US2130824A - Radio circuits - Google Patents

Description

RADIO CIRCUITS Filed Oct. 29, 1929 3 Sheets-Sheet 1 A a m H. V v m L M E m j m 4 I a n u: U. m n U m m m w m 7 m m a n J:: v w m a 3/! i m n H mm y Z. n n Ik m J i n z w w :sF/lv 4 T 1 m V n J/TU. u m m a u 1 e m H. m n m w JT l 8: n H m u l 2 u H 4 4 5 i O n :1! w 6 H n I n m 0 1 m n n a u u 1. in 4 n m m m vi 6% n J m W a l a s flio t.

0R5 LESTER 1.. JONES JACOB Y LLES ATTORNEYS Sept. 20, 1938. L. JONES ET AL RADIO CIRCUITS Filed 001:. 29, 1929 5 SheetsSheet 2 /I4l H I I l I I I I f I 151 I I l l l INVENTORS LESTER L. JONES V JACOB YOLL I ATTORNEYS Sept. 20, 1938. L.. JONES ET AL. 2,130,324

RADIO CIRCUITS Filed Oct. 29, 1929 5 Sheets-Sheet 3 f .13. E. 156 142 '43 158 m4 INVENTORS LESTER L. JONES YJ'ACOB YOLLE ATTORNEYS Patented Sept. 20, 1938 UNITED STATES PATENT OFFICE Brooklyn, N.

Y., assignors to Technidyne Corporation, New York, N .Y., a. corporation of New York Application October 29, 1929, Serial No. 403,160

27 Claims.

This invention relates to radio circuits and more particularly to tuned radio circuits coupled directly in cascade.

In the copending application of Lester L. Jones, Serial No. 243,790, filed December 31, 1927, (since issued on August 14, 1934, as Patent Number 1,970,315) there is disclosed the theory underlying a selector for energy of desired frequency comprising a plurality of closed resonant circuits coupled directly together in cascade without the use of intervening relays, and there is further set forth a number of preferred structural arrangements employing the theory of and inventions residing in the said selector. Our present invention relates to improvements in such a selector, particularly with a view to effecting a simplification of and reduction in the space requirements of such a selector, and the general object of the present invention resides in the provision of a compact and simple selector which will be suitable for embodiment in the typical compact commercial broadcast receivers of today.

Frequently in the construction of radio circuits it is desirable to obtain a relatively loose coupling between coils which are compactly coupled together. This necessity arises particularly when dealing with relatively sharply tuned circuits in an arrangement wherein it is desired to avoid double resonance peaks. To place the coils nearly at right angles for loose coupling is too critical for practical manufacturing purposes. The loose coupling may be reproducibly obtained by a very wide separation between the coils, but this is wasteful of space. One object of the present invention is to make possible the accurately reproducible obtainment of a desired loose coupling between coils while securing a compact structural arrangement.

When a series of resonant circuits are coupled successively in cascade in order to select energy of desired frequency it is necessary not only that the adjacent circuits be loosely coupled in order to avoid double resonance peaks, but that the non-adjacent circuits be decoupled or insulated from one another as regards the transfer of energy from one to the other except for the energy which is caused to flow through the intermediate circuit or circuits. To obtain the desired result by spacing the circuits remotely from one another would be cumulatively wasteful of space, and to make possible a compact structural arrangement in such a situation is another object of the present invention.

Suppose, for example, that a selector having four resonant circuits coupled directly in cascade is to be constructed. The adjacent circuits should be loosely coupled together to avoid double resonance peaks. The non-adjacent circuits, as for example the first and third, the second and fourth, and the first and fourth, must be decoupled from one another in order to insure that the energy supplied to the selector passes therethrough solely through each of the resonant circuits in succession. Now in accordance with our present invention, in order to fulfill the foregoing requirements, and at the same time to obtain a compact structural arrangement, the coils of the tuned circuits, which preferably constitute the whole effective inductance of the tuned circuits, thereby dispensing with special coupling coils, are nearly completely shielded. The shielding is such that when the coils are placed in close juxtaposition the desired loose coupling is obtained, and further is such that when all of the coils are placed successively in close juxtaposition the non-adjacent coils, although separated by only the dimensions of an intermediate coil, are spaced sufiiciently to prevent direct coupling therebetween.

