US2032181A

US2032181A - Standing wave oscillating system

Info

Publication number: US2032181A
Application number: US629644A
Authority: US
Inventors: Ilia E Mouromtseff; Harrell V Noble
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1932-08-20
Filing date: 1932-08-20
Publication date: 1936-02-25
Anticipated expiration: 1953-02-25

Description

Feb 1936- l. E. MOUROMTSEFF ET AL J J STANDING WAVE OSCILLATING SYSTEM Filed Aug. 20, 1952 WITNESSE INVENTORS .ZYZUEMourOmZseff &

Harggfl 1/. Nab 6. 4 a 0 ATTOR EY Patented Feb. 25, 1936 UNITED STATES PATENT OFFICE STANDING WAVE OSCILLATING SYSTEM Application August 20, 1932, Serial No. 629,644

2 Claims.

Our invention relates to short-wave apparatus and particularly to apparatus for the generation and delivery of power at wave lengths of only a few meters.

It has been found that an efficient generator for frequencies of this order may be made by causing a vacuum tube to produce standing waves upon a pair of concentric tubular conductors. Our invention pertains to the efficient production and delivery of power by such a generator to any suitable load, such as an antenna, a furnace, or a therapeutic apparatus.

It is an object of our invention to provide a system in which the losses by radiation from the generator and similar losses from the connections between it and the load shall be minimized.

It is a further object of our invention to provide a coupling device which shall have a much greater fiy-wheel action than coupling devices usually used heretofore ordinarily have and which shall also be capable of matching impedances.

It is a further object of our invention to employ a pair of concentric tubular conductors as a coupling device by producing standing waves thereon.

It is a further object of our invention to provide connections to the inner one of such a pair of conductors, through certain of which connections power may be received to maintain the standing waves and through others thereof power may be delivered. We have found that by properly spacing the connections, the ratio of potential received over one pair thereof to potential delivered over another pair may be controlled.

To any given impedance in the output circuit there corresponds an equivalent impedance, which must be added vertically to the impedance actually present in the input circuit to give the impedance the input circuit has when coupled to the output circuit. We have found that the ratio of such equivalent impedance to the impedance in the other circuit is dependent only on the spacing of the connections.

It is a further object of our invention to provide a shield about a generator of standing waves whereby the loss of energy therefrom through radiation is minimized. We have found that by properly choosing the radius of such a shield, the phase of the waves reflected thereby may be controlled and the shield may thereby be made to possess a regenerative eifect.

It is a further object of our invention to provide for an adjustment of the radius of the shield in order to control said phase.

It is another object of our invention to employ impedance-matching devices in such way that the terminal impedance of the transmission line extending to the load shall produce a minimum of reflection. By this means we avoid the production of standing waves upon the transmission line, with the incidental losses resulting from high current density at certain points and from radiation.

It is a further object of our invention to so apportion the ratio of each impedance in the system to its corresponding equivalent impedance at the several coupling devices that the impedance presented to the oscillation generator is that for which it is most eflicient.

Other objects of our invention, details of the structures employed, and the way in which such structures are associated into a system will be readily understood from the following description and accompanying drawing, in which Figure 1 shows, partly by diagram and partly by sectional views, the system embodying the invention,

Fig. 2 is a top plan view of the generator and its shield, the sectional view of said generator and shield in Fig. 1 being upon the line II of Fig. 2, and

Fig. 3 is an enlarged view of a detail indicated by the line III-III of Fig. 2.

In Fig. l a vacuum tube, the lower portion of which is seen at I, has its anode and grid connected respectively to an outer pipe 2 and an inner pipe 3, the connections being designed to produce minimum reflection, as disclosed in the patent of C. A. Boddie, No. 1,979,668, granted November 6, 1934, assigned to Westinghouse Electric & Manufacturing Company.

Such a combination of a vacuum tube and concentric pipes constitutes an oscillation generator of high frequency producing standing waves upon the concentric pipes. The filament may be energized by a battery, a generator, or a transformer, the secondary of which has been shown on the drawing. Whatever the source of energy it is separated from the filament by choke coils. The center point of the transformer secondary or one side of the energizing battery or generator is grounded and connected through an ammeter and a source of direct-current potential indicated at 5 to the outer one 2 of the pipes. The same point is also connected through another ammeter and a grid resistor 6 to the inner pipe 3.

