US2219396A

US2219396A - Electric translating system

Info

Publication number: US2219396A
Application number: US189525A
Authority: US
Inventors: Plebanski Jozef
Original assignee: Radio Patents Corp
Current assignee: Radio Patents Corp
Priority date: 1937-09-22
Filing date: 1938-02-09
Publication date: 1940-10-29
Anticipated expiration: 1957-10-29

Description

Oct. 29, 1940. J PLEBANSK] 2,219,396

ELECTRIC TRANSLATING SYSTEM Filed Feb. 9, 1938 3 Sheets-Sheet l INVENTOR.

ATTORNEY 0d. J. PLEBANSKI ELECTRIC TRANSLATING SYSTEM Filed Feb. 9, 1938 3 Sheets-Sheet 2 IN VENT OR.

ATTORNEY.

Oct 2 1940- J. PLEBANSKI ELECTRIC TRANSLATING SYSTEM Filed Feb. 9, 1938 3 Sheets-Sheet 3 Patented Oct. 29, 1940 PATENT OFFICE ELECTRIC TRAN SLATING SYSTEM Jozef Plebanski, Warsaw,

Poland, assignor to Radio Patents Corporation, New York, N. Y., a corporation of New York Application February 9, 1938, Serial No. 189,525 In Poland September 22, 1937 20 Claims.

The present invention relates to improvements in radio circuits and a method of operating the same, more particularly to frequency discriminating circuits designed to pass a predetermined range of signalling frequencies known as lowpass, high-pass, band-pass or band-elimination filters or networks in the art.

An object of the invention is to provide an improved band-pass type high frequency or intermediate frequency filter system with sharp cutoff properties such as for use as a selective system in the intermediate section of a superheterodyne receiver or in any other radio or electrical circuit.

A more specific object is the provision of a band-pass filter or network with a response or transmission band width which can be easily adjusted electrically by controlling an electric current or potential, either manually or automatically depending on the signal strength or any other controlling magnitude, to effect a band Width or fidelity control in a radio or other signal receiver.

A further object is to provide a resonant system or filter circuit having a resonance or frequency response curve with ascending and/or descending branches of greatly increased steepness and requiring a limited number of circuit elements compared with circuits and systems having similar characteristics known in the prior art.

Band-pass circuits or selectors as known in the art such as provided in the intermediate section of a superheterodyne receiver comprise two or more resonant circuits inductively or otherwise coupled with each other. Usually two coupled circuits are employed one of which is connected in the anode circuit of an amplifying valve and the other is connected in the grid circuit of the succeeding amplifying valve of a cascade amplifier. In practice, at least two band-pass selectors of this type are required with pentode or other amplifying valves arranged therebetween in order to obtain a desired selectivity or cut-off effect. This is equivalent to four tuned circuits connected in cascade, whereby in the case of the comparatively long wave lengths or low intermediate frequency commonly employed in superheterodyne systems the attenuation for signals about 30 kc. of resonance is approximately 10 db. or more for each circuit, that is 10 4=40 db. total attenuation for all four circuits together. For the wave lengths in closer proximity to the resonance wave length, such as for a wave length of about 10 kc. off resonance, the attenuation is considerably less, in practical cases only about 3 db. for each circuit or a total attenuation of 12 db. or all four circuits combined. This attenuation is very low and in order to obtain in the latter case an attenuation of 40 db. for frequencies 10 kc. off the resonance point a prohibitive number of cascaded circuits or amplifying stages, in the example under discussion 40+3, i. e., 13 circuits, would be required. In other words, six band-pass twin circuits would be necessary with five amplifying valves interconnecting the same. Furthermore, such a large number of circuits would entail a narrowing of the band-pass region resulting in a cut-off or weakening the higher signal frequencies and in turn a substantial impairment of the fidelity of reproduction of the receiver,

By the present invention there is provided a filter or selective system requiring in its simplest form only a single composite or multiple amplifying valve with three to four tuned circuits and having a considerably improved selective or cut-off characteristic compared with circuits constructed according to the prior art methods embodying an equal number of valves and circuit elements.

By a system according to the invention, an adjacent channel selectively can be obtained with a limited number of valves and amplifying stages equivalent to a cascade system of standard type known in the art requiring about 20 circuits or 9 amplifying valves, with the further advantage that the band-pass region can be adjusted in any manner desired, that is without sacrifice of the fidelity of the received signal. In a system according to the invention embodying three filters of the improved type in cascade, it can be shown that the adjacent channel selectively will become so high as to be practically unobtainable with any other system irrespective of its construction and number of circuit elements and parts used.

As is known, the selectivity can be improved at the cost of the gain or degree of amplification of the system, that is if four circuits are connected between two amplifying valves each coupled to the succeeding one, the selectivity is substantially higher than when only two coupled circuits are employed. However, the signal strength in the former case will drop considerably and in many cases cannot be offset by the gain of the amplifying valves. Furthermore, every valve in a circuit of a receiver is subject to a certain extent to direct pick-up from interfering electro-magnetic fields. If a disturbing field in a receiver has a field strength of about microvolts and supposing the attenuation in the filter is such that the signal picked up from this field is decreased to about one microvolt and that simultaneously the direct pick-up produces a disturbing potential of about microvolts on the grid of a valve, the high attenuating properties of the filters in such a case are substantially without use. The direct pick-up can of course be minimized by screening and shielding, but unless very careful screening methods are employed a certain amount of direct pick-up has always to be reckoned with.

From the above it follows that a specially advantageous and efiicient filter should be constructed in such a manner as to attenuate all frequencies lying outside the band-pass region,

but should not introduce appreciable attenuation for frequencies within the band-pass region. This requirement is fulfilled to a high degree by a filter of the type according to the present invention, which, While substantially improving the selectivity or cut-off characteristics also causes an increased gain for the desired frequencies, or at least acts to prevent appreciable attenuation of these frequencies.

