US2213103A - Energy absorbing device - Google Patents

Description

Aug. 27, 1940. T. M. GLUYAS. JR 313,103

ENERGY ABSORBING DEVICE Filed larch 15, 1959 Load.

Carrier Frequency Sou-roe Z7 Vraii Patented Aug. 27, 1940 UNITED STATES PATENT OFFICE ENERGY ABSORBING DEVICE of Nevada Application March 15, 1939, Serial No. 262,041

8 Claims.

This invention relates to improvements in controllable energy dissipating means for use in modulating systems of the energy absorption type. More particularly, the invention relates to energy dissipating means employing space discharge devices, and to a method of and means for eliminating the undesired effects produced by the fortuitous capacities in the space discharge devices.

In a copending application of William N. Parker, Serial No. 84,534, filed June 10, 1936, there is disclosed and claimed a modulating system of the energy absorption type which is particularly useful in the generation of a modulated high frequency carrier signal for television purposes where a wide band of frequencies must be transmitted for satisfactory picture reproduction. In that application, there are provided means for accomplishing modulation at a high level and with a considerably, greater efficiency, as well as for a wider band of frequencies, than is possible with prior systems. The principal feature of the Parker system resides in shunting a high impedance source of carrier frequency energy by a controllable energy dissipating impedance which is variable in response to a modulating signal. In order that the system shall function in the most satisfactory manner, it is desirable that the modulating impedance be purely resistive, variable in magnitude in response to a modulating signal, and reduceable to zero for a reasonable value of the modulating signal on the valleys of modulation. The Parker application discloses a very satisfactory form of modulating impedance comprising a plurality of space discharge devices which serve to dissipate carrier frequency energy and thereby generate sideband components in response to the modulating signal which is impressed on their grids. The resulting impedance, which is a combination of the plate impe iances of the space discharge devices, is inverter! by means of a quarter wave-length transrmssion line or other suitable impedance-inverting means. Thus there is produced an impedance which is variable from zero to a very high value, as clearly set forth in the said Parker application.

It is observed in the Parker application that a certain amount of capacitive reactance is introduced at the modulator endof the impedanceinverter due to the inherent capacitance between the several anodes, grids and cathodes of the energy dissipating tubes. This capacitive component is inverted by the transmission line and contributes an inductive component to the impedance appearing at the other end of the line.

ASeveral means are disclosed in the Said Parker application and in a subsequent continuation-inpart thereof, Serial No. 252,204, filed January 21, 1939 whereby it is possible to overcome the effect of the tube capacitance and to produce a modulating impedance which is substantially purely resistive. One method consists in shunting the output circuits of the energy dissipating tubes by an inductance of suitable magnitude to tune out the capacitance of the tubes at, the carrier frequency. Another method consists in shortening the effective electrical length of the transmission line or other impedance-inverting means coupled to the modulating tubes. In this case a capacitance may be introduced at the load end of the impedance inverter. This capacitance, in conjunction with that of the tubes at the other end of the line, operates to fill out the shortened line and to make its electrical length equal to one quarter wave length of the carrier frequency.

The present invention is directed particularly to this phase of the production of an energy dissipating device of the type disclosed in the said Parker applications. Its principal object is to provide an improved means for obtaining an inductive component in shunt with the outputs of the energy absorbing tubes in such a device. An advantage of the method of this invention is that it permits this inductive component to be introduced without the use of an actual physical inductance shunted across the outputs of the said modulating tubes.

Further features of the invention will appear from the following description and the accompanying drawing in which:

Fig. 1 is a schematic diagram of one embodiment of the invention;

Fig. 2 is an explanatory diagram which will be referred to in explaining the operation of the system of Fig. 1; and

Fig. 3 is a schematic diagram showing a modification of a portion of the circuit of Fig. 1.

Referring first to Fig. 1, there is shown a modulating system which, aside from the features of the present invention is substantially the same as that shown in the aforementioned continuationin-part application Serial No. 252,204. For convenience of showing and for purposes of emphasis, only that portion of the circuit which constitutes the modulating impedance is shown in detail, the other portions being given conventionalized representations. Carrier frequency energy is obtained from the source S which is coupled to a junction point 2 by means of a transmission line I having an electrical length substantially equal to one-quarter wave length of the signal.

' gether.

