US2383463A - Spread band tuning device - Google Patents

Description

Aug. 28, 1945. z BENlN 2,383,463

SPREAD BAND TUNING DEVICE Original Filed Oct. 10, 1940 2 Sheets-Sheet 1 Aug. 28, 1945. BEMN I 2,383,463

SPREAD BAND TUNING DEVICE Original Filed Oct. 10, 1940 2 Sheets-Sheet 2 M35151 5.5 15.5 l5 17 I777 I7.5 I5 is l lidcvgl or:

Potented Aug. 28, 1945 UNITED STATES PATENT OFFICE sraaan BAND TUNING navror:

Zolmon Benin, Glen Ellyn, 11L, asslgnor to Zenith Radio Corporation, a corporation of Illinois Claims.

This invention relates to spread band tuning circuits and is particularly useful in radio receiving sets, but is applicable to any apparatus employing tuning circuits, such as signal generators, transmitters, etc.

This application is a division of the copending application Serial No. 360,670, filed October 10, 1940, for Spread band tuning device, and assigned to the same assignee as the present application.

It is well known that various portions of the radio spectrum are much more crowded than other portions. For example, in short wave broadcast reception it is found that frequencies, and corresponding portions of the dial, from 9.5 to 9.7 megacycles and from 11.7 to 11.9 megacycles, being respectively the 31 and meter short wave bands, are very crowded, whereas the frequency band from 9.7 to 11.7 megacycles contains very few stations. Likewise, the frequency bands from 15.1 to 15.35 and from 17.75 to 17.85 megacycles, being respectively the 19 and 17 meter short wave bands, are crowded, while the band from 15.35 to 17.75 megacycles contains practically no stations. In conventional receivers wherein modified straight line. frequency tuning condensers are ordinarily employed to tune through a, relatively wide frequency band, it is found to be almost impossible to tune accurately a station in the crowded portion of the dial, for the reason that a very slight movement of the tuning control results in a considerable change in the capacity of the condenser, and accordingly, in the resonant frequency of the tuned circuit. Thus, a slight rotation of the dial is apt to tune the receiver through the frequencies of a number of stations, resulting in great difliculty in accurately tuning a desired station and eliminating others.

,The terms-spectrum" and bands are used throughout this specification in'their commonly accepted meanings, for example, the radi frequency spectrum includes all of the above mentioned allocated short wave bands, i. e., the 31, 25, 19 and 17 meter bands and the so-called dead" ranges of frequency similar to the range from 9.7 to 11.7 megacycles and 15.35 to 17.75 megacycles mentioned above.

It is an object of this invention to provide a new and improved tuning circuit which produces rapid frequency changes in certain frequency ranges and slow frequency changes in other ranges, upon movement of the tuner at a uniform rate throughout its range of adjustment.

It is another object of the invention to provide such a tuning circuit which spreads the scale indications of those portions of the radio spectrum containing large numbers of stations and which condenses the scale indications of those portions which are little used.

A further object of the invention is to provide such a tuning circuit in which the inductive reactance is so modified locally as to produce desiredrapid frequency changes in certain ranges and desired slow changes in other ranges.

In accordance with the invention the tuning circuit is arranged and constructed so that a single scale encompasses at least two separate crowded portions of the frequency spectrum, and so that these two separate crowded portions are expanded substantially uniformly, the intermediate portion of the frequency spectrum being condensed on the scale.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with e the accompanying drawings in which:

Figure 1 is a perspective view of a condenser constructed similarly to the present invention;

Figure 2 illustrates the shape of a single rotor plate of the condenser of Figure 1;

Figure 3 is a perspective view of two condensers mounted on a single shaft, ne being constructed like that illustrated in Figure 1;

Figure 4 is a perspective view of a modified form of condenser similar to that illustrated in Figure 1;

Figure 5 illustrates a single stator plate of the condenser of Figure 4;

Figure 6 is a. view, partly in section, of a variable inductance constructed in accordance with my invention;

Figure 7 is a modified form of inductance similar to that shown in Figure 6;

Figure 8 is a schematic diagram of a tuned amplifier circuit including a condenser, as illustrated in Figures 1 and 4;

Figure 9 is a schematic diagram of a tuned amplifier circuit including a variable inductance constructed in accordance with my invention, as illustrated in Figures 6 and 7;

Figure 10 illustrates a pair of tuning scales arranged to cooperate with a pointer adjustable simultaneously with the condenser of Figure 8 or the inductance of Figure 9;

Figure 11 is a schematic diagram of a modified form of tuning circuit constructed so as to pro- 2 aaaacea duce results similar to those produced by the circuits of Figures 8 and 9; and

Figures 12 and 13 show other modified forms of tuning circuits.

