US2126541A - High frequency oscillating circuit - Google Patents

Description

1938. L. DE FOREST 2,126,541

HIGH FREQUENCY OSCILLATING CIRCUIT Filed Sept. 20, 1935 2 Sheets-Sheet 1 INVENTOR.

Lee de Forest ATTORNEYS A11g- 9, 1938. L; DE FOREST 2,126,541

HIGH FREQUENCY OSCILLATING CIRCUIT Filed Sept. 20, 1935 2 Sheets-Sheet 2 INVENTOR.

Lee d6 Fewest BY Ewan? ATTORNEYS Patented Aug. 9, 1938 UNITED STATES PATENT OFFICE HIGH FREQUENCY OSCILLATING CIRCUIT Application September 20, 1935, Serial No. 41,410

17 Claims.

My invention relates to improvements in high frequency and ultra-high frequency circuit con.- structions, and particularly for that range of wave-length, known as ultra-short range, lying between or 12 meters and 1 or 2 meters.

Particularly in the field of ultra-short-wave therapy or radio therapy, it has been found desirable to place at the physician's disposal a powerful ultra-short-wave oscillator, the wave- 10 length of which can be readily and continuously varied within wide limits, for example between 3 and 13 meters. I-leretofore the design of such continuously variable oscillator circuits has depended upon the use of conventional helices with sliding contacts thereon, inducto-meters, or variable condensers or a combination of both. Such arrangements present many mechanical difliculties and complications, and it is found that the eiiiciency of such oscillating circuit with lumped inductance and capacity varies unduly as the natural period of such circuits is changed from maximum to minimum by means of varying said lumped inductance or capacity.

It is well-known that the Lecher system of parallel conductors lends itself particularly well to such high frequency oscillating circuits. The wave-lengths of such Lecher systems are practically identical with the actual physical length thereof, which means that with wave-lengths even as short as 3 or 4 meters the physical dimensions oi the system become impractically large.

I have found however that by coiling a pair of Lecher parallel conductors, either in the form of a spiral or of a helix, the advantages of distributed capacity and inductance of the Lecher system are maintained, while at the same time the physical overall dimensions of the system are very greatly condensed, so that such oscillating systems lend themselves very readily to the practical requirements of ultra-short-wave therapy and the like.

In the accompanying figures which illustrate several methods of applying my invention in 45 practical form,

Figure 1 is a schematic diagram of my invention comprising spiral Lecher conductors used as a wave meter;

Fig. 2 is a schematic diagram of an ultra short wave oscillator embodying the spiral Lecher conductors of Figure 1, used as a therapy device;

Fig. 3 is a modification of the system illustrated in Figures 1 and 2, in which helical Lecher conductors are used;

Fig. 4 is a detail of a mechanical construction of a Lecher spiral of flat ribbon conductors;

Fig. 4A is a detail of the structure of Figure 4 showing one of the insulating rods;

Fig. 5 is an elevation of a system employing flat ribbon Lecher conductors constructed in accordance with Figs. 4 and 4A;

Fig. 6 is a fragmentary detail of the structure of Figure 5 showing the structure as it appears when shaft l3 has been rotated somewhat more than 90 clockwise from the position of Figure 5;

Fig. 7 is a plan view of a portion of the structure of Figure 5 showing the spiral broken away at its inner end and omitting the insulating supports for the said spiral;

Fig. 3 is a fragmentary View of an alternative spiral Lecher system.

