US1491349A - Electrical receiving or repeating apparatus - Google Patents

Description

Apri122,1924. 1,491,349

. B. w. KENDALL,

ELECTRICAL RECEIVING OR REPEATING APPARATUS Original Filed Feb. 20. 1917 ri-M Patented Apr. 22, i924.

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me it? at BURTON W. KENDALL, OF NEW YORK, N. Y., ASSIGNOR TO WESTERN ELECTRIC COM- PANY, INCORPORATED, OF NEW YORK, N. 'iZ'., A CORPORATION OF NEW YORK.

. ELECTRICAL RECEIVING OR REPEATING APPARATUS.

flriginal application filed February-20, 1917, Serial No. 149,782. Divided and this application filed January 16, 1920, Serial No. 351,873. Renewed June a, 1923. v

To all whom it may concern:

.Be it known that I, BURTON \V. KENDALL, a citizen of the United States, residin New York, in the county of New York, State of New York, have invented certain new and .useful Improvements in Electrical Receiving or'Repeating Apparatus, of which the following is a. full, clear, concise, and exact description.

This invention relates to electrical receiving or repeating apparatus, and constitutes a division of m application Serial No. 149,782 filed Feb. 20, 1917 issued as Patent No. 1,453.982-011 May 1, 1923.

A particular application ofthe invention is to receiving apparatus or repeaters for submarine cables or similar conductors, in

connection with which it will be described. Its object is, in this case, to amplify and repeat messages from an incoming cable to an outgoing cable while permitting duplex operation of said cables. A further object is to receive and amplify signals with fidelity so that the recorded signals shall be enlarged and faithful copies of the signa wave-forms.

These objects are a complished by inserting atransformer winding in'the circuit from which signals are to be received, connecting another winding of thc'transformer to anamplificr which has in its output circuit an electrical network of special form,

- plex cables, reference'being made to the to be more particularly described later, amplifying the power appearing in one branch of this network, and transferring it to an instrument or circuit in which it is to be utilized; The advantages secured by this invention and the diihculties which are overcome will be better understood after a' brief explanation of the operation of dudrawings.

Referring to the drawing, thereference numerals 4 and 5 represent two cables, and it is desired to send signals from the station 7 tothe station 8, making use of arelay between the terminals of the cables 4 and 5 in such a manner as to permit of duplex operation. i there are two artificial cables 10 and 11 arranged to have characteristics similar respectively to those of the actual cable. At the station? there are connected, between At the terminals of the cablethe cable 4 and the artificial cable 10, the

two condensers l2 and 13, across which isbridged in the usual manner some indicating instrument 14.. The opposite terminal of the cable 4: likewise has the usual condensers 16 and 17, across which would ordinarily be connected some indicating instrument in the same manner as at the station 7 When a signal is sent from the station 7 by the operation of the key 18 in series with the grounded battery 19, an impulse An impulse impressed across the points 28, 29 and coming from any source such as a battery with a key or from the output circuit of a relay, as indicated in this fig me, will produce a current which divides equally between the paths 4 and 11 of equal impedance, and because of this symmetry, there is for such a signal or impulse no difference of potential. between the points 21 and 25, across which a. receiving instrument might be connected. Such a receiving instrument will, therefore, not be influenced by signals impressedv between the points 215 and .29. The arrangement of cable 5 with its artificial cables is the same as that of cable 4 with its artificial cables. If now it is desired to relay a message from cable 4 to cable 5, it will be necessary to connect, through an amplifier, the receiving terminals 24,25 of the first cable with the transmitting terminals 30, 31 of the second cable, and similarly to connect the receiving terminals 33, 34 with the transmitting terminals 28, 29.

' lit has been found that an ordinary relay or mechanical amplifier is not suitable for this class of -work but that a thermionic amplifier of the audion type may be made to operate very efiicien-tly. Such amplifiers have been used extensively in telephony, and are now wellknown in the art. This type of amplifier consists of an evacuated vessel in which are contained three electrodes, a hot electron-emitting cathode, a cool anode and an auxiliary electrode usually located between the anode and the cathode. The auxiliary electrode and the cathode, constituting the input terminals of the amplifier, are Connected to the circuit the power of which is to be amplified, and the cathode and the cool electrode or plate, constituting the output terminals are connected to the circuit in which theamplified power is to appear.