With reference to Figure 1, the condenser is provided with rotor plates l mounted on a shaft II, the rotor plates being adapted to be rotated into position between stator plates I! which are secured together by suitable fastening means ii.

The effect of this type of rotor plate can best be described with reference to Figure 2. As the rotor plate is rotated from the position shown in Figure 1 into the space between the stator plates, it is apparent that segment A first enters this space. As the radius and the area of segment A are relatively large, a substantial change is produced in the capacity of the condenser for each increment of rotation. As the segment B begins to enter the space between the stator plates, the amount of change of capacity for a given rotary movement is reduced materially since segment B is of small radius and area, and each increment of rotation introduces only a small additional area. As segment C enters the space between the rotator plates, the capacity of the condenser again changes very rapidly for at the same rate of rotation because of the large radius of the segment being introduced. Segment D produces a slow change of capacity at the same rate of rotation for the same reason as segment B. Segment E again produces a rapid change in capacity similar to that of segment A.

This invention is particularly adapted for use in short wave broadcast reception, since it is in the short wave broadcast band that local overcrowding of stations occurs. In a radio receiver designed to receive standard broadcasts, as well as short Wave broadcasts, a second condenser, such as a modified straight line frequency condenser may be provided, which cooperates with more or less uniform markings on the standard broadcast dial. These two condensers may be separately provided. However, it has been found advantageous to combine the two condensers into a single unitary structure.

Such a combined unitary structure is illustrated in Figure 3, in which the modified rotor plates iii and the standard rotor plates 20 are mounted upon the same shaft i l, and are all electrically connected. The stator plates l2 may be divided into two sections between which electrical insulation 2| is provided. That is, two separate condensers may be built together, one serving for the standard broadcast range, and the other for the shortwave range. The rotor plates are usually connected to ground and, therefore, there is no necessity for electrically insulating the two sections of rotor plates of the condenser, although these sections may be insulated if required by the circuit employed. The electrically insulated stator sections of the condenser are connected to a suitable band changing switch (not shown) so that either one may be included in the tuned circuit, depending upon the station which it is desired to receive. As shown in Figure 3, the rotor plates exceed by onethe number of stator plates, so that when the rotor plates are in engagement with the stator plates they surround the stator plates. Substantial space is provided between the two stator sections of the condenser, so that the capacity between the two stator sec- 1011s is minimized.

In Figure 4 a modification of this arrangement is illustrated in which the rotor plates ID are solid and in which the stator plates l2 have been perforated to produce the desired effect. The contour of a stator plate is clearly illustrated in Figure 5, wherein segments Ar, Bl, C1, D1 and E1 correspond to segments A, B, C, D and E in Figure 2. It is apparent that the working of this modification is the same as that of Figure l, the effect being produced by the stator plates as distinguished from the rotor plates.

Figure 6 illustrates a variable inductance of the variable permeability type which may be used in accordance with my invention to produce an effect similar to that of the variable condensers of Figures 1 and 4. This variable inductance may include an insulating tube 3| about which a coil 32 is wound. The conductors forming the coil are uniformly distributed over the tube 3|. A core 33 of low loss magnetic material is arranged to move into and out of the tube 3!.

