US2695385A - Alternating current switch - Google Patents

Description

Nov. 23, 1954 c. F. SHUNEMANN ALTERNTING CURRENT SWITCH 2 Sheets-Sheet l Filed March 4, 1952 /lll @an H f f77-1E Nov. 23, 1954 c. F. SHUNEMANN 2,695,385 ALTERNATING CURRENT SWITCHr l Filed March 4, 1952 2 Sheets-snaai 2 az/ alzuzzezzzazzzz b al-5 HZHE United States Patent O ALTERNATING CURRENT SWITCH Carl F. Shunemann, Cleveland, Ohio, assignor to Thompson Products, Inc.; Cleveland, Ohio, a corporation of Ohio Application March 4, 1952,- Serial'No-.274,805

14 Claims. (Cl. 333-7) This invention relates to an alternating current switch and more particularly .to a switch arranged for connecting transmission lines or the like without impedance mismatch and without introduction of standing waveson the lines.

lt is an object of this invention to provide an alternat- L,

ing current switch which is simply and-economically con.- structed, which is reliable in operation even at high speeds and which has a substantially constant characteristic impedance over a range of frequencies so as not to produce an impedance irregularity and associated ineiicient power transmission.

According to this invention, a switch is provided which is reliable in operation at high speeds and which, in operative position, forms either a high-pass or a low-pass filter section. As will appear, such filter sections may have a substantially constant characteristic impedance over a wide range of frequencies and may connect transmission lines, or other electrical devices, without an impedance irregularity and the associated standing waves and ineicient power transfer.

In one embodiment of this invention, a spring-carried contact is supported within a housing and is r*arranged to be actuated into engagement with a first conductor insulated from the housing. A second conductor is connected to the spring-carried contact and the rst and second conductors are arranged for connection to terminals of transmission lines or the like while the housing forms a conductor for connecting other terminals of the transmission lines. The first conductor, together with the spring-carried contact structure form a lirst inductance and the second conductor is so connected to the contact structure as to form a second inductance in series with and substantially equal to the rst inductance. Support structure for the contact means is arranged to provide a capacitance from a point intermediate the first and second inductances to the housing. It will be apparent that this arrangement thereby provides a substantially symmetrical low-pass T filter section. As will appear, such a lter section may have a substantially constant characteristic impedance over a wide range of operating frequencies. It will also be apparent that the spring-carried contact arrangement will be reliable in operation and may be operated at comparatively high speeds.

lf desired, a plurality of the spring-carried contact arrangements may be provided for selectively connecting one transmission line to a plurality of lines or to provide a switch for connecting a balanced two or three-wire transmission line to one or more balanced transmission lines. It will also be apparent that the above-described arrangement is particularly adapted for connecting coaxial transmission lines since the housing forms a conductor and may, if desired, be enclosed so as to effectively eliminate external radiation.

ln another embodiment of this invention, a conductor is supported within ahousing and is arranged to be actuated into a position closely adjacent a second conductor so as to define therewitha capacitor. Means connected to the first conductor are arranged in relation to a third conductor to define therewith a capacitor substantially identical to the above-mentioned capacitor, and a support structure for the movable rst conductor is arranged to form an inductance from the housing to a point intermediate the two capacitors so that a substantially symmetrical high-pass T filter section is provided. Such a filter section may have a substantially constant characteristic impedance over a wide range of fre- 2,695,385 Patented Nov. 23, 1954 quencies so asto elici'e'ntly'trahsfer power. "It will be apparent that the movable first conductor, which doesnot make direct contact with the second conductor,Y may be efficiently and reliably operated at high speeds. 1t will also be apparent that, as with the first embodiment described, such a'switch"`is'particularly adapted for connectionof coaxiallines and may be readily duplicated for selective connection' of a plurality of lines or for Switching balanced two or threecouductor lines.

