US2849691A - Wavemeter - Google Patents

Description

Aug. 26, 1958 Filed Nov. 3. 1954 D. R. DE TAR WAVEMETER 2 Sheets-Sheet 2 Filed Nov. 3, 1954 Ezel-:ZEE DONALD Q. DETAR WAVEMETER Donald R. De Tar, Stratford, Coun., assigner to Aladdin Industries, Incorporated, Nashville, Tenn., a corporation of Illinois Application November 3, 1954, Serial No. 466,508 s claims. (Cl. ssa-s2) One principal object of the invention is to provide an improved wavemeter or the like for use at ultrahigh frequencies, particularly in the ultrahigh frequency (U. H. F.) television band extending from 470 to 890 megacycles.

A further object of the invention is to provide an absorption type wavemeter which is inexpensive and small in size, yet is accurate and entirely reliable.

It is another object of the invention to provide an improved wavemeter which is simple and rugged in construction, easy to use and convenient to carry.

Further objects and advantages of the invention will appear from the following description, taken with the accompanying drawings, in which:

Figure l is an elevational view of an exemplary wavemeter constituting an illustrative embodiment of the invention;

' Fig. 2a is a fragmentary double-size longitudinal sectional view taken generally along fa line 2 2 in Fig. 1;

Fig. 2b is a continuation of Fig. 2a showing the opposite end of the wavemeter;

Figs. 3, 4, and 5 are cross-sectional views taken generally along lines 3 3, 4 4, and 5 5 in Figs. 2a1 and 2b;

Figs. 6 and 7 are plan and elevational'views of an inductance element embodied in the wavemeter of Fig. 1;

Fig. 8 is a diagrammatic representation of the wavemeter; and

Fig. 9 is an approximate equivalent schematic diagram of the wavemeter.

Considered in greater detail, the drawings will be seen to illustrate an exemplary wavemeter 10 which in this instance comprises an elongated cylindrical tubular housing 11 made of a dielectric material. One end of the housing 11, shown at the left in Figs. l and 2a, is closed by a dust cap 12.

To provide an inductance loop, a conductive metallic sleeve 13 is mounted within the left hand end of the insulating housing 11 and in this instance is suitably secured to the housing 11 as by the illustrated screw 14. In order that the sleeve may define an inductance loop, a pair of diametrically opposite longitudinal slots 15 are formed in the right hand end portion of the sleeve 13. As shown to best `advantage in Fig. 6, which is a view of the inductance element 13, the slots 15' extend part way from the right hand end of the element 13 toward its left hand end. By virtue of the slots 15, the sleeve 13 constitutes a generally U-shaped inductance loop having a pair of elongated arms 16 which are interconnected at their left hand ends by a ring-shaped portion 17 of the sleeve 13. Adjacent the ring portion 17 the arms 16 have narrowed down portions 18 which are defined by cutouts 19 in the sleeve 13. Adjacent the right hand end of the sleeve 13, the arms 16 are provided with externally reduced portions 20 having terminal elements 21 which are reduced in width by cutouts 22. Internally, the sleeve 13 is formed with a continuous cylindricalsurface 23.

United. States Patent O 2,849,691y Patented Aug. 26, 1958 ICC In order to vary the capacitance between the arms 16 of the inductance loop defined by the sleeve 13, the wavemeter 10 is provided in this instance with a capacitive tuning member, indicated generally by the character 24. While the member 24 may assume various forms, it is illustrated as comprising inner and outer concentric cylindrical elements or sleeves 25 and 26 in capacitive relation to the arms 16 of the stationary sleeve 13. In this instance, the arms 16 are telescopically disposed between the sleeves 25 and 26. The sleeve 26 is adapted to be received over the externally reduced portions 20 of the arms 16, while the inner sleeve 25 is adapted to be received within the internal cylindrical surface 23. Thin walled insulating bushings 27 and 28 are interposed between the stationary sleeve 13 and the inner and outer capacitive tuning sleeves 25 and 26. It will be seen that the inner tuning sleeve 25 is relatively long, while the outer sleeve 26 is relatively short. In the illustrated construction, the outer sleeve 26 is mounted on and conductively connected to the right hand end of the inner sleeve 25. More specifically, the outer sleeve 26 is formed with an internally reduced or necked-down right hand portion 29 which is mounted on an externally reduced end portion 30 of the inner sleeve 25. The connection between the sleeves 25 and 26 is primarily for mechanical rather than electrical reasons, and hence need not be conductive. Both sleeves 25 and 26 are at substantially the same electrical potential, amounting to the mean between the potentials of the arms or terminals 16 of the inductance element 13. Accordingly, no substantial current flows between the sleeves 25 and 26.