Another characteristic of a filter of the type according to the invention, especially in the form of a band-pass filter, consists in the possibility of a simple and easy adjustment of the band width or frequency transmission characteristic. It is known that the band width or transmission characteristic of filters of known type can be adjusted by varying the degree of coupling between the circuits such as by moving the coupling coils towards or away from each other. In a bandpass filter of the type according to the invention this coupling is maintained constant and the band Width of the filter adjusted by varying the relative magnitudes of the exciting potentials impressed upon the individual circuits of the filter system. This is accomplished in an easy and efficient manner by varying the gain or degree of amplification of one or all valves associated with each of the circuits of the filter system. In this manner automatic fidelity or selectivity control can be effected by using variable mu valves and adjusting the grid bias thereof either manually or in dependence of a control potential varying in accordance with the receiving signal field strength similar as in automatic volume control systems well known in the art. The selectivity control can further be combined with the volume control of the receiver in such a manner that the receiver automatically becomes highly sensitive and selective for weak and distant signals and less selective (increased fidelity) and less sensitive for stronger signals received from a local transmitter.

Band-pass filters according to the invention have a further advantage as described in the following. As is known, band-pass filters comprising a pair of coupled circuits can be easily and efficiently designed and constructed for frequencies of about kc. or about 470 kc. employed at present as intermediate frequencies in superheterodyne radio broadcast receivers and with an effective band width or frequency response of about 10 kc. as required for distortionless reception of broadcast signals. For the higher frequencies, however, for instance 1600 kc. such filters would have a band width of about 40 kc. or more and would no longer be selective for receiving signals comprising a 10 kc. frequency band. A filter constructed according to the invention, however, can be designed for practically any frequency and band Width; that is, the filter can be designed for 0.2 kc. band Width at 100 kc. or for 10 kc. band width at 1600 kc. Moreover, the filter according to the invention can be tuned and adjusted by the normal methods which is not the case with other and more complicated filter systems. If an especially sharp cut-off is required for the filter, one or more resonant circuits of the filter may have quartz crystal resonators suitably connected therewith.

It is furthermore possible to combine a filter of the type according to the invention with filters of known construction, especially filters comprising two or more coupled circuits to obtain the benefits and advantages of the invention.

The above and further objects of the invention will become more apparent from the following detailed description taken with reference to the exemplifications of the invention illustrated by the accompanying drawings forming part of this specification and wherein V Figure l is a simple circuit diagram of a selective amplifier and filter system constructed in accordance with the invention,

Figure 2 shows a number of resonance curves illustrative of the function of the circuit according to Figure 1,

Figure 3 is a diagram combining a pair of filter systems of the type shown in Figure 1 to secure a band-pass response characteristic,

Figure 4 shows the resonance curves for the circuit according to Figure 3,

Figure 5 illustrates an alternative system for obtaining a band-pass effect,

Figure 6 shows the resonance curves for the circuit according to Figure 5,

Figure 7 is a diagrammatic representation of a multiple valve adapted for use in a filter system of the type according to the invention,

Figure 8 is a vertical cross-section through a practical embodiment of a valve as illustrated in Figure 7,

Figure 9 is a horizontal cross-section through the valve shown in Figure 8,

Figure 10 is a partial perspective view of Figure 8 showing the mounting of the separate anodes,

Figure 11 illustrates a practical construction of a coupling coil system for use in a filter circuit according to the invention,

Figure 12 is a complete circuit diagram of a superheterodyne radio receiver embodying bandpass filters and selective circuits as Well as automatic selectivity control in accordance with the invention, and

Figure 13 shows resonance curves for the circuit according to Figure 12.

Similar reference characters designate similar parts throughout the different views of the drawings.

Referringto Figure 1 of the drawings, there are shown two amplifying valves !0 and H of known construction having, in the example illustrated, cathodes, control grids, screen grids and plates or anodes and having their grid circuits excited from a common source l2 of high frequency or low frequency energy through a coupling transformer comprising a primary l3 and secondary M, grid coupling condensers l5 and i5 and grid leak resistances H and I 8, respectively. The grid leaks I1 and [8 may be connected to suitable biasing sources to provide suitable operating grid bias for the valves. There is further shown a tunable circuit comprising a condenser l9 shunted by an inductance coil 20 in series with a further inductance coil 2!,

inserted u in the plate circuit of valve 10, and a similiar tunable circuit comprising a condenser 22 shunted by an inductance 23 in series with an additional inductance coil 24 connected in the anode circuit of the valve II. The anodes of the valves are connected to the positive pole of a high potential source indicated by the plus symbols in a known manner, further well known details such as the return leads to the cathodes and grids having been omitted for simplicity of illustration.

The coils 2i and 24 which may form a part of the

inductances

23 and 23 or, as in the example shown may be separate coupling coils in series with the

inductances

20 and 23, respectively, are arranged in inductive coupling relation with each other. The amplified signal currents are impressed upon a subsequent circuit or apparatus such as a furtser amplifier or detector or the like through a coupling condenser 25 connected to the anode of valve l0.

