US1687244A - Signaling system - Google Patents

Description

Oct. 9, 1928.

1,687,244 R. A. HElSlNG SIGNALING SYSTEM Filed Dec. 22, 1 2

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fay/77 0/747 A fie/isvky. b y My Patented Oct. 9.1928.

x i UNITED STATES 1,687,244 PATENT OFFICE.

RAYMOND A. HEISING, 01E MILLBUItN, NEW JERSEY, A SSIGNOR '10 WESTERN ELEC- TRIO COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION NEW YORK.

SIGNALING SYSTEM.

Application filed December 22, 1820, Serial No. 432,444. Renewed November 20, 1924.

This invention relates to signaling systems, and more particularly to systems employing electron discharge devices as amplifiers and modulators.

In the well-known application of three-electrode electron discharge devices as amplifiers, it has been the general practice heretofore to maintain the grid or impedance controlling element at all times at a negative potential with respect to the cathode or heated filament, if such be used. Likewise, when such a device has been used as a modulator wherein carrier waves of constant amplitude may be modulated by current of signaling frequency, 1 the potential of the grid has heretofore been maintained negative. In each of these cases the grid has been maintained at a negative potential in order that none of the electrons emit-ted by the cathode might pass to the grid and so reduce the otherwise very high input impedance of the device. Due to this high input impedance, a negligible amount of energy was consumed in the input impedance; but to maintain this condition, during operation, the amplitude of the impressed voltage was necessarily limited.

When using electron discharge devices in the manner just described, it has been customary to connect a very high impedance, for example a resistance of the order of one-half a megohm or more, across the input terminals of the amplifier or modulator tube and to connect a secondary of a speech transformer to thishresistance;

According to this invention the grids of thedischarge devices are allowed to become positive,thereby increasing the allowable im-' pressed voltage amplitude. It has been'found 1 that a maximum of energy can be obtained in the output circuit of the discharge devices with a minimum of distortion of the signaling wave by providing an impedance across the secondary of the speech transformer and impedance. This impedance may take the form of a substantially pure resistance.

When large amounts of power are obtained from an electron discharge device, such as an' amplifier or a modulator by allowing the peaks of the input voltage waves to make the grid positive with respect to the cathode, cur

rent flows from the grid to the cathode as soon as the grid becomes positive. Under this the input circuit of the discharge devices of. approximately the value ofthe' positive grid f the signal cycle when the grid is positive with respect to the cathode.

condition, the input circuit of the discharge device has a finite ,resistance which is often uite low. The in ut impedance of'such a evice supplymg arge amounts of power may, therefore, be large over most of a signal cycle (say 500,000 ohms for 300 degrees) and fall to a low value during the rest of the cycle (say 12,000 ohms for degrees). If the circuit working into the grid is a high impedance circuit, it will produce pro er potentials for the 300 degrees of the eye e, but during the remaining 60 degrees the impedance of 12,000 ohms will practically act as a short circu1t therefor. Distortion of the signal results, due to the fact that the positive potentials corresponding to the signal, are not faithfully reproduced and impressed upon the grid. To prevent such distortion, means must be provided to maintain the desired voltage across the low 12,000 ohms internal impedance as well as across the high internal impedance of the discharge device during the two parts of the cycle. The input circuit impedance external of the discharge device should, therefore, not be high (500,000 ohms) but should be low (12,000 ohms or lower), in

order that it may supply suflicient current to the 'd without excessive potential drop therem, to maintain on the grid the desired positive potential in spite of the current which flows. A- circuitthus pro ortioned will give greater out ut with less distortionthan is the case for hlghimpedance input circuits. Distortion, due to'current flow in the internal input circuit path, approaches zero as the.

impedance of the input supply circuit external of the discharge device is made to approach zero.- For high grade tone quality voice current, it has been found sufiicient to make the Impedance of the connected line or and articulation, of repeated or modulated supply circuit below andto the left of points i 31, 32 of the same order of impedance as the minimum internal impedance between the grid and cathode reached during that part of 12,000 ohms) during the cycle. The supply circuit" is then proportioned accordingl In a radio transmitting system embo ying this invention, an electron discharge or vaccircuit of which is connected transformer, across the secondary whichmaybe connectedan impedance substantially equal to the input impedance of the modulator'tube at signaling frequencies when the grid is at a positive potential. This impedance, in practice, ma be a'substantially pure resistance of the or er of 12,000 ohms. Resistance values of 500 to 50,000 ohms have been used.

