US1768418A - Space discharge system - Google Patents

Description

June 24,1930; A,A,OSV'VALDE AL 7 1,768,418

SPACE DISCHARGE SYSTEM g /2h 20 if LEE Filed Dec. 1924 INPUT II; 4 OUTPUT //7ve/2f0r s--1 fifty/A flan Mi CST Patented June 24,

"STATES Nil" ARTHUR A. osWALD, or EAsT ORANGE, Ann mm: c.- soHELLENG, onMILLBUnn, New

JERSEY,

nssrenons To 'WES'IERN nLncTn-rc coiarANY, .moonrona'rnn, or new YORK, N. Y., A. CORPGBATION OF NEW YORK SPACE ms'cnanen sYsTEM Application filed December 4, 1924. Serial No. 758,805.

This invention relates to prevention of undesired oscillations in an electric system includmg parallel connected electrlc discharge devices. It is particularly applicable to carrier wave signaling systems in which three electrode discharge devices are used to supply carrier waves or impulses of high power and high voltage to a transmitting circuit.

As is well known, when electric discharge devices each comprising a closed vessel having an electronic cathode, an anode and control electrode 01' grid, are connected in parallel to supply energy to a load circuit, there is a tendency toward the production of tree oscillations or singing in the system com prising the devices and their associated circuits. These oscillations are especially undesirable in cases where the system is to be used faithfully to reproduce high frequency waves impressed on the input circuit of the devices, as in carrier si naling systems; since, among other disadvantages their production often prevents the system from operating at the desired frequency, causes distortion oi the form of the wave to be repeated, wastes energy by diverting it from a useful purpose thereby reducing the efficiency of the system and causes serious overheating of the circuit conductors and lead-in wires for the electrodes of the discharge devices, whereby the devices are liable to be destroyed. I a I 7 It is generally accepted that the production of undesired or spurious oscillations is due to the cyclic transfer of energy from the output circuits of the devices to their input circuit, the amplitude and phase of this energy relative to that traversing the output circuits being such as to set up and maintain a current flowingin the system, the frequency of which is determined by some or all of the inherent reactances of the system. The inherent r'eactances of a system of this kind may be defined as consisting of the small inductances of the leads connecting their grids, the smallinductances of the leads connecting their plates, and the internal grid-filament, grid-plate and filamentplate capacities of the parallel connected devices, as well as the difl'ere'nt inductances small power low voltage simple installations.

Owing to the complexities involved in placing a large number of tubes in simple parallel relation it has been found advisable to group the tubes into separate banks and then to connect the banks in parallel relation.

When this is done it has been found that there are several'possible modes of singing which become effective as the power is in creased. I 7

One mode of singing which may be styled intra-tube singing has been readily eliminated by the proper geometrical positioning of the tubes and their associated circuits.

Inter-tube singing, that is singing vresulting from the cooperation of a pair, or groups of tubes in a bank has been substantially eliminated by the arrangements shown and described in the application of Oswald and Schelleng, Serial No. 645,027 filed June 13,

1923. Forthat purpose the system there disclosed includes a network of inductances and resistances (fragmentarily shown in the bank 9) interconnecting the plates or the grids or both the plates and the grids of the tubes comprising the bank. When this was done, however, it was found that the tubes in the two banks still coacted to produce interbank singing. a

Interbank singing may be defined as singingresulting from the cooperation of r a plurality of banks oftubes and has been eliminated in practice. bya system shown and described in an application of J. G.

Sche'lleng, Serial No. 700,554, iiled March] 20, 11924, in which aninterbank reactor is used in the common grid or the common plate connections of the two banks of tubes. The interbank'reactor comprises, an inductance having a resistance connected in parallel thereto and has its terminals connected to the common conductors or bus bar's c0nnecting the corresponding electrodes of the discharge devices of the different units. Intermediate points of the elements of the re actor device are connected together and to the common circuit connecting the input or output apparatus to the space discharge systerm.

