US2208091A - Frequency variation response circuit - Google Patents

Description

y 15, 1940- I. zAKARlAs 2,208,091

FREQUENCY VARIATION RESPONSE CIRCUIT Filed June 5, 1957 PLHTE CURRENT FREQUENCY FREDUENCY f0 6 Fig-40 Fi9n2- AxourPgr AF. bu rpur 8 l-LEINPUT 2 I a owc ifafiu pick-140 Fig.3. Fig.4

INVENTOR- ATTORNEYS Patented July 16, 1940 FREQUENCY VARIATION RESPONSE CIRCUIT Imre Zakarias, Budapest, Hungary, assignor to Radio Patents Corporation, New York, N. Y., a corporation of New York Application June 3, 1937, Serial No. 146,180 In Hungary June 10, 1936 14 Claims.

The present invention relates to means of and a method for converting frequency variations including both the frequency of an alternating or oscillating current and the natural or tuning frequency of a resonant circuit into corresponding amplitude or intensity variations of an electric current or potential.

In practice, the problem arises in many cases to convert frequency changes into corresponding intensity changes of a current or voltage. An

example is the case of the electrostatic or condenser microphone having a diaphragm vibrated in accordance with air pressure variations produced by speech or music and causing corre- 18 sponding variations of its electrical capacity. In order to convert the capacity variations of such a microphone it has been proposed to connect the same in a resonant circuit excited by a high frequency potential having a frequency slightly dif- 30 ferent from the natural frequency of the circuit in the normal or unmodulated condition of the microphone or in other words to operate the circuit on the steep portion of its resonance characteristic. Thus, capacity variations of the ml- 35 crophone produced by speech or music cause corresponding potential variations at the terminals of the resonant circuit. If the latter are applied to an electronic device or the like operating as a rectifier, a rectified output current fluctuating 30 according to the original capacity variations or in turn the vibrations of the microphone diaphragm is obtained.

An object of the present invention is the provision of an improved method of and system for 35 converting variations of the frequency of an oscillating current or of the natural or tuning frequency of a resonant circuit into corresponding variations of amplitude or intensity of a unidirectional current or potential requiring only 40 a limited number of circuit elements compared with arrangements and methods known in the prior art.

Another object is to provide a conversion system for changing varying frequencies into corre- 5 sponding variations of amplitude characterized by greatly increased sensitivity and freedom from noise and other interference compared with prior art arrangements.

A more specific object is to convert variations 50 of electric circuit constants determining the tuning characteristics of a resonant circuit into corresponding variations of amplitude or intensity of an electric current or potential.

Still another object is to convert small variaw tions of electric capacity into corresponding relatively large variations of a direct current or potential.

A further object is to provide a discriminator circuit for producing a varying direct current or potential in accordance with the degree of de- 5 tuning of a resonant circuit relative to an alterhating potential impressed thereon.

The above and further objects of the invention will become more apparent from the following detailed description taken with reference to 10 the accompanying drawing forming part of this specification and wherein:

Figures 1 and 2 are characteristic curves explanatory of the function and operation of an electron valve conversion system for transform- 1' ing variations of frequency into corresponding variations of amplitude or intensity of an electric current or potential,

Figure 3 shows a basic circuit arrangement for practicing the invention, and 20 Figure 4 shows a modification of a circuit according to the invention.

With the above objects in view, the invention is based on what is hereafter referred to as the space charge coupling effect in multi-electrode electronic devices. This eifect may be explained by the following. Considering a four-element electron valve or tetrode of standard type comprising a cathode, a first or control grid, a second or screen grid electrode and a plate or anode and assuming further that the screen grid is biased positively in a known manner and that the plate, contrary to known practice, is given a zero or negative bias relative to the cathode,

a space charge cloud or concentration of elec- 5 trons also known as a virtual cathode will be formed between the screen grid and the plate due to the deceleration or slowing down of the electrons passing the meshes of the screen grid by the negative or zero potential on the plate. 40 This space charge will vary in accordance with s the variations of the electron current, that is in accordance with the potential impressed upon the control grid. and if the latter is a high frequency potential the space charge will oscillate at the same frequency and induce by electrostatic coupling a corresponding potential upon the plate. As a result a current will be set up in the plate circuit and corresponding voltage variations obtained at the terminals of a load impedance included in the plate circuit.