It is preferred to tune the resonant circuits of the selector by capacitive tuning and to employ uni-control of the several. tuning condensers. In order to further effect a reduction in the size of the selector it is possible and desirable to arrange the various tuning condensers on a common shaft, the shaft of the condenser usually being grounded and electrically connected in common to all of the condenser rotors. However, when this is done we have discovered that there is an undesired coupling between nonadjacent resonant circuits, this coupling being caused by the flow of the high frequency currents of non-adjacent tuned circuits through at least a common portion of the condenser shaft on their return to the coils of the respective circuits, which, as previously mentioned, will ordinarily be at ground potential, and for convenience we may hereinafter refer to this simply as a return to ground. In spite of the large cross sectional area and relatively short length of the condenser shaft We have nevertheless found the impedance of the common portions of the shaft to be sufficient to cause an appreciable and injurious coupling between non-adjacent circuits. To overcome this difficulty is still another object of our invention, which we fulfill, briefly, by forming a direct path to ground from the condenser shaft between circuits which are to be decoupled. More specifically, we employ as direct and as low impedance a connection to ground (more generally, to the coils of the circuits) as is possible between the second and third condensers of the four-gang condenser. Such a connection comes between the first and third condensers, the second and fourth condensers, and the first and fourth condensers, and therefore decouples the corresponding circuits. A slight coupling may remain between the first and second condensers and between the third and fourth condensers, but this is not injurious, inasmuch as these circuits are anyway loosely magnetically coupled together. Even this slight coupling through the condenser shaft may optionally be avoided, if desired, by additional direct low impedance connections to ground between the first and second and between the third and fourth condensers.

Further objects of our invention reside in the provision of suitable structural arrangements embodying our invention, and particularly such arrangements which will permit of the close juxtaposition of the coils, and the placing of the coils with parallel axes for the sake of simplicity, and the ganging of the tuning condensers upon a common shaft for uni-control.

To the accomplishment of the foregoing and such other objects as will hereinafter appear, our invention consists in the elements and their relation one to the other as hereinafter are more particularly described in the specification and sought to be defined in the claims. The specification is accompanied by drawings in which:

Fig. l is a wiring diagram for one form of our invention;

Fig. 2 is a partially sectioned elevation of a self-shielded coil system which may be used in the arrangement of Fig. 1;

Fig. 3 is a partially sectioned elevation of a metallically shielded coil system which may be used in the arrangement of Fig. 1;

Fig. 4 is a plan View of a complete selector embodying the circuit of Fig. 1;

Fig. 5 is a wiring diagram for a modified selector; and

Fig. 6 is a structural arrangement embodying the circuit of Fig. 5.

Referring to Fig. 1, the selector consists of four tuned circuits, l, 2, 3 and 4. Each of these circuits is a closed tuned circuit having a high degree of selectivity. The logarithmic decrement of all of the circuits is preferably kept equal and low so that the resonance curve near its peak is very narrow, and a slight broadening of the peak due to coupling of the individual circuits together may therefore be tolerated.

The tuned circuits consist essentially of inductance coils H, l2, l3 and M, and variable condensers 2!, 22, 23 and 24. The last tuned circuit is coupled to an amplifier or other circuit, constituting a load across the tuned circuit. The amplifier may be made reactionless, in accord ance with the teachings of the copending application of Lester L. Jones, Serial No. 397,632, filed Oct. 5, 1929, since issued as Patent 1,788,197, dated January 6, 1931, so that the input circuit thereof is equivalent to a small fixed loss free condenser. This capacitance is in parallel with condenser 24 and alters the total effective capacitance of circuit 4, and small compensating condensers 32 and 33 are therefore connected in parallel with condensers 22 and 23 in order that all of the variable condensers may be made identical in construction. A small adjustable or trimmer condenser 34 may be connected in parallel with variable condenser 24 so that the fixed capacitance in parallel with the variable condenser 24 may be brought to a predetermined Value, corresponding to the capacitance of condensers 32 and 33, even though the capacitive load of the amplifier may differ from that of condensers 32 and 33. Tuned circuit I has connected thereacross an antenna circuit I6, [8, which is equivalent to considerable capacitance connected across circuit 1. We connect a small adjustable condenser E! in series with the antenna circuit to reduce the capacitive load across the first selector circuit to a small value, which by adjustment of condenser 36 "lay be made equal in capacitance to the condensers 32 and 33, as is indicated by the dotted condenser 3| in parallel with the variable condenser 21. Condenser 3| also avoids substantial increase in the decrement of circuit 1, by loosening the coupling between the antenna and the selector circuit.

As so far described, there are four circuits each having identical tuning characteristics and similar constants for the sake of uni-control and simplicity of structtue. It next is necessary to couple these circuits together. The circuits must be loosely coupled together so as to avoid the production of double resonance peaks. For the sake of efficiency we prefer to couple the circuits together with what We term the optimum coupling, by which we mean the loosest coupling which will give the maximum voltage in the second circuit of a pair of circuits which are not coupled to any other circuits, each of the pair of circuits being a circuit similar to those in the selector. This coupling gives a slightly broader resonance curve for two or more circuits near the peak of the resonance curve than would be the case for a single tuned circuit. This is, however, a desirable feature in that it tends to give the receiver a more uniform response to all of the side band components of the radio frequency wave.- The form of the resonance curve near its base, or for frequencies widely different from resonance, is substantially similar to that of the curve obtained when the coupling between the tuned circuits is made so extremely loose that it leads to a great reduction in signal amplitude. The optimum coupling is greater than this, but less than the value producing double resonance peaks, and in the ordinary case is of the order of magnitude of one or two percent coupling coefficient. With our system we obtain selectivity in geometric progression in the frequency range in which selectivity is important, and we obtain a form of curve near the resonance peak which is like the characteristic of a band pass filter, resulting in equal response for slightly different frequency components, as is desirable in order to avoid signal distortion.

