US2064220A - Radio receiver - Google Patents

Description

Dec. 15, 1936. I ROCARD 2,064,220

RADIO RECEIVER Filed Sept. 29,1952 2 Sheets-Sheet 1 INVENTOR -YVE5 ROCARD I /.g/w

ATTORNEY Dec. 15, 193 6. Y. ROCA'RD RADIO RECEIVER Filed Sept. 29, 1932 2 Sheets-Sheep 2 v @9- 6 flaw/7525 Ma 711 5 INVENTOR YVES ROCARD BY 4* ATTORNEY Patented Dec. 15, 1936 UNETED STATES 2,064,220 RADIO RECEIVER Yves Rocard, Paris, France, assignor to Compagnie Generale dc Telegraphic Sans Fil, a

corporation of France Application September 29, 1932, Serial No. 635,370

In France January 30, 1932 9 Claims. (01. 250-20) tion (D=193,000 cycles), P that ofthe Radi "#3 This application is based on and corresponds to French Patent No. 745,631, granted February 21, 1933. The present invention relates to improvements in radio receivers, and especially to frequency-changing devices.

The present invention discloses a general principle, and improved methods, adapted to insure in the proper manner a change in frequency particularly by the aid of a radio modulator twin-grid tube without creating, or permitting the production of, stray waves whose interference with the wave of the new frequency, or with the component or constituent waves, would result in inconvenience that would manifest itself at the acoustic output end of the equipment in the form of fundamental noises, whistling, etc. Its chief application is in connection with the superheterodyne type of radio receiver set.

The efficiency of the methods here disclosed may be explained by, and is based upon, an observation made by the inventor according to which the curvature of the characteristic of the tubes which, in one stage of amplification, as is well known in the art, results in diaphony (or cross-talk), and an apparent growth in the depth of the modulation, will also cause, inside a tube intended and designed to insure a change in frequency, waves having a frequency close to that of the new frequency which is desired to be obtained; and these waves on passing into the succeeding amplifier produce upon final detection a heat of a relatively low and audible frequency.

Taking the case of a tube whose plate currentz' developed as a function of the voltage at the grid Vg is expressed by and assuming that the grid potential is due to a certain number of signals (2) Vg=cz sin wt+,3 sin w't+' sin w"t+ among which is contained the desired signal w, a heterodyne signal intended to enter into beat relations with the former in order to bring about a change of frequency, and a certain number of confused or indeterminate ones, by developing Equation (1) of z in the light of Equation (2) for Vg, and transforming the terms so as to bring out the purely sinusoidal terms, there will finally be found in i a very large number of sinusoidal components of different frequencies.

Taking as a practical instance the case of the Daventry station received while the Radio-Paris and the Eifiel Tower stations are in operation, if D designates the frequency of the Daventry sta- Paris station (174,000 cycles), and F that of the EifielTower station (207,000 cycles), among the beat waves that will arise the following frequencies may be noted:

square of the Radio-Paris field times the Daven-- try field. Whence the result that this beat will be proportional to the sixth power of the effective height of the antenna or aerial, all other things, of course, being equal.

heterodyne set located close to the Radio-Paris or the Eiffel ,Tower broadcasting stations, all of the waves hereinbefore enumerated will arise, and there will occur furthermore beats of the waves of the three sending stations with the heterodyne wave, a fact that should also be taken into consideration. Suppose that 60,000 cycles per second is the value of the mean frequency. In the amplification of the mean frequency adjusted to 60,000 cycles, with a certain band pass, the beat 3F 2D-P just as the beat 3D-3P will pass, and as a result of subsequent interference between them and with the mean frequency wave of 60,000, whistling notes of 1,000, 3,000 and 4,000 periods will be produced in the detector. If the carrier-wave of the Eifiel Tower station is stopped, the whistles of 1,000 and 4,000 periods If it is desired to receive Daventry by a super--; V

A way adapted to diminish the whistling according to the present invention consists in causing the change in frequency by the aid of a distinct detector constituted by a variable mu tube. It is known in the art (see the Institute of Radio Engineers for December, 1930, page 2102) that the structure of the variable mu tube has as its object an attenuation in the development (1) of the terms of cV eV resulting incross-talk, or diaphony, if the tube does amplifier work; but the same structure further has this effect that it reduces the terms of dV Vg which are responsible for the whistling of superheterodynes. The use of a variable mu, screen grid type tube as the first detector in a superheterodyne set will thus be eflicient and suitable'fromthis viewpoint.