In Figure 1 I have shown a pair of parallel wires coiled in the form of a spiral, the distance between the turns of which is larger than the distance between the parallel wires constituting the Lecher conductors. I have shown a small loop 3 at one end of the system and joining the two parallel conductors l and 2. The other two ends of the Lecher wires are shown open, although these may also be closed if desired. A sliding bridge 4 is shown bridging the two parallel conductors. When this system is used as a wave meter I prefer to bring the loop end 3 into close inductive coupling with the oscillating system whose wave-length it is desired to measure, as is here shown where coil 33 and radio frequency ammeter form part of said oscillating system. With such an arrangement the amount of current flowing in coil 33 as indicated at 39 will be more or less varied when the bridge l is slid along the Lecher conductors to a point where the natural period of the closed Lecher system t, i, 3, 2, 4 becomes that of the oscillations in the coil 33. Or instead of placing the indicating instrument in series with the high frequency oscillating circuit, dip readings may also be obtained in a milliameter supplying the plates of the oscillating tubes which are exciting the coil 33, as is well known to those skilled in the radio art. Instead of reading the indication of a meter placed in the oscillator or supply circuit, the indication of resonance between wave meter and exciting circuit may be equally well obtained by the use of a glow tube 60, the terminals ll of which are connected together by insulating arm H3 and are thus slidable along conductors I, 2, so that they may be connected across any two opposite points on the Lecher system, preferably midway between the loop 3 and the sliding bridge 4 where exists a potential loop in the standing wave therein set up.

The same system of spiraled Lecher conductors above described I have shown in Figure 2 as connected to the plates of a push-pull ultraaudion oscillation generator. Here the plate 8 of one oscillator tube is shown connected to the grid I! of the other tube through a variable condenser 9. In this Figure 2 I have shown the plate supply as being led to the sliding bridge 4 by means of a flexible conductor I00. However it is usually more convenient to supply the plates at a point where the conductors enter the audion tubes through radio-frequency choke coils llli, IN. I have shown the sliding bridge 4 held in a slot 5 in the radial arm 5 which is pivoted at the center of the spiral formation at H, in such a way that when said arm is rotated around its pivot the bridge 4 is held in close contact with the two Lecher conductors and can thus be moved from the center to the outer periphery of the Lecher spiral. For this purpose a crank handle I at the end of the radial arm affords convenient means.

In this figure, I have shown the secondary circuit which consists, for therapy purposes, of two insulated applicator pads 49, 49 as connected to opposite points on the Lecher conductors l, 2, through the medium of the wiping contacts 4i 42 mounted on the insulating arm H3. The proper location of these connection points obviously depends upon the position of the shortcircuiting bridge 4 upon the Lecher system. There is an optimum location for these secondary take-off points. When these are located too near the bridge 4 it is obvious that there will be only small or no potential diilerence applied across the two applicator pads. On the other hand when the flexible cables leading to the applicator pads are connected too close to the plates of the oscillator tubes the secondary circuit is apt to absorb too large a load from the oscillating system, causing the tubes to overload and to become undulyheated. I have found that the optimum location of the slidable secondary contact points 4|, 4| is roughly midway between the tube terminals of the Lecher system and the short-circuiting bridge 4. However, these contact points may sometimes be advantageously located along the Lecher conductors well beyond the sliding bridge contacts.

In order to safeguard the patient against any possible shock from the high voltage applied to the plates of the oscillator, I prefer to insert stopping condensers B8, 88 in the leads from the Lecher conductors to the applicator pads.

As an alternative to the above spiraled Lecher system I have shown in Figure 3 the two Lecher conductors while close together wound in the form of a helix. In the axis of this helix is shown a shaft I! over which slides a hub 45 carrying an arm 5 (preferably of insulating material) which carries at its end a sliding bridge 4 which short circuits the two Lecher conductors. which the hub 45 is keyed to permit same to travel longitudinally along the shaft while it is being rotated by means oi? the crank arm 5 and handle 1. Two ends of the Lecher conductors are again shown connected to the two plates of the oscillator tubes, as in Figure 2.

It is obvious of course that other types of oscillation generator circuits can be connected to the Lecher conductors in place of the push- At 8 is shown a longitudinal slit in pull ultra-audion arrangements here shown, and I do not wish to be limited to any particular type of high frequency oscillation generator. However the one here shown I have found especially efllcient and convenient as oscillating satisfactorily over a wide range of frequencies, e. g., as represented by a wave-length range in actual practice lying between I and I4 meters.