To obtain the desired loose coupling between adjacent circuits by separation of the circuits would require a great deal of room, while to place the coils nearly at right angles results in a critical construction which is difficult to reproduce with uniform results under quantity production conditions, besides necessitating an unsymmetrical and therefore inconvenient structure. In accordance with our arrangement each of the coils ll, l2, l3 and M is nearly completely shielded, as by the shields M, 42, 43 and 44 shown in dotted lines on the drawings. These shields reduce the external fields of the coils to such an extent that the coils may be positioned in close juxtaposition with parallel axes and yet be loosely coupled, as is desired.

Eddy currents in the shielding generated by the initial flux cause a counter-flux opposed to the initial flux, and thereby limit or condense the external field. In the modification shown in Fig. 2, the outer winding carries current and itself acts to generate the desired flux opposition. In the arrangements shown in Figs. 3, 4 and 6, the condensation of the field is through the in termediary of eddy currents, as explained above. With reference to Fig. 3, for example, it should be understood that even though the ends of the cylindrical shielding members are open, there nevertheless is a shrinkage or condensation of the fiux field produced by the coil, which shrinkage takes place not only radially but also axially. Consequently the coils, even though positioned nearly together, are linked not by normal flux, but by a greatly reduced flux component. From one viewpoint it may be said that the coils are linked by leakage fiux instead of the full flux.

Not only is it necessary that adjacent circuits be coupled with the optimum coupling, but also, in order'to obtain the desired selectivity or exclusion of frequencies off resonance, that nonadjacent circuits be decoupled from one another to a high degree, which may be quantitatively defined as follows. Consider any three adjacent circuits. For energy in resonance the intermediate circuit is efficient and of low impedance and nearly all of the energy is transferred therethrough. Furthermore, such energy if transferred directly can do not harm, even if appreciable, though actually the voltage transferred will be only say a fifth of a percent of that transferred through the intermediate circuit. Now, at a given large percentage of frequency off resonance, say 20%, only a small part of the energy is transmitted through circuit two to circuit three. If direct coupling exists between circuit one and circuit three another small fractional part of the energy will be transmitted from circuit one to circuit three through this direct coupling. Our measure of the necessary decoupling is that the voltage transmitted directly must be less than 10% of that transmitted through the intermediate circuit. This would correspond to 1% energy ratio.

These fractional parts can be determined from the resonance curves for the individual circuits. A typical resonance curve for such sharply tuned single circuits has a sharp peak with a rapid decline of amplitude starting at frequencies one or two percent off resonance. The curve then becomes relatively fiat, so that for frequencies approximately 20% off resonance there is no further substantial reduction in amplitude. The fraction of voltage off resonance previously discussed as transferred through the intermediate circuit may be taken substantially as the ratio of the maximum to minimum voltage amplitude for the single circuits. This ratio corresponds closely to a factor which is often termed the resonance rise of the tuned circuit, and is of the order of one hundred to two hundred for the best types of tuned circuit-s used in radio receivers.

An intermediate circuit therefore operates to cut down the amplitude of voltage transmitted, as between energy in resonance and energy far off resonance, by a factor corresponding to this resonancerise. In order for the non-adjacent circuits to be sufficiently decoupled, therefore, that is, to have a coupling which creates a voltage transfer of only one-tenth or less than that through the intermediate circuit for energy for off resonance, the ratio must be of the order of only one part in one thousand to two thousand for circuits separated by a single tuned circuit, and of the order of one part in one hundred thousand to one part in four hundred thousand for circuits separated by two intermediate tuned circuits. The coupling between non-adjacent circuits should be reduced to a value equal to the coupling between adjacent circuits divided by the foregoing ratios, i. e., one or two percent divided by one hundred thousand to four hundred thousand is the maximum coupling coefiicient which may be tolerated between first and fourth circuits.

The situation is somewhat analogous to the prevention of feed back in tuned radio frequency amplifiers, where, because of the amplification in the successive stages, feed back from remote stages must be guarded against with even more precaution than feed back from adjacent stages. But in the case of our selector the energy transfer to be guarded against is in the other direction and is of energy off resonance, that is, energy transfer from the first selector circuits to the last selector circuits must be effectually prevented, for frequencies ofi' resonance, in order to obtain substantially geometric selectivity.

To accomplish the desired decoupling of nonadjacent circuits the shields which we employ around the coils are designed to condense the field of the coils, so to speak, that is to say, the leakage flux which they permit is not leakage flux in the ordinary sense, but is a confined leakage flux which is confined to the immediate vicinity of the coil. Because of this, when the coils are positioned in close juxtaposition the non-adjacent coils, although separated only by the dimension of an intermediate coil, are sufiiciently spaced to substantially eliminate direct coupling between the non-adjacent circuits.