In the case of frequency change insured by a radio modulator twin-grid tube in which case a control grid modulates an oscillation created by coupling between the plate, another grid and an oscillation circuit, exactly similar actions are producible.

During oscillation the plate current as amatter of fact may be expressed thus:

(3) i=A+B sin wt+C sin 2wt+D sin 3wt A, B, C, D being functions of the control grid potential whose form depends further upon the impedances of the various circuits used in association with the twin grid tube and being thus expressible:

Referring to equation (3), what has been neglected are the phases of the various harmonics orovertones of the oscillation for they are of no importance in this connection.

w is the pulsation of the heterodyne; if, then, a station with a pulsation wl accompanied by jamming or interfering waves m2, m3, etc., is received it will have to be kept in mind. that V comprises not only terms on sin wl 18 sin wzt, 'y sin w3l'1, etc.,

but also a very substantial term n sin wt due to the heterodyne current which, by virtue of interelectrode capacitance returns to the impedance acting upon the control grid.

The term' blVg which by the intermediary o B, and multiplied by sin wt is introduced in i, then results in the change in frequency by control of the oscillation of the twin-grid tube in accordance with the well known process as ex- 7 plained by its inventors (Nozieres, Scott-Taggart,

ole Mare, and others). But it will be noted that the term CoVg will also produce the mean frequency as a result of simple detection as in a standard. detector with separate heterodyne.

Finally, in A, B, C, a great number of terms of a highde'gree of Vg will further produce, either as a result of interference between themselves or with the overtones of the oscillator, terms of mean frequency which most frequently will be associated with doubled, tripled, etc. modulation depth, and thus be extremely distorted. Finally, in the case where interfering stations, or waves, are received there will arise an entire gamut of the following, arranged in the order of diminishing effectiveness:

(1) To reduce as far as feasible the force of the signal at the instant of change of frequency in the radio modulator twin-grid tube, while insuring sufiicient protection against stray.

(2) Reduce in the developments A, B, C, the size of the terms do, etc. 01, d1, etc., and b2, 02, (12, etc.

(3) Reduce in the oscillation of the twin grid tube the amplitudes of the harmonics.

(4) Lessen or eliminate completely the terms with 1; sin wt which occurs, in the expression for V Now, the present invention discloses ways and means adapted to realize each of these various points and the arrangements suggested with that end in view offer additional advantages some of which shall be hereinafter cited. The means and ways hereinafter to be described may be adopted and used simultaneously (combinedly), or else singly and independently of oneanother according to the nature of the case and the difficulties to be solved.

In order to overcome the first condition hereinbefore mentioned the invention discloses the simultaneous use of a radio frequency filter designed to lessen as far as feasible the stray compared with the signal, and an arrangement acting upon the control grid by the output of this filter, though in combination with coupling means making the regulation of the radio frequency circuits practically independent of the regulation of the heterodyne.

In order to realize the second condition, the invention suggests the construction and utilization of a twin-grid tube of a special kind where the control action exercised by the control grid is of what has become known as the variable mu kind.

' In order to satisfy the third condition it is will be maintained; but the'special design of twin-grid tube suggested to satisfy demand (2) will be helpful also in satisfying condition (3).

The fourth condition is satisfied according to the invention either by the aid of neutrodyning, or by satisfying by way of choosing a special construction'for the twin-grid tube and the oscillator, and further by the addition of small capacitors, a condition that shall hereinafter be indicated.

The invention will be better understood by reference to the drawings attached to this specification and the description in connection therewith giving merely by way of example several modes or embodiments of the basic ideas of the invention.

In the accompanying drawings the various circuit elements are designated by the customary symbols used for condensers, inductance coils, resistances, etc., as well known by the man trained in the art. To simplify the description details will'be given only where needed. Moreover, tubes arrangement RI, R2.

comprising a. plurality of electrodes are schematically indicated only by single electrodes, the filament being shown by a solid line, the grids by a broken line, plates by a rectangle, the screen grids being shown as surrounding the plates. .As regards the first condition it must be noted that the most conventional showing of the radio modulator twin-grid tube is as shown in Fig. 1. Inthis circuit scheme the tuned condition of the coil, or loop, L by capacity C depends, clue to the capacities between the grids C, C" and grid C" and the plate, upon the tuning of the heterodyne circuit comprising the capacity C1. This circumstance has so far precluded a chance to act upon the twin-grid tube by more than one tuned circuit for, in the circuit scheme shown in Fig. 2, for instance, owing to the presence of stray capacities due to grids c, c, the adjustment of capacity C3 is by no means the same as that of the capacity C2, and this precludes all attempts at a simple regulation of the set and all chances of uni-control.