Let it be assumed for the sake of explanation that the circuit 22, 23, 24 is removed and that a resonance curve (signal response in db. or any other unit as a function of the frequency f) is plotted for the circuit IS, 20 and. 2| by varying the frequency of the source i2. In this case, a resonance curve of known shape will be obtained as shown at A of Figure 2. If the second circuit 22, 23, 24 is now coupled to the circuit i9, 20 and 2| in the manner shown and tuned such as by adjusting the condenser 22, the signal or current in the circuit I9, 23 and 2! will increase and its frequency response or resonance characteristic will be changed as shown by the curve B in Figure 2. If subsequently the excitation of the circuit 22, 23, 24 is reduced such as by controlling the gain of the valve II by adjustment of the grid bias-for which purpose preferably a variable mu valve is employed-the frequency characteristic or resonance curve for the circuit I9, 20 and 21 will assume a shape as shown at C in Figure 2. From this it is seen that the effect of the circuit 22, 23, 24 excited separately from the same input circuit or signal source l2 through an individual amplifier (valve II), in the first place results in an increase of the desired frequency or signal strength and in the second place in a rejector effect at one side of the resonance curve for a frequency adjacent to the desired or resonance frequency or in other words, in a sharp cut-off effect close to the resonant frequency. Moreover, by varying the exciting potential impressed upon the circuit 22, 23, 24 the amount of the improvement (gain and rejector effect) can be controlled within a substantial range to obtain a desired shape or sharpness of the resultant resonance characteristic.

In most practical cases it is desirable to obtain the above rejector effect or sharp cut-off at both sides of the resonance point, that is to secure a true band-pass response, especially for use in a radio receiver or similar signalling device. Such a band-pass effect can be obtained according to a further feature of the invention by employing two circuits of the type as shown in Figure 1 in cascade or in parallel wherein the first circuit is designed to produce a rejector eifect at one side of the resonance frequency and the second circult is designed to produce a rejector effect on the other side of the resonance frequency, in such a manner as to obtain a resultant band-pass response characteristic.

Referring to Figure 3 showing an arrangement of this type, the first stage of the system comprising the valves lil and H and associate resonant plate circuits I9, 20, 2| and 22, 23, 24, respectively, are substantially identical to Figure 1. There is further shown a second stage similar to the first one comprising a pair of valves 33 and 34 both coupled to the anode of valve I0 through coupling condensers 25 and 28, respec tively. Both valves have associated therewith resonant plate circuits, the first comprising a condenser 35 shunted by an inductance coil 33 in series with a coupling coil 31 and the second comprising a condenser 38 shunted by an inductance coil 39 in series with a coupling coil 40. The coils 3'5 and 46 are inductively coupled with each other in a sense opposite to the coupling of the coils 2| and 24 in the first stage, thereby obtaining a rej ector or cut-off effect at both sides of the resonant frequency in the output circuit of the system. The signals are applied to a further circuit or translating device through a coupling condenser 41 connected to the anode of valve 33. There are further shown in Figure 3 a pair of potentiometers 30 and 3! connected to the grids of valves in, 33 and H, 34, respectively, for adjusting the gain and rejector effect in both stages in a manner described hereinabove.

Referring to Figure 4 there is shown at A a resonance curve for the circuit 35, 36, 32 taken independently which is similar to curve A in Figure 2; B is the resonance curve for the circuit 3'5, 3B, 31 before adjustment of the gain of the valves 30 and 3t, and C represents the resonance curve after adjustment of the grid bias or gain in the amplifying stages. These curves have true band-pass characteristics with a sharp frequency cut-off at both sides of the resonant frequency.

Instead of using two stages in cascade as shown in Figure 3, three or more parallel circuits connected to a common output circuit as shown in Figure 5 may be used to obtain an improved band-pass response in a system constructed in accordance with the invention. In the figure, valves l0 and H and the associated plate circuits are substantially similar to Figure 1. In addition, a further valve 44 is excited from the secondary M of the input transformer through a coupling condenser 45 and grid leak resistance 46. Valve 44 has a resonant circuit inserted in its plate circuit comprising a condenser 41 shunted by an inductance coil 48 in series with a coupling coil 49, the latter being in inductive coupling relation with a further coupling coil 50 serially arranged with the inductance 23 of the plate resonant circuit associated with the valve II. The couplings 2i, 24 and 49, 50 correspond to the couplings El, 24 and 37, 40 in Figure 3 and are such as to impress potentials of opposite phase upon the circuit 22, 23, 24, 50 resulting in an improved cut-off effect on both sides of the resonance curve. The output signals may be derived in the same manner as shown in Figure 1 from the anode of valve il through a coupling condenser or the like. Alternatively, as shown in the example illustrated a further resonant circuit is provided comprising an inductance coil 5! coupled with the inductance 23 of the plate resonant circuit of the valve H and shunted by a condenser 52. In this manner the selectivity of the system is further improved by a combination of the inventive circuit with a normal twin coupled circuit (22, 23, 24, 50 and 5!, 52).

The resonance curves for Figure 5 are shown in Figure 6. In the latter D represents the resonance curve for the highest amplification or gain and narrow band width; E is the curve for lowest amplification and greatest band width; and F corresponds to an intermediate adjustment, any of these curves or any intermediate curve being easily obtainable by adjusting the gain of the amplifiers of the valves I I], H and 44. A in Figure 6 represents for comparison the individual resonance curve for the single circuit 22, 23, 24, similar as in Figures 2 and 4.

In arrangements of the above described type an increased number of amplifying valves may be required. In order to limit the number of valves according to a further feature of the invention, composite or multiple valves constructed in a known manner with a sub-divided anode structure may be employed in connection with filter circuits according to the invention. Such a valve of the pentode type which may be used in connection with Figure 5 is diagrammatically shown in Figure 7 and comprises a common vessel or envelope 55, a heater 56, common cathode 51, common control grid 58, common screen grid and

suppressor grids

59 and 60, respectively, and three separate anodes 6!, 62, 63, arranged in such a manner as to provide three separate discharge paths from the cathode 5! simultaneously controlled by the grid 58. In place of a pentode type valve any other type may be constructed in this manner for use in connection with the invention, such as an ordinary three-element amplifier valve or triode,a converteror mixer valve as shown in Figure 12 or a valve of any other type. If a composite valve is to be used in a circuit according to Figure 1, it is understood that only two anodes are required.

