Title:
COMBINED TELEVISION STAND AND ANTENNA SYSTEM
United States Patent 3604007
Abstract:
A combination stand or table and antenna system for television receivers, in which the legs of the stand are used as antenna segments. Two legs at opposite corners of the stand are used together to form one dipole antenna, and another pair of legs is used to form a second dipole antenna. A circuit is provided for varying the proportion of the signal which is delivered from each antenna to the receiver, thus effectively rotating the antenna system for best signal reception.
US Patent References:
Selective receiving apparatus for wireless telephone or telegraph sets
Pratt - September 1937 - 2093158
Antenna system
Case - July 1942 - 2291450
Directional antenna system
Root - May 1951 - 2552816
Circuit tuning device
Morton - September 1953 - 2654034
Simplified electrically steerable antenna
Mural - December 1953 - 2664507
Selective receiving apparatus for wireless telephone or telegraph sets
Pratt - September 1937 - 2093158
Antenna system
Case - July 1942 - 2291450
Directional antenna system
Root - May 1951 - 2552816
Circuit tuning device
Morton - September 1953 - 2654034
Simplified electrically steerable antenna
Mural - December 1953 - 2664507
Application Number:
04/813594
Publication Date:
09/07/1971
Filing Date:
04/04/1969
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
342/371, 343/797, 343/816, 343/722
International Classes:
H01Q1/44; H01Q1/00
Field of Search:
343/702,720,742,748,797,799,803,816,854,856,894
US Patent References:
Other References:
Cartoon from The Sunday Star, Washington, D.C., May 7, 1961; captioned "This New TV Table Gives Us Perfect Reception" 343-720.
Primary Examiner:
Saalbach, Herman Karl
Assistant Examiner:
Gensler, Paul L.
Claims:
I claim
1. A combination table and antenna system for television receivers, said combination comprising a table with a plurality of leg members made of conductive material and forming antenna segments, an upper support surface for supporting a television receiver above said leg members, and means for coupling the input terminals of a television receiver to selected ones of said leg members, said coupling means comprising a plurality of coils connected to said leg members, each of said coils having at least one loop and being arranged with its plane at an angle to the plane of at least one other of said coils, and a pickup coil movable relative to said first-named coils to vary the relative inductive coupling between the pickup coil and the first-named coils and thereby change the direction of maximum sensitivity of said antenna system.
2. Apparatus as in claim 1 in which each of said leg members has a horizontal conductive member coupled to it by means of an inductor whose impedance is high at UHF frequencies and relatively much lower at VHF frequencies.
3. Apparatus as in claim 1 in which said leg members are arranged symmetrically in opposed pairs, and in which said coupling means is operable to couple said receiver input terminals to a selected one of said pairs.
4. Apparatus as in claim 3 in which said coupling means is adjustable to deliver signals from a plurality of said pairs of elements simultaneously, in amounts variable in indefinite increments.
5. Apparatus as in claim 4 in which said coupling means includes a rotatable knob with an index mark on it, and a dial with corresponding index marks on it positioned adjacent said knob.
6. A television receiver stand, said stand comprising, in combination, a nonconductive support member, four vertical, symmetrically located legs fastened to said support member, each of said legs being made of conductive material, four horizontal elongated conductive stubs, each being connected at one end to one of said legs, said stubs being arranged in two pairs of opposed stubs, the stubs in each pair being aligned with one another and being perpendicular to the alignment of the other stubs, four inductors, each being connected between one of said stubs and one of said legs, a potentiometer with two opposed wipers and a complete annulus of resistive material making contact with said wipers, each of said stubs being connected to said resistive material at one of four symmetrically located points, and means for connecting said wipers to the input terminals of a television receiver, each of said inductors having an impedance which is high at UHF frequencies and relatively much lower at VHF frequencies.