The selector circuits are preferably grounded, thereby simplifying the shielding problem, by eliminating capacitive coupling to at least the grounded portions of the circuits. There is capacitance between the condenser stators and leads thereto, etc., to the shield 20, represented by the dotted condensers 21. If a single ground to the shield 20 were used for all of the circuits there would be a partially common path for energy circulating through condensers 21, and the circuits would therefore be coupled. Each of the circuits is therefore grounded to the shield 20 by independent and direct low impedance connections, marked 5|, 52, 53 and 54, which avoids having circulating energy of any two of the circuits fiow through a common portion of the shield, because even a slight impedance is sufficient to result in undesired coupling.

It will also be noticed that the ground connection SI of circuit I is connected to the shield 20 at the same point as the real ground connection l8 of the antenna circuit, this being done in order to avoid coupling of the antenna circuit to nonadjacent selector circuits through a portion of shield 20. The connection 28 is connected to the shield 20 at a point coinciding with the connection 26 to the amplifier, in order to avoid having the output energy of the selector flow through any appreciable portion of the shield 20, which might cause undesired coupling between selector circuits.

Fig. 2 shows one form of coil system which may be used in a circuit such as is shown in Fig. l. The coils I I, l2, l3 and I4 in this case are each of a self-shielded type, consisting of an outer winding and an inner winding connected in series there with, said windings being so physically related that the outer winding acts as a capacitive and magnetic shield for the inn-er winding, and only a compacted or confined magnetic field is obtained. Such coils are described in a patent to Lester L. Jones, No. 1,608,560, issued November 30, 1926. In the particular structural embodiment here set forth the inner coils 60 are wound on cylinders provided with spacer arms 62, which fit tightly within an outer cylinder 64. The finished coils are provided with supporting legs 66 and 61, and in order to permit of close juxtaposition of the coils the legs 66 of coils II and I3 are fastened to the side 68 of the supporting frame, while the legs 61 of coils I2 and I4 are fastened to the side IU of the frame, the sides 68 and ID of the frame being substantially at right angles. The ground connections of the shields, illustrated in the case of coil I! by connection III, are preferably separate, direct, and of low impedance, and must be to the condensers more importantly than merely to a common member like frame 88, III, so that the circuits will not have common paths.

In Fig. 3 we have shown another form of coil system in which the coils I I, I2, I3 and I4 consist of single coils wound on cylinders I2, provided with spacer arms I4, around which there are fitted metallic shielding cylinders ll, 42, 43 and A l. These cylinders may be open ended, as shown, and need not be directly electrically or otherwise connected together, although, of course, in practice they are eventually grounded. The ground connections are preferably separate, direct, and of low impedance, like the connections III, IIZ, I I 3 and I M, but must be to the condensers as well as to the frame I8, to avoid common paths for the tuned circuits.

The shields are preferably about twice the diameter of the coil and preferably extend beyond the ends of the coil a small distance. It is important that the sheilding be efficient and have no high resistance joints and that the material selected be highly conductive. The coils and shields may be supported in any desired manner, as by pedestals III, H2, H3 and H4, fastened to a suitable supporting frame I8. The coils are positioned in close juxtaposition, but because of the shielding effect of the cylindrical shields G I, 42, 43 and 44, which capacitively and magnetically shield the coils, and confine the magnetic field thereof, the coils are loosely coupled with only the desired optimum coupling, and non-adjacent coils are sufficiently spaced to be substantially decoupled.

In Fig. 4 we have shown a structural arrangement for a complete selector embodying the circuit set forth in Fig. 1. This arrangement includes coils II, I2, I3 and I4, and tuning condensers 2 I, 22, 23 and 24. Compensating or trimmer condensers 3I, 32, 33 and 34 are provided, the latter three of which are in parallel with the corresponding tuning condensers, while condenser 3I is connected in series with the antenna, as was previously explained. With these condensers we adjust the minimum capacitance in each of the circuits to be identical, including allowance for the antenna capacitance and the amplifier input capacitance.

The coil system here differs from that described in Fig. 3 in that a continuous shield is employed for all of the coils. While it is not necessary for the ends of the shield to be closed, nor for the shields to be electrically connected together, it is structurally convenient to employ such an arrangement. Also, in order to obtain highly efficient shielding it is more economical, as a manufacturing proposition, to use cups or cans which are pressed out of sheet metal than to use seamless or other tubing of sufficiently good electrical properties. In the arrangement shown in Fig. 4 the shield for the coils consists of two pressed cups and 82, having closed ends 84 and 8G, and open ends provided with flanges 88 and 90. The flanged ends may be fitted together and suitably fastened for mechanical rigidity. The coils within the shield may be supported on an axial member 92, which may also be used to fix the complete coil assembly within the external shield 29.