Referring to Figures 8 to 10, there is shown a practical construction of a valve of the type according to the diagram of Figure '7. The cathode 57 has the form of an oblong cylinder coated with thermionically active material at the respective discharge sections and surrounded by a concentric spirally shaped control grid, a screen grid and a

suppressor grid

58, 59, 60, respectively, and by three separate concentric cylindrical anodes 6|, 62, 53 supported by

rods

65, 67, 68, respectively, the latter being secured to spacing mica discs or supports 54 and 65 in a manner well known in the construction of discharge devices.

If a valve of this type is to be used for band width adjustment as described hereinabove, several winding turns maybe omitted in the control grid to provide a variable mu characteristic for the particular section of the valve. In the example illustrated, the portion of the control grid opposite the anodes 6i and 63 have a greater controlling eifect than the portion of the grid opposite the anode 52. This is obtained by varying the numbers of turns in the respective control grid portions such as by omitting two turns in the central portion of the control grid and omitting one turn in the outer portion of the control grid as shown in the drawings. In this manner, if the bias of the control grid 58 is increased, the amplification of the section of the valve enclosed by the anode 52 will decrease to a lesser degree than the amplification of the sections enclosed by the anodes 6| and 53, whereby the over-all amplification of the receiver and with it the band width of the system can be controlled easily. As is understood, any other known method to obtain a variable mu effect can be used, such as a variation in the winding pitch of the respective grid sections. It is only essential for the invention that the variable mu characteristic is different for different discharge portions within the valve to obtain different degrees of control for the separate discharge paths.

In order to screen the separate anodes from each other a separate screen may be used as indicated in Figure 7 or the suppressor grid 65 may be constructed in a suitable manner to screen the anodes both from the rest of the tube elements and from each other. As will be understood, any other type of valve may be constructed in the manner described for use in a filter system according to the invention.

Referring to Figure 11, there is shown by way of example, a construction of the coil arrangement as shown in Figure 5. The entire unit is surrounded by a metallic enclosure 12. The inductance 23 of the central circuit comprises two

sections

23 and 23 the latter having a smaller number of turns and serving as a coupling element in inductive coupling relation with the inductance 5! of the associated resonant circuit. In order to decrease the coupling between the

coils

20, 23 and 48, metal rings or discs 10 and H consisting preferably of copper may be mounted between the coils. These rings may be further arranged for adjustment in order to effect or correct the tuning of the circuits and obtain a most favorable operating characteristic. The coils 23 and 5| are shown screened by a separate compartment 53 within the main screen 12, but if desired can be arranged separately and screened or shielded individually. There are. further provided leads I4, 75, 16 and 17 for connecting the separate coils in the circuit shown in Figure 5.

In order to obtain a sharp cut-off characteristic it has been found that the additional circuits (22, 23, 25 according to

F'gures

1 and 3, 38, 39, 40 according to Figure 3, and I9, 20, 2! and 47, 48, 49 according to Figure 5) should preferably be less damped than the main circuits (I 9, 20, 2i according to Figures 1 and 3, 35, 35, 3'! according to Figure 3, and 22,23,24,50 according to Figure 5). On the other hand, if the damping is substantially reduced, the saddle in the curve B according to Figure 4 will become more pronounced. This can be avoided if an additional ordinary filter circuit is connected to the inventive circuit such as shown in Figure 5 (circuit 5!, 52). In the latter case the resonance curves will be of the type shown in Figure 6. Moreover, the saddle in curve B according to Figure 4 can be removed and a square-top curve obtained with reduced band width if the additional circuits (22, 23, 24, etc.), are detuned to a substantially lesser degree. EX- tremely sharp characteristics with very narrow band Width can be obtained by embodying quartz crystal resonators in the additional circuits 22, 23, 24, etc., such as by the provision of high frequency choke coils in the anode circuits of the valves l5 and 44, Figure 5, and by feeding the circuits I9, 20, 2| and ll, 48 through condensers and/or the quartz crystals. By means of such crystals sharp cut-offs are obtained equivalent to the sharpness of ordinary circuits using quartz crystals but with a fiat top resonant curve and a band width substantially wider than can be obtained with a single circuit of known type embodying quartz crystal resonators. If greater band widths are required the damping of all circuits used in the filter unit should be higher. From this, it is obvious that any desired frequency characteristic may be obtained in accordance with the invention for any frequency by reason of the fact that the additional circuits also increase the volume of the signals thereby increasing the over-all efficiency or amplification of the system.

The adjustment tion is extremely of a filter system of the invensimple. Thus, in an arrangement according to Figure 3, first the condensers 22 and 38 are detuned to a substantial degree, that is adjusted to zero capacity to eliminate the effect of the additional circuits upon the main circuits. The latter are then tuned to resonance. Thereupon, the circuit 22, 23, 24 is tuned so as to increase the current or potential in the output circuits connected to points 4| and 4| and finally the

circuit

38, 39, is tuned while observing the increase of the output current. During the tuning of the additional circuits, it will be noted that by increasing the capacity of the condenser, the signal will first disappear and then after further increase of the capacity will reappear with substantially greater volume. If the coupling is reversed, that is as shown at 31 and 40 in Figure 3, the behavior of the

additional circuit

38, 39, 40 will be opposite, that is if the condenser 38 is increased at first the volume of the signal will increase and then disappear for a certain capacity of the condenser 38. The explanation for this is the fact that the rejective effect now occurs on the other side of the resonance curve. This reversing of the coupling of the filter unit such as for the

coils

20 and 48, Figure 11, may also be efiected by reversing the anode or high tension connections of the respective circuits, that is by reversing the relative phase of the exciting potentials by 180.

