US1778377A - Telegraph repeating device - Google Patents

Description

Patented @at 14, 193@ UNITED STATES- iguaa'zfz PATENT i carica' Y EVEBETT T. BURTON, OF'MILLBULBA, NEW JERSEY, ASSIGNOB. T0 BELL TELEPHONE LABORATORIES, INCORPORATED, OF NEW YORK, N. Y., A CORPOMTION OF `HER? Yoan Y TELEGRAPE BEPEATING DEVICE .Application filed July 18,

This invention relates to marginal repeating devices-and particularly to thermionic relays of the type which, in response to an input voltage exceeding a predetermined value, produces in an output circuit a voltage of substantially constant value independent of the exact value of the input volt.-

a e.\ gAn object is to increase the reliability and to reduce the maintenance expense o a repeating device of the above type.

Another Objectis to adapt a thermionic marginal repeating device or three element operation. x

Heretofore, two general types of repeaters .have been employed, i. e., electromagnetic relays and vacuum tube ampliiers. Electromagnetic relays have been commonly used for reproducingsquare top waves such as are used in telegraphy, while vacuum tube ampliers have been preferred for reproducing without distortion, waves of varying intensity. y p

However, arepeating circuit for telegraph signalshas been proposed which utilizes vacuum tubes in place 'of electromagnetic relays and which may produce in its output. circuit a substantially square topped wave. United potential at which the space current becomes constant depends on the characteristics of the filament and on its temperature. The characteristics of the filament may change during its life, and the temperature, which is a function of the filament current, may change .from time to time.

In accordance with thisl invention the maximum space current of a square top wave 1928. Serial No. 293,772.

repeater tube is limited by a resistor in the plate circuit and/ or a resistor in the grid cir`- cuit which eliminate variations in the maximum space current due to variations in the emissivity of the filament. Another feature' of this invention is acircuit utilizing two vacnum tubes for repeating three element signals, that is, signals comprising positive, negative, and zero impulses. Y

Fig. l of the accompanying drawings is n diagram showing one arrangement oi apparatus suitable for practicing the invention.

Fig. 2 is a diagram containing a curve which shows the grid voltage-anode current characteristic of a suitable type of vacuum tube when used in the circuit of Fig. l.

Fig. 3 is a diagram containing a curve which'shows the relation between the input voltage eg and the output voltage e1 of the thermionic relay tube circuit in Fig. l.

Fig. 4 is a diagram containinoF curves representing two-element telegrap signals be- Vfore transmission over a cable, after transmission, and after being repeated bythe relay circuit of Fig. l. Y

Fig. 5 shows a modification-of the circuit of Fig. l. Y Fig. 6 is' a diagram containing a curve which shows the relation between the input voltagelcg and the output voltage e2 of the two tube relay circuit in Fig. 5; and ,d

Fig. 7 is a diagram containing curves which show two element telegraph signals before transmission over a cable, after transmission, and after being repeated by a relay circuit in accordance with Fig. 5.

pemtz'onofoffze circuit of Fig, 1.-In the system diagrammatically shown in Fig. 1,

signals received over a cable conductorl are amplied, by an amplifier Arend applied to Y the input circuit of a vacuum tube relay circuit comprising a relay tube RT. This tube i is preferably of a type 4which has a high ampliiication factor and which; with the vproper value of anode potential for use in this cir-u cuit, has a grid voltage-anode current characteristic curve similar to curve 12 1n Fig. 2.

' Ihis characteristic is very steep so that the anode current-becomes zero ,with a negative potential of only a few volts on the grid.

Greater negative values of grid potential can therefore produce no further changes in the` output current of the tube. ,On the other hand, when the grid becomes positive the anode current would normally increase until limited by the electron emission of the cathode. To prevent further changes in the plate current when the grid potential exceeds a predetermined positive value, la resistor 5,

having a resistance considerably higher than;

the normal output impedance of the tube, is inserted in the anode circuit, and a resistor I4 is inserted in the grid circuit. These limit the anode current to a definite maximum 1 value asshown by curve 13 in Fig. 2; The

manner in which they function will be exstantially twice that with zero grid, and the that of battery 6 and in the opposite sense.