7. A combination table and antenna system for television receivers, said combination comprising a table with a plurality of leg members made of conductive material and forming antenna segments, said leg members being arranged symmetrically in opposed pairs, and means for coupling the input terminals of a television receiver to a selected one of said pairs of leg members, said coupling means including a plurality of fixed coils, each connected to one of said leg members, each having at least one loop of wire, the planes of said loops which are connected to opposed leg members being parallel to one another, the planes of the loops of one pair of elements being perpendicular to the planes of loops of the other pair of elements, and a pickup coil rotatably mounted between said loops, and means for connecting said pickup coil to a television receiver.
1. A combination table and antenna system for television receivers, said combination comprising a table with a plurality of leg members made of conductive material and forming antenna segments, an upper support surface for supporting a television receiver above said leg members, and means for coupling the input terminals of a television receiver to selected ones of said leg members, said coupling means comprising a plurality of coils connected to said leg members, each of said coils having at least one loop and being arranged with its plane at an angle to the plane of at least one other of said coils, and a pickup coil movable relative to said first-named coils to vary the relative inductive coupling between the pickup coil and the first-named coils and thereby change the direction of maximum sensitivity of said antenna system.
2. Apparatus as in claim 1 in which each of said leg members has a horizontal conductive member coupled to it by means of an inductor whose impedance is high at UHF frequencies and relatively much lower at VHF frequencies.
3. Apparatus as in claim 1 in which said leg members are arranged symmetrically in opposed pairs, and in which said coupling means is operable to couple said receiver input terminals to a selected one of said pairs.
4. Apparatus as in claim 3 in which said coupling means is adjustable to deliver signals from a plurality of said pairs of elements simultaneously, in amounts variable in indefinite increments.
5. Apparatus as in claim 4 in which said coupling means includes a rotatable knob with an index mark on it, and a dial with corresponding index marks on it positioned adjacent said knob.
6. A television receiver stand, said stand comprising, in combination, a nonconductive support member, four vertical, symmetrically located legs fastened to said support member, each of said legs being made of conductive material, four horizontal elongated conductive stubs, each being connected at one end to one of said legs, said stubs being arranged in two pairs of opposed stubs, the stubs in each pair being aligned with one another and being perpendicular to the alignment of the other stubs, four inductors, each being connected between one of said stubs and one of said legs, a potentiometer with two opposed wipers and a complete annulus of resistive material making contact with said wipers, each of said stubs being connected to said resistive material at one of four symmetrically located points, and means for connecting said wipers to the input terminals of a television receiver, each of said inductors having an impedance which is high at UHF frequencies and relatively much lower at VHF frequencies.
7. A combination table and antenna system for television receivers, said combination comprising a table with a plurality of leg members made of conductive material and forming antenna segments, said leg members being arranged symmetrically in opposed pairs, and means for coupling the input terminals of a television receiver to a selected one of said pairs of leg members, said coupling means including a plurality of fixed coils, each connected to one of said leg members, each having at least one loop of wire, the planes of said loops which are connected to opposed leg members being parallel to one another, the planes of the loops of one pair of elements being perpendicular to the planes of loops of the other pair of elements, and a pickup coil rotatably mounted between said loops, and means for connecting said pickup coil to a television receiver.
Description:
This invention relates to antennas for television receivers, and to furniture especially adapted for use in supporting such receivers.
One very commonly used type of antenna for television receivers comprises a pair of telescoping arms (commonly called "rabbit ears") which can be adjusted to various different positions for best picture reception. The arms usually extend upwardly and outwardly from the top of the receiver. Such antennas have several undesirable features. One such feature is that it often requires a great deal of time and manipulation to adjust the antenna to the best position for a given station, especially since the optimum location of the arms for one station is difficult to remember. Furthermore, the telescoping arms often extend outwardly from the sides of the television set and are easily hit by people walking near the receiver. In hitting the antenna, the people are subjected to possible injury, and the antenna setting is changed. Still further, one usually must grasp the telescoping arms of the antenna to adjust it, thus adding the capacitance of his body to the antenna system and making the proper adjustment of the antenna more difficult.