In a similar manner a high frequency potential is induced upon the fourth grid usually the input control grid of a pentagrid converter of standard construction wherein the first and sec- 56 to generate a high frequency oscillation. In this case, the voltage induced upon the fourth grid through the space charge coupling has the same a frequency as the oscillator frequency. Since the current is induced capacitatively it leads the space current potential controlling the same on the first grid by 90.

If according to the present invention in a pentagrid valve of the aforedescribed type a resonant circuit is connected to the fourth grid electrode which circuit is tuned to a frequency equal to the frequency of the induced displacement current, the voltage and current in this circuit will be in phase or in other words the circuit will represent a pure resistance to the electron discharge current. As a result, the induced voltage leads the controlling voltage by 90 thereby exerting no influence on the plate or output current of the valve. If the resonant circuit connected to the fourth grid is detuned relative to the inducing space charge frequency the induced displacement current will lead the controlling voltage by an angle greater or smaller than 90 dependent on the sense of detuning. As a result, a component of the induced voltage will be in phase with or in counterphase to the inducing voltage in such a manner that the average plate current is increased or decreased accordingly.

Referring to Figures 1 and 2 there are shown characteristic curves of a frequency converter constructed and operated in the above described manner. In Figure 1, curve A shows the output or plate current as a function of the frequency of the potential impressed upon the first control grid while curve B of Figure 2 shows the corresponding variation of the screen grid (third and fifth grid in a pentagrid valve) current f0 representing the natural or tuning frequency of the resonant circuit. Curves A and B correspond to a low damping of the resonant circuit connected to the fourth grid while curves A and B correspond to a high damping of the resonant circult. The latter is preferably a parallel tuned circuit such as shown in Figures 3 and 4 to be described presently. a

Practical experiments have shown that by'impressing a signal voltage having a frequency of about 1000 kc.upon the first control grid and by-providing a resonant circuit connected to the fourth grid having an average Q value, a detuning of the circuit by about 30 kc. resulted in a change of the plate current of about 3 ma. A'

detuning of 1% resulted in a change of 1 ma. Thus, by providing a plate load impedance of .3 megohm, voltage variations of the order of 300 volts are obtained making it possible to use the system for controlling considerable energies.

For further discussion, a converting or mixing tube of simplified construction will be considered comprising a pair of control grids, one of which serves for applying a signal or oscillating potential, while the other grid has connected to it a resonant circuit in the manner described hereinabove. The first control grid is usually placed next to the cathode and preferably a further positively biased screen grid is provided between the two control grids.

a space charge or virtual cathode is produced in the space adjacent to the second control grid. If desired, the latter may be further screened from the anode and an additional suppressor grid provided in a manner well known.

By biasing both control grids negatively relative to the cathode ond grids are connected to an oscillator system As seen from Figures 1 and 2, the damping of the resonant circuit has an influence on both the magnitude of the plate direct current changes as well as on the frequency band width which can be'transmitted and demodulated faithfully. It is furthermore possible to utilize the effect of variable damping on the output current similar to the utilization of the changes of detuning of a resonant circuit or of the impressed frequency variations as described hereinabove. If the effect of variable damping is utilized, it is advisable to operate the tube at a point of maximum plate current, point a as indicated in Figure 1.

. The resonant circuit connected, to the second grid may also be in the form of a series tuned circuit in place of a parallel tuned circuit shown in Figures 3 and 4. It may furthermore be an aperiodic circuit and comprise capacity and resistance elements only, in which latter case the circuit inductance is formed by the wiring or connecting leads. In this case, it is preferable to operate the tube not within the central or straight line portion w-b of its characteristic but rather within one of the outer branches. These branches are similar to the grid voltage-plate current characteristic of a variable mu type electron valve of the pentcde type. This operation is advantageous if the frequency-amplitude conversion is to be carried out in accordance with a non-linear such as a logarithmic function. A further characteristic of the outer branches is the fact that one is below and the other above the normal plate current by which is understood the plate current flowing through the tube if the second control grid is grounded with regard to high frequency. This feature of the characteristic may be utilized to determine whether a frequency applied to the first control grid is smaller or greater than the frequency applied to the second control grid as is often desirable in carrying out inductance, capacitance or frequency measurements by meansof a system of the type of the invention.

The plate direct current of a multi-grid converter valve of the type described varies in accordance with the phase difference between the i voltages applied to the different grids either directly or by space charge coupling as explained above thereby enabling such a valve to be employed as a power measuring device.