When a voltage is impressed upon the input circuit of such an amplifier, its effect is to vary the strength of the thermionic current which fiows between the hot cathode and the cool anode or plate, and since the variations of this current, whose source is a battery in the output circuit, represent larger amounts of power than those required to produce the variations, the device acts as an amplifien Furthermore, the current in the output circuit of such an amplifier depends only upon the voltage impressed upon its input terminals, the input circuit itself having a'very high impedance, and,

therefore, taking practically no current and acting as an open circuit. Any variations in the input voltage will be faithfully rendered as corresponding variations in the output current.

Any desired number of amplifiers may be employed for amplifying the signals coming from either line. In the drawing two amplifiers 35 and 40 are shown for amplifying signals to be repeated from i to line 5. Two similar amplifiers are shown for re peating in the opposite direction.

An important feature of a thermionic amplifier is that its input and output circuits have one point in common namely. the connection to the hot cathode, so that there is an electrical connection between the two circuits. Inusing the amplifier as described in connection withthe problem of repeating cable messages, there will, therefore, be an electrical connection betweenv the receiving terminals of one cable and the transmitting terminals. of the, other into which the sig; nals are to be relayed.- Examination of the drawing will show-that when such a connection exists, thatis, when the input terminals of a thermionic amplifier are connected di-- rectly-to the receiving terminals "24, 25 or 33, 34, the artificial lines will be shunted,

and their usefulness, therefore, destroyed. .In this-case. duplex operation can not be maintained. L 1

One method of eliminating the circuit connection just noted would'be to connect one winding of a transformer across eachpair of receiving terminals, one of thesetransformers being shown as36 in thedrawing, and to connect the other windin'g to the input terminals of the amplifier. The out-..

put terminals of the amplifier would then current in the primary but: is proportional to the rate at which this current-changes, for example, a voltage is'present in the secondary only when the current in the primary is actually changing. It will, therefore, be clear that the repeated current will not be a faithful copy of that of the incoming signal. To overcome this difficulty, that is, to make the voltage over the input terminals of amplifier 4.0 a copy of the current to be repeated, is the object of the correcting network comprising resistance 37 and condenser 38 whose design and operation are now to be described.

As mentioned above, the electromotive force induced in. the secondaryof the transformer 36 is proportional to the rate at which the primary current changes, that is, it is proportional to the time derivative of the primary current, and the transformer may, therefore, be spoken of as a differentiating device. In this invention advantage is taken of the fact that a condenser acts as an integrating device, for the potential difference across the terminals of acondenser placed in such a circuit. as'shown is proportional to the total quantity of electricity which has passed therethrough, and

is, therefore, proportional to the time in tcgral of the current flowing in such a circuit. If the condenser 38 were short-circuited, the current through the resistance 37, there being then in'circuit only the internal resistance of the output circuit of .the tube 35 and the resistance 38, would be entirely similar to and'in phase with the voltage generated in the output circuit of the tube 35. This voltage would .be equal to the voltage impressed on the first circuit of the tube multiplied by the amplification .factor which expresses the ratio of voltage generated on the output circuit to the voltage impressed on the input -circuit. input voltage, since the transformer 36 "has The essentially an open circuited "secondary,

'wouldzbe proportional to the derivative of the current flowing in the primary of the transformer, i.- voltage is With the interposition of the condenser 38,

its value being such that its impedance to all the freq encies concerned is substantially neglig le" compared to the sum of e., if 2' is this current, the

menses resistances 37 and the internal output resistance of the tube -the impedance of the condenser 50 being negligible to the same or a greater extent, the current flowing through the condenser will still be sensibly proportional to But as the voltage across the condenser is proportional to the integral of the current flowing through 37 this voltage is then substantially proportional to the current flowing through the input-transformer. It only remains, then, to provide a grid leak 44 for the tube of such a value as not appreciably to. affect this effect of the condenser 38. It is therefore necessary for the proper operation of the arrangement that the impedance of the condenser 38 to the lowest frequency to be transmitted be at once small compared to the resistance 44 and small compared to the sum of the resistance 37 andthe output resistance of tube 35. The

resistance 37 may even be omitted in case' the internal resistance of tube 35 alone is high compared to the impedance of condenser 38.