Fig. 3, by way of example, shows a method of coupling according to the invention which contrasted with the conventional arrangement shown in Fig. 1 increases selectivity, reduces the amplitude of the signal at the instant of frequency change, while insuring simple uni-control of the different capacities such as C2 and C3. This end is attained'by coupling the filter L2 C2, L3 C3 with the control grid by the aid of a potentiometer R2 is the leak resistance of the grid, and the same is of an order of magnitude of 1 megohm. RI should be chosen sufficiently high in order that the shunt constituted, for instance, by the capacity between the cathode and grid c' in series with C1L1 will not disturb the regulation of the circuit L3, C3. RI, on the other hand, should yet be made sufficiently small in order that an appreciable potential across the terminals of L3 should be transferred and fed to the control grid. With the usual twin-grid tubes and within the range of radio broadcasting it is found that RI =40,000w is a size adapted to insure the desired results.

Referring to Fig. 3, 1" represents a capacity serving to couple the two tuned circuits L2, C2 and L3, C3. Z stands for the mean-frequency filter which is provided at the output end of the twin-grid tube.

Fig. 4 shows a modification wherein the two circuits (for instance) that constitute the filter are coupled by the mutual inductance M between the coils L2 L3 of the resonant input circuits, the upper end of coil L3 being connected to the signal control grid through a high resistance R1, as in Fig. 3. Since the lower end of L3 is grounded, R1 serves also as a grid leak and R2 is useless in this arrangement.

Fig. 5 shows a modification where one screen type tube L serves as an aperiodic coupling according to the invention, the resistance R1 consisting then of the very high internal resistance of this tube. In such a scheme it is necessary that the tube L should be carefully connected and polarized in order that no cross-talking may be occasioned; and withthat end in view a variable mu tube is appropriate. As shown, the plate of tube L is resistance coupled by the condenser r to the signal control grid of the oscillator-detcctor tube, the control grid of which is provided with the leakage resistor R2. Fig. 6 shows another modification which will be self-understood and where the use of the resistance RI according to the invention makes it possible to practice uni-control of capacities C2, C3. In this case, instead of the resonant circuits being inductivelycoupled together, the selectivity is secured; by connecting one, including the condenser a greater number of circuits, indeed, as many as may be needed. It should also be noted that the method of this invention insuring uni-control of C2, C3 by perfect balancing out by the aid of CI allows of uni control also of all of the variable condensers of the superheterodyne C2, C3 and CI, for instance, by using the methods disclosed in French Patent No. 727,054, filed on January 30, 1931, entitled Improvements in means insuring uni-control of several circuits tuned to dissimilar frequencies.

What should also be emphasized is the fact that the means here disclosed makes it readily feasible, without impairing quality to produce a diminution of the intensity of the signal at the time of changing the frequency. As a matter of fact it is generally deemed desirable to preserve the. signal at a certain prior amplitude in order that, at the time when the frequency-change takes place, it may exceed the noise level known as the twin-grid blast.

Now, the applicant believes to have ascertained that, save in the very exceptional instance of twingrid tubes of poor quality, the said typical noise would manifest itself by a large increase in the ratio between signal and noise, even in cases where the signal is efiectively reduced.

The invention further furnishes ways and means so as to insure simultaneously a more or less adequate fulfillment of the second and the third condition hereinbefore mentioned.

With this end in view it suggests the construction of twin-grid tubes with accelerator grid (contra-distinct from screen grid twin-grid tubes) involving the properties of variable mu in reference to the control grid, such variable mu feature. being obtained by ways and means entirely similar to those nowadays known in regard to screen grid tubes. It further discloses the use of such twin-grid tubes comprising an accelerator grid and the variable mu feature for radio modulator twin-grid tubes for insuring frequency change. In the case of an autodyne circuit scheme, also according to the invention, it is possible to use for the autodyne tube a variable mu screen grid tube.