This arrangement was found to eliminate the interbank singing but when high power is used, such as 200 k. W. in the output circuit in an amplifier consisting of two blanks of ten tubes each, very troublesome singing was still noted.

In a'particular installation such as noted above which was operated to amplify a speech band in the general-region of 57,000 cycles, it was found that spurious oscillations were being set up at a frequency of about 1,100,000 cycles greatly interfering with the operation of the systems. After investigation it was concluded that these oscillations resulted from the coaction of inductances and capacity to ground of certain elements and leads in the input and output circuits.

Whatever the nature or cause of these undesired oscillations, their presence, for the reasons given above is detrimental to the proper operation of the system.

Consequently, a general object of this invention vis to eliminate undesired high frequency oscillations in a high power carrier wave transmission system. A further ob ject is to improve the quality of the transmitted signal. A still further object is to reduce the losses, increase the overall efficiency and reduce interruptions to service in a radio transmission system employing high power vacuum tube arrangements.

A particular object is the prevention of singing in a high power vacuum tube installation consisting of a bank of tubes or a plurality of banks of tubes to which previous methods of preventing intra-tube, intertube, and interbank singing have been applied.

A special object of the invention is the accomplishment of the above named objects in a push-pull amplifier system.

The circuit arrangement so far found most useful in accomplishing the objects of the invention consists of a resistance and a capacity connected between the common grid connections of the high power amplifier banks and ground. This path is of high impedance for signal and carrier frequencies but is of low impedance for the undesired oscillations. This path may be regarded as shunting to ground and dissipating the undesired oscillations or alternatively as altering the constants of the oscillation circuit in which the spurious oscillations tend to occur so that it is incapable of producing free oscillations.

The novel features which are believed to be characteristic of this invention will be pointed out with particularity in the claims appended hereto. The invention itself, however, as to its objects and advantages, the details of its organization and the mode of its operation will be better understood by referring to the following description taken in connection with the accompanying drawing in which Fig. l is a diagrammatic rep resentation of a radio signaling system embodying one form of this invention and Fig. 2 shows this invention applied to a pushpull amplifier.

In the system shown in Fig. 1, a modulator M is supplied by current of signal frequency from source S and by a current of carrier frequency from the source 0, which currents are combined to form a modulated carrier current. This modulated current is then impressed upon filter F which may be designed to pass the side bands and carrier frequency component and suppress the components of signal frequency. Filter F, however, is preferably designed to pass only one side band. The components passed by this filter are impressed upon amplifier A which may consist of any number of stages but in this particular system consists of three stages of amplification. The output energy from this amplifier is impressed. by means of transformer 1 upon an amplifying device 2 comprising a fourth stage of amplification. The output energy from the device 2 is impressed upon the fifth stage of amplification consisting of banks 9 and 10 through conductors 3 and 5 and tuned coupling circuit 4, in which R, is an inductive resistance of 100 ohms; L is an inductance of such value that its impedance at 57,000 cycles equals 100 ohms; C and L in connection with R and L are of such value that the circuit is resonant at 57,000 cycles.

Resistance R across the secondary of transformer 1, equal to one half the minimum input impedance of tube 2 serves to stabilize the output impedance of amplifier A when tube 2 is operating at substantially maximum output.

The details of the apparatus and manner of connection of the fifth stage of amplification are described in the application of Oswald and Schclleng referred to above. Space current is supplied to the anodes of the fourth and fifth stages from source 21 through inductances 17 and 18 which offer a high impedance to high frequency currents. Condenser 25 serves as a by-pass around source 21 for high frequency currents. Grid potential is applied to amplifiers 2 and 9 by source 24 and filters F and F respectively. Potentiometers 22 and 23 of 2,000 ohms and 34; ohms resistances respectively, provide means for adjusting the grid potential applied from source 24. The grid polarizing potential is supplied through filters F and lli) 'F which are so designed that the impedance between the grid connection and the ground terminal is low for all frequencies except zero (D. C.) to prevent a blocking action vhich might otherwise occur under certain conditions. Although the values of the elements of these filters may be varied over wide limits the following values have been found useful. C and C 2 mf.; C i not; C and C mi; L and L 1 to 5 henries; L 1 to 5 milhenries. The direct cur- I rent to the grid in the fifth stage is from .5 to 2 amperes, and in order to prevent distortion caused by changes in the grid polarizing potential which result from variations inthis current, the impedance of the potentiometer 28 is made relatively low. About 2.5 k. w. is expended in the potentiometer, the grid polarizing potential being of the order of 290 volts. The current flowing through the potentiometer is five times the grid current.