'F his invention contemplates other objects, features and" advantages *which willv become more fully apparent from the following'detailed vdescription taken in conjunction with the accompanying drawings which illustrate preferred embodiments and in which: i

Figure l is a sectional `view of one form of switch constructed according to the principles of this invention; Figure 2 is a sectional view taken substantially along lines ll-II of Figure l;

Figure 3 is lalsectionalxview taken substantially along lines lll-Ill of Figure 2; s Figure 4 is a circuit diagram equivalent to a portion of the switchof-Figure 1;

Figure 5 is a graphical illustration of the relation between characteristic impedance and frequency obtained with'the switch of Figure 1;

Figure 6 is a graphical illustration of the relation of the voltage standing wave ratio to frequency obtained with the switch illustrated in Figure l;

Figure 7 is a sectional; view similar to Figure 2, but illustrating a modified switching arrangement;

Figure 8 is asectional `view taken substantially along lines VIII-VIII of Figure 7;

Figure 9 is a circuit diagram of a portion of the switch of Figures 7 and 8 Figure 10 is a graph illustrating the relation between characteristic impedance and frequency obtained with the switch of Figures 7 and 8; and

Figure 1l is a graph illustrating the relation between voltage standing wave ratio and frequency obtained with the switch modification of Figures 7 and 8.

A switch assembly constructed according to this invention is generally designated by reference numeral 20 in Figure l and includes a pair of sub-assemblies 21 and 22 each of which is herein arranged to alternately connect one coaxial line to one of two other coaxial transmission lines. This switch is particularly designed as a lobing or sensing switch for coaxial lines, but it will be understood that the principles of this invention may readily apply to many other types of switches.

The switch sub-assemblies 21 and 22 include housings 24 and 25, respectively, the housing 24 herein having a recessed face 26 receiving one face of the housing 25 with a gasket 27 disposed therebetween. The housings 24 and 25 may be secured together by any suitable means. A clging cover 28 is secured to the left face of the housing For actuating the switch sub-assemblies 21 and 22, a rotatable shaft 29 is centrally disposed within the housings 24 and 25 and is arranged to be rotated by means of a motor generally designated by reference numeral 29 andA secured to the right face of the housing 24 by bolts 30. A drive plate 31 is secured to a reduced diameter right end portion 32 of the shaft 29 by a pin 33 and is connected to the motor 29 by a coupling assembly generally designated by reference numeral 34. The drive plate 31 is rotatably supported within an opening in the right-hand face of the housing 24 through a bearing assembly 36 while a reduced diameter left end portion 37 of the shaft is rotatably supported within a recess 38 in the cover plate 28 by a bearing assembly 39.

The housing 24 of the switch sub-assembly 21 herein has peripheral openings 40, 41 and 42 receiving coaxial linee connectors 43, 44 and 45, respectively. As illustrated, the opening 40 and the connector 43 and the opening 42 and the connector 45 have mating internal and external threads and nuts 46 and washers 47 may be screwed on the connectors to tightly secure the same to the housing 24. An alternative connection is illusto the housing 24. The connectors 43, 44 and 45 are Y 3 adapted for connection to the outside conductors of coaxial liues. For connection to the inner conductors of coaxial lines, conductors 50, 51 and 52 are supported by dielectric spacers 53, 54 and 55, respectively, within the connectors 43, 44 and 45, respectively.

By this invention, means are provided for alternately connecting the conductor 51 to the conductors 50 and 52. -For this purpose, a pair of arms 57 and 58 are pivotally supported on posts 59 and 60, respectively, within the housing 24. Generally U-shaped resilient spring members 61 and 62 are secured to the ends of the arms 57 and 58, respectively, and carry contacts 63 and 64, respectively, arranged to conductively engage enlarged end portions 65 and 66 of the conductors 50 and 52. The arms 57 and 58 are urged toward each other and toward the shaft 29 by a tension coil spring 67 secured therebetween. To alternately engage the contacts 63 and 64 with the conductor end portions 65 and 66, an eccentric cam 68 of a dielectric material is secured to the motor-driven shaft 29, rotation of the shaft serving to alternately cam the arms 57 and 58 into operative position.l The eccentric 68 is herein disposed in a reduced diameter recess in the shaft 29 and is held in position by a bowed retaining ring 69 and is held against rotation by a pin 70. i

As shown in Figure 3, plugs 71 and 72 of a suitable dielectric material are disposed in recesses of the housing 24 and are internally threaded to receive externally threaded end portions of the posts 59 and 60. The threaded end portions of the posts 59 and 60, together with the facing surfaces of the housing and the dielectrics 71 and 72 form a capacitance between the binding posts and the housing.

The`binding posts`59 and 60 are connected together and to the conductor ,51 by means of a bar 74 disposed between the posts and the lug 75 having a bifurcated end portion receiving a central portion of the bar 74, the lug being secured to or integral with the conductor 51.