According to the Parker system, the impedance of the carrier source is low and is inverted to appear as a high impedance at the junction point 2. Thus there is produced at the junction point 2 an effective high impedance carrier frequency source. A second quarter wave line 3 connects the junction point with the load L which may be an antenna suitable for radiating the carrier frequency signal. Modulating tubes 4 have their plates coupled to the junction point 2 through the line 5. The electrical length of this line is not necessarily equal to one-quarter wave length but the line may be of such a length as to form, in

conjunction with the capacities appearing at its two ends, an impedance inverter of effective electrical length equal to one-quarter wave length. between the plates of the tubes and the junction point. Such impedance-inverter is resonant at a frequency within a certain frequency range comprising frequencies in the vicinity of the carrier frequency, and it forms an impedance substantially inversely proportional to the effective impedance of the tubes 4 for wave signals within said range. Modulating voltage is supplied between the grids and cathodes of the tubes 4 through the chokes l3 from the source Em, the grids and cathodes respectively being tied to- A return lead 6 is provided between the cathodes of the modulating tubes and a center tap on the inductance 1 shunted across the junction point 2, as taught by Parker, to provide a path for rectification products resulting from the modulation process. The inherent capacity introduced by the modulator tubes is represented at 8, and any capacity which may appear at the junction point due to the end effects of the transmission lines, as a result of the junction of several lines at a single point, or which may purposely be introduced at that point, is represented at 9.

According to the present invention, an inductive reactance is, in effect, made to appear in the output circuits of the space discharge devices 4 by causing a component of the carrier frequency plate current, when considered as flowing out of the line 5, to lag the carrier frequency plate voltage by ninety degrees. This is accomplished by applying to the grids of the modulator tubes a voltage of carrier frequency which lags the voltage in the plate circuit by the same amount. Such a voltage is obtained by changing the phase of the voltage derived from any one of a number of points in the circuit at which carrier frequency voltage appears. The change in phase may be produced by a transmission line of appropriate electrical length. For example, in Fig. 1 the carrier voltage is derived from the junction point 2 and is fed back in the opposite phase to the grids of the tubes 4 by means of the transmission line H] whose electrical length is substantially equal to a half-wave length or an odd number of halfwave lengths. It will be noted that blocking condensers are interposed between the transmission line ill and the grids of tubes 4 to prevent shortcircuiting of the modulating source Em while permitting the desired feed back of the carrier voltage. The voltage on the plates of the tubes lags that at the junction point by ninety degrees, and hence a component of the plate current will lag the plate voltage by ninety degrees. The manner in which this obtains will be seen more clearly upon reference to Fig. 2 which is a vector diagram showing the inter-relations in phase between the various currents and voltages. The magnitude of the carrier frequency voltage in the grid circuit and that of the lagging component of plate current are exaggerated for purposes of clarity. In the diagram the following vector symbols are used:

The magnitude of the voltage which must be fed back will depend on the magnitude of the capacitance for which it is desired to compensate. For example, when the capacity shunted across the junction end of the line is negligible it may be desirable to neutralize. or balance out the entire tube capacity in "which case the electrical length of the line 5 itself may be made equal to a quarter wave length. On the other hand, when an appreciable capacity appears at the junction point, it is preferable to have a certain amount of the tube capacity unbalanced to form in conjunction with the line 5 and the junction capacity an impedance inverter whose effective electrical length is a quarter wave length of the carrier frequency. In this case the line itself may be appropriately shortened. Whatever the magnitude of the capacitive component desired t may be obtained by-applying to the grids of the tubes 4 a carrier frequency voltage of suitable magnitude determined, for example, by the choice of the characteristic impedance of the transmission line I.

Fig. 3 illustrates another method of feeding back carrier frequency voltage. Only that portion of the circuit is shown which is associated immediately with the modulator tubes 4. The remainder of the system may be similar to Fig. l. The principal modification introduced in Fig. 3 is the derivation of carrier frequency voltage from the plates of the modulating tubes. In the embodiment shown this is accomplished by means of high resistances H and capacitances l2, the resistors being connected between the plates and grids, and the condensers being connected between the grids and cathodes of the respective tubes. With the resistances sufficiently large by comparison with the carrier frequency reactance of the condensers l2, the current through the series combination will be in phase with the plate voltage. The carrier voltage impressed on the grids will lag this current and the plate voltage by approximately in accordance with the diagram of Fig. 2.