A choke coil 1 in the first of these connections and a choke coil 8 in the other, ensure that the high frequency does not pass through these connections. The coils l and 8 are so located relative to Teach other that they are not eIectromagnetically coupled. The connection 9 from the coil ii through the outer pipe 2 to the inner pipe is 'inade by providing a hole in the outef; 5 pipe which-may for may not be occupied by an in sulator as desired.

The connections 9 and ID from the

coiis

1 and 3 are at as small a distance as possible from the neutral point of the

pipes

2 and 3. That is, 10 when the generator has produced standing waves upon the pipes, these connectioms are on opposite sides of and comparatively near to a potential node. The direct-current connections are, for this reason, without substantiai influence-upon the distribution of the high frequency potentials. It is desirable to build the two-'plpe structure so that it shall have a great flywheel street; that is, so that the amount of energy which can be, stored therein, changing from current to elec-' trostatic charge and back to current each half cycle, shall be large. Theoretical considerations show that the "greatest flywheel effect can be obtained if the

pipes

2 and 3 are of equal radii but this is, of ci iurse, physically impossible. Instead'of attempting to approximate it we have chosen the radiijof the pipes to accord with those radii of plate and grid in the'vacuum-tub'e design which seem best adapted to this purpose. In the chosen frform, the Outerpipe 2' has an inner diam eter equal to twice the outer diameter of the inner pipe 3. V i The pipes 2'and'3 are mounted in any desirable way, for example, by means of insulators I l cone nected to a mast l2. They are located at the center of a shield l3 which is made of sheet metal,

' wire mesh or other suitable 'materiaL' for reflecting electromagneticiwaves of a wave length of a few meters. The shield may be grounded if ,desired. 7 V i Q The radius of the shield, which is approximately the same 'asthe distance between the'pipes and the shield, is approximately one-quarter of the wave length but provision isf nade for adjusting it. One method for providing adjustment is indicated at M and Why showing theshield as composed of two halveswhich overlap. The extent of overlap can be regulated by means of bolts it which have been illustrated in more de-' 'tailinFig.3.

Insulators I? and l8 are provided in the wall of the shield for accommodation of the connec-' tions 5 and It; to the-coils 1 and 8 which are preferably located inside of the shield.

Connections 2| and 22 extend from the inner pipe 2 through

insulators

23 and 24 in theshield to a coupling device 25. The conductors 2| and 22 pass through the pipe 3 and holes are provide-d for their accommodation, which may, if desired, be equipped with insulators. The conductors ecand 22a're symmetrically placed relative .to the 7 potential node upon the pipe .and the distance from the node is greater than that separating the connections 9 and H! from said node. Instead of the conductorsr2l and 22 being con- .7 nected as shown, they may, if desired be both connected to the outer pipe 2 or one to one pipe and the other to the other'pipe. V

The coupling device 25 comprises an inner pipe 26 mounted upon a mast 21 by means of an in- .sulator 28 and an outer pipe-30 mounted upon the same. mast by means of insulators 3| and 3-2; In the illustration,.the length of the pipes 26 and 30 "is not. 1 shown. They are substantially the same length :as the

pipes

2 and 3, namely oneihalf of a wave length.

The conductors 2i and 22 extend through holes in the pipe 3lLand are connected to the pipe .26 at points spaced away from the center thereof, which is a potential node. The pipe 26 is also connected to two conductors;35 and 36, which likewise extend through holes in the pipe 30. Insulators may, if desired, be supplied in the holes. The further from the potential node, the, more necessary insulators will be. The

connections

35 and 35 are symmetrical relative to the potential node and, in the embodiment chosen for illustra- 7 tion, are spaced closer to that node than the connections 2| and 225 I The

conductors

35 and 36 extend to a second" coupling device-40 meunted upon a mast 4| by means of one 'or more insulators 42. 'In the form chosen for'illustration, the coupling device 40 has been shown as a helix which will function as an auto-transformer, but, if desired, the second 5. The frequency of, the standing waves is determined by the length of the concentric pipes,

and will be such that the pipes are. exactly j 0116-.

half a Wave-length long. i c,

, Although it is intended that substantially an the energy departing from the

pipes

2 and 3 should,

be conducted over the lines 21-22, some energy leaves the pipes by radiatio'n. Such radiated energy is reflected from the shield I3 back onto the

pipes

2 and 3. The radius of the shield is approximately one duarter' of a =wave-length.

