US1757469A - Space-discharge system - Google Patents

Description

A. A. OSWALD May 6, 1930.

SPACE DISGHARGE SYSTEM ig w Filed Dec. 31

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Awe/War A/MWA 0a wa/o Patented May 6, 1930 warren stares earner clerics,

ARTHUR A. OSWALD, OF EAST ORANGE, NEV JERSEY, ASSIGNOR T0 WEFA'EER-N ELEC- TRIO COMYANY, INGORPGRATED, 0E IIEN YORK, 11'. Y., A C(EBPDB-ATIGN 01 NEW YORK SPACE-DISCHARGE SYSTEM This invention relates to space discharge systems and more particularly to a balanced input circuit for systems including threeelectrode devices of the type adapted for use as. repeaters or. amplifiers.

As is well known, when system including space discharge devices are operated so that the grids or control electrodes of the discharge devices are positively charged during successive positive half cycles of the impressed wave, the corresponding half cycles of the output wave are considerably distorted. This is due in part to the fact that the circuit, through which the wave is impressed upon the input electrodes of the dis charge device, includes impedance when the positive half cycle of the wave to be repeated is impressed upon the input circuit. When the positive halt cycle is applied across the grid and cathode grid current flows, with the result that the E. M. F. eliective across the input electrodes is reduced. On the other hand,when the negative half cycle of the wave is impressed upon the input electrodes, no grid current flows and the E. M. F. impressed upon the input electrodes is the full voltage of the source. Under these conditions, the two half cycles of the output wave are different from each other.

In order to overcome this disadvantage, it has been the practice heretofore to impress the wave to be repeated on the input electrodes of the devices through a circuit provided with means for limiting variations in its impedance. This has been accomplished by connecting in parallel with the circuit coupling the wave source to the system, and hence in parallel with the input electrodes of the device or devices, a resistance or other impedance element which is continuously conductive for the impressed wave. For both half cycles of the impressed wave, variations in impedance of the input circuit are limited by the shunt conductive element, and a current flows through and is dissipated in this element with the result that its use repre sents a waste of energy.

The symmetry of theoutput wave will be improved by using a shunting element, the impedance of which is small compared wlth the grid-cathode impedance of the repeater when its grid is positive. This method, however, may require the use of a shunting resistance so low that a very large amount of energy is dissipated in the resistance, and a large part of the E. M. F. is absorbed in the impedance of the line or wave source.

As a compromise, it has been, in general, the practice to employ a shunt element, the impedance of which is equal to one half the grid-cathode impedance oi the repeater when its grid is positive. lVith the ordinary impedance in the wave source, the conductance of the shunt element is not suihcient to eliminate distortion of the impressed wave and, as a result, the repeated wave is unsymmetrically distorted. Thus, the use of a continuously conductive path while serving to reduce the dissymmetry of the repeated wave,

achieves this result only with the expenditure of an excessive loss of power.

The present invention provides a balanced input circuit, the impedance of which for both half cycles of the impressed wave is equal to that of the space path between the input electrodes of the discharge devices, whereby the input circuit losses are material- 1y reduced and both half cycles of the wave are distorted to the same extent.

In accordance with this invention, a two electrode space discharge dcvicehaving the same impedance characteristics as the three electrode space discharge repeating device is connected in shunt to the input circuit of the repeater. The filament of the two-electrode device is connected to the grid of the repeater and its plate is connected to the filament of the repeater.

The arrangement described above, sets forth briefly and in a general way one embodiment employing the principles of the invention. However, this description is not to be construed as limiting the scope of the invention. The various combinations and features of the invention which are believed to be novel will be defined in the attached claims.

One obj ect of this invention is to reduce the power losses in space discharge repeating systems.

A feature of the invention is the provision of a balanced input circuit for power amplifiers, whereby the amplifying system may be operated at high efficiency.