The foregoing description of the invention has dealt solely with its application in a particular type of modulating system with reference to two embodiments thereof but this should not be regarded as restricting the method to application only in the arrangements shown. For example, both of the embodiments show a pair of tubes operating in push-pull to give greater efficiency and to obviate the need for a D. C. supply to their plates. It will appear that it would be feasible under certain circumstances to employ but a single tube or a plurality of tubes to which the method herein disclosed could be applied with but a slight modification of the apparatus here disclosed. My invention contemplates such varia tions and may be regarded as applicable to modulating systems in general subject only to the restrictions imposed by the following claims.

I claim:

1. In a device for dissipating electrical wave energy having a frequency within a certain range, at a rate variably in response to a control signal; energy dissipating means including a space discharge device having an anode, a cathode, and a control grid, said space discharge device having a fortuitous capacity appearing between its anode and its cathode; a source of a control signal coupledto the grid circuit of said space discharge device for controlling the energy dissipation therein; an impedance-inverter comprising a transmission line resonant at a frequency within said range, said line having one end coupled to the anode circuit of said space discharge device for forming an impedance substantially inversely proportional to the impedance of said dissipative means for wave signals within said range; and further transmission line means having an input circuit and an output circuit and having an electrical length substantially equal to an odd number of half wavelengths for wave signals within said range, said last-mentioned means having its input circuit coupled to the other end of said first transmission line and its output circuit coupled to the grid circuit of said space discharge device, for supplying thereto a signal whose frequency is the same as that of the energy to be dissipated and whose phase is substantially in laggingrelation with respect to the signal in the anode circuit of said space discharge device.

2. In a system for dissipating electrical wave energy, at a rate variable in response to a control signal; a source of wave energy to be dissipated; an energy dissipating space discharge device having at least a cathode, a grid, and an anode; means for coupling said anode to said source and for forming an effective impedance invefler for inverting the impedance of said space discharge device; a source of control signal coupled to the grid of said space discharge device for controlling the dissipation of energy thereby; means for deriving from the system a signal of predetermined magnitude whose frequency is substantially equal to that of said wave energy and whose phase is substantially in 90 lagging relation with respect to the signal appearing at said anode; and means for applying said derived signal to the grid of said space discharge device, whereby an inductive component is introduced in the impedance appearing between said anode and said cathode, said inductive component varying in such a manner with the control signal applied to said grid that said inverted impedance is substantially purely resistive for all values of control signal applied to said grid.

3. In a system for dissipating electrical wave energy having a frequency within a certain range, at a rate variable in response to a control signal; energy dissipating means including a space discharge device having an anode, a cathode and a control grid, said space discharge device having fortuitous capacity appearing between its anode and its cathode; a source of a control signal coupled to the grid circuit of said space discharge device for controlling the energy dissipation therein; means coupled to the anode circuit of said space discharge device forming an effective impedance inverter resonant at a frequency within said range to invert the impedance of said dissipative means for wave signals within said range; means for deriving from the system a signal whose frequency is the same as that of the energy to be dissipated and whose phase is substantially in 90 lagging relation with respect to the signal in the anode circuit of said space discharge device; and means for applying said derived signal to the grid circuit of said space discharge device, the magnitude of said derived signal being such as to substantially neutralize the undesired capacity of said space discharge device, whereby the inverted impedance of said space discharge device is caused to be substantially purelyresistive.

4. In a system for dissipating electrical wave energy having a frequency within a certain range, at a rate variable in response to a control signal; energy dissipating means including a space discharge device having an anode, a cathode and a control grid, said space discharge device having fortuitous capacity appearing between its anode and its cathode; a source of a control signal coupled to the grid circuit of said space discharge device for controlling the energy dissipation therein; a transmission line coupled to the anode circuit of said space discharge device, said transmission line being of proper length to form in cooperation with said fortuitous tube capacity an eifective impedance inverter resonant at a frequency within said range to invert the impedance of said dissipative means for wave signals within said range; means for deriving from the system a signal whose frequency is the same as that of the energy to be dissipated and whose phase is substantially in 90 lagging relation with respect to the signal in the anode circuit of said space discharge device; and means for applying said derived signal to the grid circuit of said space discharge device, whereby an inductive component is introduced in the impedance appearing between said anode and said cathode, said inductive component varying in such a manner with the control signal applied to said grid that said inverted impedance is substantially purely resistive for all values of control signal applied to said grid.