In employing a system of 'the aforesaid type embodying a resonant circuit connected to the second control grid and means for impressing a potential upon the first control grid having a frequency near the natural frequency of said resonant circuit, the voltage induced in said resonant circuit through space charge coupling may attain extremely large values particularly in case of short waves in such a manner that if the second control grid is not sufficiently negatively biased a grid current will start to flow. This grid current constitutes an additional damping of the resonant circuit whenever the amplitude of the high frequency potential exceeds the normal or steady biasing potential. This additional damping results in an improvement of the linear portion of the mid-section a--b of the average plate element is subject to slow fluctuations caused by external influences such as in the case of a condenser microphone operating in open air whereby displacements may be caused by air currents or drafts, an extended linear portion of the characteristic will enable a stable and faithful operation irrespective of such variations.

According to a modified arrangement, the signal input grid and the grid having the resonant circuit connected to it may be mutually exchanged, that is the resonant circuit may be connected to the first control grid of a simplified converter valve of the type above mentioned and a high frequency input potential impressed upon the second control grid. In this case the interelectrode capacity between the grids will produce the necessary coupling especially in the case of short waves whereby the same converting effect may be obtained as described and frequency changes transformed into corresponding changes of amplitude of the average plate current. For longer waves the operation can be improved by the addition of an external capacitative, inductive or galvanic coupling. However, a pure elec tron coupling has proved to be superior to other couplings for reasons similar to those well known in the operation of frequency changing electronic converter or mixer valves used in superheterodyne radio receivers.

The electron coupling effect for the purpose of the invention may also be secured in a pentagrid converter tube of standard construction by connecting the resonant circuit to the second positively biased or oscillator grid and by coupling the circuit connected to this grid with the circuit of the first grid. Since the second grid draws electrons from the space charge formed near the fourth grid a similar effect on the output current is obtained as in the previously described arrangements.

If the modulating frequencies are not to be translated uniformly in the plate circuit a frequency discriminating load impedance of desired characteristic may be provided in the latter.

As is evident from the foregoing, the present invention contemplates the employment of a multi-grid electronic discharge valve with means for impressing a voltage of constant or variable frequency upon one of the grid electrodes and a resonant circuit of constant or variable resonant frequency connected to another grid electrode, whereby said resonant circuit is excited by said impressed potential solely by coupling with the electron discharge current through said valve.

Referring to Figure 3, there is shown a basic circuit of the type according to the invention. This circuit among other uses may serve as a receiver or demodulator for frequency modulated signals. The demodulator valve 2 comprises a cathode 24 and anode of known construction, a first or signal input grid I, a second control grid and a screen grid I4 interposed between the former to prevent mutual interaction between the grids. The received frequency modulated input signals which may be derived from an antenna or any other source of high frequency signals connected to the terminals designated H. F. input in the drawing and which may have been amplified by a preceding amplifier are impressed upon the first control electrode I and the cathode 24, of the valve 2 through a grid coupling condenser 4 and a grid leak resistance 3 in a manner well understood. There is connected to the second control electrode or grid 5 and cathode 24 a'resonant impedance means such as a tuned circuit comprising an inductance 6 shunted by an adjustable condenser I and a variable resist- V ance O. In the example shown the control electrode 5 is connected to a tap point of the inductonce 6 near the high potential side of the resonant circuit 6, I, 8 to ensure most favorable operation of the system. The natural or tuning frequency of this circuit is adjusted so as to be near the carrier frequency or near one of the side-band frequencies of the impressed input signal. The resistance 8 serves to adjust the damping and operating characteristic of the circuit. It is also possible to vary the tuning or natural frequency of the resonant circuit according to a prearranged schedule in synchronism with corresponding variations of the transmitting frequency for secret communication purposes. The circuit GI is further designed to accommodate the desired modulation band width for which purpose it may be constructed as a band-pass circuit or have its damping suitably adjusted by means of the resistance 8. The demodulated output voltage is derived from the plate circuit by the aid of a low frequency load impedance orresistance 9. The high tension plate supply source is shown at I ii, and the heating supply sourceat I I. The grid biasing potential is provided in a known manner by means of a resistance I 2 inserted in the cathode lead and by-passed by a condenser I 3. The screen grid l4 surrounding the grid 5 is biased positively relative to the cathode by connection in a known manner to the positive pole of the high tension source III through a resistance l5 by-passed by a condenser I6. The high frequency currents are further by-passed in the plate circuit by a condenser I 1 while a further resistance I8 is provided in the output circuit to prevent regeneration of high frequencies. The demodulated output signals obtained from terminals A. F. may be further amplified and impressed upon a translating or reproducing device such asa loudspeaker or the like.