One approach to the solution of these problems has been to provide, in the receiver housing, a plurality of opposed conductive elements fixed in position with respect to each other, each pair of opposed elements comprising a dipole antenna. Switching means are provided to switch the input terminals of the television receiver from one to another of the antenna pairs, thus effectively rotating the antenna without having to manipulate telescoping arms or the like. Typical examples of such prior art antenna systems are found in U.S. Pat. Nos. 2,602,892 to Koch, and No. 2,552,816 to Root. However, such prior systems are complicated and impractical to manufacture, or for other reasons are not suitable as replacements for the "rabbit ears" antenna.
It is an object of the present invention to provide a television antenna system which can be effectively rotated without the use of telescoping arms or "rabbit ears." Furthermore, it is an object to provide such an antenna system which is practical and inexpensive to manufacture, which provides a substantially infinite number of effective positions to which the antenna can be rotated, and which has a pleasing appearance.
The foregoing objects are satisfied, in accordance with the present invention, by the provision of a television receiver stand and antenna system for the receiver, in which antenna elements are incorporated into the legs of the stand. In the preferred embodiment, two metal legs located at opposite corners of the stand are used together to form one antenna, and two similarly positioned metal legs are used to form a second antenna. Continuously adjustable means is provided for varying the proportion of the signal which is delivered from each antenna to the receiver at a particular time, thus effectively rotating the antenna system, in steps of indefinite size, for best signal reception.
Further aspects and advantages of the invention will be set forth in or apparent from the following description and drawings. In the drawings:
FIG. 1 is a perspective view of one embodiment of the present invention;
FIG. 2 is a schematic perspective view of the antenna system of the structure shown in FIG. 1;
FIG. 3 is an electrical schematic circuit diagram of the antenna system shown in FIG. 2;
FIG. 4 is a perspective view of a component of the antenna system shown in FIGS. 2 and 3; and
FIG. 5 is a perspective, partially broken-away view of another embodiment of the invention.
FIG. 1 shows a rectangular television table or stand 10 with a television receiver 24 resting upon it. The stand 10 includes a top portion 12 made of nonconductive material such as wood or plastic, and four legs 14, 16, 18 and 20 secured to the top portion 12. Plastic wheels 22 are fastened to the bottoms of the legs. An antenna system (see FIG. 2) is incorporated in the table, and a knob 42 is provided at the front of the table for adjusting the antenna system.
As is illustrated in FIGS. 2 and 3, the legs 14, 16, 18 and 20 of the table 10 are used, in accordance with the present invention, not only to support the table, but also as antenna elements. Each of the legs is made of a conductive material such as metal, and preferably comprises a square or round metal tube. It is secured at its upper end to the top portion 12. The legs are positioned symmetrically at the four corners of the table.
Four horizontal metal tubes or stubs 26, 28, 30 and 32 are mounted in the upper portion 12 of the table. These tubes are arranged in pairs, the tubes in each pair being aligned with one another and extending between legs at opposite corners of the table. Each of the tubes is connected to the top portion of one of the legs by means of an inductor, 34, 36, 38 or 40. The other ends of the tubes are located adjacent one another near the center of the table, and are connected to a resistance bridge circuit 44 which is adjustable by means of the knob 42 at the front of the table.
Referring now particularly to FIG. 3, the resistance bridge circuit 44 comprises a potentiometer with a closed-loop resistance element 50 and a pair of opposed wiper arms 60 and 62 making contact with the resistance element 50. Each of the wiper arms 60 and 62 is connected to one input terminal of the television receiver 24 by means of a cable 68. The ends of the horizontal tubes or stubs 26, 28, 30 and 32 are connected to the resistance element 50 at four symmetrically located points.
