US2482393A - Ultra high frequency tuner - Google Patents

Description

Sept. 20, 1949. F. WILBURN 2,482,393

ULTRA HIGH FREQUENCY TUNER Filed March 4, 1946 2 sheets-sheet 1 2 Sheets-Sheet 2 y y. mm W. 9. m a m G. V r I m a r F 7L 0 W IA Z 2 K N X 5 v 58o OS 82. 4 fam n Sdi w m Xbtc. C3

Sept. 20, 1949. F. wlLBuRN ULTRA HIGH FREQUENCY TUNER Filed March 4, 1946 c 088@ OSSOS. 4

IIIIIIIL latented sept. 2o,A 1949 UNITED STATES PATENT oEFlcE ULTRA HIGH FREQUENCY TUNER Frank Wilburn, Los Angeles', Calif. Application March'4, 1946, Serial No. 651,908

(Cl. Z50-40) 8V Claims. l

'This invention relates generally to ultra highfrequency tuners and oscillators.

Resonant circuits of the conventional type using coils and condensers fail to operate satisfactorily above about 100 megacycles, and eiorts have been made in the past to provide tuners more suitable for the range of 100 to 1000 megacycles. The quarter-wave coaxial cable is known to constitute a satisfactory electrical solution to the problem, though it involves complications of a mechanical nature. Another class involves, speaking generally, av parallel tuned circuit wherein the inductive and capacitive features are combined in a pair of relatively movable structural elements. It is to this latter class that the present invention particularly appertains.

A general object of the invention is to provide an improved ultra high-frequency tuner of the type mentioned characterized by increased tuning rangeand high Q.

A further object is to provide such a tuner which is extremely simple in mechanical construction and relatively inexpensive to manufacture.

A further object is to provide an improved ultra high-frequency tuner in which a pair of relatively rotatable tuning members are capable of simultaneously increasing both the inductance and the distributed capacity of the combination.

A still further object of the invention is to pro.s vide an ultra high-frequency tuner wherein the voltage is at substantially its maximum value in the high-frequency position.

Another object is to provide a tuner which approaches a substantially uniform output throughout a wide tuning range.

The invention in its preferred form provides a pair of relatively rotatable inductor elements of one turn each, which may, in effect, be progressively converted from parallel to series connection to increase their inductance, while at the same time the distributed capacity between them is increased through a substantial range. A great tuning range is thereby achieved, while at the same time the device is highly efficient and characterized by an unusually high Q.

The invention will be most readily understood by referring now to the following detailed description of certain present preferred forms thereof, reference being had to the accompanying drawings in which:

Figure l is a diagrammatic perspective view of one simple embodiment of the invention;

Figure 2 is a vertical medial section through the device shown in Fig. 1;

Figures 3 through 6, inclusive, are diagram- Figure '7 is a view similar to Fig. 4 but showing a modified method of making electrical connection to the device;

Figures 8, 9 and 10, inclusive, are electrical diagrams showing substantially theelectrical equivalents of the device in several different operating positions;

Figure 11 is a diagram showing the use of the device as the coil of an oscillator;

Figure 12 is a somewhat diagrammatic perspective view of a modification; and

Figure 13 is a vertical medial section through the device of Fig. 12.

With reference rst to the `embodiment of the invention shown in Figs. 1 through 8, the tuner comprises a stator I0 and a rotor II, each comprising a one-turn inductor loop, and being in this instance in the form of coaxial and concentric split or slotted cylinders, annularly or circumferentially spaced from one another a short distance as indicated. The split in each cylinder forms a one-turn loop with spaced end portions forming a gap. These members I0 and I I may bev referred to generally as coaxial ring sectors, and as will later become evident, they are sufficiently close spaced as to have substantial inductive and capacitive effects on one another throughout the frequency band of interest. In general, the spacing between the ring sectors will not be in excess of twenty percent of the inside diameter of the outer cylinder. The cylinders may be of various lengths, or, to achieve particular capacitive characteristics, of varying widths circumferentially, though they are here shown in a simple form having comparatively short length and uniform width. In general, the effect of increasing width is to increase the capacitance and thereby reduce the lowest frequency of operation, without, however, appreciably affecting the highest frequency of operation. As diagrammatically indicated in Fig. 2, stator I0 may be secured at one circumferential edge, as by cementing, to an insulation mounting plate l2, and rotor I'I is tightly mounted on an insulation disk I3 fixed on coaxialoperation shaft I4. In the specic embodiment .of

