GB2035699A - Base-loaded whip antenna - Google Patents

Abstract

In a base-loaded whip antenna the loading coil 22 and a ferromagnetic core 20 are arranged so that the lines of magnetic force are not continuous within the core, but pass through the core and then external of the core to form the magnetic loop. An electrically conductive ring 60 is placed in the external portion of the magnetic loop. Varying the position of the ring in relationship to the coil-core assembly varies the total inductance of the circuit. A base 32 can mount the antenna on a car boot. Two loading coils may be provided. <IMAGE>

Description

SPECIFICATION Variable mutual transductance tuned antenna Background of the invention The present invention relates to radio antennas, and more particularly to standing whip antennas.

The antennas with which we are concerned convert electrical frequencies, or waves in a conductor, to radio waves and vice versa. It is a property of such converters that the electrical current in the antenna must oscillate freely at the same frequency as the radio waves that it receives in order for the antenna to have its maximum efficiency. In the case of transmitting antennas, the electrons in the antenna must oscillate freely at the frequency of the wave received from the transmitter if the antenna is to have its maximum efficiency. The oscillating flow of electrons in the antenna produces (electromagnetic) fields around the antenna, and the build up of electrons at spaced apart crests produces electrostatic fields. The antennas, therefore, have both inductance and capacitance which give the antenna a natural frequency of oscillation that depends upon its electrical length.It is a property of antennas that their electrical length must be an even fraction of the length of the radio wave to be transmitted, as for example: a quarter wave length, a half wave length, a full wave length, or multiples thereof. The capacitance of an antenna is altered by surrounding metallic structures, so that the natural frequency of oscillation which the antenna has is changed somewhat when it is installed upon an automobile, a ship, or airplane. It is also a property of antennas that the frequency of an antenna can be changed by atmospheric conditions, as for example, when precipitation connects the antenna to ground.

It is another property of antennas that the transmission line between the radio, or transmitter, should have an impedance which exactly matches that of the antenna itself for maximum efficiency.

When the impedance of the transmission line differs from that of the antenna, a mismatch occurs, and therefore, greater power is required to drive the antenna than would be required if the impedance of each were matched.

An object of the invention is the provision of a new and improved antenna, the radiating rod of which is physically shorter than the antenna's electrical length by reason of the inclusion of an inductance coil, and which is so constructed and arranged as to be free of frequency changes by reason of precipitation.

Another object of the present invention is the provision of a new and improved antenna of the above described type whose frequency can be easily and conveniently changed to tailor the antenna to the environment in which it is installed.

Another object of the invention is the provision of a new and improved antenna of one of the above described types which also includes means for conveniently adjusting the match of the transmission line to the antenna at the time that it is installed.

Brief description of the drawings Figure 1 is a side elevational view of an antenna em bodying principles of the present invention; Figure 2 is a bottom view of Figure 1; Figure 3 is an exploded view of the unassembled parts which form the antenna shown in Figure 1; Figure 4 is a longitudinal sectional view of the antenna and base shown in Figure 1; Figure 5 is a side elevational view, with portions broken away, of another embodiment of the invention; Figure 6 is a side elevational view, with portions broken away, of still another embodiment of the present invention; Figure 7 is a side elevational view with portions broken away, of still another embodiment of the invention; and Figures 8 and 9 are an exploded view and an assembly respectively of another embodiment of the invention.

Description of the preferred embodiments The antenna shown in Figure 1 is generally what is called a base loaded, electrical quarter wave length whip antenna, and comprises a thin, flexible rod 10 having a knob 12 pressed onto its upper end. The bottom end of the rod 10 is received in an insulator tube 14which is in turn received in an axially extending opening 16 of a metallic attachment member 18, which serves as a support, and input terminal. The portion of the rod 10 which projects out of the member 18 is surrounded by an annular ferromagnetic coil insulator and core 20, which in turn insulates and spaces an inductance coil 22 from the rod 10. The upper end of the coil 22 is soldered to an annular soldering lug 24 and the soldering lug 24 is crimped to the rod 10 to make an electrical contact therewith.The bottom end of the coil 22 is soldered to the upper thin walled section 26 of the attachment member 18, so that electrical conductivity is established between the attachment member 18 and the rod through the coil 22. The bottom end of the attachment member 18 is drilled and tapped as at 28, and a machine screw 29 is threaded therein to fasten the end of a transmission line leading to a radio or a transmitter, as the case may be. The lower end of the attachment member 18 is of reduced diameter and is threaded as at 30, so that it can be screwed into a support 32. The support 32 consists of a metal sleeve 34 having a threaded internal opening 36 for receiving the threads 30 of the attachment member 18. The metal sleeve 34 in turn is received in a molded plastic inverted cup-shaped base 38.The side walls of the bottom open end of the base 38 have an end section removed as at 40, while the remaining section of the sidewalls have a horizontal groove 42 therein which receives one leg 44 of a U-shaped slide 46 - the other leg 48 of which has an opening 50 which is drilled and tapped to receive a set screw, not shown. Once the leg 44 is slid into the groove 42, a plastic abutment 52 is pressed down and snapped into the lower end of the cup-shaped base 38 to hold the U-shaped slide 46 in position. The U-shaped slide 46 is intended to be slid over the edge of a piece of sheet metal, as for example the trunk lid of an automobile, and the set screw is fastened against the sheet metal to hold the antenna in place. The U-shaped slide 46 is notched out as at 54 to accommodate the end of a transmission line, not shown.