The filters can be more accurately tuned and adjusted by means of an oscillographic method whereby the resonance curves may be directly viewed on the screen of a cathode ray tube or the like. In this latter case also, at first the main circuits are tuned and then the auxiliary circuits adjusted in the manner described above or both circuits may be adjusted simultaneously until the proper resonance curve appears on the screen of the cathode ray tube. In order to obtain an adequate band-pass action with a sharp cut-ofi effeet, the coupling between the circuits should be correct. Thus the coupling between the circuit 22, 23, 24, 50 and 5|, 52, Figure 5, should be considerable higher than is used in band-pass filters of usual construction. The coupling between the additional or

auxiliary circuits

41, 48, 49 and I9, 20, 2|, Figure 5, and the main circuit 22, 23, 24, 50 should preferably be such that M w /R1R2 wherein M represents the coefiicient of mutual inductance between the circuits, to is the frequency of the signals in radians per second, R1 represents the ohmic or loss resistance in the main circuit 22, 23, 24, 50 and R2 the corresponding resistance in the additional circuits I9, 20, 2| and 41, 48, 49.

From the above it follows if the circuits I9, 20, 2| and 41, 48, 49 are lowly damped, a rather low coupling is required and care should be taken that no other spurious coupling occurs beyond a permissible limit in the external circuit connections or through the valves between the circuits. For this reason every circuit in the inventive system is associated with a special exciting valve or a separate plate of a composite or multiple valve of the type described. Moreover, as previously explained, the connection of the additional circuits with separate valves or a valve with a plurality of anodes has the advantage of enabling an easy adjustment of the band width according to a further feature oi the invention. Since thecircuits of the filter unit are coupled with each other, they may be placed in a screened container as shown in Figure 11 or in two or more containers if desired.

Resonance curves of the type shown at B or C', Figure 2, may be very useful for demodulation of frequency modulated signals. For this purpose the steep rectilinear portion of the curve B may be utilized and the operating point for the unmodulated carrier adjusted in a manner to fall within the steep rectilinear portion of the characteristic. The steepness of the curve and accordingly, the ei'ficiency of the demodulation can be further increased by using two or more circuits in cascade such as shown in Figure 5 in which case, however, the coupling 31, 40 should not be reversed as previously described where a band-pass effect is desired. Furthermore, a system according to Figure 5 may be used to secure a steep characteristic for demodulation of frequency modulated signals in which case the third valve 44 and associated

circuit

41, 48, 49 may be dispensed with as will be understood. The steepness of the curve B can further be increased by employing a greater number of twin parallel circuits in cascade such as shown in Figures 1 and 3. The adjustment of the grid bias in proportion to the variations of the strength of the received signals in this case provides an efiicient control of the steepness of the resonance curve and may be used for pure volume control of the frequency modulated signals.

Referring to Figure 12 there is shown a complete diagram of a superheterodyne radio receiver incorporating filters with composite valves and automaticvolume and selectivity control according to the invention. There is shown an antenna circuit comprising an antenna 80, antenna coupling condenser 8|, coupling coil 82 and ground connection 81. Coil 82 is coupled with a filter of usual design comprising a first resonant circuit constituted by an inductance 83 shunted by a capacity 85 and a secondary resonant circuit comprising an inductance coil 84 shunted by a condenser 88. The antenna coupling coil is in coupling connection with either or both of the inductance coils 83 and 84 of the resonant circuits. The circuit 84, 86 serves to excite the input or signal control grid 93 of a composite mixer or frequency converter valve 89 of otherwise usual construction having a cathode 90, oscillator control grid 9|, oscillator or anode grid 92, signal input grid 93 enclosed by a screen grid 94 and three separate anodes 95, 96 and 91 mounted and arranged relative to the other electrodes in a manner substantially as described in connection with Figures 8 to 10. The cathode 90 is connected to ground through a biasing resistance 99 shunted by Icy-passing condenser I00 to provide adequate operating grid biasing potential for the signal input grid 93. The screen grid 94 is connected to the plus terminal of a high tension source indicated by the plus symbol through a voltage drop resistance IM and to ground through a decoupling condenser IOI' in the manner well known. The oscillating grid 9| is connected to an oscillating tank circuit comprised of an inductance I02 shunted by a variable condenser |03 through a coupling arrangement consisting of a grid coupling condenser I04 and grid leak I05. In order to maintain sustained local oscillations in the tank circuit I02, I03, a feedback coil I06 inductively coupled with the inductance I02 is connected in the lead from the positive or anode grid 92 to the positive pole of the high tension source through drop resistance I01. The lower end of the latter is shunted to ground through a by-pass condenser I08. In this manner, sustained oscillations are maintained in the oscillator tank circuit I02, I03 with the steady bias for the oscillating grid 9I being produced by the direct current drop through the grid leak I 95. The oscillating condenser I63 is ganged and tracked in the usual manner with the input tuning condensers 85 and 86 by mounting upon a common shaft as indicated at I32 to maintain a constant frequency difierential equal to the intermediate frequency of the system obtained in the output circuit of the valve by the modulating or mixing action of the latter.