A system of the type described may also serve as a discriminator for automatic frequency control in a radio receiver. For the latter purpose, there is usually provided in connection with a superheterodyne receiver an error detector or discriminator system producing a steady potential varying in accordance with the degree of detuning of an incoming signal frequency relative to the fixed intermediate frequency for which the receiver is' designed and which serves to control a tune adjusting element associated with the local or heterodyne oscillator of the receiver, so as to control the intermediate signal frequency to correspond with the tuning frequency of the intermediate frequency amplifier. In using a system according to Figure 3 as a discriminator or tune responsive circuit, a potential derived from the intermediate amplifier is impressed upon the grid I through terminals H. F. and the resonant circuit 6! tuned accurately to the intermediate frequency of the receiver. The variations of the average plate current or alternatively of the screen grid current (see Figures 1 and 2) as caused by a change of the frequency of the local oscillator or detuning of the receiver are utilized in a known manner to compensate the frequency change by readjusting the local oscillating frequency. The regulating or tune adjusting voltage in this case is supplied from-the terminals A-F. The regulating range can be adjusted by controlling the damping of the resonant circuit such as by varying the resistance 8 as is understood from Figures 1 and 2, or alternatively a second intermediate frequency may be produced by double heterodyning to obtain the same purpose. Automatic frequency control can also be used in cases where the local oscillator frequency of the superheterodyne receiver is subject to variations or drift caused by external influences or for secret communication purposes.

The arrangement of Figure 3 may also be used for controlling or stabilizing the frequency of a transmitter in which case the resonant circuit 8-1 may contain a piezo crystal having a frequency corresponding to the transmitting frequency. In this case the plate current variations may serve to control the frequency of the master oscillator of the transmitter through mechanical, electro-magnctlc or pure electric means in a manner well known. Furthermore, the transmitter may be frequency modulated in a simple manner by applying frequency modulation to the circuit li| such as by the provision of a condenser microphone in the circuit provided that the frequency control is sufficiently free from inertia.

Another group of applications of the invention applies to all cases where the natural frequency of the resonant circuit is subject to periodic or irregular variations caused by external influence on the circuit constants such as the inductance, capacitance and resistance value of the circuit. In all these cases the tuning or natural frequency can be kept constant by the provision of a variable circuit element such as a plate condenser, one electrode of which has the form of a diaphragm of thin sheet metal vibratable by small variations of air pressure similar to a condenser microphone.

In this manner, mechanical displacements such as the movement of a pick-up in a phonograph, the strings of musical instruments, etc., can be transformed into electrical variations through a variable plate condenser of this type.

The invention has further use in connection with safety, alarm and signalling systems, counting and Sorting arrangements wherein variable capacities produced by the movements, etc., to be controlled may be converted in the manner described. Other details such as amplifiers, both before and after the converting system, etc., are obvious.

Referring to Figure 4, there is illustrated a modification of the invention for converting capacity variations such as those produced by a condenser microphone or other electrostatic pick-up into corresponding direct current variations. In this embodiment there is shown a valve 20 of the pentagrid type having a first grid I and a second positively biased grid l9 serving as an oscillator grid to produce a local high frequency oscillation in a manner well known. For the latter purpose the capacitative pick-up 2! serves as the tuning capacity of an oscillatory or tank circuit further comprising an induction coil 22 in parallel to the microphone 2| and connected to the grid I through a coupling condenser 4 and a grid leak 3. In order to maintain sustained oscillations in the circuit 2|, 22 the output circuit of the grid l9 includes a feedback inductance 23 coupled with the inductance 22 of the tank circuit. The third and fifth grid are biased positively in the conventional manner. The resonant circuit 6, I, 8 is tuned close to the oscillator frequency and connected to the grid and cathode 24 in a manner previously described. As a result, average plate current fluctuations caused by variations of the oscillator frequency in accordance with the vibrations of the pick-up 2| are obtained across the load impedance 9 at output terminals A. F. The system may be modifled by using an oscillator tank circuit of constant frequency (fixed condenser 2|) ,and by replacing the condenser 1 of the resonant circuit by a condenser microphone or the like as is readily understood from the above.

It will be evident from the above that the invention is not limited to the specific arrangements and methods described herein for illustration and that the underlying inventive thought and basic principle are susceptible of numerous variations and modifications coming within the broader scope and spirit of the invention as defined in the appended claims.