One embodiment of the invention will now be described in detail in connection with the accompanying drawing. Fig. 1 of the drawing illustrates one arrangement of a radio signaling system. The dotted lines indicate a transmission line such as an ordinary telephone or telegraph line, or a connection to a power transmission line which may be substituted for the antenna. Fig.2 shows a circuit arrangement which ma be substituted for a part of the circuit of ig. 1.

Referring now to Fig. '1, the modulator M supplies energy to an antenna A. A generator of sustained oscillations O, and a speech frequency circuit S, are adapted to supply energy to the modulator M.

Modulator M, as shown, may comprise a plurality of three electrode thermionic vacuum tu es, having filaments 5, 5, anodes or plates 6, 6 and impedance controlling elements or grids 7, 7. The filaments may be heated by a battery 8, while the amount of filament current is controlled in the wellknown manner by a variable resistance 9. Energy for the plate circuit is supplied by a source of unidirectional current 10. The plate circuit of the modulator may be coupled to the antenna A through a. transformer 11.

The enerator 0 may also comprise a three electro e thermionic vacuum tube of any well-known type. As illustrated, it comprises a'filament 12 heated by battery 13 through a controlling resistance 14. The plate circuit is supplied with energy by a unidirectional source 15. The plate circuit and grid circuit are coupled together and to the input circuit of the modulator M through a transformer 16. The frequency of the generated oscillations are determined by the tuned circuit comprising the primary windings of transformer 16, and the condensers 17 and 18.

The speech frequency circuit S may comprise a microphone 19' adapted to impress current upon the input circuit of the modulator M through transformers21 and 22, thermionic vacuum tube amplifier SA and step-down auto transformer 23. Energy for the microphone may be supplied by battery serves to maintain the may be of the step-up type, in order to transform the energy of low potential from the microphone circuit to energy of high potential suitable for impressing upon the input circuit of the speech amplifier SA. A high resistance 24 is also connected across theinput of the speech amplifier SA. Battery 25 rid 26 at a negative potential at all times wlth respect to the filament 27. Battery 28 supplies energy to the plate circuit of the speech amplifier through an impedance coil 29, in a well-known man'- ner. By this method of connecting a microphone 19 to a speech amplifier SA, a large amount of energy of undistorted wave shape is made available at the output terminals 33, 34 from a limited amount of energy supplied by the microphone. Suchan arrangement is not new.

According to this invention there is connected across the secondary circuit of the stepdown antotr'ansformer 23 a resistance 30. This resistance is of the order of 12,000 ohms, and its value is so chosen that it substantially matches the input impedance of the'modulator M measured across the terminals 31, 32 when the grids 7 7 are at a potential positive with respect to the filaments 5, 5. The primary of the autotransformer 23 is connected to the output of the speech amplifier SA at the terminals 33, 34.

Condenser 35 serves as apath for oscillations from generator 0 around the transformer 23 and the resistance 30. Condenser 36 provides a high frequency path around battery 38, which serves to place a certain negative potential on the grids of the modulator M, or condenser 36 may act as a storehouse of negative potential, if it is provided with a leak resistance (not shown), due to grid current. The secondary of the transformer 16 the antenna A. During such operation the potential of the grids 7, 7 become positive, and as is Well known under thoseconditions, the otherwise almost infinite impedance of the tube is materially reduced. In orderto utilize this reduced input impedance eflicient of energy-in the; output circuit of the modulator M, this low' ered input impedance of the tube has been ly, and to obtain a maximum matched by a substantially equal external impedance such as the resistance 30. In this way it has been found that a larger amount I'Ill i of energy can be obtained in the output circuit former 37 of Fig. 2, with the impedance 30 connected across its secondary winding may be connected to the rimary terminals 33, 34, and secondary termmals 31, 32. The operation is not chan ed by this modification, and thereforen'o further description is necessary.