Provision is made for effecting relative longitudinal movement between the inductance element 13 and the capacitive tuning element 24. In this way, the capacitance between the arms 16 may be varied so as to change the resonant frequency of the inductance loop delined by the element 13. In this instance, the capacitive tuning element 24 is movable relative to the housing 11, while the element 13 is stationary, but it will be understood that this arrangement might well be reversed. In the illustrated construction, the inner sleeve 25 of the capacitive tuning element 24 is connected to the left hand end of an insulating rod 31, which is received within an axial bore 32 formed in the sleeve 25 and is pinned or otherwise suitably secured to the sleeves 25 and 26. The rod 31 extends axially within the housing 11 toward its right hand end. In order to advance and retract the rod 31, its right hand end is connected to a micrometer lead screw 33 which in this instance is provided with a quintuple left hand thread. The screw 33 is in threaded engagement with a nut 34 fixed in the right hand end of the housing 11. To reduce friction and wear, the

screw 33 is preferably made of metal, while the nut 34 is made of nylon or other similar plastic. For the purpose of preventing play or backlash between the screw 33 and the nut 34, the latter is formed with an externally reduced or necked-down portion 35 which is longitudinally split by diametrically opposite slots 36. A split circular wire spring or C-ring 37 is mounted on the outside of the reduced portion 45 to compress the split halves of the nut 34 into intimate engagement with the screw 33.

To provide for manual adjustment of the wavemeter 10, a generally cylindrical thimble-shaped dial or barrel 38 is mounted on the right hand end of the lead screw 33. In the illustrated construction, the lead screw is formed with a reduced end portion 39 received within a bore 40 in the dial 38. A setscrew 41 or some other fastening element is employed to secure the dial 38 to the lead screw 33. The dial 38 is provided with a tubular left hand portion 42 which is telescopically received over the housing 11 and thus is effective to enclose the screw 33 and the nut 34. Asuitable scale 43 may be applied to the outside of the dial 38. It will be understood that the scale 43 may be calibrated in terms of frequency or wave length. In this instance the scale 43 is helical in form. A pointer 44 is mounted on the housing 11 to cooperate with the indicia on the scale 43. Due to the helical lead of the scale 43, the pointer 44 remains opposite the scale as the dial is rotated to advance the screw 33.

In operation, the inductive element 13 of the wavemeter is coupled to a resonant circuit or other element, the operating, frequency of which is to be determined. This is done by holding the wavemeter 10 with its lefthand end adjacent the coil or other inductive element of the resonant circuit. In this way, the slotted sleeve 13 is positioned in the magnetic field of the coilv under test. The dial 38 isthen adjusted until thewavemeter absorbs the maximum amount of energy from the circuit under test. The absorbtion of energy may be indicated in various ways, as will be understood by those skilled in the art. For example, ifV the device under test is an oscillator utilizing an electronic discharge device, the absorption of energy by the wavemeter may be manifested by the complete cessation of oscillations in the oscillator, or by a variation in the current to the grid or other electrode of the electron discharge device. In the typical oscillator, the grid current will drop when energy is absorbed from the oscillator by the wavemeter. It will be understood that the grid current may be measured by means of a suitablemilliameter or the like. It will also be understood that rotation of the dial 38 advances the screw 33 through the split nut 34 and thereby moves the sleeves 25 and 26 in a longitudinal direction relative to the sleeve 13. Accordingly, the

extent of telescopic engagement between the sleeve 13 and the sleeves 25 and 26 will be varied. The greater the extent of telescopic engagement, the greater will be the capacitance between the arms 16 of the inductance loop defined by the sleeve 13. It will be understood that the inductance provided by the slotted sleeve 13 is resonated by the capacitance between the arms 16. Accordingly, theresonant frequency of the wavemeter is varied by shifting the sleeves 25 and'26 longitudinally relative to the sleeve 13. The resonant frequency decreases progressively as the movable sleeves 25 and 26` are shifted into telescopic relation with. the stationary sleeve 13.