For a complete understanding of this invention, both -as to its organization and method of operation, reference should be made to the following specification read'in conjunction with the "attached drawing in whichthe'invention'is illustrated,-by way of example, as applied to an amplifier included in a high power radio telephone system. Figs. 1 and 2 show different circuit arrangements embodying the invention. 7

Referring now to Fig. 1, there is shown a circuit ladapted to supply'a carrier wave n'od'ulaijted in accordance with speech currents. The modulated wave is transmitted by the'transf'ormer 2 tothe 'input'circuit 'ofan amplified hfshown by way-of example as comprisingtwo parallel connectecbspa'ce discharge d'evices '3, each including a cathode, an anode and grid or control electrode.

curi'ent'forheating the cathodes-of devices 3 is supplied by the alternating current 'source' through tlie'transforni'er 5. The terminals of the parallel connected cathodes areconnectedto 'the'te'rminals of the secondary' of the transformer 5 and the midpoint of this winding isconnecte d to the conductor 6 which is grounded'at 7 Space current: is'suppl-ied to'the devices 3 from the source8over the following circuit: *From the" p'ositiveterminal'of the source 8, 'choke"c'oil"9, anodes of the 'devices to' their cathodes, secondary of "transformer 55, 'con- 'ducter 6, tothe other terminal ofs'o'u'rce 8.

Alternating current "output energy from the devices 3" flows 'throug-h *the condenser 10, tlieiclosed'loop, including the inductances lland 12sl1'u'ntechby the condenser 13 in series with the'condenser l h'cond-uctor 6; condensers-5 in'shunt to the secondary winding of transformer-5, to t'he cathodes of devices 3 and across the space within-them to their anodes. The condensers '5 provide 1 low impedance' p aths' for high i frequency current.

The path comprising't-he closed'loop 11, 12 and-13 in serieswith'the condenser leis also i'ncluded'in -the input circuit of the higl'i power "ainpli'iierA This path, thereforefc'on'stitntes a coupling circuit, whereby the amplified Wave supplied by the devices 3 is impressed upon the input electrodes of the l'iiglr power amplifier A *The amplifier A is shownas comprising three parallel connectedthree-electrode space (lischargedevices 15. r lhe cathodes of the devices 1-5 are connected in parallel across" a-circuit '16 connected to" the terminals efthe secondary winding of a transformer 17. The midpoint of this windis connected to the conductor 6. "The pri- Hia'ry windingof'transformer 17 is connected to an alternating current source 18,wh1ch supplies heating current to the cathodes. Obviously, heating current for the filaments of the devices 15 could be supplied by the source 4, through the transformer 5.

Space current is supplied to the devices 15 by the source 8 over the following circuit. From thepositive terminal of the source 8,

-cho-kecoil 19 to the anodes, across the space within the devices 15 to their-cathodes,-secon dary of transformer V 17, t and conductor "6 to the negative terminal of source 8.

The high power modulated wave flows through the following circuit: from the anodes 'of 15 through condenser 20, tuned circuit consisting of the coil 21 in parallel with the condenser 22, conductor 6, Icond'ensers'l? in shunttotheseconda'ry of transformer 17 to the cathodes of devices #15,: and across i the space-paths"within them to "their anodes. Condensers 17 prov-idea dowimpedance path F for the high frequency wave.

,Goil 21, inductively associated with thecoil the conductor extendin'g from the contact 27.

Contact 28' serves= to determine the steady negative fpotentialfi impressed uponthe control electrodesof the device's 1 5. This-potential is impressed 'across the@followingpath: from the contact- 28, through'coil 12 to control electrodes of 15 across the space within them to I their cathodes, secondary 0f -the transfor1ner 17 "and conductor'6 tothepositive terminal of the resistance26.

Coils'9 and 19 arehigh'frequency:choke coils whichserve to prevent the highfrequency energy being short-circu-ited through the-source 8.

Condensers ll an-d 291serve-to determine the paths over whichare impressed the steady potentials 'forthe control-electrodes ofdevices 3'and 15.