Radiations departingfrom the pipe 2 undergoa reversal ofphaseupon reflection from the shield l3 and pass a secondtime over a quarter wave distance before they again arrive at 'thepipe 3, They are, therefore; approximately in phase with the waves upon the pipe 3 when these'radiations arrive there. r

If' the vacuumltube generator producedno lag and the plateand the grid voltage were therefore maintained; is-strict phase-opposition, this wouid be the desirable phase for therefle'cted radiations, but there is usually a small lag be tween the plate voltage and exact opposition to the-grid voltage. 'It is, therefore, desirable that the reflected radiations arrive at the pipes with substantially the same degree of lag and, by slightly increasing the radius of the shield over the quarter wave-length, this relation can be obtained. This is done by adjusting the bolts l6 until the generator is operating most efficiently,

which fact willbe indicated by thereadings of the meters in the plate and grid;leads.

The conductors 2i and 22 deliver alternating currentenergyto the inner pipe 25 of the coupling device 2-5. Standing waves are thus produced upon the 'devioe'25, a potential node being established at the middle of the pipes, The

lines

35 and 36 are on opposite sides of this potential node.

The distance along the'pipe 25 from the node determines what potential shall be impressed upon these lines. The ratio between the voltage delivered to the

lines

35 and 35 and that received from the lines 2| and 22, is dependent upon the;

distance separating 'each pair of lines from the potential node. In the structure, as illustrated, a smaller potential is delivered to the

lines

35 and 36 than is received from lines 2| and 22, but this ratio may be reversed, if desired.

Lines

35 and 36 deliver potential to the coupling device 40 which may step up or step down the potential in the familiar way of an autotransformer if a helix is used, or if a second coupling device of the form illustrated at 25 be used, the change in potential will be effected in the way just described.

A vacuum tube generator of the kind here described is like other generators, in at least one respect, namely, that it will deliver power most efiiciently to one particular impedance. One of the considerations which govern the design of this apparatus is that best efficiency will be obtained when the impedance presented to the generator is of this amount.

The coupling devices herein described resemble an ordinary wound transformer in at least one respect, namely, that the impedance in the output circuit may be represented by an equivalent impedance in the output circuit. The ratio between the actual impedance in the output circuit and the impedance which should be considered as added in the input circuit, in order to represent the effect of the impedance in the output circuit, we have called the impedance transformation ratio, because of its close similarity to the similar ratio when ordinary transformers are used as coupling devices.

This ratio may be controlled in each coupling device by controlling the ratio between the spac ing of the input connections and that of the output connections. An equivalent impedance must be added to the lines 2l--22 to represent the effect of its being coupled to the lines 35-36 by the device 25. Because the connections of the conductors 2| and 22 to the pipe 26 are farther apart than the connections of the

conductors

35 and 36 to that pipe, the equivalent impedance will be larger than the impedance in the line 3536. On the other hand, if the distance separating conductors 2! and 22 along pipe 26 be smaller than the

distance separating conductors

35 and 35 along that pipe, the equivalent impedance will be smaller than the impedance in the line 35-36.

The impedance of the line as the expression is used herein means the resultant of its own impedance and the load impedance whether the coupling be by an auto-transformer as shown or by another device like the device 25.

It is possible theoretically, by taking advantage of this property of the coupling device 25, to match the impedance of the load with the optimum impedance for the generator, by which is meant that the effective impedance at the generator, after the several impedance transformation ratios have been applied to the load impedance, can be made to equal the impedance for which the generator is most efficient.

Sometimes a single coupling device may not accomplish this result without requiring conductors to be more closely spaced than is physically possible or voltages at certain points to be greater than convenient. Under these circumstances the use of several coupling devices in tandem can be made to match impedances.