-ulation.

To those skilled in the art, other embodi- It is'to be understood that this invention is not confined to radio signaling systems, nor in fact to signaling systems employing sustained oscillations as carrier waves. It may find application wherever signaling waves are imposed upon amplifiers or modulators, especially where a thermionic vacuum tube is used for the purpose of amplification or modments of this invention will be apparent. All

such embodiments, as defined by the appended claims, come within. the scope of this invention. l

What-is claimed is: 4

1. A thermionic vacuum tube, an impedance controlling elementand a cathode for said tube, an input circuit comprising said im edance controlling element and said catho e, a

source of signaling current adapted to im-- press a voltage on said input circuit which 7 causes the impedance controlling element to become positive with respect to. the cathode during operation, and an impedance connected across said input circuit of value substantially the same as that of the input impedance of said tube when said impedance controlling element is positive.

2. In a carrier wave signaling system, a modulator, an input circuit for said modulator including a cathode and an impedance controlling element, a source of carrier waves and a source of modulating waves associated with l said input circuit, said waves having an amplitude of such value as to cause said impedance controlling element to become positive with respect to the cathode during operation, and'means tocause the impedance of said source of modulating waves to" substantially equal the minimum impedance of said input circuit due to the impedance controlling element becoming positive.

grid to "go positive with respect to said cath-' dance connected across said input circuit 0 3.- In a slgnahng system, a three electrode thermionic vacuum tube, an input circuit comprising the grid andcathode of said tube, an alternating currentsource connected to said input circuit, current from said source having an amplitude of such value as to cause said ode, and an im I value substantially matchmg the'positive grid andcathode impedance.

4. In a signaling system,

'a three electrodev thermionic vacuum tube, an input circuit comprising the grid and cathode of said tube, an alternating current source connected to said input circuit, currentfrom said source having an amplitude of such valueas to cause said grid to go positive with respect to said cathode, and an impedance connected across said input circuit of value not substantially greater than the positive grid to cathode impedance. v 5. The method of operatin an electron discharge device having a gri and cathode, which method comprises supplying the grid circuit of the electron discharge device with alternating current impulses of values sufficient to make the potential of said grid positive with respect to said cathode, and compensating for the loss occasioned by the consumption of energy in said rid circuit due to the potential of said gri becoming positive wit respect to its cathode.

6. A supply circuit adapted'to supply electrical impulses, an electron discharge device connected .to said supply circuit and comprising a cathode, an anode, and a control electrode, the magnitude of the impulses sup.- plied by said supply circuit being suflicien't to make said grid positive at times with respect to said cathode, the control electrode circuit exterior to said discharge device having an impedance of the order of the impedance between said control electrode and said cathode when said control electrode is at a vpositive potential.

A supply circuit adapted to suppl electrical impulses, an electron discharge evice, means reactively connecting said discharge device to said supply circuit, said discharge device having a control electrode and a cathode, the magnitude of the impulses of said supply circuit being suflicient to make the potential of said control electrode at times positive with respect to said cathode, and

means on the input side of said discharge device for reducing the distortion ofthe wave pedance substantially matching the impedance valueof the grid circuit of said second mentioned discharge device under the condi tion that the grid of said circuit is at a positive potential.

' 9. In a signaling system, an electron discharge device, an input'circuit for said device I I including a grid and cathode, a source of inputener adapted to cause the grid to be come pos tive with respect to the cathode durin operation, and animpedance con-' necte across said input circuit of value sub-- I pedance between said grid and said cathode when said grid is at its greatest positive potential.

11. In combination, a speech frequenc C11- cuit, an electron discharge device, a gri and a cathode for said device, a speech frequency transformer connected between said .speech frequency circuit and said grid and cathode, means for causing said grid to become positive with respect to said cathode, and an impedance connected across the discharge device side of said transformer of value substantially equal to the impedance between said grid and cathode when said grid is at a positive potential.