In Figs. 7A, 73 by inclining the electrode relative to the vertical the method whereby the tube is made of variable mu has been indicated schematically by modification of the construction of the said electrode, though it willbe understood that also such other methods like a simple shift of the grid, variable spacing of the grid wires, etc., resulting in variable mu couldijust as well be employed.

Referring to Fig. 7A, if g2 is the control grid,

the tube is of variable mu according to the sense of this invention; but if gI is thecontrol grid,

it will be understood that this will not be so and that the plate current 2}; expressed as a function of Vg will comprise terms of a high order with substantial coefficients for V l and far lower ones for V Z. In Fig. 713 there will be seen a twin-grid tube which involves the variable mu feature for both gl as well as 92. In both illustrations just referred to C designates the cathode and P the plate.

Fig. 8 shows the characteristics of such a twingrid tube. There are shown by the solid lines the curves of the plate current and of the current of the first grid gl, for a certain potential applied to these two electrodes, as .a function of the potential of the control grid V 2. These characteristics present a very regular curvature, while the characteristics traced by broken lines of the ordinary twin-grid tube present rectilinear portions throughout a wide range of variation of V 2.

The following effects result, to wit: The standard twin-grid tube as soon as it starts to oscillate, oscillates at a large amplitude, the variable mu twin-grid tube oscillates with a smaller amplitude and a lower number of harmonics. This effect will be more conspicuous if the said twin-grid tube with the variable mu feature has been designed with a rather slack grid pitch and is operated on a low plate potential.

On the other hand, in Equations (4) the functions of A, B, C, no longer contain terms of V of a high order and of substantial amplitude, and this always as a result of the variable mu property. The stray whistling noises are thus greatly diminished for this two-fold reason, namely, that the construction intended to insure variable mu satisfies requirements and that in the following equation for V 5) Vg=ot sin wilH-p smmt Asinwt the very important term A sin wt has been greatly diminished, the variable mu twin-grid tube oscillating less strongly. It is true that this efiect manifests itself also in the form of a substantial reduction in sensitiveness; but it will be preferable to put up with this loss in order to insure a proper frequency-change process.

In the following shall be disclosed the method of this invention with a view to cause the practical disappearance of the term sin wt in equation V as a result there is caused the disappearance in the plate current of a large number of beats wherein the said term occurs in the form of a component.

Fig. 9 illustrates in a suificiently evident way the means adapted to neutralize perfectly the capacities c c" by similar (or proportional) capacities according to whether the windings LI L2 are divided into equal (or proportional) parts. As shown, the top of winding L1 is connected to the oscillator grid, the lower portion of this winding and condenser C providing a circuit to neutralize the capacity efiect between the two grids. The plate output circuit is connected to a midpoint of the coil L2, whereby it is possible to neutralize the capacity between the plate and outer grid by connecting the lower end of L2 to this grid through the condenser C.

Fig. 10 shows a neutralizing arrangement that is far simpler, but efiicient only if the oscillator of the twin-grid tube is coupled very closely. In this instance it is possible to show that if or sin wt is the expression of the signal that would be impressed upon the control grid g2 in the absence of all capacities c' and. c, the reaction in the twin-grid tube due to c' and e" has the result of imparting to V 2 the following values, to wit:

Vp=Vpo sin wt is the oscillating part of the plate potential, Z (w) is the impedance encountered by the heterodyne wave w between the control grid and the filament return, expression (6) being valid only if the oscillator is coupled strongly.

A perfect neutralizing for all frequencies is then obtained if this condition is fulfilled, to wit:

and this will always be practicable by an appropriate construction either of the twin-grid tube for a given oscillator or of the oscillator for modulator twin-grid tube, but it is employed merely for producing the sum of voltages oz sin wit+x sin wt in Equation (5) which here assumes the shape of Equation (6) the said aggregate potential being applied to the grid of the detector tube of mean frequency E which preferably should be a variable mu tube resulting in extremely pure detection of median frequency. As shown, the signal frequency is applied to the outer grid of tube B through the resistor RI, the

oscillation frequency! being. generated by the,

feedback coupling between the plate circuit and the resonant circuit connected to the inner grid. The sum of the signal and oscillation frequencies is transferred from the signal grid of B to the control grid of the detector tube E by directly connecting these grids, as shown.

While I have indicated and described several systems for carrying my invention into effect, it

will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention as set forth in the appended claims.