Figs. 1 through V7, one end of stator l0 carries aV spring contact or brush I 5 bearing on the periphery of rotor ring II. This device constitutes a resonator, the dimensions being usually such as to afford a natural period of resonance above 30 megacycles.

In Figs. 3 through 6, which are diagrams indicating' several relative positions of the stator and rotor, the two ends of the one-turn stator inductor IU are identified by letters A and B and the two corresponding ends of the one-turn rotor inductor I I are designated by letters C and D, the midpoint of the stator I0 being designated by letter X. Assuming use of the tuner as an absorption wave meter, external terminal connections for a suitable indicating instrument may be made to the stator I'U at points A and B, as has been indicated by the short leads 20 and 2|. As will become evident as the description proceeds, the tuner presents a high parallel resonant impedance across points A and B, and While alternative modes of making connection to the device are feasible, that indicated has certain advantages as will appear.

The extreme high frequency position of the device is shown in Fig. 3, and the extreme low frequency position thereof appears in Fig. 6, with intermediate positions shown in Figs. 4 and 5. In the position of Fig. 3, the slots or air gaps in the stator and rotor are directly alined, i. e., opposite one another, and it will be evident that all corresponding points around the circumference cf the two one-turn inductor loops are equipotential. The sliding contact or brush l5 might therefore theoretically be one of a multiplicity of such contacts placed at all positions around the inductor loops without affecting the electrical characteristics of the device, no current ow occurring between stator and rotor by way of such brush or brushes. In this position of the tuner as a whole, it comprises a coil of one turn, with minimum capacitance. the stator and rotor being equipotential about the circumference, there is no electric field between them in a radial direction. The tuner is not, of course, entirely without capacitance in this position, points around the stator and rotor will be at different potentials, and particularly between their end portions there is some electric eld. Such eld is relatively weak, however, and the capacitance is in any event at a minimum in the position of Fig. 3.

Fig. 4 shows the inner inductor loop or rotorl rotated 90 counterclockwise from the position of Fig. 3. The two ends of the circuit are now at points A and D, and the circuit is traced counterclockwise from A to B, then through the brush l5, and finally to D, it being seen that the inductance has been increased by adding one quarter of a turn to the original one-turn coil. At the same time, capacitance has been added to the circuit, as represented by the overlapped areas of the inductor loops between A and D, where an electric lield is now established, as indicated by the dotted lines e. The remaining space between the stator and rotor is in the original condition, that is, equipotential for all points opposite one another, and has therefore no tuning effect upon the circuit.

Figs. 5 and 6 show the rotor rotated, respectively, 180 and substantially 360 counterclockwise from the position of Fig. 3, and illustrate, in the instance of Fig. 5, an increase in the coil to one and one-half turns, with an increase in capacitance as indicated by the increased area of electric field lines e, and in the instance of Fig. 6, an increase in the coil to substantially two turns, with a corresponding increase in capacitance as represented. In the latter instance, all of the space between the twoinductor loops provides effective tuning capacity, the inductance having been increased over that provided in the position Corresponding points of :1r

since circumferentially spaced of Fig. 3 by increasing the effective length of the coil to substantially two complete turns, and the tuner having reached its minimum frequency position.