The central anode 96 is connected to one terminal of a resonant circuit comprising an inductance coil III? in series with a pair of coupling coils III and H2, and shunted by a condenser H3, The other terminal of the resonant circuit is connected tothe positive pole of the high tension source through a resistance I I4 Icy-passed by a condenser II 5. The anode 95 is connected to'one terminal of a parallel tuned circuit comprising an inductance H3 in series with a coupling coil III and shunted by a condenser I II), the other terminal of the circuit being connected to the positive pole of the high tension source through a resistance H9 by-passed by a condenser I29. Furthermore, the anode 91 is connected to one terminal of a parallel tuned circuit comprising an inductance coil I2I in series with a coupling coil I 22 and shunted by a condenser I23, the other terminal of the circuit being-connected to the positive pole of a high tension source through a resistance I24 by-passed by a condenser I25. There is further shown a resistance I26 connected between the positive pole of the high'tension source and the cathode 99 to stabilize and fix the cathode potential. The coupling coils III, I I1 and I I2, I22 are in inductive relation with each other thereby forming a filter system together with valve 89 substantially similar as shown in Figure 5. As is understood, the circuit III III, II2, H3, circuit H6, H1, IIB and circuit I 2|, I22, I 23 are tuned in respect to the intermediate frequency of the system obtained by the mixing or frequency changing action of the valve 89.

The inductance III? of the tuned anode circuit connected to anode 96 is coupled with the inductance'I30 of a resonant input circuit for an intermediate frequency variable mu type amplifying valve I32 also constructed as shown in Figures 7. to 10. The input circuit of this valve is completed by the condenser I3I shunting the inductance I39. The valve I32 includes a control grid I33 connected to the upper terminal of the input circuit I30, I3I, a screen grid I3 3 connected to the positive pole of the high tension source througha resistance I35 shunted by a condenser I36, a suppressor grid connected to the cathode in a known manner and I39. The cathode of the tube is connected to ground or the negative potential point of the system through a'biasing resistance I 49 shunted by a by-pass condenser III. The anodes I31, I33, I39 are connected to three interconnected resonant circuits similar as shown in Figure 5, the resonant circuit inserted in the circuit of anode 53! comprising an inductance coil I42 in series with a coupling coil I43 and shunted by a condenser I I I, the resonant circuit inserted in the circuit of anode I33 comprising an inductance coil I26 in series with a pair of coupling coils Hi1 and I48 and shunted by condenser I69, and the resonant circuit inserted in the circuit of anode I39 comprising an inductance I 53 in series with a coupling coil II and shunted by condenser I52. Coil I33 is in coupling relation with the coil I 41 and coil IE8 is in coupling relation with coil three anodes I31, I38 and.

I5I The cathode of the valve I32 is' connected to the positive pole of the high tension source through a resistance I53 by-passed by condenser I 54 to stabilize the steady or quiescent cathode potential. A resonant circuit comprising an inductance coil I55 shunted by a condenser I 56 is coupled with the central filter circuit I46, I41, I48, I49 in a manner similar as in the previously described arrangements, This resonant circuit serves to excite a duplex-diode valve I69. For this purpose the upper terminal of the circuit is connected to the anode of one of the diode sections and the lower terminal is connected to the grid of the valve I 39 through a coupling condenser I6! and a grid leak I62. The lower terminal of the circuit I55, I53 is further connected to ground through a resistance I63 shunted by a condenser III I to form a coupling impedance network for applying the low frequency or demodulated signal potentials generated by rectification to the grid of the valve for further amplification in the output circuit. The cathode of the valve is connected to ground through a biasing resistance I 65 bypassed by condenser II'IIE to provide adequate operating grid biasing potential. The amplified demodulated or low frequency signals are applied from the anode of the valve I 60 through a low frequency or audio transformer having a primary I35 and a secondary I'IIS to a pair of further audio frequency amplifier valves connected in push-pull in a known manner and serving to operate a translating device such as a dynamic loud speaker I 86 through an output push-pull transformer having a primary winding I 93 and secondary winding I 85. The anode of valve I69 is connected through the primary I75 to the positive pole of the high tension source in series with aresistance I11 bypassed by a condenser I 18. There is further provided a shunt circuit from the anode of valve I66 to ground comprising a variable resistance I13 and a condenser III in series and serving as a tone control circuit in a manner well known. The center point of the secondary of the push-pull in put transformer is connected to ground through aresistance I BI, and the common cathode point of the push-pull amplifier valves I19 and I89 is connected to ground through a grid biasing resistance I82 by-passecl by a condenser I83. The anodepotential for the valves I19, I80 is supplied direct from the high tension source to the center point of the primary I83 of the push-pull output transformer which center point is bypassed to ground by a condenser 181.

The second anode of the valve I60 is utilized to generate a volume or selectivity control potential and for this purpose is connected to the upper terminalv of the central resonant circuit of the filter system I46, I41, I38, I49 through a coupling condenser I31 on the one hand, and to ground through a pair of resistances I68 and I69 in series In this manner, there is produced at the junction of the resistors I68, I99 a steady potential varying in accordance with the field strength or carrier amplitude of the signals received in the input circuit. This potential is applied to the control grids the valves 89 and I32 through resistances I 12 and Il'il, respectively connecting the junction between the resistances I 68 and I69 to the lower terminals of the input circuits 84, 86 and I39, I3I, respectively, thereby completing the cathode return for the latter. In this manner combined automatic volume and selectivity or fidelity control of the receiver is efiected as described hereinbefore. In addition, the bias resistors 99 and III! inserted in the cathode leads of the valves 89 and I33 are shown to be variable and arranged for common control by a coupling element indicated at I89 to allow for manual adjustment of the volume and fidelity level of the receiver in addition to the automatic adjustment described.

The over-all fidelity and volume control curves for a receiver of this type are shown in Figure 13 wherein curve G is the over-all resonance characteristic of the receiver for high gain and high selectivity, J the resonance curve for low gain and low selectivity or high fidelity, and H a curve for an intermediate adjustment.