The rotors of the condensers 2|, 22, 23 and 24 are all formed integrally with a single shaft, 94, and arranged for uni-control. The shaft 94 may be grounded in the usual manner through end bearings 96, the condenser frame 98 being mounted directly on the shield 20. We have found that this customary grounding of the condenser shaft is insufficient because the ordinarily negligible coupling provided by the common portions of the short heavy condenser shaft is sufficient to spoil the desired selectivity characteristic. We therefore provide a short direct low impedance path, preferably by means of a heavy double spring contact brush I00, connected directly between the shaft 94 and the condenser frame and grounded shield 26. With this center ground connection some coupling remains between the first and second, and between the third and fourth circuits, but this is not injurious because these adjacent circuits are anyway coupled together. Meanwhile the first and third, the second and fourth, and the first and fourth circuits are separated by the ground connection I00, so that undesired coupling of non-adjacent circuits is effectively prevented. Additional ground connections may optionally be provided between the first and second and between the third and fourth condensers, as is indicated by the additional brushes I02 and I04, similar in construction to the brush IE9, which prevent coupling between even the adjacent circuits other than the desired magnetic coupling between the coils thereof. Meanwhile the non-adjacent circuits are then separated by a plurality of ground connections with consequent additional safety.

As is indicated by the connections III, H2, I13 and H4 in Fig. 1, not only should the circuits be grounded directly to the nearest point of the shield 20, but also the coil shields M, 42, 43 and d4 should be grounded with the circuits to the shield 20. This grounding is indicated by the connections III, H2, H3 and H4 in Fig. 4. The connections should be short, direct, and of low impedance, to avoid common couplings between non-adjacent circuits.

It should be observed that the supporting means 92, even if made of metal, is not alone as good a ground for the shielding cups 8d and 82 as we prefer to use, inasmuch as the ground will then be through a considerable portion of the shield 20. We therefore prefer to use the connections III, H2, H3 and H4, and the rod 92 may be insulated or may provide an additional ground connection for the shield of the coils, as desired.

The cups 80 and 82 shown in Fig. 4 are inconveniently long and are therefore diflicult to manufacture. For the sake of economy it is better to use cups than to use tubing, but for the sake of further economy it is better to use short cups than to use long cups. We have therefore also provided a selector in which two pairs of short cups are used instead of one pair of long cups.

The general arrangement may be understood by reference to Fig. 6 in whichv cups numbered HI and I42 form one pair, and cups numbered I 43 and I44 form another pair. In such an arrangement the second and third coils are completely shielded from one another, assuming that the cup ends are imperforate, and these coils must therefore be coupled together by auxiliary coupling means.

A wiring diagram for such a selector is given in Fig. 5, in which the selector is generally similar to that shown in Fig. 1, it consisting of four tuned circuits, I, 2, 3 and 4, each including a main coil, II, I2, I3 and I4, and a variable tuning condenser, 2|, 22, 23, 24. The additional adjustable fixed condensers 3|, 32, 33 and 34 are provided to equalize the minimum capacitance of the circuits. The first selector circuit is energized by an antenna to ground circuit I6, I8, while the last selector circuit is coupled to an amplifier or other circuit for the utilization of the selected energy. The selector is surrounded by a shield 20.

Coils II and I2 are surrounded by shields MI and I 42, while the coils I3 and I4 are surrounded by shields I43 and I44. These shields are like shields 4|, 42, 43 and 44 in Fig. 1 in that they cause coils II and I2 to be coupled with only the optimum coupling, although positioned close together, and similarly cause coils I3 and I4 to be coupled with only the optimum coupling, although positioned closely together. Shields I42 and I43 have closed adjacent ends, and coils I2 and I3 are therefore decoupled from one another. In order to couple circuits 2 and 3 these circuits include auxiliary coupling means I50, which may be a conductive or auto transformer coupling with a single winding, or a two winding transformer coupling, as is shown in the drawings by the coils I52 and I53. These coils are closely coupled together, preferably by being bifilarly wound, because it is desirable to have very small coils in order not to upset the electrical symmetry of the circuits, and also because if small they may be left relatively unshielded. The total inductance of the auxiliary coupling means I50 is made small relative to the total inductance of the circuits 2 and 3 in order to obtain the desired loose coupling, as well as for the foregoing reasons.

As before, the circuits are grounded as directly as possible to the shield 20 by low impedance connections indicated at 5|, 52, 53 and 54. The Shields MI and I42 may be grounded by a connection I46, while the shields I43 and I44 may be rounded by a connection I48, the connection of Fig. 1 not being readily applicable to this circuit due to the presence of auxiliary transformer I50. Connections I8, 26 and 20 are arranged with the same precautions as in Fig. 1.