It will be seen that an electrical connection is made from the transmission line through the attachment member 18, coil 22, annular solder lug 24to the rod 10. The rod 10 preferably has a length that is less than a quarter wave length of the frequency to be received or sent by the antenna, with the balance of the quarter wave length being made up electrically by the coil 22. Inasmuch as it is an object of the present invention to maintain the period of vibration of the antenna at a predetermined frequency, regardless of atmospheric conditions, the parts are so constructed and positioned that a plastic envelope 56 can be molded about the coil 22 to simultaneously seal off the electrical connection and provide an insulated gap between the rod 10 and the attachment member 18.The envelope 56 extends down over the upper reduced diameter section of the attachment member 18 and terminates above its threaded external surface 58. The envelope 56 is of slightly less diameter than is the root of the threads 58, so that a threaded annular tuning sleeve 60 can be slipped down over the rod and envelope 56, and be threaded onto the attachment member 18. The sleeve 60 is metallic and ferrous, so that it is an electrical conductor. By th reading the sleeve 60 upwardly, eddy currents are produced therein which resist the magnetic lines of force to reduce the lines of force of the coil 22. By threading the sleeve 60 downwardly, the coil 22 can be caused to have a greater inductance.It can, therefore, be seen that since the sleeve 60 is external of all structure, the antenna can be mounted, the transmission line connected, and the antenna easily tuned for maximum signal strength. After the sleeve 60 is adjusted, a thin lock nut 62 may be threaded againstthe bottom end of the tuning sleeve 60 to hold the sleeve 60 in its adjusted position.

The embodiment shown in Figure 5 is generally similarto the embodiment shown in Figures 1 through 4, but differs principally therefrom in that it does not contain the tuning sleeve 60, and so is cheaper to produce. Those portions of the embodiment shown in Figure 5 which correspond to similar portions of the embodiment shown in Figures 1 through 4 are designated by a like reference numeral characterized further in that a suffix "a" is affixed thereto. The embodiment shown in Figure 5 contains the impedance producing coil 22a and molded envelope 56a, which arrangement prevents precipitation from changing the radio wave frequency to which the antenna is tuned.

The embodiment shown in Figure 6 is quite similar to the embodiment shown in Figures 1 through 4, but differs principally in that it contains a tubular shield over the coil to greatly reduce changes in the capacitance of the antenna due to the surrounding structure. Those portions of the embodiment shown in Figure 6 which are similar to corresponding portions of the embodiment shown in Figures 1 through 4 are designated by a like reference numeral characterized further in that a suffix "b" is affixed thereto.

In this embodiment, the antenna rod 1 0b has a glass fiber reinforced plastic coating over the center electrical conductor. A compression ferrule 64 is fitted over the plastic coating, and a tubular shield 66 having an inwardly tapered upper end is fitted down over the ferrule 64 to laterally support the antenna rod lOb. The bottom of the tubular shield 66 is threaded over the upper end of attachment member 18b. The upper end of the coil 22b is soldered to the ferrule 64, and the lower end of coil 22b is soldered to the center conductor of the antenna rod 10b. Itwill be seen, therefore, that an electrical connection is established from the attachment member 18b through the shield 66, ferrule 64, and coil 22b to the antenna rod 10b.A plurality of longitudinally extending holes or windows 68 are provided in the shield 66 opposite the coil 22b, so that some magnetic lines of force extend outwardly of the shield 66. A molded plastic 70 fills the space between the shield 66 and the rod 10b to insulate the coil and its connections, and to support the antenna rod lOb. By moving the ring 60b relative to the windows 68, the impedance of the coil is changed as is done in the previously described embodiment. The shield 66, however, isolates electrostatic changes in the environment from the coil 22b, so that once the tuning sleeve 60b is adjusted, very little, if any, change occurs in the tuned frequency.

