US1257381A - Low-frequency-signal repeater. - Google Patents

Description

n.w. NICHOLS. LOW FBEQUENCY SIGNAL REPEATER. APPLICATION "LIED SEPT. 2. I915- Phtented Feb. 26, 1918.

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UNITED STATES PATENT orrron.

HAROLD W, NICHOLS, 0F MAPLEWOOD, NEW JERSEY, ASSIGNOR, BY MESNE ASSIGN MENTS, TO WESTERN ELECTRIC COMPANY, INCORPORATED, A CORPORATION OF NEW YORK.

LOW-FREQUENCY -SIGNAL REPEATER.

Specification of-Letters Patent. v

Patented Feb. 26, 1918.

Application filed September 24, 1915. Serial N 0. 52,509.

.vented certain new and useful Improve ments in Low-Frequency-Signal Repeaters, of which the following 13 a full, clear, concise.,and exact description. Y

This invention relates to a method of and apparatus for the repeating of messages from, one submarine cable or similar line to another. Its object is to amplify and re peat in one line low frequency currents originating in another without destroying the property of duplex operation of either line, and' to perform this operation efiiciently and with fidelity.

These objects are'aocomplished by employing auxiliary circuits between the two lines in question, supplying these circuits with lternating current, varying the characteristics of the currents in these circuits by means of the incoming signal, and translating these variations to the forms of signals to be transmitted to the outgoing lines. These operations are desirable for reasons which will appear in the following discussion of the problems involved in the efiicient repetition of signals betweentwo duplex cables, telegraph lines or, other circuits carrying low frequency signaling currents.

It has been found that repeaters of the mechanical type, for example, those in which an electromagnetic receiving device actuates a microphone, are not suitable tor 'use in connection with .lowfrequency signaling circuits. On the' other hand, the thermionic repeater of the audion type, by reason of its high sensitiveness and its freed'o'm from distorting effects, is especially fittedfor this kind of work. Thisrepeater consists of an electron-emitting cathode, an anode, and an auxiliary electrode, all inclosed in an evacuated vessel.

'An important feature of this device in connection with this problem is that its input circuit and its output circuit necessarily have one point in-common, since the repeater has but three terminals. This fact introduces into the problem of repeat?- from one duplex cable to another some di culties which are overcome in this invention;

and which will be explained in connection with the drawings.

In these drawings, Figure 1 shows the circuit arrangements of two duplex cables terminating at a repeater station; Fig. 2 shows a method of repeating from one of these cables to the other in accordance with this invention; and Fig. 3 shows a modified form ofthe' invention in which greater amplification of signals is secured. In all. of these figures, corresponding parts are denoted by like numerals.

Referring to Fig. 1, 1 and 8 are cable condoctors and 2 and 4 their balancing artificial cables introduced, as usual, to permit duplex operation in connection with the condensers 5. 6 represents a ground connection.

In receiving a signal over cable 1 the re I ceiving instrument is connected to the re; ceiving ternnnals 7-8, and in sending through this cable an ele'otromotive force is the condensers 5 are equal, this sending electromotive force produces no difi'erence of potential between the terminals 7-8, and, consequently, the receiving instrumentv is not affected in sending fromthe station at which it is located. Duplex operation is therefore possible over these two cables, and its success dependsupon the accurate simulation'of the actual line by its artificial line.

'Now, if it is-desired to relay signals from cable 1 to cable 3, it will be necessary to connect the receiving terminals 7 -8 of cable 1, through an amplifier, with the transmitting terminals 1237, of cable 3, and simi larly terminals 1011 with terminals 359 and, as stated before, it is desirable to use the thermionic amplifier for this purpose.

connection between input and output circuits, and an examination of Fig. 1 will Qaow that no matter how such an amplifier is connected fromthe receiving terminals of one cable to the transmitting terminals of the other, it will short-circuit one of the lines and destroy the property of duplex operation- 1 There must be 11;; conducting path, except for the earth, :{xfom one cable to the other if duplex operation is to be maintained. To

, amplifier, to the transmitting terminals of the other cable.

This is the invention of another and is, moreover, open to theserious objection that the transformation of currents, ofthe wave forms and frequencies used in tclegraphy,

is not eflicient and that it requires specially designed and expensive transformers. This invention eliminates the necessity for inefiiciently transforming currents of the low fundamental frequency and complicated wave form here encountered, and substitutes therefor efiicient transformation of sinusoidal currents of a single relatively high frequency in a manner more completely de scribed in connection with Fig. 2 which represents a preferred form of'the invention, and also in connection with Fig. 3 in which an additional amplifier is used tosecure greater amplification.