Aing the value of e1 from zero to plained later.

Wh no signals are received over cable 1 the voltage@g between the cathode and grid i of the relay tube RT is zero and the anode current is at its mean value as may be seen by referring to Fig. 2. Under these conditions the total voltageof the two equal sections of the anode 'battery 6 and 7 is equally divided between the .space path in the tube and the resistor 5, since their resistances arel va value greatly in excess of that whicl1,when v applied to the grid of RT, is suflicient to reducethe4sp'ace current to zero. With the anode current reduced to zero the voltage drop across the resistor 5 becomes zero,thus raisthe voltage of battery 6. l

On the other hand, a positive impulse from the-cable of approximately the same value as the preceding negative impulse reduces the output impedance of the tube'RT to a value small as compared to that of resistor 5 that the` anode current is determined, to a large extent, by the. latter impedance alone. Since, as stated above, the resistance of re- A sistor 5 is made high in respect to the normal cathode-anode impedance of the tube, the anode current with a positive grid is subvoltage drop across the element 5 is twice The voltage e1 is, therefore, equal in value v'but of opposite polarity to what it was when the grid of tube RT was negative. The relation betweeneg-and el' is shown graphically in Fig. 3. For all values of eg in excess of small fixed positive and negative values el is constant.

The grid-resistor 4 may, or may not, hav an appreciable limiting. effect on the maxiance relative to that of the resistor 5 and to mum space current, depending on its resist- 1 the cathode-grid and cathode-anode resist-` ances of the tube when the grid is positive with respect to the filament. Thus, when a positive impulse Ais received the grid becomes positive with respect to the filament and at` tracts electrons. If 'resistor 4 'has a sulficiently low impedance the electrons can leave the grid as fast as they accumulate'and thel grid will remain positive. Under these conditions the maximum current will be "con-I however, the resistance of resistor 4 is sufli.- ciently great, the grid potential becomes rtrolled largely by the anode resistor 5. 'Iff 'much less than the input potential, due to the' drop of potential along resistor 4, and the grid will no longer alter thespace current.

InFig. 4 the curve 14 indicates a series ofl square-topped' waves representing telegraph signals. After being transmitted over a conductor such asa submarine cable these waves become rounded as shown in curve 15, and

if they are not restored, or at least partiallyl restored, to their 'original square-topped shape before being retransmitted over a second cable, they may be unintelligible when' finally received. A repeater'in accordance with the circuit of Fig. 1 repeats waves re` ceived in the form lshown by curve 15 as flatvtopped Waves ofthe type shown in curve 16.

The horizontal lines above and below the zero llne 4in curve 15 represent the values of eg at Iwhich e1 becomes constant. Except for short" periods when eg is changing from positive to negative, or vice versa, the output wave is flat topped and of constant amplitude.

Since the output resistance of relay tube ART and theresistance of resistance element 5 are relatively large, the relay is incapable of supplying an appreciable amount of current without reducing the value of the output voltage el. It therefore should work into an extremely high impedance, voltage operated device such as a vacuum tube amplifier. Such an arrangement is shown in Fig. 1. The-transmitting vacuum'tube TT may be a tube of relatively low output impedance 'and therefore capable of handling considerable power. A grid biasing battery 17 is insertedl to prevent distortion and particularly to prevent the grid of transmitting tube TT from becoming positive and drawing current from battery 6., As an additional protectionv against the grid drawing current a large resistance 8 is inserted irl" series with it.