In the system, as illustrated, the vacuum tube l and its associated

pipes

2 and 3 may be regarded as an oscillation generator of a type which produces standing waves; from which viewpoint the illustrated system includes two coupling devices.

It is also possible to regard the vacuum tube as itself a generator of high frequencies and the pair of concentric pipes associated with it as a coupling device; from which viewpoint the illustrated system includes three coupling de vices. In this latter aspect, the impedance to which the load impedance must be matched is that at which the vacuum tube itself most efficiently generates oscillations.

The plate and grid leads are connected to the

pipes

2 and 3 near to the potential node. Nevertheless, they are a certain distance apart. The leads 2] and 22 are placed at a distance apart which is selected in accordance with the voltage it is desired to impress upon the conductors 2| and 22. The ratio between the distance separating these connections and the length of the system comprising pipes and tube determines not only the voltage delivered to the line but also the impedance upon the vacuum tube, regarded as an oscillation generator, which will be equivalent to the impedance presented by the conductors 2| and 22.

If the line 2|--22 is long, it would ordinarily be convenient for the line 35-35 to be short, although the first line may be short and the other one long. With either arrangement, the long line, because it is carrying a high frequency, will have a pronounced tendency to produce standing waves, and in order to avoid this, the terminal impedance of the line would have the value corresponding to what, in the theory of transmission lines, is called perfect termination. This may be accomplished by selecting the proper impedance transformation ratio for the coupling device at the delivery end of the line. Under these conditions, regardless of the impedance at the end of the line connected to the generator, reflections will be avoided and standing waves on the line will thus be impossible.

The correct terminal impedance for the line is dependent upon the characteristic line impedance. The most effective transmission of energy over the line will thus be secured by so selecting the impedance transformation ratio at the output end of the line that the impedance, looking from the line into the coupling device, has the proper relation to the characteristic line impedance. It is, therefore, possible by the use of two coupling devices, one at each end of the line to obtain the necessary impedance transformation ratio between the load at the one end of the system and the generator at the other end of the system, select a convenient value for the characteristic line impedance and still avoid standing waves on the line.

The connections from the coupling device 25 have been shown as extending to the inner pipe. It is possible to obtain coupling with all of the connections going to the outer pipe only. It is also possible to obtain coupling with one pair of connections going to one pipe and the other pair to the other pipe, but of all these methods we have found that that in which all connections extend to the inner pipe is the more efficient.

Although we have illustrated an auto-transformer at 40, as an alternate form of coupling device, we find that usually better results are obtained by using a single coupling device like that shown at 25, or, if two coupling devices are used, by making both of them of this form. This is partly because a coupling device of the form depending upon standing waves and comprising two concentric pipes radiates less energy and thus loses a smaller percentage of power in the form of radiation than older forms and also because such a coupling device has a greater fly-wheel effect than an auto-transformer or a coupling device comprising a tuned circuit.

The greater fly-wheel effect also reduces the tendency to parasitic oscillations and thus economizes power. It also tends to eliminate the effects 'of any brief or rapid changes in the output of the generator, but if the changes in the output be slower, they will be faithfullyreproduced in the final output from the system. For example; a

modulation of standing waves of a few meters length by a frequency corresponding to an audible note is in no wayjnterfered with by using a coupling device having a, large fiy-wheel eifect. Although we have specifically described and illustrated only, oneformof our invention, it will be obvious to thoseskilled in the art that many modifications thereof are possible. We; therefore, do not intend any limitation except such as is required by the prior art or indicated by the accompanying claims.

aosaisr cylindrical conducting shield substantially co- 7 axial with the first-named cylinder and having a diameter substantially equal to a half-wave length of the oscillations produced by said generator. V

2. In'combination a source of alternating current and a conductor attached thereto, said conductor having a length in proportion to the frequency of said alternating current whereby standing waves are produced thereon and a cylindrical reflecting shield concentric with and surrounding said conductor and having a diameter standing waves. o

' ILIA E. MOUROMTSEFF.

HARRELL V. NOBLE.

substantially equal to a half-wave length of said