In Fig. 3 the secondary circuit, which may be identical with the secondary circuit of Fig. 2, is shown connected to wiping contacts 4|, 4|, which are arranged to move along the conductors I, 2, in unison. In order to effect this movement of the brushes an insulating sleeve is provided, which sleeve is free to rotate on shaft i3. Carried by this sleeve, and spaced from each other by the large diameter portions El, 82 thereof, are the three crank and commutator portions 56a, 58b and 55c. Each of the portions 55a and 561) carries an arm 55 on which is slidably mounted an arm 65 carrying a wiping contact 4| adapted to make contact with a corresponding one of the Lecher conductors l, 2.

A connection is made, through the insulating sleeve, from the part 560., to crank part 56c.

Since contacts 4i, arms 55, crank portions 55a, 56b and 560 are of metal the brushes 4i bearing as they do on crank portions 561:: and 56c take oif current to the secondary circuit, as indicated above.

It is clear from the above description of Figures 2 and 3 that the operator may obtain a completely continuous change of frequencies as he rotates the radial arm 5 and thereby causes the short circuiting bridge to move over the entire length of the Lecher conductors from one end to the other. With the push-pull ultraaudion circuit here shown I have found it un-- necessary to vary the capacity of the grid coupling condensers 9, 9 through any wide limits as the wave-length of the Lecher system is changed from 3 to H meters; although for a certain length of the oscillating Lecher system the efficiency oi: the generator may be increased by suitably varying said coupling condensers S, 9. A convenient way of effecting this is to have the two shafts of these variable condensers coupled mechanically together, but well insulated from each other and to slowly vary the capacity of these condensers by mechanically coupling their shaft through a suitable train of gears or a cam arrangement whereby the capacity of the condensers is varied as the arm 5, carrying the short circuiting bridge, is rotated.

In Figure 4 I have shown in detail a mechanical construction of a Lecher spiral which I have found particularly suitable to the ends in view. I prefer to employ in place of a round conductor, a flat ribbon as shown here which is wound in a spiral formation with the various turns of the spiral held rigidly in place through the use of spokes built up of short sections of suitable insulating material, such as Isolantite, porcelain, glass or quartz rods. Bakelite, or similar plastic, or synthetic insulators are quite unsuitable where large amounts of energy in this range of frequencies are to be employed. As shown in Figure 4 short Isolantite rods, as shown in detail in Figure 4A, are nested end to end with sections of the flat spiraled ribbon intermeshed between the opposing ends of the isoiantite rods. When thus assembled the Joints are cemented together with a suitable non-conducting cement, e. g., quartz cement so that the entire structure is held rigidly together.

Two such spirals as I have here shown are then mounted co-axially close together in parallel planes as shown in Figure 5. Through the center of these two spirals I locate an inner shaft l3 of insulating material, e. g., a quartz rod on which I rigidly mount two radial arms 55, 55. These arms are of metal. Each arm 55 carries a sliding collar 65 which in turn carries a suitable brush of spring material 4|, 4| adapted to travel over the outside edge or margin of each spiral ribbon as the arms 55 are rotated about the axis i3. Each arm 55 makes contact at the shaft i3 with a wiping contact brush 45, 46 to which are connected the flexible cables leading to the secondary or output circuit which in radio therapy work will be the applicator electrodes as shown in Figure 2 at 49, 49.

Surrounding the central insulating shaft I3 is a tube 23, preferably of insulating mamrial, in the center of which is mounted a radial arm 5. On this radial arm slides the short circuiting bridge 4 which is mounted on the slide 45 so that as the arm 5 is rotated the brushes 4, 4 make close contact with the sides or inner edges of the parallel ribbons I, 2 of the Lecher system and can thus travel from the inner to the outer ends of the Lecher spiral while the secondary contact brushes 4|, 4| can also travel over said spirals entirely independently of bridge 45.