FIG. 4 illustrates the preferred construction of the potentiometer. An insulating board 46 has an annular ring 50 of resistive material such as carbon coated on one surface. The resistive material 50 has four symmetrically located tabs 52, 54, 56 and 58, each of which is connected to one of the four tubes or stubs 26, 28, 30 and 32. Each of the wiper arms 60 and 62 is half moon-shaped, and has a pair of contact arms 64 or 65. Each of the wiper arms is bent so as to make contact with the resistance ring 50 at a point which is located centrally between the arms 64 or 65. The points of contact are located at an angle of 180° with respect to one another. The contact arms 64 of arm 60 make contact with a first conductive slipring 67 which is mounted on the insulating block. The contact arms 65 of the second wiper arm 62 make contact with a second slipring 66 which is smaller in diameter and inside of the first slipring 67. Conductive terminal posts (not shown) extend through the mounting board, each making contact with one of the sliprings 66 or 67. The cable 68 is connected to the terminal posts and thence to the receiver 24, as is shown in FIG. 3. The knob 42 is connected to a shaft made of low-loss nonconductive material such as polystyrene, and a coupling structure (not shown) is provided to secure the wiper arms 60 and 62 to the shaft 48 so that the wiper arms are rotatable by means of the knob 42.
The operation of the above-described antenna system is as follows: The circuit 44 is a resistance bridge circuit with each of the stubs 26, 38, 30 and 32 connected at one of the four corners of the bridge. In a specific embodiment of the invention which has been successfully tested, the total resistance of the resistance element 50 is 600 ohms between two points 180° apart on the element. Thus, there is a total resistance of approximately 300 ohms separating adjacent stubs. Each of the legs 14, 16, 18 and 20, together with its connected stub, forms half of a partially folded dipole antenna when receiving signals in the very high frequency (VHF) television band. Each such combination is approximately a quarter wavelength long with respect to wavelengths in the center of the VHF band. Thus, two stubs and two opposed legs together form a single-dipole antenna. At ultrahigh frequencies (UHF), the inductors 34, 36, 38 and 40 have a very high impedance, thus effectively removing the legs as antenna elements.
As the wiper arms 60 and 62 are moved into contact with different portions of the resistive element 50, either more or less resistance is connected between them and the two pairs of antennae. For example, if the wiper arm 62 contacts the tab 56 (see FIG. 4) while the wiper arm 60 contacts the tab 52, the wipers are connected through substantially zero resistance to one antenna consisting of elements 20, 40, 32, 28, 36 and 16. Thus, the signal from that antenna is delivered to the receiver 24 at substantially full strength, whereas the signal from the other antenna is equally divided by each arm of the ring-shaped bridge circuit 44, with the result that the same signal is applied to both wiper arms 60 and 62, and no signal is supplied to the receiver from the second antenna. When wiper arm 60 is shifted into contact with tab 58, and wiper arm 62 is moved into contact with tab 54, the signal from the second antenna is received full strength, whereas the signal from the first antenna is balanced out by the bridge circuit. When the wiper arms are at positions in between the tabs, the signals from the different sets of antenna elements are received in the receiver in varying amounts dependent upon the position of the wiper arms. In the latter case, both sets of antenna elements are operative to receive signals, and the effective plane of the antenna system is rotated through an indefinite number of positions by rotation of the knob 42.
Knob 42 has an index mark on it, and a dial 82 is located behind the knob 42. By means of the marks on the knob and dial, one easily can relocate the optimum antenna setting for a given station.
Variation from one set of tabs to the next changes the effective plane of the antenna through an angle of 90°. Further rotation reverses the polarity of the signals received and effectively changes the angular position of the antenna by up to 180°. Rotation of the knob 42 in the opposite direction provides another 180° of effective rotation, so that a full 360° of rotation is provided by the system.
The use of horizontal stubs 26, 28, 30 and 32 and the coupling inductors 34, 36, 38 and 40 makes the antenna system usable both at VHF and UHF frequencies. At ultrahigh frequencies (UHF), the inductors isolate the legs from the horizontal stubs since the inductors represent very high impedances at such high frequencies. This causes the horizontal stubs to act alone as simple broadband dipoles. At lower frequencies (UHF) the inductors have a much lower impedance and, together with a stray capacitance and distributed inductance of the legs 14, 16, 18 and 20, couple the stubs to the legs and serve as a form of partially folded dipole structure. The lower ends of the legs are electrically isolated from the floor by the plastic wheels 22.
