US2582673A - Circuit arrangement for wave length modulation - Google Patents

Description

1952 w. w. BOELENS 2,582,673

CIRCUIT ARRANGEMENT FOR WAVE LENGTH MODULATION Filed July 15, 1946 6 2 a r J M 7.

INVENTOR AG NT Patented Jan. 15, 1952 1 I Clitoolr ARRANGEMENT FOR WAVE LENGTH Mon LA'noN Willem Wig-gar Boele ns, Eindhoven, Netherlands, assignor to Hartford National Bank and Trust Company, Hartford, Conn, as trustee Application July 15, 1946, Serial No. 683,696 In he. etherland February 25, .343

Section 1, Public Law 690, August 8, 1946 I Patentvexpires February'25, 1963 By r aetaoce ube is me n ber inaiter a di -ii;

char e tube which is c nnecte in. such man that f r the os ill ti ns to be odu ated th occurs b tween two el trodes a eac anee w ic depends upon he s o e of: one of the tube s e-racteris ics For his purpose it rae-;

ie o utilize. n the tube in qu tion to h oscillations o be medulat se ea led wattles cedbacla 1 ea feedback with wh h there occur i the .feedbacs ,nu t a Phase displac m nt i anproxii ately 0 In a cireuibarrai sement kno n :ior this our case th re is provided betwe n t e a ils an th on rol. g d oi a ischar e tube. for exampl t ede or a osmot c, such a phase-ro at n network that the control grid alternating voltago of the frequency of the o cilla i ns to bi? me la is o of phase by approx mately 9.0.' with re pec to the anode alternating voltage. Th anode 5 c aims. (oi. 332%18) iii).

ouency or phase-displacement and of the frealternating current exhibits in this case likewise v a phase displacement of approximately 90 with" respect to the a de lternating voltage, so tha between he anode an e ca ode .thereoccur a al eae nee Wh se ue is inversely proportional to the slope of the discharge tube. The phase-rotating network consists as a rule of an ohmic resistance and a reactan-ce, or which olements the one is located between the anode and the control grid and the other between the trol grid and the cathode whilst the impedance the control grid is large relatively to that oi the other element, In another known, circuit-arrangement with wattless feed-back use is made of a similar phaserotating network of which the one element is of a discharge tube and the other, which has a considerably smaller impedance, is conhecte d between the anode and the cathode of this tube whilst between the control grid and the cathode I of the element provided between the anode and connected between the anode and the control grid there exists a virtual reactance which isinversely i proportional to the slope of the tube.

The modulating oscillations are supplied to a control electrode 01 the reactance tube for example to the previously mentioned control grid or to a second control grid, so that the slope of the reactance tube varies in the rhythm of the modulating oscillations. Between two electrodes of the reactance tube (in the above-mentioned known circuit-arrangements between the anode ula in osc lations 2 and the cathode and between the control grid and the cathode respectively) there occurs in this case a virtual reactance Whose value varies in the rhythm of the modulating oscillations. By coupling this virtual reactance. to the frequencydetermining oscillatory circuit of an oscillator which generates the oscillations to be modulated, we obtain modulation of the frequency of these oscillations Whilst phase modulation may be realized by including the said virtual reactance in a p a et ns ne work; to. which h oscination to be mo u ated a e su p ed,

In order to r nd r p ssib e r pr ductio witht i ortion n h ception of oscilla modulated either in frequency or in phase, it is es rabl ha the ns antaneous value. of: the freque avr ph s disp a em t rou ht about by the modulation should always be proportional to the instantaneous value of the modulating gsoillations. With those values of the maximum frequency of the oscillations to be modulated which occur in practice, this condition is always fulfilled with sufficient exactitude when for the oscillations.

to be modulated the slope .Oi the reactance tube is a linear function of the instantaneous value of the modulating oscillations, The latter condition implies that the characteristic which represents the anode current of the reactance tube as a function of the voltage or the control grid to which the modulating oscillations are supplied, should he an exactly square function if the oscillations in be modulated are supplied to the same control grid, a d a e a tl linea function if the o il a ion o be d l a supplied to a second control grid.

Discharge tubes with an exactly square or linear characteristic are generally not available in pracrtice, so that in the case of modulation there occurs nearly always a certain distortion. It is lgnown obtained are combined in anti-phase with the i i his me hod ha th drawback "that the desired modulation without distortion is only obtained if the detection of the modulated oscillations takes place without any distortion. The latter requirement leads in map,-

t e to ery e si eatsd si e arran eme tsihe has for its. object tqr vs the sa drawb s a d to pr i e me s whi pa- .mit to bt a simple mann ir queac a shasamed laticii Without distort oii' with the aid of a discharge tube of any type.