Reverting to Fig. 6, the coils are housed in short cups or cans I4I, I42, I43 and I44, the cups being bolted together in pairs and to the shield 20. The condenser is substantially similar to that described in Fig. 4, consisting of four condensers 2|, 22, 23 and 24, mounted on a common shaft 04, which is provided with at least one and, if desired, three intermediate ground connections by means of short heavy spring brushes I00, I02 and I 04. Compensating or trimmer condensers 3|, 32, 33 and 34 are provided for adjusting the fixed capacitance of the circuits. The pair of shields I4I, I42 may be grounded to the shield 20 near brush I02 by a lead I46, in addition to being grounded to the shield 20 by the supporting bracket I56, and shields I43, I44 may similarly be grounded to the shield 20 near brush I04 by a ground connection I48, in addition to being grounded to the shield 20 by the supporting bracket I58.

From the foregoing description it will be understood that we have provided a selector which may consist of any desired number of tuned circuits arranged in a simple symmetrical mechanical arrangement which, while compact, provides a desired loose and optimum coupling of adjacent circuits, and a desired decoupling of nonadjacent circuits. By our arrangement each of the tuned circuits is a closed and highly efficient and sharply tuned circuits, and none of the circuits are so coupled to external loads as to appreciably broaden the tuning thereof. The selectivity is extremely high with respect to frequencies oif resonance, so as to provide a band pass characteristic with extremely sharp cutoff, but without distorting the amplification of frequencies within the modulation or side band range of the desired channel. The arrangement is readily reproducible and well adapted for quantity production manufacturing conditions. The coils may. be positioned with parallel axes, and need not be placed at critical angles with respect to one another. Uni-control of the selector is provided for in a simple manner, and undesired coupling through the condenser structure as well as through the shielding structure and wiring leads is prevented.

It will be apparent that while we have shown and described our invention in the preferred forms, many changes and modifications may be made in the structures disclosed without departing from the spirit of the invention, defined in the following claims.

We claim:

1. A selector for energy of a desired frequency comprising four sharply tuned circuits loosely coupled directly in cascade for the transfer of energy forwardly through the selector, each of the coils of the four tuned circuits being placed in close juxtaposition in order to obtain a compact structural arrangement, and each of said coils being nearly but not completely magnetically isolated by means around the coils confining the flux field thereof in order to obtain the desired loose coupling between adjacently successive circuits to avoid double resonance peaks.

2. A selector for energy of a desired frequency comprising three or more tuned circuits coupled directly in cascade for the transfer of energy forwardly through the selector, each of the coils of the tuned circuits being placed successively in close juxtaposition in order to obtain a compact structural arrangement, and each of the coils being so nearly completely magnetically isolated by means around the coil serving to condense or localize the flux field of the said coils to the immediate vicinity thereof that the non-adjacent coils are spaced sufiiciently to prevent direct coupling therebetween.

3. A selector for energy of desired frequency comprising three or more circuits coupled directly in cascade for the transfer of energy forwardly through the selector, the coils of the circuits being placed end to end successively in close juxtaposition in order to obtain a compact structural arrangement, and at least some of the coils being nearly completely magnetically shieldedby means serving to condense or localize the fiux field of the said coils to the immediate vincinity thereof, the localization being suitably designed, first, to obtain a desired loose coupling between adjacently successive circuits, and second, to obtain decoupling of non-adjacent circuits.

4. A selector for energy of desired frequency comprising three or more sharply tuned circuits coupled directly in cascade for the transfer of energy forwardly through the selector, each of the coils of the tuned circuits being placed successively in close juxtaposition in order to obtain a compact structural arrangement, and each of the coils being nearly completely magnetically isolated by means around the coil serving to condense or localize the flux field of the said coils to the immediate vicinity thereof, the localization being suitably designed, first, to obtain desired loose coupling between adjacent successive circuits so as to avoid double resonance peaks, and second, to obtain a desired decoupling of nonadjacent circuits.

5. A selector for energy of desired frequency comprising a plurality of tuned circuits coupled directly in cascade for the transfer of energy forwardly through the selector, the condensers of said tuned circuits being arranged on a common shaft, the coils of at least some of said tuned circuits being nearly completely magnetically isolated by means around the coils confining the flux field thereof in order to obtain loose coupling of adjacent tuned circuits and decoupling of nonadjacent tuned circuits, and the condenser shaft being short circuited to ground at a point between the condensers of circuits which are to be decoupled.

6; A selector for energy of desired frequency comprising a plurality of tuned circuits coupled directly in cascade for the transfer of energy forwardly through the selector, the condensers of said tuned circuits being arranged on a common shaft and each of the coils of said tuned circuits being placed successively in close juxtaposition in order to obtain a compact structural arrangement, each of the coils being nearly completely magnetically isolated by means around the coils confining the flux field thereof in order to obtain the desired loose coupling between adjacent tuned circuits and the desired decoupling of nonadjacent tuned circuits, and the condenser shaft being short circuited to ground at a point between the condensers of circuits which are to be decoupled, in order to prevent coupling between such circuits through the impedance of the con-- denser shaft.