In a specific example of the antenna system, the tubes 26, 28, 30 and 32 are metal tubes approximately 1 inch in diameter and 8 inches long. The inductors 34, 36, 38 and 40 are coils of approximately two and one-half turns and 1 inch in diameter with 1/2-inch spacing between turns. The diameter of the resistive ring 50 of the potentiometer is approximately three-fourths inch. The vertical legs are metal tubes 1 inch square and approximately 16 inches long. The legs also can be cylindrical, and 1 inch in diameter. It is desired that the legs and stubs be of relatively large diameter (e.g., 1 inch) so as to give them a relatively low Q factor, thus making them relatively broadband antenna elements and avoiding tuning problems at UHF frequencies.
FIG. 5 shows another embodiment of the invention which is the same as the embodiment described above except that the potentiometer-bridge 44 is replaced by an array of coils 70, 72, 74, 76 and 78 located in the space between the inner ends of the stubs 26, 38, 30 and 32. The array of coils is used to selectively couple the receiver input terminals to the antennas.
Each of the coils has slightly less than one turn. The planes of a first pair of coils 70 and 72 are parallel to one another and perpendicular to the horizontal axis X--X. The planes of a second pair of coils 74 and 76 are mutually parallel, but are perpendicular to the planes of coils 70 and 72, and to the vertical axis Z--Z. Another coil 78 is secured to the shaft 48, and, by means of the knob 42, is rotatable about an axis Y--Y which is perpendicular to both axes X--X and Z--Z.
The coils 70 and 72 are connected in series aiding with one another and between the stubs 26 and 30. Similarly, the coils 74 and 76 are connected in series aiding with one another and between the stubs 28 and 32. The terminals of coil 78 are connected to the input terminals of the receiver 24 by the cable 68, which is capable of flexing with the rotation of the shaft. FIG. 5 actually is an "exploded" view of the coil assembly. Each coil actually is approximately one-fourth inch in diameter, except for the movable coil 78, which is slightly smaller. The four outer coils are spaced about one-fourth inch from one another.
Each pair of series-connected coils constitutes, in effect, the primary winding of a transformer of which the movable coil 78 is the secondary winding. Coupling between the movable coil and one of the other coils is a maximum when the coils are parallel to one another, and is a minimum when they are perpendicular to one another. As the coil 78 is rotated, the amount of inductive coupling between that coil and each antenna varies and changes the magnitude of the signal delivered from each antenna so that the antenna effectively are rotated in much the same manner as they are in the embodiment disclosed in FIGS. 1 through 4.
The present invention has several advantages. The antenna system has a substantially infinite number of different possible orientations. This provides improved selectivity and accuracy in adjusting the system. The system is operable at both UHF and VHF frequencies. The invention is very simple in construction, and advantageously uses the legs of a television table for the purpose of supporting the table itself, and also as antenna elements. The table and antennae are esthetically appealing in appearance. "Ghosts" or other unwanted reflected or spurious signals tend to be cancelled by the selection network, since such signals usually are propagated in a direction at an angle to that of the main signal, and since signals from such angles are nulled in the bridge circuit. Further, the capacitance of the legs at VHF frequencies is believed to provide a tuning effect which increases the selectivity of the system, and aids in rejecting noise signals from adjacent channels.
The above description of the invention is intended to be illustrative and not limiting. Various changes or modifications in the embodiments described may occur to those skilled in the art and these can be made without departing from the spirit or scope of the invention as set forth in the claims. For example, the table legs need not themselves be antenna elements, but instead can be housing or supports for metallic antenna elements, without deviation from the principles taught by the present invention. The term "leg member" which is used in the following claims defines such antenna elements forming a part of the table legs, as well as conductive legs.
One very commonly used type of antenna for television receivers comprises a pair of telescoping arms (commonly called "rabbit ears") which can be adjusted to various different positions for best picture reception. The arms usually extend upwardly and outwardly from the top of the receiver. Such antennas have several undesirable features. One such feature is that it often requires a great deal of time and manipulation to adjust the antenna to the best position for a given station, especially since the optimum location of the arms for one station is difficult to remember. Furthermore, the telescoping arms often extend outwardly from the sides of the television set and are easily hit by people walking near the receiver. In hitting the antenna, the people are subjected to possible injury, and the antenna setting is changed. Still further, one usually must grasp the telescoping arms of the antenna to adjust it, thus adding the capacitance of his body to the antenna system and making the proper adjustment of the antenna more difficult.