According to the invention a feedback for the modulating oscillations is utilized in the reactance tube in such a sense and with such an intensity that the instantaneous value of the frequencyor phase-displacement brought about by the modulation is always proportional or at least approximately proportional to the instantaneous value of the modulating oscillations.

The invention will be explained more fully with reference to the accompanying drawing forming a part of the specification and in which:

Fig. l is a schematic diagram of a circuit arrangement for wave length modulation according to the invention, and

Fig. 2 is a schematic diagram of an alternate embodiment of the invention.

Fig. 1 represents a circuit-arrangement for frequency modulation wherein the oscillations to be modulated are generated by an oscillator tube 1 which is connected for this purpose in three-point connection to 'an oscillatory circuit, which consists-of an inductance coil 2 and a condenser 3. That portion of the oscillatory circuit 2, 3 which is located between the anode and the cathode of the tube i has connected in parallel with it a reactance tube 4 constructed as a pentode whilst in parallel with the remainder of the said oscillatory circuit is connected the seriesconnection of a separating condenser 5, an ohmic resistance 5 and a condenser l. The condenser 5 forms a short-circuit for the oscillations to be modulated whilst the resistance 6 is large relatively to the impedance of the condenser 1 and forms, jointly with the latter, a phase-rotating network by which a phase-displacement of approximately 90 is brought about. The voltage set up across the condenser l, which voltage is out of phase by approximately 90 with respect to the voltage across the circuit 2, 3, is supplied to the control grid of the tube 4 so that for the oscillations to be modulated this tube behaves as a reactance.

The value of the reactance formed by the tube 4 is controlled in the rhythm of the modulating oscillations by supplying these oscillations via terminals 8 and 9 and a high-frequency reactance coil I 0 to the control grid. The oscillations modulated in frequency are taken via terminals H and H. from that portion of the circuit 2, 3 which is located between the anode and the cathode of the tube I.

With the aid of the circuit-arrangement described so far it would only be possible to obtain frequency-modulation without distortion if the anode current-control grid voltage characteristic of the tube 4 were an exactly square function.

According to the invention, with a characteristic of arbitrary shape frequency modulation without distortion is rendered possible by utilizing feedback for the modulating oscillations. This feedback is so chosen that for the modulating oscillations the resulting dynamic characteristic of the reactance tube is a square function or approximately a square function. With the major part of the pentodes the static characteristic may be represented by a function of the shape wherein the exponent n is more than 2. In order to obtain a square dynamic characteristic, use must be made in this case of negative feedback. If, on the contrary, the static, characteristic can be represented by a similar power function with an exponent less than 2, use should be made of positive feedback.

With the circuit-arrangement represented in Fig. 1, negative feedback for the modulating oscillations isobtainedby-means of a resistance l3 which is included in the cathode lead of the reactance tube 4 and which, for the frequency of the oscillations to be modulated, is preferably shunted by a condenser M.

It may be observed that it is known to linearize the characteristic of an amplifying tube by utilizing a resistance Rk in the cathode lead. In this case the desired linear dynamic characteristic is the .better approximated the higher R1; is chosen. For this purpose use is generally made of a value of R1; with which SRK4 wherein S represents the slope. Apart from the fact that, instead of relating to an amplifying circuit-arrangement, the invention has reference to a circuit-arrangement for frequencyor phase-modulation, th circuit arrangement according to the invention also differs from the known circuitarrangements with negative feedback in that in the case under consideration it is possible to ascertain an exactly determined value of Be With which the characteristic approximates the desired square shape with the greatest exactitude whereas such is not the case with larger or lower values of Rk. The value of R}: which is utilized in accordance with the invention, is generally considerably smaller than in the known amplifying circuit-arrangements with negative feedback, and this'to such an extent that SR10.5. The desired negative feedback may also be obtained by incorporating an ohmic resistance in the screen grid circuit or, when a triode is utilized as the reactance tube, in the anode circuit. In those cases in which positive feedback is required, this may be obtained in the known manner by coupling the circuit of one of the current-carrying electrodesby means of a transformer to the control grid circuit.

Fig. 2 represents a circuit-arrangement according to the invention wherein the reactance tube 5 is constructed as an hexode. The oscillations to be modulated are supplied to the inner control grid whereas the modulating oscillations are supplied to the outer control grid. According to the invention, use is made in this case of such a negative feedback for the modulating oscillations that the dynamic characteristic, which represents the anode current as a function of the voltage of the outer control grid, has a linear or at least an approximately linear course. Since the cathode current .does not comprise a component with the frequency of the modulating oscillations, the incorporation of a resistance in the cathode lead would not lead to the purpose in view. For this reason the feedback resistance I 3 is connected into the screen grid lead whilst that end which is remote from the screen grid is earthed through the" intermediary of a condenser !5. If desired, it would also be possible to obtain the effect aimed at by. means of a resistance included in the anode ulating an electric wave, comprising means to generatesaid electric wave, a reactance tuoe cuit coupled to said generating means and comprising an electron discharge tube having a plurality of electrodes, means to apply modulating potentials to said reactance tube to wavelength modulate said wave, means comprising an impedance element coupled to one of the electrodes of said discharge tube to derive a voltage proportional to the amplitude of said modulating potentials, and means to combine said voltage and said modulating potentials, said impedance element having a negligible impedance value at the frequency of said electric wave and a given impedance value at the frequency of said modulating potentials thereby to produce wave length modulation of said electric wave proportional to the instantaneous amplitude of said modulating potentials.