If the repeater tube RT has a suiiiciently 1 high amplification factor and the voltage.- of

the anode batteries 6 and 7 is sufficiently low,

both the upper and the lower inflection points of the characteristic curve 13 in Figa-2 may be very sharp. 0n the other hand if a `tube having -alower amplification factor, together with an anode battery of high voltage, is used, thelower inflection point of curve. 13

lill) .in 2 may become less abrupt. Since when the anode current of tube RT is zero,

the voltage e1 is at its maximum possibler avoided bymaking the voltage of biasing battery 17 slightly less than the maximum value of voltage e1, and making the impedance of resistor 8 veryilarge comphred' to the filament-grid impedance of tubeTT when the grid of the latter is positive with respect to its filament. In operation, when e1 approaches its maximum positive value, current flows through resistor 8 and produces a voltage drop which checks any fur- I 20 ther change in the potential of the grid of tube TT, and in the output current`represented by curve 16 in Fig. 4. In brief, with this arrangement tube RT squares up the positive halves of the waves represented by curve 15 and inverts the wave. Tube TT thereupon squares the positive half of the inverted ,/'f' wave and reinverts it so that the output wave represented by curve 16 is in phase with `the input wave and has both its positive and p negative halves restored to a iiat topped sha pc more nearly resembling the original Wave shown in curve 13.

A shunt resistance 3, which :is small as compared to the average input impedance o l the tube, is connected across the input circuit of tube RT. Therefore, variations `in the input impedance of the tube as the potential of its grid changes from'one polarity to the other have negligible effecton the in- ,43' put voltage es.

Operation of the of Fig. 5.-Fig. 5

- f discloses a modification of the circuit of Fig.

1. I t contains-two,tubes with their input A circuits in parallel and with equal, but op- 5 posite, biasing voltages'on the twogrids. It

is designed for use as a three-element relay, that is, one capable of repeating eitbher positive, negative, or zero impulses depending onwhether the input voltage exceeds given 0 .positive or negative values or lies between the two. Y The output' circuit of the lowertube lRT2 is similar to that of tube RT in Fig. 1. The upper tube RTl has its anode connected to the anode of the lower tube RT2 through 5 an additional resistor 18 which has the same resistance as resistor 5. Y Y y The grid biasing batteries 22 and 23 have values such that'when eg is zero the cathodeanode resistance of tube RTl is low in com- C) parison to that of the two anode circuit resistors 5 and 18. Therefore, the two anode battery units 6 and 7 are, in effect, connected directly across-the two plate circuit resistances 5 and 18 and the voltagedrop in resistor 5 due to the anode current flowing therethrough is practically equal, and opposite,

to the voltage of battery 6. When eg is zero,

the grid of tube RT2 is maintained at such a negative voltage by biasing battery 23 that its space currentis blocked. The voltage e2 measured across resistance element 5 and battery 6 is therefore approximately zero.

(as eg becomes equal and opposite to the voltage ofl battery 22) with respect to the filament, the anode current rapidly decreases and passes from its previous maximum value to zero with a change of only aew volts in the grid potential. The anode current is then reduced to zero, and since there is no current fiowing through and no voltage drop in resistance element 5, e2 rises to the value of battery 6.

On the other hand, when the input voltage eg changes from zero to positive no change occurs in the output voltage c2 until the input voltage eg becomes nearly equal and opposite to the voltage of battery 23, whereupon space current begins to flow through the lower tube RT2. Vith a slight additional increase element 5. The eect of the lower tube RT2 becoming Conductive is to short-circuit resistance element 18 and connect battery 6 and 7 directly in series with resistor 5. This practically doubles the current flowing from battery 6 and 7 through element 5 and changes e2 to a value equal but opposite in polarity to the value it had when eg was negative.

The operating characteristics of the relay circuit of Fig. 5 are shown graphically in Fig. 6. Within certain positive and negative values of eg, e2 is zero, whereas if eg is increased in either a positivev or negative direction beyond those limits, e2 rapidly rises to a new constant Value. T he operating margin of the relay, which determines the values of eg for which e2 remains zero, may be regulated, within limits, by properly choosing the potentials of the grid biasing batteries 22 and 23. Thus if the biasing batteries are removed entirely the curve of Fig. 6 assumes the same shape asA that f Fig. 3.