The configuration of the core is such as to produce the desired result, such as that produced by the condensers of Figures 1 and 4. The large section A2 at the end of the core 33 produces a rapid change in inductance when inserted in the tube 3| and accordingly 2. large change of frequency. As section B2 enters the tube 3!, the rate of change of frequency is lower, since the cross-sectional area of the core is smaller. Section G2, which is of large cross-section, produces a rapid change of frequency. Section D2, like section B2, produces a slow change of frequency because of its small cross-section. Section E2 of large cross-section, like section C2, produces a rapid change of frequency. It is apparent that by suitably adjustin the cross-sectional areas of the sections referred to, this variable inductance of Figure 6 may be made to produce the same effect as the previously described variable condensers of Figures 1 and 4.

Figure 7 illustrates a variable inductance having a uniform core 36 arranged to move into and out of a non-uniformly wound inductance coil. The inductance illustrated is designed to produce a result similar to the result produced by the reactances illustrated in Figures 1, 4 and 6. It includes a tube 35 about which a conductor may be wound in sections, each section having the requisite number of turns to produce the desired rate of change of frequency for that section. Sections A3, C3 and E3 are closely wound and contain many turns per unit length. Sections 13: and D3 contain a few turns per unit lengthwise. It is evident that as a. uniform core 36 enters the tube 35, there is produced in sequence a rapid change, a slow change, a rapid change, a slow change, and a rapid change of inductance, and therefore of frequency.

While the condensers as described above and as illustrated in Figures 1 and 4, have been described as being constructed with either the stator plates or the rotor plates modified to expand certain portions of the spectrum while compressing other portions, it is apparent that the same result can be produced by partially modifying both the stator plates and the rotor plates, so that the modified portions of both plates cooperate to produce the desired result. Similarly the inductances illustrated in Figures 7 and 8 achieve the desired result in the one case by reason of a modified core shape and in the other case by reason of modified winding distribution. It is apparent that the desired results according to the invention may be produced by making both core shape and winding distribution non-uniform so as to produce the same result described as produced by the non-uniformity of either one of these constructional features of the inductance.

In Figure 8, the condenser 8 is connected in shunt to an inductance l3, illustrated as a transformer, and is a condenser such as that illustrated in Figures 1 or 4. The condenser 8 and inductance l3 form a tuned input circuit for a stage of tuned amplification, in which the tuned frequency may be adjusted.

In Figure 9 there is shown a similar tuned amplifier in. which the tuned input circuit includes an inductance 40, such as the inductances illustrated in Figures 6 and 7. This inductance 40 is connected in series with an inductance 4| which is illustrated as an input transformer, and a fixed condenser I2 is connected in shunt to the series combination of inductances l and 4|.

In Figure there is illustrated a pair of scales suitable for cooperation with a pointer attached to the movable element of the inductance of Figure 9, or the condenser 9 of Figure 8. The upper of the two scales of Figure 10 shows that the portion of the frequency range from 9.5 to

9.7 megacycles has been spread out considerably to take care of the large number of stations in that area. Likewise, from 11.7 to 11.9 megacycles there are many stations, and this portion of the scale has also been spread out considerably. The portion from 9.7 to 11.7, which contains few stations, has been crowded together. This upper scale of Figure 10 shows that the two standard short wave bands from 9.5 to 9.7 megacycles, and from 11.7 to 11.9 megacycles have been spread substantially uniformly and equally. Each of these two short wave bands covers 200 kilocycles, and each is spread for substantially the some linear distance along the scale. The segments B and D of the adjustable reactance in the tuning circuit are so formed as to produce this substantially uniform spread in each of the two separated spread band portions.

Comparing the shape of'the condenser rotor plate illustrated in Figure 2 with the lower scale of Figure 10, it is evident that segment A produces a rapid change in frequency from 18.5 to 17.85 megacycles. This insures complete coverage of the upper end of the range. When segment B is rotated into the space between the stator plates, the slow change of capacity and of frequency corresponds to the large distance on the scale between 17.85 and 17.75 megacycles. Then, as segment C enters between the stator plates, the rapid change in capacity produces a large change in frequency corresponding to the relatively short distance along the lower scale from 17.75 to 15.35 megacycles. As segment D enters between the stator plates, its slow change of capacity corresponds to the long part of the scale between 15.35 and 15.1 megacycles. Segment E produces a rapid change of capacity from 15.1 to 14.5 megacycles so as to insure complete coverage of the lower end of the range.