One approach to the solution of these problems has been to provide, in the receiver housing, a plurality of opposed conductive elements fixed in position with respect to each other, each pair of opposed elements comprising a dipole antenna. Switching means are provided to switch the input terminals of the television receiver from one to another of the antenna pairs, thus effectively rotating the antenna without having to manipulate telescoping arms or the like. Typical examples of such prior art antenna systems are found in U.S. Pat. Nos. 2,602,892 to Koch, and No. 2,552,816 to Root. However, such prior systems are complicated and impractical to manufacture, or for other reasons are not suitable as replacements for the "rabbit ears" antenna.
It is an object of the present invention to provide a television antenna system which can be effectively rotated without the use of telescoping arms or "rabbit ears." Furthermore, it is an object to provide such an antenna system which is practical and inexpensive to manufacture, which provides a substantially infinite number of effective positions to which the antenna can be rotated, and which has a pleasing appearance.
The foregoing objects are satisfied, in accordance with the present invention, by the provision of a television receiver stand and antenna system for the receiver, in which antenna elements are incorporated into the legs of the stand. In the preferred embodiment, two metal legs located at opposite corners of the stand are used together to form one antenna, and two similarly positioned metal legs are used to form a second antenna. Continuously adjustable means is provided for varying the proportion of the signal which is delivered from each antenna to the receiver at a particular time, thus effectively rotating the antenna system, in steps of indefinite size, for best signal reception.
Further aspects and advantages of the invention will be set forth in or apparent from the following description and drawings. In the drawings:
FIG. 1 is a perspective view of one embodiment of the present invention;
FIG. 2 is a schematic perspective view of the antenna system of the structure shown in FIG. 1;
FIG. 3 is an electrical schematic circuit diagram of the antenna system shown in FIG. 2;
FIG. 4 is a perspective view of a component of the antenna system shown in FIGS. 2 and 3; and
FIG. 5 is a perspective, partially broken-away view of another embodiment of the invention.
FIG. 1 shows a rectangular television table or stand 10 with a television receiver 24 resting upon it. The stand 10 includes a top portion 12 made of nonconductive material such as wood or plastic, and four legs 14, 16, 18 and 20 secured to the top portion 12. Plastic wheels 22 are fastened to the bottoms of the legs. An antenna system (see FIG. 2) is incorporated in the table, and a knob 42 is provided at the front of the table for adjusting the antenna system.
As is illustrated in FIGS. 2 and 3, the legs 14, 16, 18 and 20 of the table 10 are used, in accordance with the present invention, not only to support the table, but also as antenna elements. Each of the legs is made of a conductive material such as metal, and preferably comprises a square or round metal tube. It is secured at its upper end to the top portion 12. The legs are positioned symmetrically at the four corners of the table.
Four horizontal metal tubes or stubs 26, 28, 30 and 32 are mounted in the upper portion 12 of the table. These tubes are arranged in pairs, the tubes in each pair being aligned with one another and extending between legs at opposite corners of the table. Each of the tubes is connected to the top portion of one of the legs by means of an inductor, 34, 36, 38 or 40. The other ends of the tubes are located adjacent one another near the center of the table, and are connected to a resistance bridge circuit 44 which is adjustable by means of the knob 42 at the front of the table.
Referring now particularly to FIG. 3, the resistance bridge circuit 44 comprises a potentiometer with a closed-loop resistance element 50 and a pair of opposed wiper arms 60 and 62 making contact with the resistance element 50. Each of the wiper arms 60 and 62 is connected to one input terminal of the television receiver 24 by means of a cable 68. The ends of the horizontal tubes or stubs 26, 28, 30 and 32 are connected to the resistance element 50 at four symmetrically located points.