5. In a system for dissipating electrical wave energy having a frequency within a certain range, at a rate variable in response to a control signal; a source of wave signal energy to be dissipated, said source having a capacitive reactive impedance component appearing'across its output terminals; energy dissipating means including a space'discharge device having an anode, a cathode and a control grid, said space discharge device having a fortutious capacity appearing between its anode and its cathode; a source of a. control signal coupled to the grid circuit of said space discharge device for controlling the energy dissipation therein; a transmission line connected between the anode circuit of said space discharge device and said first source, said transmission line being of proper length toform in cooperation with said fortuitous tube capacity and the capacitive reactance of said first source an effective impedance inverter resonant at a frequency within said range for inverting the impedance of said dissipative means for wave signals within said range; means for deriving from the system a signal whose frequency is thesame as that of the energy to be dissipated and whose phase is substantially in 90 lagging relation with respect to the signal in the anode circuit of said space discharge device; and means for applying said derived signal to the grid circuit of said space discharge device, whereby an inductive component is introduced in the impedance appearing between said anode and said cathode, said inductive component varying in such a manner with the control signal applied to said grid that said inverted impedance is substantially purely resistive for all values of control signal applied to said grid.

6. In a device for dissipating electrical wave energy having a frequency within a certain range, at a rate variable in response to a control signal; energy dissipating means including a space discharge device having an anode, a cathode and a control grid, said space discharge device having a fortuitous capacity appearing between its anode and its cathode; a source of a control signal coupled to the grid circuit of said space discharge device for controlling the energy dissipation therein; means coupled to the anode circuit of said space discharge device for forming an effective impedance inverter resonant at a frequency within said range to invert the impedance of said dissipative means for wave signals within said range; and transmission line means having an input circuit and an output circuit and having an electrical length substantially equal to an odd number of half-wave lengths for wave signals within said range, said last-mentioned means having its input circuit coupled to said impedance inverter and its output circuit coupled to the grid circuit of said space discharge device, for supplying thereto a signal whose frequency is the same as that of the energy to be dissipated and whose phase is substantially in 90 lagging relation with respect to the signal in the anode circuit of said space discharge device, whereby an inductive component is introduced in the impedance appearing between said anode and said cathode, said inductive component varying insuch a manner with the control signal applied to said grid that said inverted impedance is substantially purely resistive for all values of control signal applied to said grid.

'7. In a device for dissipaating electrical wave energy having a frequency within a certain range, at a rate variable in response to a control signal; energy dissipating means including a space discharge device having an anode, a cathode, and a control grid, said space discharge device having a fortuitous capacity appearing between the anode and its cathode; a source of a control signal 'coupled to the grid circuit of said space discharge device for controlling the energy dissipation therein; means coupled to the anode circuit of said space discharge device for forming an effective impedance inverter resonant at a frequency within said range to invert the impedance of said dissipative means for wave signals within said range; means for deriving a signal from the anode circuit of said space discharge device of the same frequency as the energy to be dissipated; means for shifting the phase of said derived signal so as to cause it to lag the voltage in the anode circuit of said space discharge device by approximately 90; and means for applying said derived signal to the grid circuit of said space discharge device, whereby an inductive component is introduced in the impedance appearing between said anode and said cathode, said inductive component varying in such a manner with the control signal applied to said grid that said inverted impedance is substantially purely resistive for all values of control signal applied to said grid.

8. In a device for dissipating electrical wave energy having a frequency within a certain range, at a rate variable in response to a control signal;

energy dissipating means including a space discharge device having an anode, a cathode and a control grid, said space discharge device having a fortuitous capacity appearing between its anode and its cathode; a source of a control signal coupled to the grid circuit of said space discharge device for controlling the energy dissipation therein; means coupled to the anode circuit of said space discharge device for forming an effective impedance inverter resonant at a frequency within said range to invert the impedance of said dissipative means for wave signals within said range; and means including a transmission line for supplying to the grid circuit of said space discharge device a signal whose frequency is the same as that of the energy to be dissipated and whose phase is substantially in 90 lagging relation with respect to the signal in the anode circuit of said space discharge device, whereby an inductive component is introduced in the impedance appearing between said anode and said cathode, said inductive component varying in such a manner with the control signal applied to said grid that said inverted impedance is substantially purely resistive for all values of control signal applied to said grid.

THOMAS M. GLUYAS, JR.

Images