In the previous paragraph the condenser has been described as covering the range from 14.5 to 18.5 megacycles. This condenser is also used to cover the range from 9.0 to 12.5 megacycles, by changing the inductance with which it is connected in shunt so as to make the tuned circuit resonant within the range 9.0 to 12.5 mega.- cycles. That is, two inductances are used, one being connected in shunt with the condenser for the high frequency range and the other for the low frequency range. The circuit is switched from one inductance to the other depending upon which wave band it is desired to tune.

Complete coverage of the range from 9 to 18.5 megacycles can also be accomplished by a single condenser without a change of inductance by forming a condenser plate so as to give rapid coverage of the ranges 9.0 to 9.5, 9.7 to 11.7, 11.9 to 15.1, 15.35 to 17.75, and 17.85 to 18.5 megacycles; and to give slowcoverage of the ranges between 9.5 and 9.7, 11.7 and 11.9, 15.1 and 15.35, and 17.75 and 17.85 megacycles. That is to say, condensers or inductances as described hereinabove can be employed wherever it is desired to extend substantially uniformly selected portions of a tuning range while compressing intermediate portions of the range.

In the previously described circuits the desired results have been produced by forming one or more elements of the adjustable tuning reactance so as to give the desired non-uniform frequency change. In Figures 11, 12 and 13, similar results are produced-by introducing into, or removing I from, the tuning circuit one or more reactances separate from the variable tuning reactance. This is brought about by switch means operated in unison with the tuning reactance and arranged to control the connection of additional inductance or capacity to the circuit such as to vary the rate of tuning in the various sections of the radio frequency spectrum in the desired manner while maintaining a continuous change of frequency across the entire range.

In Figure 11 there is illustrated a tuning circuit having a variable capacity II and a fixed inductance 12. Operatively connected to the variable condenser 11 are switches 13 and H. The switch 13 is adapted to introduce additional capacity into the circuit while switch 14 is arranged to introduce additional inductance to the circuit. When the condenser H is adjusted to minimum capacity to tune the circuit to high frequencies in the desired range, switch 14 connects inductance 15 in series with inductance 12 across condenser II, the only capacity in circuit. Since condenser H is the only capacity in the tuning circuit, a change in its capacity produces a relatively rapid change of frequency.

At a desired point in the adjustment of condenser H, as its capacity is increasing, switch 14 removes inductance 15 from the circuit and introduces another inductance 16, which is a smaller inductance.

Simultaneously, switch 13 introduces condenser into the circuit in shunt to the condenser II. The condenser 80 and the inductance 16 are selected to be of such appropriate values that there is no' change in the product of inductance and capacity, and therefore no change in frequency, as the switches 13 and 14 move from one contact to the next. Thus, the frequency immediately before the change is the same as the frequency immediately following the change.

With the additional capacity 80 in the circuit in shunt to capacity ll, further adjustment of condenser II to increase its capacity results in a slower change of frequency because of the reduced rate of change of the overall capacity. This effect is used to spread out a desired portion of the spectrum, as from 17.85 to 17.75 megacycles. At the end of that portion of the spectrum, as condenser H is being adjusted in the direction of still greater capacity, switches" and H move to the next contact, thereby introducing inductance 11 into the circuit. and removing condenser 80 therefrom. The inductance I1 is of suitable value to maintain the product of inductance and capacity constant, and therefore to keep the frequency the same as it was immediately before condenser 88 was removed from the circuit. The inductance 11 is larger than the inductance 18, as is necessary because the condenser 88 has been removed from the circuit. with inductance II in the circuit, and condenser 88 out of the circuit, the change of frequency is rapid, since a change in the capacity of condenser II now produces an equal change in the overall capacity of the tuning circuit. The part of the frequency spectrum covered by the tuning circuit with inductance 11 in the circuit and condenser 88 out may, for example, be used to cover a little used portion of the spectrum rapidly, as from 17.75 to 15.35 megacycles.