In this Figure 5 I have shown the two plates of the oscillating tubes 8, 8 connected to the outer ends of the two spirals.

Figure 6 shows more in detail the above described arrangement where the short circuiting bridge 45 carries the two wiping brushes 4. 4 arranged to traverse the inner edges of the two parallel spiral ribbons 2, while the secondary brushes 4|, 4| are attached each to its respective collar 85 which slides along and makes contact with the conducting radial arms 55, 55. The position of arms 55, 55. has been altered in Fig. 6 in the manner described above.

=Flgure 7 shows a plan view of the above arrangement. Here the metal arms 55 travel outside of the spiral ribbons to take off current to the secondary circuit through the wiping contacts 46 while the insulatedly mounted arm 5 travels on the inner sides of the spiral ribbons and carries the bridge 4 which short circuits the two parallel spiral ribbons.

Instead of taking off energy to the secondary or load system from the same Lecher conductors as constitute the primary oscillator which I have above described I might use 4 Lecher conductors, two close together for the primary oscillating system and two parallel spiral conductors each lying outside of but close to the primary Lecher conductors. Such an arrange- .ment I have shown fragmentally in Figure 8 where the conductors in place of being flat ribbons as shown in Figures 4, 5 and 6 are shown as tubes or wires of circular or oval cross section. Here I have shown the short-circuitin bridge 45 with the two wiping brushes 4, 4 as sliding over thetwo primary Lecher conductors and 2 and two brushes 4|, 4| travelling over the two outside Lecher conductors I02. The

radial arm arrangement for sweeping the bridge.

45 around the spiral as well as the two insulated but mechanically connected secondary brushes 4|, 4| are similar to the arrangement already described in connection with the preceding figures.

I wish it understood that while the above described system is particularly useful in ultrashort-wave therapy work the system may be equally well used for any radio application where it is desirable to be able quickly to sweep continuously through a wide range of frequencies. I do not wish therefore to be limited to application of this invention to radio therapy purposes.

In my United States Patents 730,246, 730,247 and 730,819 all of June 9th, 1903, I show for .the first time Lecher conductors as applied to commercial wireless telegraph purposes, and for the first time twisted insulated Lecher wire conductors. I also show these latter arranged in helical formation. These twisted conductors are not strictly parallel conductors however, whereas in the present application I limit myself to strictly parallel conductors, arranged in spiral or helical formations.

What I seek to secure by United States Letters Patent is:

1. An oscillating circuit containing distributed inductance and capacity consisting of two parallel-insulated conductors wound in spiral formation, the distance separating the two parallel conductors being small relative to the pitch of said spiral.

2. An oscillating circuit containing distributed inductance and capacity consisting of two parallel insulated conductors wound in helical formation, the distance separating the two parallel conductors being small relative to the pitch of said helix.

3. An oscillating circuit containing distributed inductance and capacity consisting of two parallel insulated flat ribbon conductors, wound in col] formation, the distance separating the conductors being small compared to the pitch of the coil.

4. An oscillating circuit containing distributed inductance and capacity consisting of two parallel insulated fiat ribbon conductors in coil formation, the distance separating the conductors being small compared to the pitch of the coil, and a wiping brush arranged to connect said parallel conductors and to slide along them.

5. An oscillating circuit containing distributed inductance and capacity consisting of two parallel insulated conductors arranged in coil formation with the distance separating the con ductors small compared with the pitch of the coil, a wiping brush arranged to connect said conductors and to slide along them, and two additional brushes arranged to wipe over said parallel conductors.

