US2475464A - Switch for radio-frequency currents - Google Patents

Description

y 1949- R. G SHANKWEILER 2,475,464

' SWITCH FOR RADIO-FREQUENCY CURRENTS Filed April 8, 194

*g i i 57 INN/ HIE I INVENTOR. RHY 13.5HHNKWEILER Patented July 5, 1949 SWITCH FOR RADIO-FREQUEN CY CURRENTS Ray G. Shankweiler, Cranbury, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application April 8, 1944, Serial No. 530,220

2 Claims.

This invention relates to improvements in switches and has for its principal object to provide an improved switch for high frequency work, and one characterized by its freedom from coupling problems and by its freedom from undesired radiation beyond the switching points.

Another and important object of the invention is to provide an improved and compact bank or assembly of sequence switches for radar and other electrical systems of the type wherein the several radio and audio frequency channels are designed to be operated in a desired sequence and at a certain rate.

Another and specific object of the present invention is to provide an improved motor-driven switch assembly for synchronously switching (a) an audio circuit, (b) a radio frequency circuit, a modulating circuit, and wherein the switching rate for the modulator circuit is at some fixed multiple of the switching rate for the radio frequency and audio circuits.

While the invention will be described as applied to a switch assembly for a frequency modulated radio locater system, such as the one described in Patent No. 2,459,457, January 18, 1949, resulting from copending application Serial No. 527,292, filed March 20, 1944 in the name of Royden C. Sanders, Jr. and entitled Comparator circuits for radio locators, it is to be understood that the disclosure in this respect is merely illustrative and 1 should not be interpreted in a limiting sense.

Other objects and advantages together with certain preferred details of construction will be apparent and the invention itself will be best understood by reference to the following specification and to the accompanying drawing, wherein:

Figure l is a sectional elevation of a switch panel including a switch assembly wherein the switch elements are designed, positioned and arranged in accordance with the present invention,

Figure 2 is a side elevational view partly in section showing the switch panel of Fig. 1 supported upon a driving motor, and

Figure 3 is a sectional view taken on the line IIII1I of Fig. 2.

In the drawing I designates the casing of a motor or dynamotor having a gear box 3 mounted on one end thereof as by means of a bracket 5 (Fig. 3). The motor has a main shaft I which extends beyond the end of the casing I and term-inates, within the gear box 3, in a reduction gear mechanism comprising a driving gear 9, a driven reduction gear I I, and a stub shaft I3 upon which the driven gear II is fixed. The front surface to of the gear box 3 comprises a switch panel and the stub shaft I3 extends to the front of the said panel at which point it is provided with an eccentrically mounted ball bearing or cam I5 which serves, in a manner later described, to drive a pair of single-pole, double-throw switches I1 and I9, respectively. A similar cam 2| (see Fig. 3) is affixed to the opposite end of the main shaft '1 and provides a reciprocating motion for opening and closing a single-pole, single-throw switch 23. As shown in Fig. 3 the switch 23 is mounted upon an insulating panel or disc 25 which is received within the casing I of the motor. This single-pole, single-throw switch 23 comprises a spring metal arm 21, which is secured to one end of the panel 25 as by means of a stud 29. The switch arm 21 is provided at its free end with a contact 3I. A cam follower 33, constituted of insulating material, is mounted intermediate the ends of the arm 21 and is biased (by the spring action on the said arm) to bear against the peripheral surface of the eccentrically mounted cam 2|. The contact 3| on the free end of the arm 21 is in register with a second contact which is carried by a U-shaped member 3'! constituted of spring metal. The part 3'! is secured, on one of its legs, to a rigid conductive arm 33% which is supported on a stud on the panel or disc 25. The flexible arm of the U which carries the contact 35 is biased outwardly into engagement with a flexible stop 4| Which may be bent, if desired, to fix the initial spacing between the contacts 3| and 35 and thereby control the interval between the closing of said contacts.