Referring to 'Fig. 2, numerals 35, 37 and 1 to 12 inclusive, represent two duplex cable terminals, as explained in connection with Fig. 1. 13 is a thermionic amplifier of the audion type whose function is to amplify the potential difi'ere'nceover the resistance li'inscrted between the receiving terminals, 78 of the first cable, Its action is as fol- .lows: When a potential difference is established over the input terminals of 13, the effect is to change the current set up by the battery-16 in the output circuit of'the amplifier, which includes resistance 15. The

change in voltage drop over 15, due to that input otential difference, is much greater than t e latter. Another function of the amplifier 13 is to prevent the reaction upon the incoming cableof the current in the apparatus next to be described. This effect is secured because the thermionic amplifier is a nnilaterahdevice and permits the transfer of power in but one direction through it.

17 is another amplifier adapted to act as an oscillation gcneraton Any amplifier, when arranged so that power may be fed back from its output circuit to its input circuit, for example, by inductively connecting these circuits, will oscillate freely if the amplifying power is sufiiciently large. The

power, represented by this free oscillation isdrawn from thebattery inthe output circuit. In the oscillator of the figure a tuned circuit, comprising coil 19 and condenser 20, is included in the output circuit, while the input circuit in ludes half the coil 19, due to the fact that t e filament or cathode of the repeater is connected to cpil9 at the point 21. Since the two halves the coil further increase 19 are related by mutual inductance, the two circuits are inductively connected and the device acts an alternating current generator of oscillations whose frequency is de termined by the tuned circuit 1.9 20.

The input circuit of this oscillating amplifier is also connected across resistance 15, by which connection the amplified signal voltage is impressed upon the input circuit of 17, preferably through the battery 18, which is used to maintain the potential of the grid at a suitable value with respect to that of the filament. The effect of impressing this variable signal v'oltage upon the amplifier 17 is to change its amplifying power and, therefore, to vary the amplitude of the alternating current in its output circuit in accordance with the signal received oven the cable 1. This method of modulating. the amplitude of an alternating current is not the invention of this applicant and is not claimed in this 'ipplicaton.

The coil 19 is inductively coupled to coil 22 of the tuned circuit 22--24, and since. now .a pure alternating current of relatively high frequency is in question, the transformation by the transformer 19-22 is efiicient in contrast to the ease in which the signal waves themselves must be transformed.

It is now necessary to rectify this modulated current so that the effect of the-high frequenc ylplternating current shall be elimia low impedance) as follows: Suppose that an impulse of positive potential with respect to the filament 'is impressed upon the grid circuit so that the grid becomes positively chargcd. This char e will now be ra idly neutralized by the ow of electrons rom the heated filament to the grid. If now this positive impulse is followed by a negative impulse, the negative charge remaining upon the grid will be still current in the audion, whose magnitude is governed by the charge upon the grid, will be decreased more than would be the case if the negative charge first mentioned had been "free to leak away. It is prevented from so doing by the condenser 26. Howand, therefore, the space ever, it is not desirable to retainthis negative charge upon the grid indefinitely, and to prevent this the resistance 25 is shunted about the condenser. This resistance is so large that the leak of current through it in a time comparable with the period of the highfrequency oscillation is small, butthisleakage path is marleof sufficiently low resist ance to permit the complete discharge of the 7 grid in the longertime elapsing between sigelement. As in the operation of any recti-- sense 1 nals. The efi'ect of this combination of resistance and. capacity is, therefore, to increase therectifying effect of the thermlonic fier, it'responds onl to the envelop of the high frequency oscillations, that is, it produces in its output circuit a direct current upon which is superposed a current of the wave form of the'signal received from .the

first cable. The high inductance choke coil -27 permits the free assage of the necessary direct current in t e output circiiit of 23 while ofiering a high impedance to the signal currents superposed upon it, which latter are therefore impressed upon the transmitting terminals l2'*-37 of the outgoing cable, preferably'through condenser28. A condenser 32 is preferably added in the output circuit of am lifier' 17 to prevent the short-circuiting o resistance 15. A similar system of... circuits leads in the opposite direction-{that is, from the receiving terminals lO-l'l'to the transmitting terminals 359.of the first cable.