The tuning curve of the wavemeter is affected by the configuration of the sleeve 13 and the length of the sleeves 25 and 26. In the illustrated construction, the inner sleeve 25 is relatively long, with the result that it contributes capacitance betweenV the arms 16 throughoutv the tuning range of the wavemeter. It will be understood that the capacitance afforded by the inner sleeve 25 increases progressively as the sleeve is moved into the slotted sleeve 13. Theouter sleeve 26, being relatively short in this instance, comes into play primarily in the low frequency portion of the tuning range, as the sleeve 26 moves over the ends of the arms 16. The reduced width of the terminal portions 21 of the sleeve 13 affords a band-spreading' effect, particularly at the high frequency end of the tuning range.

In Fig. 9 the inductance of the wavemeter, provided primarily by the slotted sleeve 13, is indicated by a lumped inductance -coil 45, while the capacitances between the respective arms 16 and the capacitive tuning element 24 are represented by first and second variable capacitors 46 and 47-` connected in series across the coil 45. This approximately equivalent schematic representation of the wavemeter illustrates the point that the capacitances between the armsl 16 and the sleeves 25 and 26 are in series. Fig. 8 illustrates diagrammatically the capacitive relation between thecapacitive tuning element 24and the arms 16 of the U-shaped loop defined by the sleeve 13.

Inview of the small size of the tuned circuit provided 4V by the slotted sleeve 13 and the tuning sleeves 2S and 26, the wavemeter 10 may be employed effectively in cramped situations. Thus, the left hand or probe end of the wavemeter may bel inserted into an extremely small opening and thus may be coupled closely to a coil or other tuned element which is relatively inaccessible. The tuned circuit of the wavemeter may be coupled to a circuit element of small size without being affected appreciably by electromagnetic fields or other adjacent elements. This is a matter of particular advantage in testing television tuners, in which the coils or other tuned elements are often small in size and closely spaced. Because of the length of the wavemeter, the left hand or probe end may be inserted into a deep opening to secure close coupling between a circuit under test and the tuned circuit of the wavemeter, while leaving the right hand or adjustment end of the wavemeter in a conveniently accessible position for easy operation. The wavemeter may lbe made any desired length simply *by elongating the housingll and the insulating rod 31.

The helical form of the scale on the wavemeter dial provides great scale length in a small space. Since the pointer is stationary, while the scale is movable, the wavemeter may be read from a xed angle. Accordingly, readings may be taken without moving the probe end of the wavemeter from the position of optimum coupling with the circuit under test.

By virtue of the stepped configuration of the slotted sleeve 13 and the difference in length of the inner and outer sleeves 25 and 26, the frequency scale or curve of the wavemeter may be made substantially linear. It will be recalled that theouter lsleeve 26 is effective primarily at the low frequency end of the tuning range, while the reduced terminal ends 21 of the arm electrodes 16 provide band-spreading at the upper end of the tuning.

range. The capacitive relation between the movable sleeves 25 and 26 and the arms 16 eliminates any needk field from the coil will linkv the single turn loop provided' by the sleeve 13. The wavemeter may be capacitively coupled to a circuit under test by placing one of the armelectrodes 16 adjacent acircuit element charged with a radio fraquency voltage.

Since the nut 34 preferably is made of an insulating material, there is .no possibility that electrical noise will be introduced by sliding engagement between the nut and' the screw 33. The springfloading of the split nut eliminatesv all backlash between the nut and the screw.

It will be observed that the dial or thimble 38 is provided with a large knob portion 48 for making a fine adjustment of the dial, together with a smaller, axially protruding knob 49` for spinning the dial when a more rapid adjustment is desired.

The wavemeter is small in size and light in weight and, accordingly, is easy to use and convenient to carry. Because of the simple, rugged construction of the wave meter, there is little to get out of adjustment. Moreover, the wavemeter may be manufactured inexpensively.

Various modifications, alternative constructions and equivalents may be employed without departing from the true spirit and scope of the invention as exemplified in the foregoing description and defined in the following claims.