It is believed that the operation of the antennas will be readily apparent to those skilled in the art. It is contemplated that the embodiment shown in Figures 1 through 4, and 6 will first be installed at the location where they are to be used, as for example on an automobile, and the transmission line will be connected to a transmitter or receiver as the case may be. A receiver will be tuned to a desired station, and a transmitter will be adjusted to provide a predetermined frequency. Thereafter, the sleeve 60 or 60b, as the case may be, will be adjusted up and down to achieve a maximum signal strength. This can be done quickly and easily. In the first described embodiment, the jamb nut will then be locked against the tuning sleeve 60, and the installation will be complete.

The embodiment shown in Figure 7 is sufficiently significant that it will be completely and independently described. The antenna shown in Figure 7 comprises an antenna rod 110 having a plastic coating 112 thereon. The plastic 110 is removed from the lower end thereof, and the bared end is received in a ceramic insulator tube 114 containing ferromagnetic particles so that it has a high permeability to magnetic flux. A copper wire coil 116 is wrapped around the insulator tube 114, and the top end of the coil is soldered to the antenna rod 110. Another insulator tube 118, that is identical to the insulator tube 114, is positioned axially of the antenna rod beneath the insulator tube 114. Aterminal pin 120 of the diameter used in commercial coaxial cable connectors extends through the insulatortube 118 and projects a sufficient distance out of the bottom thereof to be received in a female cable connector, not shown. Another copper coil 122 is wrapped around the insulator tube 118, and the top end of the coil 122 is soldered to the pin 120 and to the bottom of the coil 116. A compression ferrule 124 is positioned over the plastic coating 112 upwardly of the bared end of the rod 110, and the inwardly tapered end of a tubular shield 126 wedges the ferrule 124 against the coating 112.

The bottom end of the shield 126 projects beneath the bottom end of the pin 120 a proper distance, and is internally threaded, to serve as a female coaxial cable connector. The sidewalls of the shield 126 are slotted longitudinally opposite the coils 116 and 122 to provide windows 128 and 130 respectively. The outside surface of the shield 126 is threaded to receive tuning nuts 132 and 134 adapted to be positioned longitudinally with respect to the coils 116 and 122 respectively. The bottom end of the coil 122 is soldered to the shield 126 and a hardened plastic 136 fills the inside of the shield from the ferrule 124 to the projecting end of the pin 120 to lock the parts together.

The antenna shown in Figure 7 is intended to be installed on the end of a male coaxial cable connector to which a transmission line is connected. The signal passes from the pin 120 through the coil 116 to the metal rod 110 of the antenna. The signal passing through the coil 116 produces magnetic lines of flux, one half ofwhich passes through the annular insulator core 114, and the other half of which passes outwardly of the coil 116 with some of the external flux passing through the windows 128.

By moving the tuning ring 132 longitudinally of the windows 128, differing amounts of flux can be intercepted by the tuning ring 132. The flux passing through the tuning ring 132 produces eddy currents around the ring 132 which opposes the lines of force from the coil 116 to thereby decrease the inductance of the coil from the value it would have if the tuning ring were not present. By adjusting the transmitter or receiver that is connected to the pin 120 to a fixed frequency and moving the ring upwardly or downwardly to a maximum signal, a precise antenna tuning is obtained.

It will further be seen that the present embodiment provides means for adjusting the impedance of the transmission line to match that of the antenna. The signal from the pin 120 passes through the coil 122 to the shield 126 which is grounded by the coaxial cable connected to the antenna. Any flow of current from the pin 120 to ground produces afield about the coil 122, the inner portion of which passes through the core 118 and the outer portion of which passes through the windows 130. By moving the tuning ring 134 longitudinally of the windows, an impedance match can be obtained with that of the transmission line. This can be easily sensed when maximum signal strength is obtained.It can now be seen that the shield 126 is grounded and is interpositioned between the electrostatic field of the coils 116 and 122, and the surrounding structures, so that a change in the capacitance of the surrounding structurves will not change the set frequency of the tuned antenna.