When condenser II is increased in capacity until the tuning circuit is tuned to the lowest frequency in this little used range of the spectrum, switch 14 disconnects inductance H from the circuit and introduces inductance I8, and simultaneously switch 83 reconnects condenser 88 in the circuit. The inductance I8 is of the value necessary so that these switching operations produce no change in frequency of the tuning circuit. The inductance i8 is smaller than the inductance ii to compensate for the introduction of condenser 88 in the circuit. Adjustment of the condenser li with these connections results in a slow change of frequency for the same reason as when the inductance l and condenser 88 were in circuit. The portion of the frequency spectrum covered by adjustment of the condenser II under these conditions may correspond, for example, to that portion between 15.35 and 15.1 megacycles.

At the end of that portion of the frequency spectrum, switch H removes inductance 18 from circuit and introduces inductance 18 into the circuit, while switch I3 removes condenser 88 from the circuit. This switching operation is also carried out without any change of frequency because the inductance 78 is made of proper value. Further increase of capacity of condenser II produces a rapid change in frequency.

It is evident from the above description that the circuit of Figure 11 produces in sequence a rapid change, a slow change, a rapid change, a slow change, and a rapid change of frequency, with uniform change in capacity of the variable condenser I I. It is evident that the shape of the plates of condenser II may be modified to produce the substantially uniform frequency change over the two short wave bands on each of the scales illustrated in Figure 10. If desired, separate fixed condensers for each of the five tuning ranges, corresponding to each of the inductances I5 to I8 may be employed instead of a single condenser 88.

In Figure 12 is illustrated a circuit which produces an effect similar to that of the circuit of Figure 11. This circuit includes a variable condenser 85, a fixed inductance 88, and a fixed inductance 89. Connected to operate in unison with the condenser 85 are switches 81 and 88. At the high frequency end of the scale, inductances 86 and 88 and the variable condenser 85 are inserted. Adjustment of condenser 85 under such condition produces a relatively rapid change of frequency. At a desired frequency switch 81 introduces condenser 88 into circuit and switch 88 short circuits inductance 88, so as to remove it from the circuit. Inductance 88 and condenser 98 are of suitable values so that the frequency immediately preceding the switching operation is the same as. that immediately following the switching operation.

Aftercondenser 88 is inserted and inductance 88 is removed, the rate of change of frequency with change in capacity of the variable condenser is materially reduced. At the end of the desired spread band portion, switch 81 removes condenser 88 from the circuit and substitutes condenser 8l, 9. smaller condenser. Simultaneously switch 88 removes the short circuit from the inductance 88, so that it is again effective in the circuit. Condenser 8| is of suitable value so that the switching operation is effected without a change of frequency to which the circuit is tuned. After this switching operation the rate of change of frequency with change of capacity of the adjustable condenser 85 is rapid.

As the capacity of condenser 85 is further increased, switch 81 removes condenser 8| from the circuit and substitutes condenser 82, a larger condenser, in place thereof. Switch 88 again removes inductance 88 from the circuit by short circuiting it. Condenser 82 is of suitable value to maintain the frequency the same before and after the switching operation. After this switching operation the rate of change of frequency is again slow over a desired range, after which switch 81 removes condenser 92 from the circuit and introduces condenser 83, a smaller condenser than 82. Simultaneously, switch 88 removes the short circuit from inductance 89 so that it is again effective in the circuit. Condenser 83 is of suitable value to maintain the frequency the same before and after the switching operation. Thereupon further increase of capacity of the condenser 85 produces a rapid change of frequency. It is thus evident that this circuit also produces in sequence a rapid change, a slow change, a rapid change, a slow change, and a rapid change of frequency.

In Figure 13 there is illustrated a circuit arranged to produce the same effect and including a variable inductance such as those illustrated in Figures 6 and 7. This circuit includes a fixed condenser and a variable inductance 85. Operatively connected to the inductance 88 for movement in unison therewith are switches 81 and 88. At the high frequency end of the portion of the spectrum covered by the tuning circuit, inductance 86 and condensers 85 and I88 are inserted. With these connections a small change in inductance produces a large change in frequency. At a desired frequency, switch 88 removes condenser I88 from the circuit and at the same time switch 81 places the additional inductance 88 in circuit in series with inductance 88. Inductance 88 and condenser I88 are of suitable values so that the frequency with which the tuning circuit is resonant is the same before and after the switching operation.