What is claimed is:

ceiver, an energy collecting means, a vacuum tube detector having a cathode, grid and plate, said grid being arranged to provide a variable mu plate current characteristic, two coupled cir-. cuits connected in cascade and each tunable to the incoming signal frequency, one of said circuits being coupled to the energy collecting means and an aperiodic circuit conductive to direct current connected to the second of said tunable circuits and to the grid of said tube.

2. In a superheterodyne receiver, the combination of a vacuum tube having a cathode, a control grid, a second grid and a plate, a circuit tunable over a range of signal frequencies connected to the control grid and cathode, said circuit comprising a plurality of similar tuned circuits and an aperiodic coupling between the last of said circuits and said control grid, a circuit tunable to: a desired oscillation frequency connected to the 1. In combination in a superheterodyne re second grid and cathode, a plate circuit having a feedback connection to said last named circuit, the control grid being so constructed and arranged as to provide a variable mu characteristic to the current between the cathode and said second grid.

3. In a superheterodyne receiver, the combination of a vacuum tube detector having a cathode, a control grid, a second grid and a plate, a circuit tunable to a desired oscillation frequency connected between the second grid and cathode, a plate circuit having a feedback connection to said circuit, said second grid being so arranged with reference to said plate as to provide a variable mu plate current characteristic, means for neutralizing the capacity between the control grid and plate, a source of signal frequency energy and means connecting said source to the cathode and control grid, comprising two coupled circuits each having means for tuning it to the incoming signal frequency, and an aperiodic coupling between one of said coupled circuits and the control grid.

4. In combination in a superheterodyne receiver, a source of high frequency energy, a vacuum tube oscillator having a control grid, a second grid and a plate circuit, a feedback connection between the plate circuit and the second grid, a detector tube having a control grid, a screen grid and a plate circuit said control grid being constructed to provide a variable mu plate current characteristic, means connecting a positive source of potential to the screen grid, a circuit tuned to the intermediate frequency connected in said platecircuit, a connection conductive to direct current between the control grids of the tubes and an aperiodic coupling means connecting one of said control grids to the said source of energy.

5. In a superheterodyne receiver, the combination of a vacuum tube detector having a cathode. a control grid, a second grid and a plate, a circuit tunable to a desired oscillation frequency connected between the second grid and cathode, a plate circuit having a feedback connection to said circuit, a source of signal frequency energy, means for coupling said source to the cathode and control grid, said means comprising a plurality of similar resonant coupled circuits each tuned to the signal frequency and an aperiodic coupling means connecting the last of said circuits to said control grid, said control grid and said second grid being constructed and arranged to provide a variable mu plate current characteristic.

6. In a superheterodyne receiver, the combination of a vacuum tube detector having a cathode, a control grid, a second grid and a plate, a circuit tunable to a desired oscillation frequency connected between the second grid and cathode, a plate circuit having a feedback connection to said circuit, a source of signal frequency energy, means coupling said source to the cathode and control grid, said second grid being constructed and arranged to provide a variable mu plate current characteristic whereby said tunable circuit is substantially free of harmonic frequencies of its oscillation frequency.

'7. In a superheterodyne receiver, the combination of a vacuum tube having a cathode, a control grid, a second grid and a plate, an input circuit connected to said cathode and control grid, means for impressing radio frequency signal currents on said input circuit, a circuit tunable to a desired local oscillation frequency connected between the second grid and cathode, a plate circuit having a feedback connection to said tunable circuit, said control grid and said second grid being disposed in oppositely inclined planes with reference to said plate.

8. In a radio receiver, the combination of a vacuum tube detector having a cathode, a control grid, a second grid and a plate, a circuit tunable to a desired oscillation frequency connected between the second grid and cathode, a plate circuit having a feedback connection to said circuit, a source of signal frequency energy, coupling means arranged to connect said source to said control grid;'said second grid being inclined at an acute angle with reference to said plate so as to provide a variable mu plate current characteristic.

9. A superheterodyne receiver comprising the combination of a vacuum tube oscillator-detector having a cathode, a control grid and twoadditional cold electrodes, a circuit tuned to a desired oscillation frequency connected to one of said cold electrodes, a circuit connected to the other of said cold electrodes including a por-' tion having a feedback connection to said tuned circuit, a source of signal frequency energy and a circuit coupling said source to said control grid and including a portion resonant to the incoming signal frequency, said control grid being constructed of wire having a variable spacing between its adjacent portions whereby to provide a variable mu plate current characteristic.

YVES ROCARD.

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