Fig. 3 represents an arrangement similar to Fig.2 eiicept that an additional amplifier is added to still further increase the energy "of the repeated signals impressed upon the second line. In this arrangement the tuned circuit 22, 24 instead of being directly connected to the rectifyin element23, is now connected to the input e ectrodes of the thermionic am lifier 30. The output circuit of this a'mpli er is completed through the re sistancc 31 and contains an energizing bate.

' tery as shown. The rectifying element 23 is then connected across the terminals of resistance 31.. This modifies. the operation of the device only in so far as it increases the ,voltage supplied to the rectifier, and consequentlyvincreases the value of the rectified current. An advantage secured by tlieuse of this amplifier, in addition to the greater 'power obtained, is that the thermionic element, when acting as a rectifier, is more efli cient when the voltage impressed across its input terminals is large. In all other respects this arrangement is similar to that s own in Fig-2.

Although this invention has been shown as applied to the amplification of signals from one duplex cable to another, it is obvious that its advantageous use will not'be restricted to thi's'type of apparatus. Its use may be desirable in any system requiring the transformingor'repeating of low frequency si als. I ifhat is claimed. is:

L In combination with two duplex lines having receiving and transmitting terminals adapted for electrical. signaling with .low frequency currents, a device for relay- "ing signals from one to the other of said lines, a .similar'device for relaying signals in the opposite direction, means for pro-.

viding for non-interference between said devices, each of said devices consisting of a circuit, means for producing therein electrical oscillations capable of eificient trans formation, means for varying the character of said oscillations in accordance with a signal received from one of said lines, said varying means comprising a resistance shunted across the receiving terminals of said line, anamplifier having an output cirwit, and a transformer whereby the effect of said variable oscillations is communicated to said amplifier and therebyaug- "mented, a detector connected with said output circuit, and means for impressing upon the other of said lines the detected current. 2. In telegraphy, two duplex lines adapted to transmit low frequency signals, each line having'separate receiving and transmitting terminals, the combination with the transmitting terminals of'one line and the receiving terminals of the second line, of a circuit containing a modulator wherein is developed an alternating CUI1Ilt,. Jf a ther 'mionic amplifier interlinked with said circult and with the receiving terminals of the first of said lines whereby the amplitude of the alternating current is varied in accordance with the electrical signals in said line.

of a transformer for inductively communicating the oscillations in said current to a second circuit, of a thermionic detector whose input electrodes are connected to said second circuit, the transmitting terminals of said line being so connected to the output circuit of said detector as to be in fluenced by the rectified currents appearing in said output circuit.

3. In telegraphy, two duplex lines adaptedto transmitlow-frequency signals, the

combination with the receiving terminals i transmitting terminals. v

4, In telegraphy, two lines adapted to transmit low frequency signals, each line having separate receiving and transmitting term'inals, the combination with the'trans-" mitting terminals of one line, and the receiving terminals of the second line, of'a resistance shunted across said receiving terminals, of an oscillati )1! generator wherein is deyeloped an alternating current, of a therng' omoiamphfierhaving an input cir- .cuit and an output circuit, said resistance serving, as a means, for impressing the electrical signals insaid line uponsai'd input circuit, of means for directly impressing the amplified signals in said output circuit upon said oscillatlon enerator, whereby the amplitude of the afiernating current is varied in accordance with said signals, of a ther mionic detector having an input, circuit and an output circuit, of a transformer for inductively communicating the oscillations in said-current to the input circuit of said detector, the transmitting terminals of said line being so connected to theoutput circuit of said detector as to be influenced by the detected current appearing in said output circuit.

5. In telegraphy, a duplex line, a vacuum tube repeater containing a cathode and an auxiliary electrode said line terminating in said electrodes and 6. In telegraphy, a duplex line, two shunt paths across said line, one of said paths auxiliary apparatus as sociated with said line and tube for the twoway transmission of signals. I

across said resistance upon t e input elec trodes of said repeater, and means comprising a second repeater connected to an inter- I mediate point of said capacity path for impre sing si alin without e ective y impressing them ,upon

said first repeats 7. In telegraph a duplex line, two shunt paths across said line, one of said paths comprising a resistance, the other be ng a capacity path, a vacuum tube repeater having its input electrodes shunted across said resistance, andmeans comprising a second currents upon said line vacuum tube repeater connected to the midpoint of said capacity path for impressing signaling currents upon said line without impressing them upon said first repeater.

1n witness whereof, I hereunto subscribe my name this 23rd day of September, A. D.,

HAROLD W. NICHOLS.

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