With the added inductance 88 in circuit, change of frequency upon change in the inductance 88 is slow so as to spread frequencies of a desired portion of the spectrum. At the end of that band over which frequencies are so spread, switch 81 again removes inductance 88 from the circuit by short circuiting and switch 88 places a relatively large condenser MI in circuit, the condenser I8| having a value such that a frequency change is not produced by the switching operation.

Further adjustment of inductance 88 produces a rapid change in frequency with such switching connections. As the inductance further increases, switch 88 removes condenser I8l from circuit and substitutes therefor a smaller condenser I82, while switch 8! simultaneously replaces inductance 99 in circuit. Condenser I02 is of suitable value to maintain the frequency the same before and after the switching operation. This change in the circuit spreads another portion of the band, so that further increase of the inductance 96 produces a relatively slow change of frequency.

Upon still further increase in inductance 86, switch 91 removes the inductance 99 from circuit [by short circuiting it, and switch 98 removes condenser I02 from circuit and substitutes a larger condenser I03 in its place. Again, there is no change of frequency before and after the switching operation. After this circuit change, change of inductance 96 produces a rapid change of fre quency. It is evident that this circuit produces much the same effect as the circuits of Figures 11 and 12,

The circuits of Figures 11 through 13 are par- 'ticularly suited for producing the results illustrated on the two scales of Figure 10. As pointed out previously, the spread-out portions of each of these scales are spread substantially uniformly and equally, the intermediate portions on each scale :being compressed. It is evident that these circuits may be employed without band switching to produce over one scale all of the changes in tuning rate illustrated in Figure 10 on two scales by merely providing the requisite number of elements to cover the entire range.

In the drawings only those elements of tuning circuits necessary to produce an operative circuit have been disclosed. It is evident that additional refinements in tuning circuits may be employed in conjunction with the present invention without departing from the spirit thereof. The switches employed in the various circuits of Figures 11, 12 and 13 may be mounted upon the same shaft or other movable member used to tune the variable tuning member, and maybe of the snapaction type. However, these switches may be separate from the tuning member and may be operated therefrom :by any suitable means such as gears, belt chain drives, etc.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention in its broader aspects, and I, therefore aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

I claim:

1. In a radio receiver for receiving signals at any frequency within a large portion of the radio frequency spectrum having a plurality of separated allocated broadcast bands in each of which there are a relatively large number of broadcast signals differing in frequency by relatively small amounts, each pair of adjacent allocated bands being separated by a relatively large contiguous so-called dead" range offrequencies within which range there are a relatively few broadcast signals differing in frequency by relatively large amounts, the combination of an adjustable tuning circuit including a capacitive reactance and an inductive reactance having an inductive winding and a relatively movable magnetic core member and a single control element arranged to adjust said inductive reactance, said inductive reactance having separate spaced portions so constructed that upon incremental adjustment of said reactance the variation of resonant frequency of the tuning circuit is at a low substantially uniform rate within said separated allocated bands of the portion of the frequency spectrum covered by said tuning circuit corresponding to said separate spaced portions of said inductive reactance and is at a substantially higher rate within said dead range of frequencies of said portion of the spectrum upon the same incremental adjustment of said reactance.

2. In a radio receiver for receiving signals at any frequency within a largeportion of the radio frequency spectrum having a plurality of separated allocated broadcast bands in each of which there are a relatively large number of broadcast signals differing in frequency by relatively small amounts, each pair of adjacent allocated bands being separated by a relatively large contiguous so-called dead" range of frequencies within which range there are a relatively few broadcast signals differing in frequency by relatively large amounts, the combination of anadjustable tuning circuit including an inductive reactance and a capacitive reactance, said inductive reactance having an inductive winding, and a relatively movable core member and a single means for producing relative movement of said core memher and said winding for changing the flux relation thereof, said relative movement between said core member and said winding changing the inductance of said winding, separate spaced portions of said core member being so constructed that upon incremental relative movement between said core member and said winding the variation of resonant frequency of said tuning circuit caused by change of inductance of said winding is at a low substantially uniform rate within said separated allocated bands of the portion of the frequency spectrum covered by said tuning circuit corresponding to said separate spaced portions of said core member and is at a substantially higher rate within said dead range of frequencies of said portion of the spectrum upon the same incremental relative movement.