According to this invention, the conductor 51, the lug 75 and the bar 74 together define an inductance preferably equal to the inductance defined by each of the arms 57 and 5S and the associated spring 61 or 62 and conductor 50 or 52. For this purpose, the bar 74 is looped intermediate the lug 75 and the posts 59 and 60 as indicated byreference numerals 77 and 7 8, Figure 3, which provides a longer path for current fiow and thereby additional inductance. The conductor 51 may be formedrinto a helix as indicated by the reference numeral 79 to provide a greater inductance between the terminal point of the conductor 51 and the binding post 66. Either the looped portions 77 and 78 or the helix portion 79-may be sufiicient to balance the inductances from the binding posts 59 and 60 to the end terminals of the conductors 50 and 52, respectively, or they may be utilized in combination as illustrated. It will also be apparent that an inductance from the end terminal portion of the conductor 51 to the binding posts 59 and 60 might be provided in other ways obvious to those skilled in the art.

An approximate equivalent circuit of the switch thus far described, in either operative position, is illustrated in Figure 4 wherein reference numeral 80 designates an inductance equivalent to the inductance between the terminal end portion of the conductor 51 and the binding post 59 or 60, reference numeral 81 designates an inductance equivalent to the inductance between the binding post 59 or 60 and the terminal end of the associated conductor 50 or 52and reference numeral 82 designates a capacitance equivalent to the capacitance between the threaded end portions of the binding posts 59 and 60 and the housing 24. In practice, this is a good approximation to the actual circuit of the switch since the inductances 80 and 81 and the capacitance 82 may be sufliciently great with respect to any stray inductances or capacitances for the stray inductances and capacitances to have a negligible value in respect thereto.

It will accordingly be apparent that the switch subassembly 21 thus far described, in either operative position, is effectively a substantially symmetrical low-pass T lter section. Figure is a graphical illustration of the characteristic impedance Zo vs. frequency for such a low-pass filter section. It will be noted that the characteristic impedance Zn is substantially constant and equal to \/L/ C up to an intermediate frequency fi after which it gradually increases and approaches zero at the cut-off frequency fc of the filter. In the formula Zo=\/'L/C, L is the total series inductance and C is the shunt capacitance.

Figure 6 is a plot of the voltage standing wave ratio VSWR vs. frequency for such a filter. Voltage standing wave ratio is conventionally used as a measure of performance of switches and other electrical devices. it will be noted that the VSWR for such a filter is substantially unity up to the intermediate frequency fi and then gradually increases approaching infinity at the cutoff frequency fc. It has been determined mathematically and confirmed by experiment that the cut-off frequency fc for such a filter is equal to It will now be apparent that the switch may have a substantially constant characteristic impedance and a voltage standing wave ratio substantially equal to unity over a wide range of frequencies by making the cut-ofi frequency fc several times the maximum operating frequency of the switch. It is, of course, necessary that the characteristic impedance Zu be equal to the characteristic impedance of the lines connected to the switch to prevent any mis-match and associated reliections and standing Waves. It may be noted that the graphs of Figures 5 and 6 are based on the assumption that the switch is terminated in a resistive load equal to the \/L/C.

The two equations Za=\`/L/C and With these equations the switch may be designed for optimum performance, keeping in mind that the cut-off frequency fc should be several times the maximum operating frequency of the switch.

The switch sub-assembly 22 may be constructed in a manner substantially identical to the switch-sub-assembly 21, and herein includes a connector 8S and an insulated conductor 86 corresponding to the connector 43 and conductor 50 of the sub-assembly 21, a connector 87 and an insulated conductor 88 corresponding to the connector 45 and conductor 52, arms 89 and 9G corresponding to the arms 57 and 58, contacts 91 and 92 corresponding to the contacts 63 and 64, posts 93 and 94 corresponding to the posts 59 and 60, an eccentric cam of dielectric material and a connector and associated conductor (not shown) corresponding to the connector 44 and conductor 51.

If desired, the two switch sub-assemblies may be used together for switching of two or three conductor balanced lines. For example, a three-conductor balanced line may be connected to the switch with two conductors of the line connected to the conductors 52. and 88 and the third conductor connected to the housing. in such a case, the switch is, in effect, two symmetrical T filter sections in opposed relation to form an H filter section. Other modifications, both in structure and use will, of course, be apparent to those skilled in the art.