I claim:

1. A system of the character described comprising an electronic device having means for producing an electron space current, a pair of control grids disposed at different points in the path of said space current. means for impressing an input potential of varying frequency upon one of said grids, a resonant circuit connected to the other grid, means whereby said resonant circuit is excited in accordance with said impressed potential by electron coupling with said electron space current, an output circuit for said device, and means for deriving output energy from said device, said output energy varying in amplitude proportionately to the frequency departure of the impressed input potential from the resonant frequency to which said resonant circuit is tuned.

2. A system. of the character described comprising an electronic device having means for producing an electron space current, a pair of control grids disposed at different points in the path of said space current, means for impressing an alternating potential of substantially constant frequency upon one of said grids, a resonant circuit connected to said other grid having a natural frequency normally equal to the frequency of said impressed potential, means for controlling the resonant frequency of said resonant circuit, an output circuit for said device, and an impedance in said output circuit being effective in building up an output potential varying in amplitude proportionately to the frequency departure of the impressed input potential from the resonant frequency to which the resonant circuit is tuned.

3. A system of the character described comprising an electronic device having a cathode and an anode, a first control grid near said cathode, a second control grid disposed in spaced relation to said first grid, a further positively biased grid between said first and second grids to produce a virtual cathode adjacent to said second grid, means for impressing a high frequency potential of varying frequency upon said first grid, a resonant circuit connected to said second grid, whereby said resonant circuit is excited by capacity coupling with said virtual cathode, an output circuit for said device, and impedance means in said output circuit being effective in building up an output potential varying in amplitude proportionately to the frequency departure of the impressed potential from the resonant frequency to which said resonant circuit is tuned.

4. In a frequency variation response circuit, a source of alternating potential, a tuned circuit, the relative frequency of said source with respect to the frequency to which said circuit is tuned being variable, an electron discharge tube comprising means for producing an'electron space current and a pair of control electrodes located in the path of said space current, means for impressing potential from said source upon the first control electrode, means for connecting said tuned circuit to the second control electrode, means to produce a concentrated electron space charge near said second control electrode, the relation between the frequency of said source and the frequency to which said circuit is resonant being such that said circuit is excited by coupling with said space charge at varying phase in accordance with the relative frequency departure between said source and the resonant frequency of said circuit, an output circuit for said tube, and load impedance means in said output circuit adapted to develop output potential varying in amplitude proportionately to said frequency departure.

5. A system as claimed in claim 4 including means for controlling the damping of said tuned circuit.

6. A system of the character described comprising an electronic device having a cathode and an anode, a first control grid disposed near said cathode, a second control grid disposed in spaced relation to said first grid, a further positively biased grid between said first and second grids to produce a virtual cathode near said second grid, means for impressing a potential of substantially constant frequency upon said first grid, a resonant circuit connected to said second control grid, said resonant circuit normally tuned to the frequency of said impressed potential, means for controlling the resonant frequency of said resonant circuit, an output circuit for said device, and load means in said output circuit for deriving output energy, said output energy varying in amplitude proportionately to the frequency departure of the impressed potential from the resonant frequency to which said resonant circuit is tuned.

7. In a frequency variation response circuit, a source of alternating potential, a tuned circuit, the relative frequency of said source with respect to the frequency to which said circuit is tuned being variable, an electron discharge tube comprising a cathode and an anode for producing an electron space current and a pair of control grids disposed in the path of said space current, means for impressing potential from said source upon the grid near the cathode, means for connecting said tuned circuit to the other grid, means to produce a concentrated electron space charge near said other grid, the relation between the frequency of said source and the resonant frequency of said tuned circuit being such that said tuned circuit is excited by said impressed potential through electron coupling with said space charge at varying phase in accordance with the relative frequency departure between the resonant frequency of said circuit and the frequency of said source, an output circuit for said tube, and load impedance means in said output circuit adapted to develop output potential varying in amplitude proportionately to said frequency departure.

8. In a frequency variation response circuit, a source of alternating potential, a tuned circuit, the relative frequency of said source with respect to the frequency to which said circuit is tuned being variable, an electron discharge tube comprising a cathode and an anode for producing an electron space current and a pair of control grids disposed in the path of said space current, a screen grid located between said control grids, means for maintaining said screen grid at a positive potential with respect to the cathode, means for impressing potential from said source upon the control grid near the cathode, further means for connecting said tuned circuit to the other control grid, the relation between the frequency of said source and the resonant frequency of said tuned circuit being such that said tuned circuit is excited by said impressed potential through electron coupling with said space current at varying phase in accordance with the relative frequency departure between the resonant frequency of said circuit and the frequency of said source, an output circuit for said tube, and load impedance means in said output circuit adapted to develop output potential varying in amplitude proportionately to said frequency departure.

