US2711519A - Lead-in system for rotatable antennas - Google Patents

Description

June 1955 E. L. BARRETT LEAD-IN SYSTEM FOR ROTATABLE ANTENNAS Filed June '7, 1951 Inventor 6U Efgward L.Barrefi l a; 0 E yt/Alg,

Unite States Patent LEAD-1N SYSTEM FOR ROTATABLE ANTENNAS Edward L. Barrett, La Grange, lll., assignor to Donald B. Alexander, Edgar R. Bourke, Henry T. Chamberlain, John F. Mannion, Ernest W. Schneider, Walter A. Wade, and Charles S. Vrtis, not individually, but as trustees of The Arthur J. Schmitt Foundation, a charitable trust Application June 7, 1951, Serial No. 230,267

2. Claims. (Cl. 339-5) The present invention relates to a lead-in system for rotatable antennas and more particularly to a lead-in system involving the use of slip rings whereby the incoming signal received by the rotatable antenna may be conducted without interruption or distortion to the receiver associated with the antenna for amplification purposes in the usual manner.

The present invention has been designed for use and is illustrated herein in connection with a directional control system wherein means are provided for rotating the antenna mast, associated with a television receiver, under the control of the operator at the television receiver location. The present application disclosescertain aspects of this directional control system which are disclosed in greater detail and also claimed in my co-pending applications as follows: Serial No. 230,266, filed June 7, 1951, and entitled Directional Control Mechanism for Antennas; Patent No. 2,692,745, issued October 26, 1954, and entitled Antenna Mast Clamp; and Patent No, 2,668,920, issued February 9, 1954, and entitled Antenna Rotator. It will be understood, however, that the principles of the invention are aplicable for use in the leading in of all manner of Hertzian waves or signals regardless of the particular type of rotatable antenna structure by means of which they are received.

Because of the relatively high frequency employed in connection with the transmission of television signals, these signals are directional and are possessed of a limited range. In order to increase the possibility of signal reception, the antennas for receiving such signals are ordinarily mounted as high as practicable above the earths surface and in order to attain maximum signal strength from the different transmitting stations, the receiving antennas are frequently mounted for rotation in azimuth so that they may readily be oriented in the direction of the particular transmitting station whose signal is to be received.

For antennas which rotate throughout only 180 it is a relatively simple matter to bring off feeders from the antenna to the receiver by leaving enough slack in a short length or section of the feeder at the region where it leaves the rotating antenna mast. Sutficient slack is pro- 5 vided so that there is no danger of twisting of the feeder line. This method is also capable of use with antennas that rotate throughout a full 360 but a stop is necessary to avoid undue twisting and jamming of the feeder line. Obviously with such antennas, provision must be made for rotating the same in opposite directions to attain the desired directivity.

For antennas which are capable of continuous rotation, the use of sliding contacts has heretofore been resorted to. However, the use of such sliding contacts has presented numerous diificulties chief among which has been the problem of maintaining all sections of th transmission circuit in conformity with the characteristic impedance of the transmission line so as to minimize the eifect thereon.

It has frequently been stated that the transmission line connecting the antenna and receiver is as important a 2,711,519 Patented June 21, 1955 ICC factor in obtaining the correct signal input to the receiver as is the antenna itself. A transmission line is primarily intended to provide a ready path for the television signal from the antenna to the receiver, with a minimum amount of signal loss. To adequately provide this ready path, the transmission line must match the impedance of the antenna to the input impedance of the television receiver. The characteristic impedance value of a transmission line is not a direct function of the length of the line and the series resistance per unit length of line is negligible. The characteristic impedance of a transmission line is represented by a relationship between the inductance and capacitance per unit length of line. For the ribbon type of twin lead transmission line commonly employed in connection with home television receivers, the characteristic impedance of the transmission line is also a function of the distance between the centers of the wires employed, the diameter of the wire, and of a dielectric constant which may vary in accordance with the nature of the dielectric material surrounding the wires.