7. A selector for energy of a desired frequency comprising tuned circuits coupled directly in cascade, the coupling coils of the tuned circuits being placed successively in close end to end juxtaposition in order to obtain a compact structural arrangement, and metallic magnetic shielding surrounding the coils, the flux of the coils being so confined by the metallic shielding surrounding the coils that the adjacent coils are only loosely coupled and the non-adjacent coils are decoupled.

8. A selector for energy of desired frequency comprising three or more tuned circuits coupled directly together for the transfer of energy forwardly through the selector, the coils of the tuned circuits being placed close together in a compact structural arrangement, some of said coils, however, being nearly completely magnetically shielded in order to obtain merely 'an optimum loose coupling between adjacently successive circuits, and such decoupling of non-adjacent circuits that the energy transmitted directly therebetween is less than ten percent of the energy transmitted therebetween through an intermediate circuit.

9. A selector for energy of desired frequency comprising three closed tuned circuits each of which has a high degree of selectivity, said circuits being coupled directly together for the transfer of energy forwardly through the selector, each of the coils of the tuned circuits being placed successively in close juxtaposition in order to ob tain a compact structural arrangement, and each being nearly completely magnetically shielded in order to reduce the coupling to an optimum loose coupling between adjacently successive circuits, and to obtain such decoupling of non-adjacent circuits that the energy transmitted directly therebetween is less than ten percent of the energy transmitted therebetween through an intermediate circuit, and additional means completely magnetically and capacitively shielding the circuits from external fields.

10. A selector for energy of desired frequency comprising four closed tuned circuits each of which has a high degree of selectivity, said circuits being coupled directly together for the transfer of energy forwardly through the selector, the coils of the tuned circuits being placed successively in close juxtaposition and in parallel relation in order to obtain a compact structural arrangement, said coils, however, being nearly completely magnetically shielded in order to obtain merely an optimum loose coupling between adjacently successive circuits, and such decoupling of alternate circuits that the energy transmitted directly therebetween is less than ten percent of the energy transmitted therebetween through the intermediate circuit.

ll. A selector for energy of a desired frequency comprising a plurality of tuned circuits coupled directly in cascade, substantially all of the in ductance of each circuit being concentrated in a single inductance element, said element comprising concentric outer and inner windings connected in series and so related that the resulting coil is substantially self-shielding and produces only a closely confined or condensed field, and the coils of the several circuits being arranged successively in close physical juxtaposition.

12. A selector for energy of a desired frequency comprising three or more sharply tuned circuits coupled directly in cascade, each of the coils of the circuits comprising concentric outer and inner windings connected in series and so related that the coil is substantially self-shielding and produces only a closely confined or condensed field, said coils being arranged in end to end relation on a single axis, and the entire group of coils being magnetically and capacitively shielded with respect to external fields.

13. A selector for energy of a desired frequency comprising a plurality of tuned circuits coupled directly in cascade, the coils of the circuits being wound on cylindrical forms and being sub stantially concentrically surrounded by cylindrical metallic magnetic shielding for condensing their normal fiux fields, and means supporting the coils in end to end relation.

14. A selector for energy of a desired frequency comprising three or more sharply tuned circuits coupled directly in cascade, each of the coils of the circuits being wound on a cylindrical form and being surrounded by a concentrically related cylindrical highly conductive metallic magnetic shielding to weaken the coupling therebetween, the coils being placed in end to end relation on a single axis, and the entire group of coils being additionally magnetically and capacitively shielded against external fields.

15. A selector for energy of a desired frequency comprising a plurality of tuned circuits coupled directly in cascade, the coils of the circuits being wound on cylindrical forms and being placed in end to end relation, and a single cylindrical metallic magnetic shield substantially concentrically surrounding the several coils to weaken the coupling therebetween.

16. A selector for energy of a desired frequency comprising three or more sharply tuned circuits coupled directly in cascade, each of the coils of the circuits being wound on a cylindrical form and being placed near one another in end to end relation on a single axis, a single cylindrical highly conductive metallic magnetic shield surrounding and concentrically related to the group of coils to weaken the coupling therebetween, the ends of said shield being closed in order to complete the shielding of the group of coils with respect to external magnetic and capacitive fields.

17. A selector for energy of a desired frequency comprising four sharply tuned circuits coupled directly in cascade, the four circuits and the four main coils thereof being divided into two pairs, the coils in each pair being placed in end to end relation, the pairs of coils each being surrounded by cylindrical metallic magnetic shielding, means decoupling one pair of coils from the other pair of coils, and additional auxiliary means coupling together one of the circuits in one of the pairs of circuits to one of the circuits in the other of the pairs of circuits, whereby the four circuits are coupled in cascade.