9. A system of the character described comprising an electronic device having means for producing an electron space current, a pair of grid electrodes disposed in one section of said space current, means comprising an oscillatory tank circuit and feedback means connected to said grids to cause sustained carrier oscillations of the electron space current, means for controlling the frequency of said oscillations in accordance with variations of a modulating magnitude, a further grid disposed in a different section of said space current, a resonant circuit connected to said further grid tuned to the carrier frequency, an output circuit for said device, and impedance means in said output circuit being effective in building up an output potential, said output potential varying in amplitude proportionately to the relative frequency departure of said oscillations from the carrier frequency.

10. A system of the character described comprising an electronic device having a cathode and an anode, a pair of grid electrodes disposed near said cathode, means comprising an oscillatory tank circuit and feedback means connected to said grids to cause sustained carrier oscillations of the electron discharge current, means for controlling the frequency of said oscillations in accordance with variations of a modulating magnitude, a control grid disposed in a different section of said discharge path, a positively biased grid connected between said first mentioned grids and said control grid, a resonant circuit connected to said control grid tuned to the carrier frequency, an output circuit for said device, and impedance means in said output circuit being effective in building up an output potential, said output potential varying in amplitude proportionately tothe frequency departure of said oscillations from the carrier frequency.

11. A system of the character described comprising an electronic device having a cathode and an anode, a pair of grid electrodes disposed near said cathode, a regenerative system connected to said grids to cause sustained oscillations of the electron discharge current between said cathode and anode of substantially constant frequency, a control grid in the path of said electron current, a further positively biased grid disposed between said first mentioned grids and said control grid, a parallel tuned resonant circuit connected to said control grid normally tuned to the frequency of said oscillations, means for controlling the resonant frequency of said resonant circuit, an output circuit for said device, and impedance means in said output circuit being effective in building up an output potential, said output potential varying in amplitude proportionately to the frequency departure of said oscillations from the instantaneous resonant frequency of said resonant circuit.

12. A frequency variation response circuit comresonant impedance means, the relative frequency of said source with respect to the frequency to which-said impedance means :is resonant being variable, an electron discharge tube comprising means for producing an electron space current, control means including circuit connections from said source to said electron-tube for varying said space current in accordance with said signal potential, a control electrode in said tube adapted to vary said electron space current in accordance with an electric potential applied to it, means for connecting said resonant impedance means to said control electrode, further means for producing a concentrated electron space charge adjacent to said control electrode, the relation between the frequency of said source and the fre: quency to which said impedance means is res; onant being such that said control electrode is excited at varying phase by said signal potential by coupling with said space charge in accordance with the relative frequency departure of said source from .the resonant frequency of said impedance means, an output circuit for said tube, and means operatively associated with said output circuitfor developing energy varying in amplitude in proportion to said frequency departure.

13. A frequency variation response circuit comprising an electron discharge tube having means for producing-an electron space current, a source of alternating signal potential of varying frequency, control means including circuit connections from said source to said electron tube for varying said space currentin accordance" with said signalpotential, a control grid in said tube, resonant impedance means connected to said controlgrid, means whereby said control grid is excited by said signal potential substantially by electron coupling with said space" current, an output circuit for said tube, and means operative- 1y associatedwith said output circuit for developing energy varying in amplitude proportionately to the frequency departure of said signal potential from the resonant frequency of said impedance means.

14. A frequency variation response circuit comprising an electron discharge tube having means for producing an electron space current, a source of alternating potential of substantially constant fr uency, control means including circuit connec ions from said source to said electron tube for varying said space current in accordance with said alternating potential, a control grid electrode in said tube, resonant impedance means connected to said grid electrode having a resonant frequency normally equal to the frequency of said source, means for controlling the resonant frequency of said impedance means, means whereby said control grid is excited by said signal potential substantially by electron coupling with said space current, an output circuit for said tube, and

means operatively associated with said output circuit for developing energy varying in amplitude proportionately to the departure of the resonant frequency of said impedance means from the frequency of said source.

IMRE ZAKARIAS.

Images