Many of the difliculties encountered in connection with the use of sliding contacts for lead-in purposes arise by virtue of varying inductance and capacitance values occasioned by virtue of the positioning of the Wires in the vicinity of the sliding contacts and of their positioning with relation to the particular installation employed, especially with respect to any surrounding protective casing which may be employed as well as with respect to any metallic supporting elements for holding the stationary and moving parts in position. These varying values of induction and capacitance have a pronounced effect upon the characteristic impedance of the transmission line and one conducive toward something less than maximum signal energy transfer to the television receiver.

In addition to the problem of conformity with the characteristic impedance of the transmission lines, previous efforts to design a suitable sliding contact type of connection for transmission lines connecting the antenna and television receiver have been generally unsatisfactory in that trouble has been experienced in making the contact surfaces wide enough to accommodate the wobble ordinarily encountered in the rotating antenna mast. Widening of the contacts has altered the inductance and capacitance values of the line and furthermore the impracticability of maintaining the widened contacts clean has lead to intermittent continuity in the line.

The present invention is designed to overcome many of the limitations that have heretofore been attendant upon the use of sliding connections for antenna transmission lines and toward this end it contemplates the provision of a novel type of slip ring construction wherein adequate contact between moving and floating or wiper contact surfaces of the construction is at all times attained while at the same time the variation in the overall char acteristic impedance of the lead-in circuit is reduced to a minimum.

The provision of a slip ring construction of the character briefly outlined above being the principal obiect of the invention, another object is to provide a slip ring construction in which the floating or wiper contact elements thereof make contact with the moving contact surfaces throughout a relatively wide area without varying the inductance or capacitance values of the line at the regions of sliding contact.

A similar and related object is to provide a slip ring construction in which the take olf wiper arms are formed of resilient material and in which the free ends thereof are grooved so as to receive the peripheral edges of the slip rings, thereby creating a sliding and interlocking connection between the parts so that, despite any misalignment arising by virtue of wobble encountered in the rotating antenna mast, adequate contact and alignment 3 between the slip rings and take off wiper arms will be maintained.

Another object of the invention is to provide such a slip ring construction wherein, despite such wide areas of contact between the stationary and moving parts thereof a selfcleaning action takes place which is conducive toward continuity of electrical contact between these parts.

Another object of the invention is to provide an antenna rotating mechanicm including a driving motor for operatively rotating an antenna mast together with a slip ring construction which is interposed in the electrical trans mission line or feeder leading from the antenna to the receiver and having associated therewith dielectric supporting elements for the stationary parts of the slip ring construction which, in addition to serving their supporting function for the stationary parts, also constitute dielectric conducting sheaths for guiding the electric power line wires leading to the antenna driving motor for the purpose of minimizing leakage conductance, inductance and capacitance between these latter wires and the transmission line.

A still further object of the invention is to provide a slip ring construction of this character in which, although the distance between the centers of adjacent conductors may vary in the region of the slip ring construction, the

effect on the characteristic impedence of the transmission circuit as a whole is not appreciable due to the fact that no large surface areas of the opposed conductors are brought into contiguity.

Another object of the invention is to provide a rotatable antenna mast support structure having associated therewith a lead-in slip ring construction which is completeiy shielded from outside atmospheric conditions.

Convenience of arrangement of parts, simplicity of construction and corresponding inexpensive manufacture are further desirable factors that have been borne in mind in the production and development of the present invention.

In the accompanying single sheet of drawings forming a part of this specification, one embodiment of the invention is shown.

in these drawings:

Figure l is a fragmentary, perspective view of an erected rotatable antenna mast to which the improved lead-in system comprising the present invention has been applied. ig. 2 is a sectional view taken along the line 22 of Referring now to Fig. 1 of the drawings, the antenna installation to which the present lead-in construction is applied may be of the conventional simple half-wave dipole antenna (not shown) which is suitably mounted upon a rotatable antenna mast section it). A fixed mast section 12 is disposed in coaxial alinement with the rotatable amst section it and the two sections are coupled together for rotation of the section 16) with respect to the section 3.2 by means of a control assembly including a housing 14 in which is disposed all of the control elements and instrumentalities at the outlying antenna station for rotating the mast section under the control of an operator at the receiver location. The control instrumentalities contained within the housing 14 form no part of the present invention and reference may be had to my copending application, Serial No. 230,266 filed 4 is a sectional view taken substantially along the June 7, 1951 for a Directional Control Mechanism for Antennas for a full understanding thereof. The housing 14 is provided with a coaxially disposed, upwardly projecting, post 16 which is adapted to be inserted in the lower end of the rotatable mast section 12. In order to accommodate masts of various internal diameter, the post 16 is provided with a split conical bushing 18 therearound having an axial bore therein for reception of the post. it will be apparent that masts of relatively small internal diameter will engage the bushing 18 adjacent the upper region thereof while masts of larger internal diameter will move further downwardly on the bushing. The rotatable mast section 10 is mounted in coaxial relationship on the housing 14 by means of a supporting structure including an expansible and contractible clamping band 2% adapted to engage the mast section 10 at a region spaced upwardly above the housing 14 and a similar contractible band 22 is adapted to engage the housing 14. A series of struts or supports 24 serves to connect the two bands and 22 and maintain the rotatable mast structure or section upright.

The housing 14 is formed in two sections including an upper section 26 and a lower section 28, the two sections being suitably secured together as by means of attachment screws 30. Means are provided whereby a rotary connection is obtained between the housing 14 and the fixed mast section 12. This means forms no part of the present invention and for a full disclosure thereof reference may be had to my above mentioned patents and copending applications.

The upper end of the non-rotatable mast section 12 is adapted to be received within a clamping mechanism 32 including a plurality of axially extending clamping arms 34. Sectional clamping bands 36 which are in turn secured to the arms 34, complete the clamping mechanism 32. One of the clamping arms 34 serves to support thereon a terminal block 38 by means of which the circuit wires 40 leading from the control station to the motor employed for rotating the casing 14 and antenna mast 10 are connected to the antenna rotating assembly.

The lead-in transmission line Which extends from the antenna television receiver includes a length 42 (Fig. 4) which extends from the antenna proper into a well or extension 44 provided on the lower casing section 28, and a length 46 extending from the well portion 44 downwardly along the non-rotatable mast section 12 and leading to the television receiver at a remote receiver location. The two lengths 42 and 46 of transmission line are adapted to be electrically coupled together inside the well 44 by means of a slip ring construction designated in its entirety at 50 which is disposed Within the well portion 44, and which, in addition to establishing electrical communication between the lengths 42 and 46 also provides for the physical passage and electrical shielding of a the circuit wires 40 leading from the receiver location to the driving motor by means of which the casing 14 and mast 10 mounted thereon may be rotated continuously in one direction. The upper ends of the socket member 33 project into the well portion 44 of the casing section 28 and is provided with a central aperture 56 through which there extends a threaded shank 58 provided on a cylindrical, central supporting post 60 (Fig. 3). The lower region of the post 60 is provided with a shoulder 62 which bears against a sealing plate 64 and a resilient ringlike sealing gasket 66 is positioned beneath the sealing plate 64 for receiving therein the inturned lower end 68 of the well portion 44 of the casing section 28. A clamping nut 71) and split washer 72 are received on the threaded shank 58 of the post 60 and serve to clamp the various parts together. The clamping arms 34, sealing plate 64 and resilient gasket 66 are nonrotatable but the well portion 44 and consequently the entire casing 14 and antenna mast 10 are capable of rotation with respect to the fixed parts of the assembly.

The upper end of the post 69 is provided with a shoulder 74 on which there is seated a supporting bracket which sup orts the driving mechanism for rotating the casing as well as the other electrical and mechaninstrumentalities of the rotational antenna control system. The driving mechanism has been fully described and illustrated in the above copending application and, for purposes of disclosure herein, it is deemed suificient to state that the bracket 75 serves to support thereon a motor M which operates through a train of gearing 76 (Fig. 1) including a ring gear 77 mounted in the upper section of the casing M to drive the casing, and, consequently, the rotatable mast section it) in a clockwise direction as viewed in Fig. 2. A threaded shank 7 8 provided on the post 64) extends through an opening '79 formed in the bracket s4, and a clamping nut 36 is received thereon to maintain the bracket 75 firmly in position on the end of the post 69.