It will be evident that the stator l0 and rotor Il may be regarded as one-turn inductors, with increasing portions of one of the inductors added in series with the whole of the other as the tuner is moved from the position of Fig. 3 to that of Fig, 6. At the same time, the self or distributed capacity of these inductors is increased from a minimum in the position of Fig. 3, wherein the equipotential condition of all points on the rings directly opposite one another eliminates capacitive effect, to a maximum in the position of Fig. 6. Figs. 8, 9 and 10 are diagrams representing the electrical circuit equivalents of the tuner for the positions of Figs. 3, 5 and 6, respectively. As represented in Fig. 8, the two inductors AB and CD are, in effect, parallel connected, with the external connections 20 and 2i made to points A and B, across Which the high parallel resonant impedance is obtained. The small and nearly negligible distributed capacity for the position of 3. Fig. 3 is represented in dotted lines at C1. The

inductance and capacitance both being at a minimum, the tuning frequency of the tuner is at its maximum. For the position of Figs. 6 and 10, the whole of the inductors AB and CD are series connected, and across these series connected inductors is the relatively high self or distributed capacitance represented in dotted lines at C2. 9 is representative of intermediate positions, in particular, that of Fig. 5. In this instance, in effect, inductor AB is in series with one-half of inductor CD, i. e., with the section XD, while the remaining section XC of the inductor CD remains in parallel with inductor AB. A relatively large capacitance (half that for the position of Fig. 6) appears across the series connected in ductors, as indicated at Cx. The relatively smaller distributed capacitance of the inductor section XC that remains, in effect, in parallel with the inductor AB, is indicated at C4. Thus in rotating the tuner from the position of Fig. 3 to that of Fig. 6, the two inductors AB and CD are progressively changed from parallel to series connection with corresponding increases in inductance, while the distributed capacitance of the inductors is at the same time increased from a nearly negligible value to a maximum. The tuner is therefore characterized by a very great tuning range.

Another advantage. inherent in the embodiment already described is the fact that the external connections 20 and 2| are made across the fixed points A and B of the tuner, which are the extreme ends of the resonant circuit for the positon of Fig. 3, but which will be one end of the circuit and a fixed point increasingly'distant from the other end of the circuit as the tuner is rotated toward the position of Fig. 6. This is of advantage, especially when the tuner is used as an oscillator, since the maximum voltage will appear across the stationary terminals for the highest frequency (Figs. 3 and 8) where the tendency to oscillate is generally least. In other words, the output from the resonant circuit tends to remain uniform over the entire frequency range, being at its maximum in the high frequency postion, where maximum feed back and highest efciency are most desired.

In Fig. 'Z is shown an alternative mode of connection, wherein one external lead 22 is connected to point A, and another external lead 23 is connected to the rotor shaft H which is in turn connected by lead 24 to the point D of the rotor. In this instance, therefore, the external circuit is at all times across the extreme ends of the resonant tuner circuit.

In another embodiment, the stator and rotor as well as the external connections 20 and 2! may be as in Figs. 3 to i3, but the sliding contact l5 is omitted, there being no conductive connection between stator and rotor. Since this embodiment may be understood simply by disregarding the brush between rings in the embodiment of Figs. 1-3, no separate illustration thereof is deemed necessary herein. With such an arrangement, the inductance is always of but a single turn, the only variable being the capacitance between the two rings, which reaches a maximum with 180D of rotation (Fig, 5).

The tuner as described has a Q of extremely high value, not exceeded, insofar as I am aware, by any previously known device of similar type save the quarter-wave concentric line. By reason of the fact that its capacitance increases over a substantial range from a low minimum to a maximum while the coil is being progressively converted from one to two turns, the tuning range is very great.