An interbank reactor 6 is shown in the grid leads of banks 9 and 10. It may, however, be inserted in the plate lead of the banks or omitted if not needed in the particular apparatus to prevent interbank singing. Switches 7 and 8 are shown for cutting this reactorout of circuit. The details of the reactor 6 and its manner of connection are fully set forth in the applicationof Schelleng above referred to.

The output energy from banks 9 and 10 is' impressed upon the antenna circuit 13 by means of tuned coupling circuit 19 and radiated therefrom. Condenser 12 serves as a blocking condenser to prevent short circuiting the source 21 to ground. Capacity 14 in connection with inductance 20 will operate as a tuned circuit to increase the efficiency of the system.

An impedance path comprising resistance 15 of 100 ohms and condenser 16 of 2,000 mmf. capacity is connected between the common grid. lead 5 and ground. Condenser 16 presents high impedance to currents of signal and carrier frequencies but will be or low impedance to high frequency currents such as are present as undesired oscillations which will be conducted to ground through resistance 15. In other words the constants of the oscillation cricuit which result in.

Reactance coil 28, connected across the ing the parallel opposing reactance of the two halves of coil 28, forming a shunt tothe grid filament circuit at thetuhes, is tuned to the frequency at which singing occurs. In a particular installation this frequency was estimated tobe 11,000 kilocycles. Re sistance introduces a damping inpedence to these oscillations which prevents them building up.

Although the 7 effect of different elements in a circuit cannot be accurately discussed without a consideration of the other ele ments, the function ofthe condenser and resistance can be qualitatively indicated as follows: In order to have sustained oscillations in any closed path, it is necessary that the sum of the impedances around that path be zero, i. e., the reacta'nces must be zero and the resistances must be zero. At frequencies for which there 1s a tendency for spurious oscillations the input impedance of the power bank has a negative resistance component. To prevent this oscillation from occurring by means of a modification in the grid circuit it is necessary to design the latter such that its impedance looking back from the tube has such values throughout the negative resistance frequency band that the above conditions are not met. That is, either (1), it must have a positive resistance greater than thenegative component of the input impedance or (2), the reactance must not balance out that of the input impedance. The function of the resistance is to meet condition (1). In case the resist an'ce is not used, the condenser maybe large enough to prevent oscillations by meeting condition (2) by effectually short circuiting the input circuit. Another function of the condenser is to avoid short circuiting the input circuit at the frequency of opera tion. It has been found advisable to use the condenser and resistance in combination for this reason.

It is presumed that capacity 14 at the high frequency of the spurious oscillations has an inductive reactance which coacts with the inductive reactance of tuned circuit 4 of possibly with other elements con nected to the grid circuit of amplifier 9, 10 and in connection therewith causes oscillations. The capacity to ground of condenser 12 becomes noticeable at high frequencies and may coact with inductance of capacity 14 to form a tuned circuit in'its plate lead. In a particular case it has been found advisable to construct, capacity lt of a large number of small units. The leads connecting these units with each other and lUl) with adjacent apparatus have an appreciable inductance which becomes effective at high frequencies to cause oscillations. Although all leads are kept as short as possible, they necessarily have some inductance at high frequency and it is these inductances which are believed to cause the oscillations above referred to. Whatever may be the cause of these oscillations, however, impedance devices 15 and 16 eliminate them.