The essential electrical elements of the thin sheet metal slip ring construction include a pair of slip rings 81 and i 52, and respective take- oil wiper arms 84 and 86. The terminals of the two lead wires associated with the length it: of the transmission line are electrically connected as by soldered joints S8 and 90 to the slip rings 81 and 82 respectively. The length 46 passes outwardly and downwardly from the well portion 44 of the casing 14 through a passage or slot as provided in the sealing gasket es. The length or section 42 of the transmission line extends 'nto a terminal block 94 which is anchored by means of screws within a rectangular opening 98 provided in the well casing. The leads of the section 42 are electrically connected to the terminal of the wiper arms 84 and 86.

The two slip rings 81 and 82 are supported in con centric relation about the center post 60 by means of a plurality of stand-ofi posts 1% of which there are three in number. For convenience, and conformity of manufacture, the stand-off posts 16% may be identical in con- .ruction and each consists of a hollow tubular member of dielectric material having cut away openings 102 at the top and bottom thereof respectively. One of the stand-oil posts serves as a conduit for passage therethrough of the circuit wires leading from the receiver location to the driving motor for the rotatable casing 14. The posts 1hr; are seated at their lower ends on a washer 101 of dielectric material which surrounds the post 60 and, in turn, rests upon the upper surface of the sealing plate 64.

The stand-oil posts are grooved as at 104 (Fig. 2) to receive the inner circular edge of the slip rings 81 and 82, and the rings are each provided with internally extending ears res which serve to hold the rings against rotational movement on the posts 100.

The rings 81 and 82 are formed of relatively thin, electrical conductive material, and the two rings are spaced apart vertically a distance somewhat greater than the distance between adjacent leads of the transmission line in order that there shall be no appreciable inter-capacitance effect between the rings tending to modify the characteristic impedance of the transmission line. The free ends of the wiper arms 84 and 86 are provided with contact elements or blocks 10:; per so having relatively narrow grooves ill) formed thereon into which the peripheral regions of the rings 31 and 32 extend when the wiper arms $4 and 36 are in assembled position within the well 44' of the casing 14. The peripheral regions of the rings 81 and $2 are thus engaged on opposite sides thereof as well as along the circular edge by the metallic surfaces of the contacts 1% and, inasmuch as the wiper arms 84 and 86 are of a flexible material, and are relatively long, the contact elements 1% will normally follow any deviation of the peripheral edges or" the rings 80 and 82 from a horizontal plane due to wobbling of the antenna mast, for example, or for any other reason whatsoever.

In assembling the slip ring construction described above, the post 64) may first be centered upon the inverted tubular socket member 33 and the nut 7 i) applied. Thereafter, the three stand-off posts 100 and sealing rings 31 and may be assembled in the respective relationship which they will occupy in the completed slip ring construction. This assembly may then be inserted over the post 69 so that the stand-oil posts seat upon the washer it'll. The assembled motor structure, including the supporting bracket 64, may then be applied to the upper end of the post 69 and the nut 86 applied so that the stand-oil posts 1th are centered between the washer 1G1 and bracket 64- as clearly shown in Fig. 4. The wiper arm assembly including the block 94 and wiper arms 8 and may then be placed in position within the opening K1 in the well 44. This operation may be effected by first alining the grooves lit) with the periphcries of the rings 8t and 82 and causing the latter to enter the slots, after which the entire assembly may be brought into position and secured by means of the anchoring screws 96.

It will be understood, of course, that the initial assembly of the slip rings S1 and 82 may be made as a factory installation and the wiper arm assembly 84, S6, 94 may e effected at the antenna location after application of the section 42 of the transmission line has been made to the insulating block 94 and electrical contact of the lead wires has been made with the wiper arms 34 and 86.