A system equipped with combined automatic volume and selectivity control of the type described has the further advantage that the volume control ratio is substantially higher than in the ordinary automatic volume control systems known. The standard variable mu valves used in the commonly known circuits allow of a variation over a range of about 35 db. per valve. In systems with combined volume and selectivity control of the type according to the invention, this control range is increased to about 35 to 40 db. by reason of the fact that the additional circuits act to increase the apparent Q or coefficient of the main circuit with low grid bias values of the amplifying valves. For strong signals the amplification of the valves is reduced and with it the Q of the main circuit due to the fact that in this case the additional circuits have the efiect of increasing the damping of the main circuit. This feature of automatically varying the Q factor of a circuit is an important characteristic of the invention.

In modern radio receivers, it is customary to provide an automatic tuning arrangement in addition to automatic volume control and/or fidelity control. In general, arrangements of this type operate in such a manner that after the receiver has been tuned approximately to a desired station, either by hand or a dialing or pushbutton mechanism, the automatic tuning system is set in operation and acts to adjust the heterodyning frequency of the local oscillator in such a manner that the intermediate signal frequency coincides exactly with the center or resonance point of the characteristic of the tuned intermediate frequency amplifier. In order to generate a tune responsive or discriminating potential for adjusting the oscillating frequency in a system of this type, it has been proposed to provide two detuned circuits, one slightly tuned below and the other slightly tuned above the intermediate frequency of the receiver from which circuits a direct potential is derived by rectification and differential combination varying in either a positive or negative direction in dependence of the degree of detuning of the signal above or below the intermediate frequency, respectively, for which the receiver is designed. If automatic frequency control of this type is used in a circuit according to the invention, such as described, the detuned or discriminating circuits may be combined with the additional circuits, according to Figure 12 (circuits I42, I43, I44, and I50, I5I, I52). In this manner a substantial saving in parts and apparatus can be effected while obtaining the combined benefits of automatic volume, automatic frequency and automatic fidelity control in a radio receiver.

It will be obvious from the above that the invention is not limited to the specific arrangement of parts and elements shown and methods disclosed herein for illustration, but that the underlying inventive thought and principle are susceptible of numerous modifications and variations differing from the embodiments described and coming within the broader scope and spirit of the invention as defined in the appended claims.

The specification and drawings are accordingly to be regarded in an illustrative rather than a limiting sense.

I claim:

1. An electric translation system comprising an input circuit, an output circuit, a plurality of amplifiers arranged in parallel and excited from said input circuit, a tunable resonant circuit in the output of each of said amplifiers, said tunable circuits being coupled in pairs and their frequency resonance curves being substantially equal, and coupling means between said output circuit and one of said tunable circuits.

2. An electric translation system comprising an input circuit, an output circuit, a plurality of amplifiers arranged in parallel and excited from said input circuit, a tunable resonant circuit in the, output of each of said amplifiers, said tunable circuits being coupled with each other and their frequency resonance curves being substantially equal, said tunable circuits being tuned to different resonant frequencies so that their frequency resonance curves overlap, and coupling means between said output circuit and one of said tunable circuits.

3. An electric translation system comprising an input circuit, an output circuit, a plurality of amplifiers arranged in parallel and excited from said input circuit, a tunable resonant circuit in the output of each of said amplifiers, said tunable circuits being coupled with each other and having substantially equal resonance curves, said tunable circuits being tuned to slightly different resonant frequencies, coupling means between said output circuit and one of said tunable circuits, and means for adjusting the gain of at least one of said amplifiers to vary the over-all resonance characteristic of the system.

4. An electric translation system comprising an input circuit, an output circuit, a plurality of amplifiers with means for simultaneously exciting the same from said input circuit, tunable circuits in the outputs of said amplifiers inductively coupled with each other sufficiently closely to effect a mutual interchange of resonant energy therebetween when simultaneously excited by similar potentials, coupling means between one of said tunable circuits and said output circuit, the remaining tunable circuits being detuned relative to said first mentioned tunable circuit to obtain a resultant frequency response characteristic of said system having a sharp cut-off close to the resonant frequency of said first tunable circuit, and means for adjusting the gain of said amplifiers.

5. A signal translation system comprising an input circuit, a resonant output circuit, a first resonant circuit, coupling means between said first resonant circuit and said output circuit, at least one further resonant circuit coupled with said first resonant circuit, said coupled first and further resonant circuits having substantially equal resonance curves, and individual unilateral signal transmission paths from said input circuit to said first and further resonant circuits.

6. A signal translation system comprising an input circuit, an output circuit, a first tunable resonant circuit, coupling means between said tunable circuit and said output circuit, at least one further tunable resonant circuit arranged in inductive coupling relation with said first tunable circuit, the mutual coupling impedance (Me) between said tunable circuits being equal or less than the square root of the product of their nonreactive impedances, the frequency response characteristics of said first and further circuits being substantially equal, and individual uni-lateral signal transmission paths from said input circuit to each of said tunable circuits.

7. A signal translation system comprising an input circuit, an output circuit, a first tunable resonant circuit, coupling means between said tunable circuit and said output circuit, at least one further tunable resonant circuit in inductive coupling relation with said first tunable circuit, the mutual coupling impedance (Mm) between said tunable circuits being equal or less than the square root of the product of their non-reactive impedances, the frequency response characterise tics of said first and further circuits being substantially equal, separate amplifiers connected between said input circuit and each of said tunable circuits, and means for adjusting the gain of said amplifiers.

8. A signal translation system comprising an input circuit, an output circuit, a main resonant circuit, coupling means between said resonant circuit and said output circuit, at least one auxiliary resonant circuit coupled with said main resonant circuit and having a damping coefiicient greater than the damping coeflicient of said main resonant circuit, said coupled main and auxiliary resonant circuits having substantially equal frequency response characteristics and being tuned to slightly different resonant frequencies, the resonant frequency of said main resonant circuit substantially equalling the signal frequency, and a plurality of amplifying valves individually connecting said input circuit with each of said resonant circuits.