In Fig. 11, I have indicated the typical use of the tuner as a three terminal oscillator coil, such as used in the Hartley oscillator. The grid and plate of a suitable oscillator tube 30 are connected to the terminal leads 20 and 2i leading from the ends A and B of tuner status I0. The tuner in this instance is of the type shown in Figs. 1-6, having rotor Il and brush l5. A grid condenser 3l and grid leak resistor 32 are shown in a conventional arrangement. The arbitrary mid-point X of the stator is connected through high frequency by-pass condenser 32 to cathode lead 34, and the B+ lead 35 is connected to the point X, as indicated, a radio frequency choke .i

coil 36 being included in lead 35. The grid and plate are thus across a iixed portion (one turn) of the tuning inductance, with a center tap at the point X, giving an arrangement basically similar to the Hartley oscillator, but with a tuner suitable for the range of 100 to 1,000 megacycles.

Figs. 12 and 13 show a modification wherein the stator and rotor rings are in the physical form of radially split washers or annuli a and lla, arranged coaxially in close-spaced parallel relation to one another. These members 10a and Ila may also be regarded generally as coaxial ring sectors. The annulus Illa is mounted on a suitable insulation support |2a, and the annulus lla is secured to an insulation disk I3a tightly mounted on operating shaft 14a. Annulus Illa carries at one end a brush 15a which makes sliding contact with the face of annulus lla. Electrical connections a and 2Ia, may be made to the two ends of annulus Illa, as diagrammatically indicated in Fig. 12. Electrically, the embodiment of Figs. 12 and 13 is the equivalent of that shown in Figs. 1-6.

Other forms and embodiments are of course contemplated as falling within the broad scope of the invention and within the spirit and scope of the appended claims I claim:

1. A tuner for controlling frequencies throughout a frequency band in the megacycle range embodying a pair of coaxial ring sectors suiiiciently close-spaced to one another to have substantial inductive and capacitive eects on each other throughout said frequency band, an electrical connection between said sectors comprising a brush fixed to one of the sectors and in wiping relationship to the other sector, and means mountingI one of said sectors for relative rotation with respect to the other about their common axis.

2. The tuner dened by claim 1 wherein said ring sectors comprise split concentric cylinders defining a gap between them, said cylinders being of such diameters that the spacing between them is not in excess of 20% of the inside diameter of the outer cylinder.

3. The tuner defined by claim l in which said sectors and their associated brush constitute a resonator and are of such dimensions as to have a natural period of resonance above 30 megacycles.

4. A tuner as dened by claim 1 for controlling the frequency of a circuit, a portion of which circuit is external to the tuner and in which the said sectors and their associated brush constitute a frequency controlling unit, and means for connecting that portion of the circuit which is external to the tuner to spaced points on said unit.

5. A tuner as dened by claim 1 wherein the ring sectors comprise annuli of equal diameter disposed in close-spaced parallel planes normal to their common axis.

6. A tuner as dened by claim 1 for controlling the frequency of a circuit a portion of which circuit is external to the tuner and in which said sectors and their associated brush constitute a frequency -control unit, said sectors comprising split concentric cylinders dening a gap between them of not more than 20% of the inside diameter of the outer cylinder and being of such size as to effect a natural resonance period above 30 megacycles. and means connecting said portion of said circuit to opposite faces of the split of the outer cylinder.

'7. A tuner as dened in claim 1 for controlling the frequency of a circuit a portion of which is external to the tuner, including means for connecting that portion of the circuit which is external to the tuner between a point on the sector to which the brush is xed which point is remote from the point of contact of the brush and a point on the other sector.

8. A tuner as dened by claim 1 for controlling the frequency of a circuit, a portion of which circuit is external to the tuner, including means for connecting that portion of the circuit which is external to the tuner between opposite faces of the gap in the sector to which said brush is fixed.

FRANK WILBURN.

REFERENCES CITED The following references are of record in the 111e of this patent:

UNITED STATES PATENTS Number Name Date 2,284,719 Bergtold June 2, 1942 2,341,345 Van Billiard Feb. 8, 1944 2,407,282 Johnson Sept. 10, 1946 2,413,451 Johnson Dec. 31, 1946 FOREIGN PATENTS Number Country Date 240,555 Great Britain Oct. 5, 1925

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