Connected'across the inputcircuit, i. e; in

shunt to the coil 12' of the coupling'circuit and'the input electrodes of the high power ampl fier A 1s a space: discharge device- 30 including a cathode-31-andanode- 32. T-he cathode 31- is" connected i to the .control electrodes of the devices -15 and the" anode 32 is connected-to the cathodes of-the devices -15.

Heating current is supplied to the cathode 31 by an alternating current source 33 through a transformer 34, the secondary of which is shunted by by-pass condensers of low impedance to the high frequency wave. The impedance characteristic of the device 30 should be substantially the same as the grid-cathode impedance characteristic of the high power amplifier.

Fi 2 illustrates a system substantially the same as that shown in Fig. 1 and corresponding elements are identified by the same reference characters in both figures.

The system of Fig. 2 differs from that of Fig. 1 only in that a transformer 35 is used to couple the amplifier A to the high power amplifier A and the anode of the device 30 is connected through the condenser let to the conductor 6. The grid polarizing source for the devices 15 is also connected to the anode 32 and hence this anode is negatively polarized with respect to the cathodes of 15 to the same extent as the grids of 15.

The amplified wave flowing through the output circuit of the amplifier A is transferred by the transformer 35 to the input circuit of the amplifier A Connected in shunt to the secondary winding ofthe transformer 35 and the input electrodes of the amplifier A, is the two-electrode discharge device 30.

In both thesystems illustrated the high power amplifier may consist of a single discharge tube or any number of such tubes connected in parallel.

For the most effective operation, the twoelectrode device 30 should have an imped ance characteristic corresponding to that of the amplifier A If a single tube is used as a high power amplifier, the internal impedance of the device 30 should be equal to the grid-cathode impedance of the amplifying tube.- If a number of discharge tubes are connected in parallel to constitute anamplifying system, for the best operation the device 30 should have an internal impedance equal to the total impedance i. e. the combined grid-cathode impedance of the parallel connected tubes. f

The operation of the high power amplifier may be described as follows: When the half cycle of the wave supplied by the amplifier A through the coupling circuit 1112-13-14 or transformer 35, as the case may be, is such that the anode 32 is negatively polarized relatively to the cathode 31, its impedance will be relatively high. However, the control electrodes of 15 will be positively charged with respect to their cathodes, and the impedance of the amplifier A, will be changed fr om normal to a low value. When the half cycle of the amplified wave flowing through the coupling circuit or transformer is so directed that the anode 32 is positive with respect to the cathode 31, the impedance of the device 30 will be changed from the normal to a low value, while the impedance of the amplifier A,, will be relatively high.

Since the impedance characteristics of the device 30 and amplifier A aresubstantially the same, the change of impedance during both half cycles of an alternating current wave impressed upon the input circuit will be substantially equal. Hence, under operating condition, the variations of the impedance of the input circuit associated with the amplifier A, will be materially reduced in magnitude and will be the same for both half cycles of the impressed wave. Moreover, the maximum impedance of the input circuit throughout a complete cycle will never be greater than the maximum grid-cathode impedance of the amplifier A when the grid is positive with respect to the cathode.

Nhile the arrangement described above may be used to advantage with any type of repeating system including space discharge devices, it is especially advantageous when employed in systems including high power devices of this type, since the input power losses for a complete cycle of the impressed wave are determined by the current flowing across the grid-cathode path within the de- VICE.

The advantages accruing from the arrangement described above, as compared with systems in which an inductive path in shunt to the input circuit of the discharge device is used, will be apparent from the following considerations: In space discharge systems heretofore known, if the grid-cathode path of the discharge device or parallel connected devices has a minimum impedance value of A when the grid is positive, it has been the practice to connect in shunt to the input terminals of the system a resistance of the order of voltage is the same for both half cycles of the impressed wave, the average power dissipated in the resistance and grid-cathode If it is assumed that the input 2 path is 2- where a is the effective applied voltage. Under similar conditions, a system in which a unidirectionally conductive device having an impedance A replaces the shunt ing resistance, the average power loss throughout a complete cycle of the impressed Again, in the previously known systems, while the negative half cycle of the output wave is a faithful replica of the wave impressed upon the input circuit, the positive half cycle included components harmonically related to the frequency of the impressed wave which are of large amplitude.