The reed 21 of switch 23 (Fig. 3) is made so that its mass is high as compared to the mass of the receiving contact 31. The spring tension of the reed 21 against the cam 2| is low, however, as compared to the spring tension of receiving contact 31 against the stop 4| In operation, the cam 2| is .in contact with the reed 33 and 21 only during the time that the contacts are separated. When the contacts are closed, the reed 27 is supported by receiving contact 37, since the spring tension of 31 is many times that of the reed 2?. During operation, at the instant the contacts make, the reed has energy stored in it due to its velocity toward the receiving contacts. This energy is dissipated by momentarily lifting the receiving contact 31 oif the stop 35. After the energy is dissipated, the receiving contact returns to its position against stop 35 since its spring tension is greater than the tension in reed 21. During this time, the cam 2! is not in contact with the reed 33 and 27. The break occurs when the cam again touches reed 21 and lifts it off the receiving contact.

The circuit connections for the single-pole, single-throw switch 23 of Fig. 3 have been omitted from the drawing; however, since its arms 21, 31 and its stop 4| are conductive it is apparent that all or less than all of them may be utilized. When this switch is employed in the frequency modulating sweep circuit of Sanders invention (Serial No. 527,292) the cam 2i ordinarily operates to maintain the contacts 3i and 35 closed during one-half of a complete cycle of revolution of the motor shaft 1'. In this case the main shaft 1 operates through the gear reduction mechanism 9, ll, l3 and cam l (at the opposite end of the motor casing) to maintain each pair of contacts on the single-pole double-throw switches H and I9 closed for a smaller (but ad- .iustable) predetermined portion of each cycle.

As previously indicated, one of the problems which the present invention solves is that of obviating undesired radiation in a compact assembly of sequence switches wherein one or more of the switches operate to make and break a circuit carrying currents of radio frequency. in the usual (i. e. manually actuated) switch for selectively connecting one coaxial cable to another electrically similar cable, coupling problems may be minimized by so constructing the switch elements that they possess substantially the same characteristic impedance, per unit length, as the cables which they are designed to connect. In such a case the switch housing forms a continuation of the outer (grounded) conductor of the cable and the shaft for actuating the switch is connected to the said grounded conductor through the bearings on which the shaft rotates so that undesired radiations at the switching point are prevented from being broadcast. While the use of bearings and a grounded actuating shaft are quite satisfactory in manually actuated switches, the friction incident to the operation of such switches makes them undesirable in a motor driven sequence-switch assembly designed for continuous operation. The present invention may therefore be said to reside, in part, in the provision of a switch wherein undesired radiations are confined to the switch cavity, (and thereby prevented from affectin nearby circuits) without the use of a grounded shaft or equivalent friction-type connection.

As shown in Fig. 1, each .of the switches I1 and it comprises a metal arm or reed 43 having contacts 45 and 45a on its opposite faces and two stationary leads 4'! and 49 arranged along an axis normal to its reed 45. An insulating extension 43a and a mechanical coupling 43 between the cam l5 and the said insulating extensions 43a serves to drive both reeds at a rate determined by the speed of the main shaft E (Fig. 2) and the ratio of its gears 9 and H.

The receiving contact on each of the stationary leads 4?, 49 comprises a bowed spring 51 and a p 5 p s 5| are restrained by their stops 53 in the position shown in the drawing. Since the amplitude of the vibrating reed 153 is fixed, the time during which the contacts make can be changed by moving one or both of the receiving contacts away from or closer to the reed. Adjustment is accomplished by bending one or both of the stops 53.

Each of the single-pole double-throw switches ll and i9 is provided with a hollow T-shaped casing iii and 5t respectively. The vibrating reed lid of each switch is supported on an insulating insert i5! within the bore of the leg of the T and a similar insert 63 is provided in each cross arm of the T for supporting the leads 3'? and as for the receiving contacts bl. It will be understood that when either switch (say switch it) is to serve a radio frequency transmission line the leads (ll, 49, and reed 43, 33a for that switch, its casing 59 and the cavity 59a therein, and the insulating inserts 6!, 63 should preferably be so dimensioned as to constitute an electrically matched continuation of the inner and outer conductors of the transmission line to which the branches of the T are to be connected. (Thus, in the case of switch It, the dimensions of the said parts and the size of the cavity 59a was, in Sanders case, so proportioned that the surge impedance through the switch was of the order of ohms.) For the purpose of making such connections to the switch it each branch of its casing 59 is provided with one or more threaded ports 65 for receiving a complementarily threaded coupling bl (Fig. 2) for the outer conductor of the transmission line. In the instant case each arm of the casing is provided with two ports arranged at an angle of and the port which is not in use is closed by a threaded cap 69.