9. A signal translation system comprising an input circuit, an output circuit, a main resonant circuit, coupling means between said main resonant circuit and said output circuit, further auxiliary resonant circuits coupled with said main resonant circuit sufficiently closely to effect an interchange of resonant energy between said circuits when all of said circuits are simultaneously excited by similar potentials, and a plurality of amplifying valves individually connecting said input circuit with each of said main and auxiliary resonant circuits, the coupling of at least two of said auxiliary resonant circuits with said main resonant circuit being such as to impress potentials of opposite phase upon said main resonant circuit.

10. A translation system for modulated carrier signals comprising an input circuit, an output circuit, a main resonant circuit, coupling means between said main resonant circuit and said output circuit, a plurality of auxiliary resonant circuits coupled with said main resonant circuit, a plurality of amplifying valves individually connecting said input circuit with each of said main and auxiliary resonant circuits, means for controlling the gain of said amplifiers, the coupling of at least two of said auxiliary resonant circuits with said main resonant circuit being such as to impress potentials of opposite phase upon said main resonant circuit, thereby to obtain a resultant input-output frequency response characteristic with a sharp cut-01f at both sides of the resonant frequency of said main resonant circuit taken individually.

11. In a system as claimed in the preceding claim including means for generating a control potential varying in accordance with fluctuations of the carrier amplitude, and means for applying said potential to a gain control means of said amplifiers.

12. A translation system for modulated carrier signals comprising an input circuit, a resonant output circuit, a main resonant circuit, coupling means between said main resonant circuit and said output circuit, at least two auxiliary resonant circuits sufiiciently closely coupled with said main resonant circuit to effect a mutual interchange of resonant energy therebetween when said circuits are simultaneously excited by similar potentials, a plurality of electronic amplifying paths having input and output electrodes, said input electrodes being connected to said input circuit and each of the output electrodes being connected to one of said main and auxiliary resonant circuits, the coupling between said auxiliary resonant circuits with and the tuning thereof relative to said main resonant circuit and the gain of said amplifying paths being such as to obtain a sharp cut-off at both sides of the resonance characteristic of said main resonant circuit in respect to signals applied to said input circuit.

13. A translation system for modulated carrier signals comprising an input circuit, an output circuit, a main resonant circuit, coupling means between said main resonant circuit and said out put circuit, at least two auxiliary resonant circuits sufliciently closely coupled with said main resonant circuit to effect a mutual interchange of resonant energy therebetween when said circuits are simultaneously excited by similar potentials, a plurality of electronic amplifying paths each comprising a cathode, an anode and a control electrode, coupling connections from said input circuit to the control electrodes of said amplifying paths, each of said main and auxiliary resonant circuits being connected in the anode circuit of one of said amplifying paths, the coupling between said auxiliary resonant circuits and said main resonant circuit, the tuning of said auxiliary resonant circuit relative to the tuning of said main resonant circuit and the relative gain of said amplifying paths being such as to cause a resultant characteristic of said main resonant circuit having a sharp cut-01f at both sides of its resonant frequency in respect to signals applied to said input circuit.

14. A system as claimed in claim 13 wherein said amplifying paths have common cathode and control electrodes and plurality of separate anodes operatively associated therewith.

15. A system as claimed in claim 13 comprising means for simultaneously varying the gain of said amplifying paths.

16. A system as claimed in claim 13 comprising means for simultaneously adjusting the gain of said amplifying paths, further means for generating a control potential Varying in accordance with fluctuations of the carrier amplitude, and means to control said gain adjusting means in accordance with said control potential.

17. An electric translation system comprising an input circuit, an output circuit, a plurality of amplifiers arranged in parallel and excited from said input circuit, a tunable resonant circuit in the output of each of said amplifiers, said tunable circuits being coupled with each other and tuned to different resonant frequencies, the resonance curves of said coupled circuits being substantially equal and overlapping so that one of said circuits acts as a receptor and another one as a rejector to a desired extent, and coupling means between said tunable circuit acting as a receptor and said output circuit.

18. In a method of translating electrical oscillatory energy through a system of parallel amplifying channels of substantially equal frequency response characteristics and adjustable gain, the steps of subdividing and passing said oscillatory energy simultaneously through said channels, tuning a first one of said channels to an average frequency of said energy and tuning another of said channels to a different frequency within the frequency response range of said first channel, causing the subdivided oscillatory energies translated through said channels to act upon each other so as to produce a resultant frequency response curve of the system of improved cut-off characteristics, adjusting the gain of at least one of said channels so as to produce a desired width of said resultant response curve, and deriving the translated oscillatory energy from the output of said first channel.

19. In a method of translating electrical oscillatory energy through a system comprising a plurality of tunable resonant amplifying paths of substantially equal selectivity arranged in parallel, the steps of applying said energy simultaneously to and passing it through said paths,

tuning a first one of said paths to the average frequency of said energy, tuning another one of said paths to a different frequency within the resonance curve of said first path, and causing by coupling the energies translated through said paths to act upon each other so as to produce a substantially sharper cut-off of the resultant frequency resonance curve of the system, and deriving the translated energy from the output of said first path.

20. In a method of translating a frequency band through a system composed of a plurality of amplifying filter networks arranged in parallel, said networks being of substantially equal selectivity and having adjustable gain, the steps of simultaneously applying said band to and passing it through said networks, tuning a first one of said networks to the average frequency of said band, tuning another one of said networks to a different frequency within the frequency response range of said first network, and causing the energies translated through said networks to act upon each other so as to produce an improved cut-off of the resultant frequency response curve of said system, adjusting the gain of at least one of said amplifying networks so as to produce a width of said resultant curve substantially equalling the width of said frequency band, and deriving the translated frequency band from the output of said first network.

J OZEF PLEBANSKI.