The output circuit of the amplifier 40 is connected,'preferably through a condenser 41, to the transmitting terminals 30, 31 of the cable 5. In order to allow the necessary flow of direct curren t, a choke coil 42 is connected across the output terminals of the amplifier. The ampliherhas an output battery 43 which may be connected up in any suitable position in the output circuit.- v

In practice the followlng arrangement and dimensions of elements have been found to be very satisfactory. The transformer 36 is arranged to step up the voltage of the incomingsignal. for example, to ten times its original value. Its secondary winding is connected to amplifier 35, the output terminals of which are connected to resistance 37 and condenser 38. To provide forthe flow of direct current in the output circuit of amplifier 35, a resistance 49 which should preferably be of several thousand ohms is added, and to restrict the direct current to this circuit a large condenser 50 is connected as shown. It has been found that the use of an amplifier between the cable terminals and the correcting network 37, 38 permits the-use of a larger transformer 36 than would otherwise be possible, which feature is of advantage in receiving signals P of low frequency. By this is meant that a transformer having alarge efiectivereactance, as is thecase when the secondary-wind-' ing has many turns, is more efiective in transmitting low frequency waves than a transformer having smaller inductance, In order to reduce-the distortion of the incoming signal to a suficiently small quanoperation.

est signaling frequency is 16 cycles, and the condenser 38 is 1, the impedance of the condenser will be about the output 'impedance of the tube. In this case the resistance 44 may be in the neighborhood of 200,000 ohms.

In addition to the circuit as described, it

may be desirable under some conditions to use a resistance 44 bridged across the condenser. This resistance is primarily intended to serve as a leak between the grid and filament of the amplifier 40,. This resistanceshould be an exceedingly high one, say of the order of one or two megohms in order that it shall not act as a substantial short-circuit of'the condenser 38 and thereby prevent a building up of the desired voltage in the condenser 38. If this re sistance 44 is large it will be apparent that the current flowing therethrough will be proportional to the voltage across the condenser 38, and will therefore, be proportional to the current through primary of the transformer 36.

To secure transmission from cable 5 to cable 1 an exactly similar arrangement of circuits is made to connect the receiving terminals 33, 34 of the cable 5 ith the transmitting terminals 28, 29 of-the cable 4. Bythis arrangement it is possible to secure amplification of signals in both directions and also to preserve the property of duplex It is to be noted that the cathode of the amplifier 40 is connected to ground through the battery 43. This grounding of the oathode of a vacuum tube through a low resistance path has the advantage that in so doing a definite potential may be maintained be tween each piece of apparatus in the circuit and ground, whereby any local circulation of power, which might lead to the tubes singing is substantially avoided. Thus if the cathode 46 of tube 40 were not grounded,

the choke coil 42 and the transformer 36,

facilitate a transfer of energy from the outut circuit back to its input circuit and to start "the tube to singing. Such a feed back, however, is prevented by grounding the cathode, asv shown, which is a common terminal for both the input and the output circuits of the tube. V

4 Vacuum tubes 55 and 56 also have-their cathodes grounded, so that all the vacuum tube repeaters in the two way repeating starot tion have grounded "cathodes, which condition diminishes considerably, if not entirely eliminating, any cross talk between the two repeating paths. Ordinarily the two circuits containing the vacuum tubes 35, 40 and 55, 56 would be situated close" enough tog'ether to establish an appreiable capacity effect between apparatus in the two circuits,

so that with ungrounded cathodes, a message being sent through one path would induce alternating currents in the other path thereby giving'rise to cross talk. This obthereto from said conductor, a vacuum tube repeater between said conductor and said network and a transformer between said repeater and said transmission conductor,

prising a line conductor, a correcting network, a vacuum tube between said conductor and said network, said network being composed of ohmic resistance and condensive reactance, and being substantially free from inductive reactance, and'a transformer between-said tube and said line.