FIG. 4 illustrates the preferred construction of the potentiometer. An insulating board 46 has an annular ring 50 of resistive material such as carbon coated on one surface. The resistive material 50 has four symmetrically located tabs 52, 54, 56 and 58, each of which is connected to one of the four tubes or stubs 26, 28, 30 and 32. Each of the wiper arms 60 and 62 is half moon-shaped, and has a pair of contact arms 64 or 65. Each of the wiper arms is bent so as to make contact with the resistance ring 50 at a point which is located centrally between the arms 64 or 65. The points of contact are located at an angle of 180° with respect to one another. The contact arms 64 of arm 60 make contact with a first conductive slipring 67 which is mounted on the insulating block. The contact arms 65 of the second wiper arm 62 make contact with a second slipring 66 which is smaller in diameter and inside of the first slipring 67. Conductive terminal posts (not shown) extend through the mounting board, each making contact with one of the sliprings 66 or 67. The cable 68 is connected to the terminal posts and thence to the receiver 24, as is shown in FIG. 3. The knob 42 is connected to a shaft made of low-loss nonconductive material such as polystyrene, and a coupling structure (not shown) is provided to secure the wiper arms 60 and 62 to the shaft 48 so that the wiper arms are rotatable by means of the knob 42.
The operation of the above-described antenna system is as follows: The circuit 44 is a resistance bridge circuit with each of the stubs 26, 38, 30 and 32 connected at one of the four corners of the bridge. In a specific embodiment of the invention which has been successfully tested, the total resistance of the resistance element 50 is 600 ohms between two points 180° apart on the element. Thus, there is a total resistance of approximately 300 ohms separating adjacent stubs. Each of the legs 14, 16, 18 and 20, together with its connected stub, forms half of a partially folded dipole antenna when receiving signals in the very high frequency (VHF) television band. Each such combination is approximately a quarter wavelength long with respect to wavelengths in the center of the VHF band. Thus, two stubs and two opposed legs together form a single-dipole antenna. At ultrahigh frequencies (UHF), the inductors 34, 36, 38 and 40 have a very high impedance, thus effectively removing the legs as antenna elements.
As the wiper arms 60 and 62 are moved into contact with different portions of the resistive element 50, either more or less resistance is connected between them and the two pairs of antennae. For example, if the wiper arm 62 contacts the tab 56 (see FIG. 4) while the wiper arm 60 contacts the tab 52, the wipers are connected through substantially zero resistance to one antenna consisting of elements 20, 40, 32, 28, 36 and 16. Thus, the signal from that antenna is delivered to the receiver 24 at substantially full strength, whereas the signal from the other antenna is equally divided by each arm of the ring-shaped bridge circuit 44, with the result that the same signal is applied to both wiper arms 60 and 62, and no signal is supplied to the receiver from the second antenna. When wiper arm 60 is shifted into contact with tab 58, and wiper arm 62 is moved into contact with tab 54, the signal from the second antenna is received full strength, whereas the signal from the first antenna is balanced out by the bridge circuit. When the wiper arms are at positions in between the tabs, the signals from the different sets of antenna elements are received in the receiver in varying amounts dependent upon the position of the wiper arms. In the latter case, both sets of antenna elements are operative to receive signals, and the effective plane of the antenna system is rotated through an indefinite number of positions by rotation of the knob 42.
Knob 42 has an index mark on it, and a dial 82 is located behind the knob 42. By means of the marks on the knob and dial, one easily can relocate the optimum antenna setting for a given station.
Variation from one set of tabs to the next changes the effective plane of the antenna through an angle of 90°. Further rotation reverses the polarity of the signals received and effectively changes the angular position of the antenna by up to 180°. Rotation of the knob 42 in the opposite direction provides another 180° of effective rotation, so that a full 360° of rotation is provided by the system.