In the present arrangement, as shown in Fig. 1, both half cycles of the output wave would be distorted to about the same extent wave is of the order of ioo an nouldiinchide ia sirnilernumberrofrcoming..the vave. .to; be amplified and a circuit of smaller lvo lt amperecapacity may be used forconpling the ,so urce to the amplifier.

WhetQisIciaimedis: ,lQA repeatensystem comprising; aspace discharge .idevice, jincluding a! control jelectrode r grid, and ,a cathode, an input circi'iitether eto gincluclin animpeda 'ce' wh c iseubstantial1y equalk th igriilw th de impedance ofthe device when" the positive peak of. antimpresse wav si eplll e there ;T'li comhinat e ofgii er s d charg der cei fil ifdinea Qn ro e ct'md O d an d avcatho d e an d an input circuit therefor theim pedance' of which for a complete cycle ot anf impressed wave is suhstantiallyrequal' tojthe; grid-cathode impedance of the device for the positive peak of t he impressed Wave.

3. "The combination of i a space "discharge device including a control electrode orgg'rid and ,a cathodeyan'dan input'circ'uit there- 'for comprising balanced impedancesthe impedance of said circuitfo r both half-cycles of: the impressed Wave beingsubstantially equal to the grid-cathode impedance of the device when the positive "peak cf the i-mpressed wave= -is--applied to said electrode.

4. An amplifying system includinga plurality. of space discharge devices each having a grid and a cathode an input circuit therefor havingfifor both half-.-cycles of the impressed iwave substantially .the same simpedancei as the'combined impedance oi the griidcathode pathsof said devicesfor the positive peak of the impressed ave.

5. An amplifyingsystem comp rising space discharge devices each including a cathode and a -grid an input circuittheretor, said circuit including means whereby its maxi- .mumimpedance for an unpressed wavecis ,-limi-ted to a value corresponding to that resulting from combiningfthe, grid-cathode impedances ofsaid devices mhen; the positive peak of the impressed WtYG v,is; impressed upon-,said grids.

..-,6.,- An amplifying. syste compr ng i a space .dischargeflldevice*having input gelecemes senting h Sam .iinpedanc j i iijimpresse wave as the combined grid hode impedanc'es Of dcalnp ying,d vice jwhe gsaid gridsare positive. w

s. Anjmmli yins sys eniiac udinspa 'discharge device having a grid .or F control electroc le, an'input circuit upon which the wave t h camplifie vi vi nur seie in shunt t sai .circui asp ii ch rg d vice of impedance substantially equal to the input impedance ofsaid' amplifier when the gridis'posit-ive.

9.' A space discharge amplifierhaving input electrodes' a circuit connected to" said electrodes, and. a space discharge device connected in shunt to said circuit to provide a path which is unidirectionally con'ductivein the opposite sense to the gri'd fcathode path o'ihthe amplifier, the characteristics of said ai nplifien an'd said .jdevice' being substantially hejsamc'. i i

10. space discharge repeater system comprising at least ,one' space" discharge repeater circuit having an input circuit of Widely varying impedance for positive and'negative half waves of an impressed alternatingwave to be repeated, and ashunt upon said input circuit having a widely but 'o g )positely varying impedance for-saidhalh Waves whereby the: tot-al impedanceyiewed from an input source ef waves is made more equal-for positi-vea-ndnegative half- Waves;

In -W1tness-- hereof, I here-unto subscribe my name th1s-30th day of-December, A. D.,

1924, v i *ART-HU-R: mosWA D.

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