave shaping means each having coupled reactances and a transmission characteristic having two maxima, of means for causing said wave shaping means to operate in succession comprising wave transmitting means between adjacent ones of said shaping means for electrically coupling them and also for preventing a change in the transmission characteristic of any one of the wave shaping means by a change in another.

12. The combination with a distorting transmission line of three reactive wave correcting units, at least two of which act upon different frequencies in the signal frequency range, wave transmitting means between adjacent units for electrically coupling them and also for preventing a change in the wave correcting action of any one of said units by a change in another one.

13. The combination with a. submarine cable, of means for impressing direct current signals thereon, an electric discharge amphfier having an anode, a cathode and an impedance control element, an inductive coupling transmitting all signal frequencies with substantially equal attenuation for transferring energy from said cable to said amplifying means, and reactive signal wave shaping means in circuit between said cable and said inductive coupling for correcting in part at least for the signal wave distortion produced by the cable.

14. The combination with a transmission line of a duplex bridge terminal arrangement therefor, a transmitting battery connected to the apex of said bridge, a transformer having its primary connected across said bridge, an electric discharge repeater having a cathode, an anode and an impedance control element, the terminals of the secondary of said transformer being connected res ectively to said cathode and to said impe ance control element, and a conductive connection between said cathode and ground, and a grounded shield between the windings of said transformer to prevent duplex jar. l

15. The combination with a transmission line which greatly attenuates transmitted signals, of a conjugate terminal arrangement therefor comprisin receiving and transm1t ting a 'paratus, sai receiving apparatus be- I ing ba anced w1th respect to transmitted current and including a high power amplifier for amplifying said greatly attenuated signals, a transformer associating said receivingapparatus with said cable and transmitting apparatus, and a grounded shield between the primary and secondary windings of said transformer to prevent electrostatic changes in said transformer .produced by said transmitting apparatus from reaching said amplifier.

16. A system for equalizing for variable line attenuation of currents of different frequencies transmitted thereovercomprising a circuit having conductors connected in series relation with said line and a circuit connected across said conductors including a capacity and an inductance in parallel and a resistance, said capacity, inductance and resistance being proportioned with respect to one another and to the constants of said line so as substantially to counter-balance the effect on said currents of the unequal attenuating property of said line.

17. In a signaling system, a transmission line over which waves of higher frequencies become attenuated in transmission to a greater extent than waves of lower frequencies, meansincluding a correcting network arranged to be traversed by the waves transmitted over said line for compensating for the difference in attenuation in said waves of dlfi'erent frequencies, and a unidirectionally conducting device connected be- I tween said line and said means.

, 18. In a transmission system, a line, the attenuation of which differs for different frequencies of current transmitted thereover, a two-stage amplifier for amplifying-currents of different frequencies received over said line, and an attenuation equalizing circuit connected between the two stages of said amplifier for correcting for the unequal at- }:enuation ofthe currents received over said we. r

19. In combinatiqn, a line for transmitting currents of different frequencies with distortion, an amplifier associated with said line, a network associated with said line throu h said amplifier for correcting for the line distortion, said network comprising resistance, inductance and capacity, and having distorting properties for the transmitted currents substantially complemental to the distorting properties of said line.

20. In atransmission system, a transmission line, the attenuation of which varies -with the frequency of the currents transmitted thereover, a repeating system associated with said transmission line and com .prisin an impedance, and an auxiliary circuit t "e attenuation" of which varies with the frequency of the transmitted currents in a manner complemental to that of the transmission line so that the resultant transmission over the line and auxiliary circuit; is substantially constant over a desired range of frequencies, said auxiliary circuit being associated with the transmission line only through said impedance.

' desired range of the currents transmitted over said line will be transmitted over the systcm with substantially uniform attenuation.

22. In a transmission system, a transmis sion line over which higher frequencies are transmitted with greater attenuation than .lower frequencies, and an attenuation equalizer associated with said line, said) attenuation equalizer comprising a parallel-series combinatlon of resistance, lnductance and capacity elements so proportioned and related to each other and the line as to increase the attenuation of lower frequencies transmitted over said line and through said equalizer to such extent that all frequencies within a desired range will be transmitted over the system with substantially uniform attenuation.

23. In a transmission system for transmitting currents of a range of frequencies, the combination of a line having different values of attenuation dependent on the frequency of current transmitted thereover,

and an attenuation equalizer comprising a.

parallel series combination of resistance, inductance and capacity elements proportioned with respect to each other and the line constants to produce a total resultant attenuation for the system substantially constant over the ran e of frequencies transmitted.

24. In combination, a. line for transmitting currents of different frequenciesvwith dis tortion, an amplifier associated with said line, a. network associated with said line through said amplifier for correcting for the line distortion, said network comprising resistance, inductance and capacity, and having distorting properties for the transmitted currents substantially complemental to the distorting properties of said line.

25. The combination with a line having a non-linear relation between the frequency of the ,wave components. transmitted thereover and the variations in the phases of the transmitted wave components, of a localized network connected in series relation to said line and comprising more than one section and having a non-linear relation between the frequency of the wave components transmitted through it and the variations in the phases of the transmitted wave components, the phase variations introduced by said network being opposite in sense to those a of said line and such that said network counteracts the effects of the said non-linear frequency-phase variatlons of $9.16. line.

with a signal transmission line having an attenuation which varies throughout the frequency range of the signals transmitted thereover, and having sufficiently great capacity. to cause the Velocity of wave propagation of the different frequency components in the signals to be sensibly different, of a network connected in series relation to the line and having more than one section, each section being of the type comprising a series and a shunt arm one of which contains reactance, the constants of said network being so related to those of said transmission line, that said network produces in the signal waves transmitted over the line and the connected network an attenuation which varies with frequency in a manner opposite to that of said transmission line, and also partially corrects for the effect of unequal rates of propagation of the different frequency components of the signaling waves of said line.

28. The combination as claimed in claim 26 in which the ratio of the series to the shunt impedance of each section of said network increases with increasing fre uency throughout the signal frequency ban 29. The combination with a signal transmission line in which the rate of propagation of the higher frequency components in the signal frequency band transmitted thereover is higher than that of the lower frequency components. of a localized network connected in series relation with the line and comprising recurrent sections, said network having the property of propagating the lower frequency components of the signaling-band at a higher rate than the higher frequency components.

30. The combination with a signal transmission line which produces amplitude and phase distortion in the transmitted signals of a localized network comprising an impedance in series relation to the line and a plurality of impedances in shunt relation to the line and connected to different points along said series impedance, said network having its constants proportioned with respect to those of said line to compensate for said amplitude and phase distortion in the transmitted signals. a

In witness whereof, I hereunto subscribe my name this 15th day of June A. D., 1918.

ROBERT C. MATHES,

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