A modified construction is illustrated in Figures 7 and 8. This construction may be used in an assembly such as illustrated in Figures l and 2 in which Figure 7 may be a cross-sectional view corresponding to Figure 2. As shown in Figure 7, this modified switch sub-assembly is generally designated by reference numeral 97 and includes a housing 98 which may be identical to the housing 24 of the sub-assembly 21, a connector 99 and a conductor 100 corresponding to ,the connector 43 and conductor 50, a connector 101 and a conductor 102 correspondingv tothe yconnector 44 fand.- conductor 51,-

and a connector 103 and conductor 104 corresponding to the connector 45 and conductor 52. This modified construction also includes binding posts 105 and 106 generally corresponding to the binding posts 59 and 60, arms 107 and 108 pivotally mounted on the posts 105 and 106 and a spring 109 urging the arms 107 and 108 toward each other and toward a central motor-driven shaft 110 corresponding to the shaft 29 of the switch sub-assembly 21. Mounted on the shaft-110 is an eccentric cam member 111 of insulating material and held against rotation on the shaft by a pin 112. On rotation of the shaft, the eccentric cam 111 alternately moves the arms 107 and 108 outwardly;

For conduction of alternating current between the arms 107, 108 and the conductors 100, 104, respectively, a pair of plates 114 and 115 are attached to the arms 107 and 108, respectively, and are alternately moved into closely spaced relation to plates 116 and 117 on the conductors 100 and 104, respectively. The posts 105 and 106 are operably connected to the conductor 102 by means of a connector bar 118 disposed between the posts, a plate 119 secured to an intermediate portion of the bar 118.and a plate 120 disposed in closely spaced relation to the plate 119 and secured to the conductor 102. The plates 119 and 12.0 deiine a capacitance for conduction of alternating current. This capacitance defined by plates 119 and 120 is preferably substantially equal to the capacitance defined by the plates 115 and 117 or the plates 114 vand 116 in operative relation, and an inductance is provided from a point intermediate the capacitances to' the housing. v

Referring to Figure 8, the posts 105 and 106 herein have looped intermediate portions 121 and 122, respectively, which provide a path of current flow of increased length and thereby an increased inductance. As in the case of the irst embodiment described, the posts 105 and 106 have threaded end portions engaged in internally threaded insulating plugs 123 and 124, respectively, which are, in turn, secured in recesses in the housing 98.

It will be apparent that, from a mechanical standpoint, the construction from Figures 7 and 8 is highly desirable since there is very little friction between .the parts in operation and an extremely high speed operation is possible.

An approximate equivalent circuit of the switch construction of Figures 7 and 8 is illustrated in Figure 9 in which capacitance 127 is equivalent to the capacitance provided by plates 119 and 120, capacitance 128 is equivalent to the capacitance defined by the plates 114 and 116 or the plates 115 and 117 in operative position, inductance 129 is equivalent to Athe inductance defined by the post 105 or the post 106, and capacitance 130 is equivalent to the capacitance defined by the threaded end portions of the post 105 or 106 and the facing surfaces of the housing 98, together with the associated dielectric. The circuit of Figure 9 is a good approximation of the actual circuit defined by the switch structure of Figure 7 since the capacitances and inductances may have values such that stray inductances and capacitances are negligible in relation thereto.

It will be apparent that the circuit defined by the switch of Figure 7, as illustrated in Figure 9, defines a substantially symmetrical high-pass T filter section. Figure is a graphical illustration of the variation of characteristic impedance of such a lilter section with frequency. It will be noted that the characteristic impedance Zo is substantially zero at the cut-off frequency fc and rises with increasing frequency, being nearly equal to \/L/ C at an intermediate frequency fi, and substantially equal to x/L/ C at frequencies greater than the intermediate frequency fi.

Figure ll is a graphical illustration of the voltage standing wave ratio VSWR plotted against frequency. It will be noted that the voltage standing wave ratio is substantially infinite at the cut-off frequency fe and gradually decreases with increasing frequency so that it is substantially equal to unity at an intermediate frequency f1 and at frequencies greater than fi. Accordingly, by making the cut-off frequency fc a fraction of the minimum operating frequency of the switch, a substantially constant characteristic impedance may be obtained with a voltage standing wave ratio substantially equal to unity over a, wide range of frequencies. g-

6 For design of the switch of Figufes '7 and 8, the following equations may be used: f

Z0 lirfc close to fc, M is preferably 0.6, although higher values upl to unity are satisfactory.