6. An oscillating circuit containing distributed inductance and capacity consisting of two parallel insulated conductors arranged in coil formation with the distance separating the conductors small compared with the pitch of the coil, a. wiping brush arranged to connect said conductors and slide along them, and two addi tional brushes arranged to wipe over said parallel conductors, said additional brushes being moved together and independently of said wiping brush. v

7. An oscillating circuit containing distributed inductance and capacity consisting of two par- 8. Two parallel Lecher conductors wound in spiral form with the distance between the conductors small as compared to the pitch of the coil, two brushes adapted to short circuit said conductors mounted on an arm capable of being rotated about the axis of said spirals, and two additional brushes adapted to complete connections to an external circuit each mounted on a radial arm, said radial arms being mounted on a common shaft and designed to rotate about the axis of said spiral.

9. A generator of high frequency electrical currents, two parallel conductors connected to said generator the conductors being wound in a coil with the distance between conductors small as compared with the pitch of the coil, a short circuiting brush adapted to be moved along said parallel conductors, and two additional brushes insulated from each other designed to be moved along said parallel conductors independently of the movement of the first brush.

10. A generator of high frequency electrical currents, two parallel conductors in coil formaticn with the distance between conductors small relative to the pitch of the coil connected to said generator, a short circuiting brush adapted to be moved along said parallel conductors, and two additional brushes insulated from each other designed to be moved along said parallel conductors independently of the movement of the first brush, the location of said first brush determining the wave-length of the primary oscillating system and the other two brushes being adapted to be so located along the parallel conductors as to supply the optimum amount of electrical energy to be taken from said parallel conductors.

11. Two parallel Lecher conductors wound in spiral form with the distance between conductors small relative to the distance between turns of the spiral, two brushes mounted on an arm capable of being rotated about the axis of said spirals, two additional brushes each mounted on a radial arm, said radial arms being mounted on a common shaft and designed to rotate about the axis of said spiral, each of said brushes being connected through flexible conductors to a flat conducting surface, said conducting surfaces forming an air spaced condenser.

12. An oscillating circuit containing distributed inductance and capacity consisting of two parallel insulated conductors wound in a coil, the distance separating the parallel conductors being small relative to the pitch of the coil windings, a wiping brush parallel to a radius of said windings arranged to connect said parallel conductors and to slide along them, and means for supplying electrical oscillations to said 05- cillating circuit.

13. An oscillating circuit containing distributed inductance and capacity consisting of two parallel insulated conductors arranged in hellcal formation with the turns of the helix widely spaced relative to the spacing of the conductors, and a wiping brush arranged to connect said helical conductors and to slide along them.

14. An oscillating circuit containing distributed inductance and capacity consisting of two parallel insulated conductors wound. in helical formation with the turns of the helix widely spaced relative to the spacing of the conductors, a wiping brush arranged to connect the two parallel conductors and to slide along them, and a radial arm rotatably mounted on the axis of the helix, said arm being free to move axially whereby said brush travels radially along the helix as the arm is rotated about the axis of the helix.

15. An oscillating circuit containing distributed inductance and capacity consisting of two parallel insulated conductors wound in helical formation with the distance between conductors small relative to the distance between turns of the helix, a wiping brush arranged to connect the two parallel conductors and to slide along them, said brush being mounted on a radial arm rotatably mounted on the axis of the helix said arm being adapted to travel along the axis as it is rotated thereabout.

16. Two parallel Lecher conductors wound in a helix with the distance between the conductors small as compared with the pitch of the helixya short circuiting brush mounted on an arm rotatable about the axis of the helix and movable along the axis when rotated, and two additional brushes adapted to complete external connections each brush being slidably mounted on an arm rotatable about the axis of the helix said arms being connected for rotation together.

17. Two parallel Lecher conductors wound in helical form with the distance between conductors less than the distance between turns of the helix, two brushes mounted on an arm capable of being rotated about the axis of the helix, two additional brushes each slidably mounted on an arm capable of being rotated about the axis of the helix, each of said last mentioned brushes being connected to a fiat conducting surface comprising one of the plates of an air spaced condenser.

LEE m FOREST.

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