The curves of Fig. 7 illustrate one useful application ofthe circuit o Fig. 5. Curve 19 represents, graphically, square-topped telegraph signals consisting of various combinations of positive and, negative impulses olifY ceived after transmission over a long cable is shown 11i curve 20. There is a greater disparity between the amplitudes of the short -and the long impulses than is shown in curve l5 of Fig. 4 because it is assumed the signals have been transmitted over a cable of greater length, or greater attenuation per unit length, or both. 'lhe unit impulses in curve 2O areA too vweak to operate a recording device and must be restored by a regenerative receiving device.a Since in a system employing a regen.- erativereceiver the impulses of unit length vare not needed at the receiving end of the y undesired unit impulses may be readily suppressed at a repeating point by passing the signals corresponding in shape to curve 2() through a repeating circuit in accordance with Fig. 5. y

When the circuit of Fig. 5-is used for the above purpose the voltages of biasing batteries 22 and 23 are so chosen that the inflexion points 25 and 26 in the curve of Fig. 6 occur at values of eg greater .than the maxi- Amum value of the received unit impulses.

These values of eg are represented by lilies 2 7 and 28 in Fig. 7 The values of eg corresponding to theinflexion points 23 and 24 in Fig. 6 are represented by lines 29'a'nd 30 in Fig. 7 The latter values of eg are .natu-A rally greater than those corresponding to inflection points 25 and 26 of Fig. 6 but are substantially less than the maximum voltages of the received waves representing impulses ot greater than unit length. .N Since, as disclosed by curve 20 of Fig. 7; the the maximum values of the received unit impulses are always less than the Valuesof eg corresponding to the inflexion points 25 and 26 in the curve of Fig. 6, these .impulses VVwill have no eect on e2, which is normally zero. Therefore, a zero impulse is repeated, as shown by curve 2l of Fig. 7;

When apositive impulse ot greater than unit length is transmitted the received impulse is of such magnitude as to exceed the values of eg corresponding to iniiexion points 25 and 23 and a flat-topped wave isretrans- .-mitted. Likewise, a negativeimpulse of greater' than unit length is received with such strength-that its voltage exceeds that of eg corresponding to inflexion `points 26 and 24 of Fig. 6 and another Hat-topped wave of l opposite polarity to the preceding one is rer-transmitted.

,The circuit of Fig. 5 is not limited in its utility to the repeating of two element signals in which short impulses are to be suppressed but may be used to advantagel in many places where three element signals are' to be repeated. Like the circuit of Fig. 1 it is of particular advantage where the frequencies of the impulses to be repeated are higher than those at which mechanical relays operate satisfactorily. What` is claimed is:

1. In a device for repeating electric waves which comprises a vacuum tube having a cathode, grid and anode, the method of attenuating all portions of said waves between Y an amplitude capable of saturat-ing the tube C cathode, grid and anode, the methodof attenuating all portions of said waves between an amplitude capable of saturating-the tube and a predetermined lesser amplitude which comprises superimposing a polarizing voltage on said waves and applying them between the grid and cathode of said tube through an impedance high relative to the cathode-grid impedance ofthe tube when the grid .is positive with respect to the cathode.

3. The method of relaving an alternating current wave by means of a vacuum tube repeating device comprising two tubes connected in cascade'relationshiu which comprises attenuating all portions if said wave between the amplitudes capable of saturating the vacuum tube and predetermined positive and negative -amplitudes less than said saturating amplitudes and not attenuating. portions not in excess tof said predetermined amplitudes by limit-ing the maximum anode current of each tube.

`4. The method of converting a rounded wave of alternating cur-rent into a substantially flat topped wave which comprises attenuating the positive portions of said wave between the ,maximum and a predetermined amplitude, inverting said wave, attenuating the positive portion of said inverted wave in excess of said predetermined amplitude, and reinverting said wave.

5. In combination, means for attenuating all portions of an alternating current wave between the maximum anda predetermined positive amplitude and for inverting said waves, and second means for attenuating all portions of the inverted wave in excess of the predetermined positiveampltude, and for 'reinverting the Wave. I

with the grid thereof tor attenuating all portions of an alternating current wave between the maximum amplitude and a predetermined positive amplitude and Jfor inverting said waves and second means for attenuating all portions of the inverted wave in excess 'and an anode with a source ofbiasing potential and a resistor connectedin series with the grid of said tube, said resistor having an impedance high as compared to the cathodegrid zeista'nce of the tube when the grid is positi fwith respect to the cathode.