12. In combination, a speech frequency circuit, an electron discharge device, a grid and a cathode for said device, the internal impedance between said grid and cathode varying between limits of the order of 12,000 and 500,000 ohms dependent upon the potential of said grid with respect to said cathode, a

- speech frequency transformer connected between said speech frequency circuit and said grid and cathode, means for causing said grid to become positive with respect to said cathode. and a resistance of the order of 12,000 ohms connected across the discharge device side of said transformer.

13. In a. signaling system, a source of oscillations, asource of signaling current, means to modulate said oscillations in accordance with said signaling current comprising an electron discharge device having a grid and a cathode, the impressed potential from said source of signaling current being of. sufficient magnitude to cause said grid to become positive with respect to said cathode, and an impedance connected across said source of signaling current of'value substantially equal to that of the impedance between said grid and cathode when said gridis at a positive potential.

14. In a signaling system, a source of oscillations, a source of signaling current, means to modulate said oscillations in accordance with said signaling current comprising an electron discharge device having a grid and a cathode, means to cause said grid to become positive with respect to said cathode,

l and an impedance connected to said last mentioned means between said means and said discharge device of Value substantially equal to that of the internal impedance between said grid and cathode when said grid is at a positive potential.

15. In a signaling system, an electron discharge device having a grid'and cathode, the internal impedance between said grid and cathode varying between limits of the order of 12,000 and 500,000 ohms dependent upon the potential of said grid with respect to said cathode, an input circuit for said device in- 7 eluding said grid and cathode, a source of signaling current, a signaling current amplifier, a step-down transformer adapted to, receive energy from said amplifier and to supply said energy to saidinput circuit, and .0 a resistance of the order of 12,000 ohms connected across the low impedance side of said transformer.

16; In an electrical system, an electron discharge device having a grid and a cathode, 5 an input circuit for said device, including said grid and said-cathode, a source of alternating current, an amplifier for said current, energy translating means connected between said input circuit and said amplifier adapted to receive energy of high potential from the amplifier and to supply energy of a lower' potential to said input circuit, said translating means having an effective shunt impedance for said input circuit of value substantially the same as that of the input imspedance of said device when its grid is at a positive potential.

17 In an electrical system, an electron discharge device having a grid and a cathode, an input circuit for said device comprising said grid and cathode, a source of alternating current associated with said input circuit, current from said source being of such amplitude. as to cause the potential of the grid to become v alternately positive andnegative with respect to the cathode, and an impedance connected v across said input circuit of value not substantially greater than the grid-cathode impedance of said device when the grid is at its max- 'imum positive potential.

18. In an electrical system, an electron discharge device having a grid and a cathode, an input circuit for said device including said grid and cathode, a source of alternating ourrent, means to connect said source of alternating current to said input circuit, whereby the potential of said id with respect to said cathode is rendere positive, and means associated with said connecting means to cause the maximum positive and negative alternating potentials impressed upon said grid to be substantially numerically equal. f

19. In an electrical system, an electron discharge device having a grid, a cathode, and an anode, an input circuit for said device including said-grid and cathode, an output circuit for said device including said cathode and anode, a source of alternating current, means to connect said source of alternating current Lea-1,24;

to said input circuit; said source being of inwith respect to said cathode is at times rensaid input rent potential dered positive, andmeans connected across circuittocause the component of current in the output circuit corresponding to the impressed alternatin current to have positive and negative amp 'tudes relatively proportional to the positiveand negative amplitudes of the impressed alternating current.

20. In an electrical translatin prising an electron dischar e an electron emitting catho e, an Impedance controlling element and an'anode, the method which comprises impressing alternating .cur-

upon said cathode and imped system comtensity such thatthe potential of sa1d grid Y device having Y therein, including a high reactance and a con- 25 denser and a resistance in multiple shunted across the filament-grid circuit.

In witnesswhereof, I hereunto subscribe w my name this 17-thday of Deeember A.,D., 1920. Y

RAYMOND A. HEISING.

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