18. A selector for energy of a desired frequency comprising four sharply tuned circuits coupled directly in cascade, the coils of each of the circuits being wound on a cylindrical form and pairs of the said coils being placed in close end to end coaxial relation, the said pairs of coils each being surrounded by a cylindrical highly conductive metallic magnetic shield concentrically related to the coils, the ends of the two cylindrical shields being closed in order to completely shield the pairs of coils against external magnetic and capacitive fields, a small external coupling transformer, and means connecting one of the coils in each of the pairs of coils to said coupling transformer.

19. A selector for energy of desired frequency, comprising a plurality of tuned circuits coupled directly in cascade for the transfer of energy forwardly through the selector, the condensers of said tuned circuits being arranged on a common shaft and each of the coils of said tuned circuits being placed successively in close juxtaposition in order to obtain a compact structural arrangement, each of the coils being nearly completely magnetically shielded in order to obtain loose coupling between adjacent circuits and decoupling of non-adjacent circuits, a large shielding container surrounding the entire selector and magnetically and capacitively shielding the same against external fields, and a plurality of means separately grounding each of the selector circuits, each of said grounding means including conductors connecting together one terminal of the coil, the corresponding point on the condenser shaft, the inductive shield on the coil, and the nearest convenient point on the large shielding container.

20. A high-frequency coupling system for intentionally loosely coupling two circuits together, said system comprising an input circuit and an output circuit, each of said circuits including an inductance element, said inductance elements being coupled together and acting as the sole means for intentionally coupling the circuits together, said inductance elements being placed so close together that there is a strong magnetic field therebetween when said inductances act alone, and means associated with said inductance elements for producing a magnetic field which is weaker than, and which opposes, said strong magnetic field, whereby the resultant magnetic field intentionally interlinking said inductances is greatly reduced from a strong magnetic field to a value producing only loose coupling of the circuits, said means for producing the Weaker magnetic field being a conducting member surrounding the body of each of said coils.

21. A high-frequency coupling system comprising two coils and an electromagnetic shielding device, said coils being electromagnetically coupled to each other and having their centers separated by a distance which is between onehalf and two times their outside diameters, said electromagnetic shielding device surrounding said coils, the diameter of said shielding device being of the same order of magnitude as the separation between the coils, whereby the coupling between said coils and said device is substantially greater than the coupling between said coils.

22. A carrier frequency transformer adapted to transmit a carrier wave and side bands corresponding to voice waves comprising a pair of coils placed in such close inductive relation to each other that when said coils are acting alone, transmission of signals through them is characterized by a pair of resonance peaks, a low resistance electromagnetic shielding means surrounding said coils and having a diameter less than twice that of said coils whereby said resonant peaks become more closely spaced or coalesced and are separated by a frequency difference no greater than the frequency range of said side bands.

23. A plurality of intentionally magnetically loosely coupled circuits, the circuits having coils which are placed in close physical juxtaposition and each coil being nearly completely magnetically isolated by conductor means extending continuously around the axis and body of the coil and confining the flux field thereof in order to obtain the desired loose coupling despite the close physical juxtaposition, said coils being coupled together and acting as the sole means for intentionally coupling the circuits together.

24. A selector for energy of a desired frequency, comprising tuned circuits coupled directly in cascade for the transfer of energy forwardly through the selector, the tuned circuits having coils which are placed in close juxtaposition in order to ob tain a compact structural arrangement, each of sail coils being nearly completely magnetically isolated by means around the coil confining the flux field thereof in order to obtain a desired loose coupling between the circuits, and the group of coils being completely shielded with respect to external fields.

25. A selector for energy of a desired frequency, comprising three or more tuned circuits coupled directly in cascade for the transfer of energy forwardly through the selector, the tuned circuits having coils which are placed successively in close juxtaposition and at least some of the coils being so nearly completely magnetically isolated by means around the coils serving to condense or localize the flux field of the said coils to the immediate vicinity thereof that the non-adjacent coils have no direct coupling therebetween.

25. A selector for energy of desired frequency, comprising three or more sharply tuned circuits coupled directly in cascade for the transfer of energy forwardly through the selector, the tuned circuits having coupling coils fixedly placed with their axes parallel and in close physical juxtaposition in order to obtain a simple compact structural arrangement, and means surrounding the coils for confining the flux thereof, said means being so disposed that non-adjacent coils are not directly coupled at all, while the adjacent coils are coupled by a relatively small component of the normal flux field, and consequently are only loosely coupled.

2'7. A high-frequency coupling system comprising an input circuit and an output circuit, each of said circuits including an inductance tuned by a capacity to a frequency which is the carrier frequency to be transmitted, said inductances being coupled together and acting as the sole means for intentionally coupling the circuits together, said inductances being located in close proximity to each other, and an electrical conducting member closely surrounding and extending continuously around the axis and body of said inductances whereby the effective coefficient of magnetic coupling between said coils is of a sufficiently small magnitude so that said system as a. whole tunes to the same frequency to which each of said. circuits is individually tuned.

LESTER L. JONES.

JACOB YOLLES.

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