8.111 combination, a source of E. M. F., the potential of which varies in each direction in excess of predetermined limit-s, with a marginal translating device and a potential responsive device, characterized in this that said marginal translating device' comprises a vacuum tube having a cathode, grid, and anode with said source of varying E. M. F: connected between said cathode and grid, a source o plate potential of constant value and a resistance element connected in series between said cathode 'and anode, said voltage responsive device being connected in shunt across said resistance element and part-of said source of plate potential of constant value, the grid potential-plate current characteristic ofthe tube and the value of the plate circuit resistance being such that for positive grid potentials in excess of said predetermined limit'the cathode-anode impedance of said'tube is small compared to. saidresistance and for negative grid poten- -tials in excess of said predetermined limit the cathode-anodedmpedance of said tube is large compared to said resistance.

9; In combination, a source of E. M. F., the potential of which varies ,in each direction in excess of predetermined limits, with a marginal translating device and a potential 4responsive device, characterized in this that said marginal translating device comprises a vacuum tube having a cathode, grid and anode, with two resistances connected in series between said cathode and grid, one of said resistances 'having an impedance' large as compared to the cathode-grid impedance of the tube with' positive grid, the other rcsistance being small relative to the first impedance and having connected in shunt to it said source 'of E. M. F., a source of anode potential of constant value and said potential responsive device connected in the cathodeanode circuit of said tube, the characteristics of the tubev being such that for applied posi- Ytive potentials in excess of said predetermined the grid-cathode voltage is substantially constant and for; applied negative potentials in excess of said predetermined limits the cathode-anode current is substantially zero. s 10. A marginal relay comprising a vacuum tube having a cathode, a grid, and an anode, two resistors connected in series between the cathode and grid, one having an. impedance large as compared to the cathode-grid impedance of said tube with positive grid and that adjacent the cathode having. an impedance substantially less, a source of input voltage connected in shunt to said second resistor, a source of plate potential of constant value and a third resistor connected in series between said. cathode and anode, the resistance of the third resistor being large as compared to the direc-t current resistance between the cathode and anode of the tube when a positive voltage in excess of a denite value less than the maximum value of saidl input voltage is impressed across said second resistor and small as compared to the cathodeanode impedance when a negative voltage corresponding in magnitude is impressed. across said resistor, and a voltage responsive device connected across Saidthird resistor and a portion of said source of plate potential.

11'. A marginal'potential translating device havin input and output lterminals, comprising a` rst and a second vacuum tube each having ,a cathode, control electrode and anode, the cathodes of said tubes being connected together and {to one input terminal and the grids associated with each other and with the other inputE terminal, a resistance element and source of constant potential connected in series between the cathode and anode of the first tube, said resistance element and source of constant potential and a second resistance connected in series between the cathode and anode of the second tube, said output terminals? being connected in shunt across said resistance element and a portion of said source of anode potential, and the value ofsaid resistance element being large compared to the cathode-anode impedance' of said tubes when their grids are positive with respect to their filaments.

12. vA marginally loperative potential translating device for4 repeating three element signals comprising apparatus as set forth in claim 1l further characterized in that there is inserted in a grid circuit of each tube a source of polarizing potential Whereby'the grid of the first tube is npqrma'lly negative with respect to the cathode and the grid of the second tube is normally positive with respect to the athode. v

13. A marginal potential` translating device having input terminals and output terminals comprising a first and a second vacuum tube each having a cathode, grid and anode, an impedance element'eonnected beanode ofthe same tube through said impedance' element, a second impedance element connected between said input terminals, n connection between one of said input termif nals and the cathodes of said tubes, a third impedance element and a. vfourth impedance element and connections between Said otherinput terminal and a grid of each tube through said third and fourth impedance elem ments respectively.

14. A marginally operative potential translating device as. described in claim 13 further characterized in this, that'the grids of the tubes are equally and loppositely biased i5 with respect to the cathodes.

In witness whereof, I hereunto subscribe my name this 16th day of July, 1928. EVERETT T. BURTON.

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