It is to be noted that by the above described arrangement, a sliding contact arrangement or slip ring construction has been provided which does not appreciably eifect the rated characteristic impedance value of the transmission line 42, 46. It is to be noted particularly that although one of the lead wires of the section 46 of the transmission line passes completely through the lower slip ring 82 in close proximity thereto, the areas of metal which are in immediate physical opposition and close proximity to each other are very minute so that no appreciable capacitance is set up between the opposed parts. The distance between the two slip rings 81 and S2 is sufficiently great that no inter-capacitance effect takes place. Furthermore, the motor lead-in wires 52, of which there are three in number in the present instance, pass upwardly through one of the dielectric stand-oil posts and present only very minute areas of opposition to the adjacent areas of the slip rings 81 and 82.

Finally, because of the fact that the section 42, which moves in unison with the rotating antenna structure, is led into the well portion of the housing 14 laterally and centrally through the relatively larger rectangular opening 98, and is anchored in an insulating block 94 of dielectric material, no appreciable capacitance, inductance, or other effects are set up that would alter the rated characteristic impedance of the transmission line.

The invention is not to be limited to the exact arrangement of parts shown and described in this specification, as various changes in the details of construction may be resorted to without departing from the spirit of the invention. Only in so far as the invention has particularly been pointed out in the accompanying claims, is the same to be limited.

I claim as my invention:

1. In an antenna rotator for rotating a directional antenna and electrically interconnecting the respective lead Wires of rotatable and non-rotatable sections of a transmission line leading from the antenna to a television receiver or the like, the combination comprising a stationary vertical cylindrical supporting post, a pair of thin vertically spaced horizontal slip rings for connection to the lead wires of the non-rotatable line section, said rings being disposed around the post coaxially therewith and having inner edges spaced outwardly from the post, a plurality of vertical dielectric spacing strips engaging the post at circumferentially spaced points and disposed between the post and the rings, said strips having vertically spaced grooves in which the inner edges of the rings are received, angularly spaced inwardly extending stops on said rings engaging each of said strips at its opposite sides for maintaining the strips in angularly spaced relation and preventing rotation of said rings relative to said strips, means on said post forming opposed shoulders engaging the opposite ends of said strips to hold the latter stationary, a casing surrounding said post and rotatably carried thereby for supporting the antenna, dielectric suporting means on said casing, and a pair of wipers mounted on said dielectric means and engaging said slip rings for connection to the lead wires of the rotatable transmission line section.

. In a motor driven antenna rotator for rotating a directional antenna and for electrically interconnecting the respective lead wires of rotatable and non-rotatable sections of a transmission line leading from the antenna to a television receiver or the like, the combination comprising a stationary vertical cylindrical supportnig post, a pair of thin vertically spaced horizontal slip rings for connection to the lead wires of the non-rotatable line section, said rings being disposed around the post coaxially therewith and having inner edges spaced outwardly from the post, a plurality of vertical dielectric spacing strips engaging the post at circumferentially spaced points and disposed between the post and the rings, said strips having vertically spaced grooves in which the inner edges of the rings are received, angularly spaced inwardly extending stops on said rings engaging each of said strips at its opposite sides for maintaining the strips in angularly spaced relation and preventing rotation of said rings relative to said strips, means on said post forming opposed shoulders engaging the opposite ends or" said strips to hold the latter stationary, one of said strips being hollow to provide a longitudinal passage therethrough for carrying motor control wires through said slip rings, there being cut-out portions in the outer wall of the hollow strip adjacent the ends theref to provide access to said passage, a casing surrounding said post and rotatably carried thereby for supporting the antenna, dielectric supporting means on said casing, and a pair of wipers mounted on said dielectric means and engaging said slip rings for connection to the lead wires of the rotatable transmission line section.

References Cited in the file of this patent UNITED STATES PATENTS 1,219,247 Carmichael Mar. 13, 1917 1,534,271 Koken Apr. 21, 1925 1,699,392 Fisher Jan. 15, 1929 2,359,351 Bruno Oct. 3, 1944 2,395,899 Morrow et al Mar. 5, 1946 2,451,959 Knudsen Oct. 19, 1948 2,557,074 Brooks June 19, 1951 2,565,334 Weingarden Aug. 21, 1951 2,570,784 Ferguson Oct. 9, 1951

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