T he above equations may be combined to give the lowing equations:

This invention accordingly providesa. switch which may be readily andecononiically constructed, whichV is reliable in mechanical operation even at high speeds, and which can be used over a wide range of frequencies without introducing reflections or standing waves and associated ineicient power transfer.

If desired, the switch of this` invention maybe constructed to approximate a symmetrical 1r filter section having similar characteristiclsto the symmetrical j filter section above described.

Other modifications and Vvariations may, of course, be`

effected without departing from thespirit and scope'of the novel concepts of the present invention.

I claim as my invention:

l. In an electrical switch for connecting transmission lines or the like, a housing, at least arpair of conductors insulated from said housing each arranged' for connection to one terminal of a line, me'ans'for connecting other terminals of lines to said housing, means in said housing connecting said conductorsl including switch means actuatable to transmit alternating current, support' means affixed in said housing and'connected to said connecting means at an intermediate point between said conductors, said connecting means and said conductors being constructed and arranged to provide substantially equal series reactances at either side of said intermediate point, and

said support means being constructed and arranged tov series reactances to thereby provide a substantially symmetrical T iilter section.

2. In an electrical switch for connecting transmission lines or the like, a housing, at least a pair of conductors insulated from said housing each arranged for connection to one terminal of a line, means for connecting other terminals of lines to said housing, means in said housing connecting said conductors including switch means actuatable to transmit alternating current, said connecting means and said conductors being constructed and arranged to provide series capacitances, and support means aixed in said housing and connected to said connecting means, said support means being constructed and arranged to provide a parallel inductance cooperating with said series capacitances to define a high-pass filter section pass band thereof.

' 3. In an electrical switch, a housing, at least two conductors insulated from said housing, support means aiiixed in said housing, switch means movably supported on said support means and actuatable into an operative position in alternating current conductive relation with respect to one of said conductors, means connecting said switch means to another of said conductors for transmission of alternating current therebetween, said switch means together with said one conductor having a predetermined reactance in said operative position of said switch means, said connecting means and said another conductor being constructed and arranged to provide a reactance substantially equal to said predetermined reactance, and said support means providing a reactance of opposite sense with respect to the above-mentioned reactances to thereby provide a substantially symmetrical T filter section.

4. In an electrical switch, a housing, at least two conductors insulated from said housing, support means affixed in said housing, switch means movably supported in said support means and actuatable into an operative position in alternating current conductive relation with respect to one of said conductors, said switch means together with said one conductor defining a first inductance, means connecting said switch means to another of said conductors for transmission of alternating current therebetween and defining therewith an inductance substantially equal to said first inductance, and said support means providing a capacitance thereby providing a substantially symmetrical low-pass T filter section.

5. In an electrical switch, a housing, at least two conductors insulated from said housing, support means atiixed in said housing, switch means movably supported on said support means and actuatable into an operative position in alternating current conductive relation with respect to one of said conductors, said switch means together with said one conductor defining a first capacitance, means connecting said switch means to another of said conductors and defining therewith a capacitance substantially equal to said first capacitance, and said support means defining an inductance thereby providing a substantially symmetrical high-pass filter.

6. In an electrical switch, a housing, at least two conductors insulated from said housing, a post affixed in said housing, a switch member pivotal on said post and actuatable into an operative position in alternating current conductive relation to one of said conductors, and means connecting said post to another of said conductors, said switch member together with said one conductor defining a first reactance, said connecting means together with said another conductor defining a second reactance substantially equal to said first reactance, and said post providing a reactance of opposite sense with respect to the above-mentioned reactances to thereby provide a substantially symmetrical T filter,

7. ln an electrical switch, a housing, at least two conductors insulated from said housing, a post afiixed in said housing, a switch member pivotal on said post and actuatable into an operative position in alternating current conductive relation to one of said conductors, and means connecting said post to another of said conductors, said switch member together with said one conductor defining a first inductance, said connecting means together with said another conductor defining a second inductance substantially equal to said first inductance, and said post providing a capacitance to thereby provide a substantially symmetrical low-pass filter.