3. In a radio receiver for receiving signals at any frequency within a large portion of the radio frequency spectrum having a plurality of separated allocated broadcast bands in each of which there are a relatively large number of broadcast signals differing in frequency by relatively small amounts, each pair of adjacent allocated bands being separated by a relatively large contiguous so-called dead range of frequencies within which range there are a relatively few broadcast signals differing in frequency by relatively large amounts, the combination of an adjustable tuning circuit including an inductive reactance and a capacitive reactance, said inductive reactance having an inductive winding and a relatively movable magnetic core member for changing the flux relation thereof, relative movement between said core member and said winding changing the inductance of said winding, said winding being so distributed along the direction of relative movement between said winding and said core member that upon incremental relative movement between said core member and winding the variation of frequency of said tuning circuit caused by change of the inductance of said winding is at a low substantially uniform rate within said separated allocated broadcast bands of the portion of the frequency spectrum covered by said tuning circuit corresponding to separate spaced evenly distributed portions of said winding and upon the same incremental relative movement is at a substantially higher rate within said "dead" range of frequencies of said portion of the spectrum corresponding to an intermediate more closely distributed portion of said winding.

4. In a radio receiver for receiving signals at any frequency within a large portion of the radio frequency spectrum having a plurality of separated allocated broadcast bands in each of which there are a relatively large number of broadcast signals differing in a frequency by relatively small amounts, each pair of adjacent allocated bands being separated by a relatively large contiguous so-called dead range of frequencies within which range there are a relatively few broadcast signals diilering in frequency by relatively large amounts, the combination of a tuning circuit having a fixed capacitive reactance and an inductive reactance, said inductive reactance having a coil member and a relatively movable magnetic core member, said inductive reactance being continuously variable by relative movement of said coil and core members for continuously varying the value of inductance of said circuit to continuously tune said circuit to any desired frequency within said bands and so-called dead" range, and a control element for continuously relatively moving said coil and cor members through a first series oi. positions and through an intermediate series 01' positions to and through a second series of positions within which first and second series of positions said circuit is tuned to desired frequencies, each of said first and second series of positions corresponding to resonant frequencies within one of said separated allocated bands and the intermediate series of positions corresponding to resonant frequencies within the intervening so-called dead" range, at least one of said memhers being so shaped as t vary relatively rapidly the resonant frequency of said circuit for a given rate of relative displacement of said members through their intermediate series of positions, said one member being so shaped as to vary the resonant frequency .of said circuit at a materially lower rate for the same rate of relative displacement of said members through said first series of positions corresponding to resonant trequencies in one of said separated allocated bands and at substantially the same rate for the same rate of relative displacement of said members through said second series of positions corresponding to resonant frequencies in the other of said separated allocated bands.

5. In a radio receiver for receiving signals at any frequency within a large portion of the radio frequency spectrum having a plurality of separated allocated broadcast bands in each of which there are a relatively large number of broadcast signals differing in frequency by relatively small amounts, each pair of adjacent allocated bands being separated by a relatively large contiguous so-called dead range of frequencies within which range there are a relatively few broadcast signals diifering in frequency by relatively large amounts, the combination of an adjustable tuning circuit including a capacitive reactance and an inductive reactance having an inductive winding and a relatively movable core member, and a single control element arranged to adjust said inductive reactance without substantial change in th quality factor of the circuit, said inductive reactance having separate spaced portions so constructed that upon incremental relative movement between said winding and core member the variation of resonant frequency of the tuning circuit is at low rates within said separated allocated bands of the portion of the frequency spectrum covered by said tuning circuit corresponding to separate space portions of said inductive reactance and is at a substantially higher rate within said dead range of frequencies of said portion of the spectrum upon the same incremental relative movement of said winding and core member.

ZOLMON BENIN.

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