2. A circuit arrangement for wave length modulating an electric wave, comprising means to generate said electric wave, a reactance tube circuit coupled to said generating means and comprising an electron discharge tube having a cathode, a gride and an anode, means to apply modulating potentials to the grid of said reactance tube to wave length modulate said wave, means comprising an impedance element coupled to the cathode of said discharge tube to derive a voltage proportional to the amplitude of said modulating potentials, and means to apply said voltage to the grid of said reactance tube, said impedance element having a negligible impedance value at the frequency of said electric wave and a given impedance value at the frequency of said modulating potentials whereby the resultant value of anode current of said reactance tube is propor-' tional to the square of the value of voltage applied to the grid thereby to produce wave length modulation of said electric wave proportional to the instantaneous amplitude of said modulating potentials.

3. A circuit arrangement for wave length modulating an electric wave, comprising means to generate said electric wave, a reactance tube circuit coupled to said generating means and comprising an electron discharge tube having a cathode, a grid an an anode, the static characteristic of said electron discharge tube being represented by a power function having an exponent greater than 2, and means to apply modulating potentials to the grid of said reactance tube to wave length modulate said Wave, means to .derive a voltage proportional to the amplitude of said modulating potentials, means to apply said voltage to the grid of said reactance tube, and a resistor interposed in the anode-cathode circuit of said tube and having a resistance value at most equal to the value one-half divided by the transconductance of said tube thereby to pro- .duce wave length modulation of said electric wave proportional to the instantaneous amplitude of said modulating potentials.

4. A circuit arrangement for wave length modulating an electric wave, comprising means to generate said electric wave, a reactance tube circuit comprising an electron discharge tube having a cathode, a first grid, a second grid, a screen grid and an anode, means to couple said generating means to one of the grids of said reactance tube, means to apply modulating potentials to the other of the grids of said reactance tube to wave length modulate said wave, and means including a resistance element coupled to said screen grid to derive a negative feedback voltage proportional to the amplitude of said modulating potentials, said resistance element having a resistance value at which the resultant wave length modulation of said electric wave is proportional to the instantaneous amplitude of said modulating potentials.

5. A circuit arrangement for wave length modulating an electric wave, comprising means to generate said electric wave, a reactance tube circuit comprising an electron discharge tube having a cathode, a first grid, a screen grid, a second grid and an anode, the static characteristic of said electron discharge tube being represented by a power function having an exponent greater than 1, means to couple said generating means to the first grid 'of said reactance tube, means to apply modulating potentials to the second grid of said reactance tube to wave length modulate said wave, means to derive a voltage proportional to the amplitude of said modulating potentials, means to apply said voltage to the screen grid of said reactance tube, and a resistor interposed in the screen grid-cathode circuit of said tube and having a resistance value at which the resultant value of anode current of said reactance tube is linearly proportional to the voltage applied to the said second grid thereby to produce wave length modulation of said electric wave proportional to the instantaneous amplitude of said modulating potentials.

6. A circuit arrangement for wave length modulating an electric wave, comprising means to generate said electric Wave, a reactance tube circuit comprising an electron discharge tube having a cathode, a first grid, a screen grid, a second grid and an anode, the static characteristic of said electron discharge tube being represented by a power function having an exponent greater than 1, means to couple said generating means to the first grid of said reactance tube, means to apply modulating potentials to the second grid of said reactance tube to wave length modulate said wave, means to derive a voltage proportional to the amplitude of said modulating potentials. means to apply said voltage to the screen grid of said reactance tube, a resistor interposed in the screen grid-cathode circuit of said tube, and a capacitive element coupled in parallel with said resistor and having a reactance value substantially equal to zero at the frequency of said modulating potentials, said resistor having a resistance value at which the resultant value of anode current of said reactance tube is linearly proportional to the voltage applied to the said second grid thereby to produce wave length modulation of said electric wave proportional to the instantaneous amplitude of said modulating potentials.

WILLEM WIGGER. BOEIENS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,279,660 Crosby Apr. 14, 1942 2,323,598 Hathaway July 6, 1943 2,361,658 Sinnett Oct. 31, 1944 2,382,436 Marble Aug. 14, 1945 2,383,848 Crosby Aug. 28, 1945 2,394,427 Clark et a1 Feb. 5, 1946

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