The construction and operation of switches ll and i9, is quite different from that of switch 23 of Fig. 3. In the case of switches l"; and the mass of the vibrating reed 43, 42a is of no consequence since the reed is driven positively by means of the eccentrically mounted ball hearing and connecting member 48. The displacement of the reed is determined entirely by the position of the eccentric. During its excursion from side to side, the reed alternately contacts the receiving contacts 5| located on each side of the reed. As the reed moves to one side, it comes into contact with the receiving contact 5| on that side, lifting it off its stop 53. Since the driving force applied to the reed is practically unlimited as compared to the spring tension of El against its stop 53, the spring 5! is lifted off the stop and flexed an amount equal to the travel of the reed. The spring tension of 5| must be high enough to overcome any tendency it may have to bounce when it is struck by the reed. Here, as in switch 23, it is desirable that the mass of the receiving contact be as low as possible.

Reference has heretofore been made to the switch cavity 59a in which the contacts 43, 45 and 5! operate and to the fact that undesired radiation at the switching points is confined to the cavity (and thereby prevented from affecting nearby circuits) without resorting to the use of a grounded shaft or equivalent friction type connection. This is achieved, in accordance with the invention by making the aperture 591) (through which the insulating extension 43a vibration reed 43 extends to the exterior of the casing 59) small as compared to the wave length of the current which the switch is designed to handle. When thus proportioned, this aperture 591) may be said to comprise an electrical filter and, in any event, has been found to reject or to attenuate the high frequency field originating within the cavity and which might otherwise be radiated beyond the switch casing. Thi flfi t rr 59?) operates in both directions, that is to say, it serves to prevent the ingress as well as the egress of undesired radiations.

It will now be apparent that the present invention provides an improved bank or assembly of sequence switches for high frequency work and one characterized by its compactness, by its freedom from couplin problems and by its freedom from undesired radiations at or beyond the switching points.

What is claimed is:

1. A switch assembly comprising a switch adapted to pass radio frequency currents of predetermined wave length and at least one other switch mounted adjacent to said radio frequency switch, said radio frequency switch comprising a casing having a cavity and an aperture which communicates with said cavity, a plurality of switching elements within said cavity and a lever arm for actuating said switching elements extending from the interior of said cavity through said aperture out of contact with said casing to a point intermediate said switches, supply means for applying radio frequency currents of said predetermined wave length to said switching elements, a lever arm for actuating said other switch terminatin adjacent to said point, common actuating means for said lever arms, said first mentioned lever arm being constituted of insulating material and the dimensions of the aperture in said casing through which said insulating lever arm passes being small as compared to said wave length whereby the electric field about said switching elements within said cavity is prevented from being transmitted through said aperture to said adjacent switch.

2. A switch assembly comprising a motor having a housing and a rotatable shaft which extends through said housing, a switch within said housing and including an actuating element coupled in direct driven relation with said rotatable shaft, a gear box mounted on said housing, a plurality of switches mounted in closely spaced relation on said gear box, means for applying radio frequency currents of a predetermined Wave length to at least one of said switches, said one of said switches comprising a casing having a cavity containing the contact elements of said switch and an aperture through which the actuating element for said contact extends, the dimensions of said aperture being small as compared to said predetermined wave length and said actuating element comprising a lever arm constituted of insulating material, whereby the electric field within said cavity is prevented from being transmitted through said aperture and affecting said other switches, and means connecting said radio frequency switch in sequential operating relation with respect to said other switches through said gear box.

RAY G. SHANKWEILER.

REFERENQES CITED The following referenices are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 653,936 Murray July 17, 1900 731,056 Jones June 16, 1903 1,541,497 Herz June 9, 1925' 2,180,948 Basset Nov. 21, 1939 2,235,010 Chaffee Mar. 18, 1941 2,264,124 Schreiner Nov. 25, 1941 2,312,723 Llewellyn Mar. 2, 1943 2,341,390 Scott Feb. 8, 1944 2,408,779 Jenks et al Oct. 8, 1946 2,417,542 Carter Mar. 18, 1947

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