The use of horizontal stubs 26, 28, 30 and 32 and the coupling inductors 34, 36, 38 and 40 makes the antenna system usable both at VHF and UHF frequencies. At ultrahigh frequencies (UHF), the inductors isolate the legs from the horizontal stubs since the inductors represent very high impedances at such high frequencies. This causes the horizontal stubs to act alone as simple broadband dipoles. At lower frequencies (UHF) the inductors have a much lower impedance and, together with a stray capacitance and distributed inductance of the legs 14, 16, 18 and 20, couple the stubs to the legs and serve as a form of partially folded dipole structure. The lower ends of the legs are electrically isolated from the floor by the plastic wheels 22.
In a specific example of the antenna system, the tubes 26, 28, 30 and 32 are metal tubes approximately 1 inch in diameter and 8 inches long. The inductors 34, 36, 38 and 40 are coils of approximately two and one-half turns and 1 inch in diameter with 1/2-inch spacing between turns. The diameter of the resistive ring 50 of the potentiometer is approximately three-fourths inch. The vertical legs are metal tubes 1 inch square and approximately 16 inches long. The legs also can be cylindrical, and 1 inch in diameter. It is desired that the legs and stubs be of relatively large diameter (e.g., 1 inch) so as to give them a relatively low Q factor, thus making them relatively broadband antenna elements and avoiding tuning problems at UHF frequencies.
FIG. 5 shows another embodiment of the invention which is the same as the embodiment described above except that the potentiometer-bridge 44 is replaced by an array of coils 70, 72, 74, 76 and 78 located in the space between the inner ends of the stubs 26, 38, 30 and 32. The array of coils is used to selectively couple the receiver input terminals to the antennas.
Each of the coils has slightly less than one turn. The planes of a first pair of coils 70 and 72 are parallel to one another and perpendicular to the horizontal axis X--X. The planes of a second pair of coils 74 and 76 are mutually parallel, but are perpendicular to the planes of coils 70 and 72, and to the vertical axis Z--Z. Another coil 78 is secured to the shaft 48, and, by means of the knob 42, is rotatable about an axis Y--Y which is perpendicular to both axes X--X and Z--Z.
The coils 70 and 72 are connected in series aiding with one another and between the stubs 26 and 30. Similarly, the coils 74 and 76 are connected in series aiding with one another and between the stubs 28 and 32. The terminals of coil 78 are connected to the input terminals of the receiver 24 by the cable 68, which is capable of flexing with the rotation of the shaft. FIG. 5 actually is an "exploded" view of the coil assembly. Each coil actually is approximately one-fourth inch in diameter, except for the movable coil 78, which is slightly smaller. The four outer coils are spaced about one-fourth inch from one another.
Each pair of series-connected coils constitutes, in effect, the primary winding of a transformer of which the movable coil 78 is the secondary winding. Coupling between the movable coil and one of the other coils is a maximum when the coils are parallel to one another, and is a minimum when they are perpendicular to one another. As the coil 78 is rotated, the amount of inductive coupling between that coil and each antenna varies and changes the magnitude of the signal delivered from each antenna so that the antenna effectively are rotated in much the same manner as they are in the embodiment disclosed in FIGS. 1 through 4.
The present invention has several advantages. The antenna system has a substantially infinite number of different possible orientations. This provides improved selectivity and accuracy in adjusting the system. The system is operable at both UHF and VHF frequencies. The invention is very simple in construction, and advantageously uses the legs of a television table for the purpose of supporting the table itself, and also as antenna elements. The table and antennae are esthetically appealing in appearance. "Ghosts" or other unwanted reflected or spurious signals tend to be cancelled by the selection network, since such signals usually are propagated in a direction at an angle to that of the main signal, and since signals from such angles are nulled in the bridge circuit. Further, the capacitance of the legs at VHF frequencies is believed to provide a tuning effect which increases the selectivity of the system, and aids in rejecting noise signals from adjacent channels.
The above description of the invention is intended to be illustrative and not limiting. Various changes or modifications in the embodiments described may occur to those skilled in the art and these can be made without departing from the spirit or scope of the invention as set forth in the claims. For example, the table legs need not themselves be antenna elements, but instead can be housing or supports for metallic antenna elements, without deviation from the principles taught by the present invention. The term "leg member" which is used in the following claims defines such antenna elements forming a part of the table legs, as well as conductive legs.