It has been found advisable to employ the resistance 15 and condenser 16 in addition to the means for preventing intra-tube, intertube and interbank singing, it having been found that, although applying means such as the resistance-inductance network illustrated in part in the bank 9 and the interbank reactor stopped certain types of spurious oscillations, a new oscillating condition persisted. This condition continued troublesome until eliminated by an impedance path comprising elements 15 and 16.

Although this invention has been shown and described as applied to particular systems, it should be understood that it is not limited to this system but only in accordance with the spirit of the invention as defined in the following claims.

What is claimed is:

1. In a space discharge system, including a plurality of units comprising one or more tubes, the method of preventing the production of undesired oscillations of a frequency higher than that of the desired waves in the system which comprises introducing a path to ground consisting of high impedance for waves of desired frequency and low impedance for said undesired oscillations.

2. A space discharge system comprising a plurality of space discharge units, means comprising a high impedance path for desired oscillations and a low impedance path extending between certain elements of said units and ground for undesired oscillations of a frequency higher than that of the desired waves.

3. In a space discharge system comprising a plurality of space discharge units having electrodes, means comprising a high impedance path for desired oscillations and a low impedance path for undesired oscillations of a frequency higher than that of the desired waves connecting the electrodes of said units to ground.

4. In a space discharge system comprising a plurality of space discharge units, means comprising a resistance and a capacity in series having high impedance for desired oscillations and low impedance for undesired oscillations of a higher frequency than that of the desired oscillations adapted to form a shunt path for said undesired oscillations.

5. In a space discharge system comprising a plurality of space discharge devices having electrodes, means comprising a resistance and a capacity in series in the alternating current portion of the system adapted to connect said electrodes to ground whereby a positive decrement is maintained for undesired oscillations.

6. In a space discharge system comprising a plurality of space discharge devices having electrodes, means connecting some of said electrodes to ground comprising a capacity and a resistance in series in the alternating current portion of the system, said capacity adapted to offer high impedance to desired oscillations and low impedance to undesired oscillations, and said resistance adapted to dissipate said undesired oscillations.

7. In a space discharge system, a plurality of space discharge devices having electrodes,

means connecting some of said electrodes to ground, comprising a capacity and a resistance in series adapted to offer high impedance to desired oscillations whereby they are caused to traverse the space discharge devices and low impedance for undesired oscillations of a higher frequency than that of the desired oscillations whereby they are passed through said resistance and dissipated.

8. A system comprising a plurality of space discharge devices connected in parallel, a system of impedance elements connecting certain electrodes of said devices including at least one grid electrode with certain electrodes of other devices to prevent oscillations, and a capacity in series with a resistance connected between the grids of said elements and ground.

9. A system of space discharge devices comprising a plurality of tubes, a source for supplying signal waves to said tubes, an inductance and a resistance connected in parallel between at least two of said tubes and with respect to said source, and a path includin a resistance extending from an intermediate point of said inductance to ground.

10. A combination in accordance with claim 9 in which said path includes a condenser.

11. A combination in accordance with claim 9 in which said path includes a condenser and a resistance in series.-

12. A system of space discharge devices comprising a plurality of tubes, a circuit coupling certain of said tubes including inductance and capacity, and means to prevent the production of undesired oscillations including a path to ground from an intermediate point in said inductance, said path containing a resistance element.

13. A system of space discharge devices comprising a plurality of tubes, a circuit coupling certain of said tubes including inductance and capacity, and means to prevent the production of undesired oscillations including a path to ground from an intermediate point in said inductance, said path containing a condenser.

14. A system of space discharge devices comprising a plurality of tubes,-a circuit coupling certain of said tubes including inductance and capacity, and means to prevent the production of undesired oscillations including a path to ground from an intermediate point in said inductance, said path containing a condenser and a resistance in series.

In Witness whereof, We hereunto subscribe our names this lst'jflay of December, A. D.,

ARTHUR A. OSWALD, JOHN C. SCI-IELLENG.

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