8. In ari electrical switch, a housing, at least two conductors insulated from said housing, a post aixed in said housing, a switch member pivotal on said post and actuatable into an operative position in alternating current conductive relation to one of said conductors, and means connecting said post to another of said conductors, said switch member together with said one conductor defining a first capacitance, said connecting means together with said another conductor defining a second capacitance substantially equal to said first capacitance, and said post providing an inductance to thereby provide a substantially symmetrical high-pass filter.

9. In an electrical switch, a housing, at least two insulated conductors in said housing, a post, means supporting said post in said housing, an arm pivotal on said post, means for actuating said arm between operative and inoperative positions, said arm having means thereon cooperating with one of said conductors to establish alternating current conductive relation therebetween in said operative position of said arm, means connecting said post to the other said conductors for conducting of at least alternating current, said arm together with said one conductor defining a first reactance, said connecting means together with said other conductor defining a second reactance substantially equal to said first reactance, and said supporting means and said post defining a third reactance between said housing and a point intermediate said arm and said connecting means to thereby provide a substantially symmetrical reactive T filter section.

10. ln an electrical switch, a housing, at least two insulated conductors in said housing, a post, means supporting said post in said housing, an arm pivotal on said post,- means for actuating said arm between operative and inoperative positions, said arm having means thereon cooperating with one of said conductors to establish alternating current conductive relation therebetween in said operative position of said arm, means connecting said post to the other said conductors for conducting of at least alternating current, said arm together with said one conductor defining a first inductance, said connecting means together with said other conductor defining a second inductance substantially equal to said first inductance, and said supporting means and said post defining a capacitance between said housing and a point intermediate said arm and said connecting means to thereby provide a substantially symmetrical low-pass T filter section.

11. In an electrical switch, a housing, at least two insulated conductors in said housing, a post, means supporting said post in said housing, an arm pivotal on said post, means for actuating said arm between operative and inoperative positions, said arm having means thereon cooperating with one of said conductors to establish alternating current conductive relation therebetween in said operative position of said arm, means connecting said post to the other said conductors for conducting of at least alternating current, said arm together with said one conductor defining a first capacitance, said connecting means together with said other conductor defining a second capacitance substantially equal to said first capacitance, and said supporting means and said post defining an inductance between said housing and a point intermediate said arm and said connecting means to thereby provide a substantially symmetrical high-pass T filter section.

12. ln an alternating current electrical switch for connecting transmission lines or the like and operating over a range of frequencies, a housing, at least two conductors adapted forV connection to said line and insulated from said housing, support means affixed in said housing, switch means movably supported on said support means and actuatable into alternating current conductive relation with respect to one of said conductors, and alternating current conductive connection means between said support means and the other of said conductors, said switch means together with said one conductor defining a first inductance, said connection means together with said other conductor defining a second inductance substantially equal to said first inductance, and said support means defining a capacitance between said housing and a point intermediate said inductances substantially according to the formulas L and C:

i switch means movably supported on said support means and actuatable into alternating current conductive relation with respect to one of said conductors and alternating current conductive connection means between said support means and the other of said conductors, said switch means together with said one conductor defining a rst capacitance, said connection means together with said other conductor defining a second capacitance, and said support means dening an inductan and a third capacitance in series between said housing and a point intermediate said capacitances, substantially according to the formulas where L is said inductance, C1, C2 and C3 are said rst, second and third capacitances, respectively, Zo is the characteristic impedance of said transmission lines and fc is the frequency less than the minimum operating frequency of the switch.

14. A switch assembly comprising: a pair of subassemblies each including a housing; iirst, second and third conductors insulated from said housing; said support means in said housing; switch means movable on said support means and actuatable alternately into con- 0 Number ductive relation to said first and second conductorsgrand means connecting said switch means to said third conductor; said switch means and each of said first and second conductors in conductive relation together dening a rst reactance; said connecting means and said third conductor defining a second reactance substantially equal to said first reactance; and said support meansdefining a third reactance between said housing and a point intermediate said first and second reactances; each sub-assembly in either aperture position of said switch means thereby defining a substantially symmetrical reactive T filter section; and said housings of said pair of sub-assemblies being connected together to connect said T lter sections in opposed relation thereby to define substantially symmetrical reactive H filter-sections.

References Cited in the file Vof this patent UNITED STATES PATENTS Name Date Chaffee Mar. 18, 1941 Patterson Dec. 3, 1946 Creaser June 24, 1952

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