A two-wayrepeating system comprising'means for repeating signals in one direction, means for repeating signals in the opposits direction, each of said means comprising an incoming conductor, a correcting network, avacuum tube repeater between said conductor and said network, said network being composed of ohmic resistance and condensive reactance and being substantially free from inductive reactance, and a transformer between said tube and said incoming conduct-or.

4. A receiving system comprising an in-.

coming conductor, and means for transmitting the component parts of the signals from said conductor with equal attenuation, said means comprising a differentiating device,

an integrating device, and amplifying means located between said devices.

J5. A transmission] system comprising an 7 incoming line, a transformer, a vacuum'tube repeater in circuittherewith, and a waveform correcting device inthe output circuit ofsaid repeater, said transformer being located between said line and said repeater.

' 6-. In a" transmission system, a transmission device 'theattenuation ofwhich varies with the frequency, an'auxiliary system the 2A receiving system for signals com-' reensae attenuation of which varies with the frequency in a manner complemental to that of said device so that the resultant transmission of said device and said auxiliary system is substantially constant over a wide range of frequencies, and a repeater between said device and said system.

7. The combination with a transmission element in which the attenuation varies with difi'erent frequencies of means for impressing on said element waves of a plurality of frequencies, means for amplifying said waves after said unequal attenuation is pro-q 'duced', and an auxiliary system associated with said amplifying means to equalize the attenuation caused by said elementso that i all frequencies within a wide range are transmitted with'practically uniform attenuation, said auxiliary system comprising a network composed of ohmic resistance and condensive reactance and being substantially .-sion element the-attenuation of which varies with the frequency, means, the attenuation of which varies with the frequency in a manner-subst'antially complemental to that of said element'so that the resultant transmission of said element and said means is'substantially constant over'a wide range of frequencies, and a vacuum tube amplifier between said element and said means.

.10. In combination, two vacuum tubes, each having an anode, a cathode and a control electrode, a connecting line between the anode of one tube and the control electrode of the second tube, comprising a condenser and a resistance serially connected between said anode and said control electrode, a connecting line'between said cathodes and a condenser connected across said lines- 11. In a transmission system for the simultaneous transmission of waves of a plurality of frequencies, transmission means in which the different-frequencies are attenuated by different amounts, a two stage am plifier for amplifying said waves, and anetwork between the two stages of said amplifier for attenuating the waves in a sense opposite to the attenuation produced by said transmission means.

12A transmission system comprising a transmission element the attenuation of which varies with the frequency, an auxiliary system the attenuation of which va- -ries with the frequency in a manner coinpleinental to that of said element so thatthe resultant transmission of said element and menses said auxiliary system is substantially constant over a Wide range of frequencies, an electric discharge repeater between said element and said system, an outgoing line, and a second electric discharge repeater between said system and said line.

13. An amplifying and wave form correcting system for distorted submarine cable signals comprising two amplifiers and a network between said amplifiers having resistance and reactance for improving the signal wave form.

14. An amplifying and wave form correcting system for distorted submarine cable signals comprising two space discharge re-.

peaters, each having an anode, a cathode and an lmpedance control element, and an attenuating network between said repeaters for improving the signal wave form.

15. A repeating and wave form correctmg system for dlstorted signal waves comprising two space discharge repeaters and a reactive network between said repeaters for improving the signal wave form, said net'- work having appreciable resistance which functions to modify the magnitude of the efiect of the reactance upon the wave form 16. A submarine cable for transmitting telegraphic signals involving onlyrelatively low frequencies and in which attenuation of signals is very great, waveform correcting means associated with said cable and comprising a reactive network having appreciable resistance which functions to modify the magnitude of the efiect of the reactance upon the wave form, and a space discharge repeater between said network and said cable, said repeater having an anode, a cathode and an impedance control element.

In witness whereof, I hereunto subscribe my name this 13th day of January, it, D. 1929.

snares w. KENDALL;

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