I claim:

1. An absorption type wavemeter, comprising an insulating elongated tubular generally cylindrical housing, an inductance element in the form of a conductive sleeve received within said housing adjacent one end thereof, said sleeve having .a pair of diametrically opposite longitudinal slots formed therein and extendinglongitudinally therealong part way from the end sleeve remote from said one end of said housing toward the end of said sleeve adjacent said one end of said housing, said slots defining a pair of opposed arm portions and an interconnecting ring portion extending between said arm portions at the end of said sleeve adjacent said one end of said housing, outer and inner movable tuning sleeves disposed in said housing, said arm portions of said rst mentioned sleeve having reduced terminal elements telescopically received between said outer and inner sleeves, said ring portion being free of said tuning sleeves, an outer insulating bushing disposed between said outer sleeve and said reduced terminal elements, an inner insulating bushing disposed between said inner movable sleeve and said rst mentioned sleeve, said outer and inner sleeves being conductively interconnected, and means for longitudinally moving said outer and inner sleeves to vary the extent to which said arm portions are received between said tuning sleeves and thereby vary the capacitances between said outer and inner sleeves and said arm portions, said means including an insulating rod connected to said movable sleeves and extending axially therefrom within said housing toward the end thereof opposite from said one end, a lead screw connected to the opposite end of said rod, a nut connected to said opposite end of said housing and in threaded engagement with said lead screw, a generally cylindrical dial telescoped over said opposite end of said housing and connected to said lead screw, said dial being manually rotatable to shift said movable sleeves, and a pointer element mounted on said housing and in indicating relation to said dial.

2. An absorption type wavemeter, comprising an insulating tubular housing, a U-shaped inductance element in the form of a conductive sleeve received within said housing adjacent one end thereof, said sleeve having a pair of diametrically opposite longitudinal slots formed in one end thereof and defining a pair of opposed arm portions on said sleeve and interconnected at one end by a bridge portion, interconnected outer and inner movable cylindrical tuning elements disposed in said housing, said arm portions being telescopically received between said outer and inner elements, said elements being free of said bridge portion, outer and inner insulating bushings disposed between said arm portions and said outer and inner elements, and means for longitudinally moving said outer and inner elements to vary the extent of telescoping between said cylindrical elements and said arm portions and thereby vary the capacitance between saidarm portions, said means including a lead screw connected to said elements, a nut connected to said housing and in threaded engagement with said lead screw, a generally cylindrical dial telescoped over said housing and connected to said lead screw, said dial being manually rotatable to shift said movable elements, and a pointer element on said housing and in indicating relation to said dial.

3. An absorption type wavemeter, comprising an insulating elongated tubular generally cylindrical housing, an inductance element in the form of a conductive sleeve received within said housing adjacent one end thereof, said sleeve having a pair of diametrically opposite longitudinal slots` formed therein and extending longitudinally therealong part way from the end of said sleeve remote from said one endof said housing toward the end of said sleeve adjacent said one end of said housing, said slots defining a pair of opposed arm portions on said sleeve and an interconnecting bridge portion extending between said arm portions, outer and inner movable tuning sleeves disposed in said housing, said arm portions being telescopically received between said outer and inner sleeves, said tuning sleeves being free of said bridge portion, an outer insulating bushing disposed between said outer sleeve and said arm portions, an inner insulating bushing disposed between said inner movable sleeve and said arm portions, and means for longitudinally moving said outer and inner sleeves to vary the capacitances between said outer and inner sleeves and said arm portions, said means including an insulating rod connected to said movable sleeves and extending axially therefrom within said housing toward the end thereof opposite from said one end, a lead screw connected to the opposite end of said rod, a nut connected to said opposite end of said housing and in threaded engagement with said lead screw, a generally cylindrical dial telescoped over said opposite end of said housing and connected to said lead screw, said dial being manually rotatable to shift said movable sleeves, and a pointer element mounted on said housing and in indicating relation to said dial.

References Cited in the file of this patent UNITED STATES PATENTS 2,575,199 Stutt Nov. 13, 1951 2,606,315 De Tar Aug. 5, 1952 2,681,999 Boothby June 22, 1954 2,710,379 Lubben et al. June 7, 1955

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