Figures 8 and 9 show a tuning assembly embody ing the present invention and which is part of a coaxial connector for attaching a transmission line to the antenna. The embodiment comprises a generally elongated cup-shaped body 200 having a central chamber 202 which opens out of one end thereof.

The cup-shaped body 200 has external threads 204 adjacent the open end of the body so that this end will receive the nut of a male portion of a coaxial connector. The closed end of the cup-shaped body 200 is provided with a threaded reduced diameter opening 206 which receives a threaded insulator bushing 208 that in turn is threaded onto a center section of a terminal pin 210. The unthreaded end of the terminal pin 210 is bored out and slotted to receive one end of a short fiberglass insulating rod 212, the other end of which is received in a tubular terminal pin of the same size as the center terminal pin 214 of a female coaxial connector. The terminal pin 210 is crimped onto one end of the fibreglass rod and the tubular terminal pin 214 is staked to the other end of the fiberglass rod.The fiberglass rod 212 passes through a tubular ferromagnetic core 216 that in turn is surrounded by a coil 218, one end of which is soldered to terminal pin 210 and the other end of which is soldered to the tubular terminal pin 214. Parts 208 through 214when assembled are installed centrally of the chamber 202 and a plastic is injected into the chamber to insulate and hermatically seal the coil and connecting portions of the terminal pins. Three windows 222 are milled into the walls of the tubular body 200 opposite the coil 218 and a threaded tuning sleeve 224 is threaded onto the external threads of the body 200 such that it can be positioned longitudinally of the windows 222 to tune the assembly after an antenna rod is affixed thereto and the antenna is installed on the structure where it is to be used.A jam nut 226 is threaded up against the tuning sleeve 224 to lock the sleeve in position.

In the embodiment shown, the threaded end of the terminal pin 210 projects out of the body 200 and through an insulator bushing 228 to be received in a cup-shaped adaptor nut 230. The adaptor nut 230 has a stepped bore extending therethrough to provide an upper chamber 232 that is threaded to receive the bottom end of a threaded antenna, not shown, and a reduced diameter bottom threaded opening 234 that is threaded to receive the upper threaded end of the terminal pin 210. The end of the pin 210 projects into the chamber 232 a slight distance to make contact with the central conducting portion of a fiberglas jacketed antenna threaded into the chamber 232.The insulator bushing 228 has a reduced diameter portion 236 on its lower face so that it will pass through and center the antenna in an opening of any sheet metal structure, as for example a fender of an automobile, on which the assembly is to be mounted. By threading the nut 230 down onto the terminal pin 210, the sheet metal is clamped between the insulator bushing 228 and the end of the tubular body 200 in a manner wherein the tubular body 200 is automatically grounded to the structure on which the assembly is to be mounted.

The insulator bushing 228 and adaptor nut 230 may not be required in all instances, since other means may be provided for connecting an antenna to the pin 210 and for mounting the assembly onto a support structure.

It will now be seen that the objects heretofore enumerated have been achieved, and that there has been provided a new and improved antenna which is of a relatively short length and the tuned frequency of which is not changed appreciably by precipitation.

It will further be seen that the antenna can be quickly adjusted for maximum efficiency after it is installed, and this adjustment compensates for the affect of the surrounding environment. In the case of the embodiment shown in Figure 7, there is also pro vided means for minimizing losses in the coupling to the transmission line for the antenna.

While the invention has been described in consid erable detail, I do not wish to be limited to the particular embodiments shown and described, and it is my intention to cover hereby all novel adaptations, modifications and arrangements thereof which come within the practice of those skilled in the art to which the invention relates.

Claims (30)

1. An antenna for reception of a predetermined band of frequencies comprising: a rod having a signal oscillating length less than an even fraction of the wave length of the highest frequency of said band, a coil electrically connected to one end of said signal oscillating length, a transmission terminal on the other end of said coil, an electrical conductor in the magnetic field of said coil, and means for changing the magnetic coupling between said coil and said magnetic field.

2. The antenna of claim 1 wherein said coil is coaxially located with respect to said rod, and said conductor is an annular member surrounding said coil.

3. The antenna of claim 1 including: a second coil having one end connected to said terminal and the other end connected to ground, a second conductor in the magnetic field of said second coil, and means for changing the magnetic coupling between said coil and said magnetic field.

4. The antenna of claim 3 wherein said second coil is coaxially located with respect to said rod, and said conductor is an annular member surrounding said second coil.

5. An antenna comprising: a base having an axially extending opening therein, an insulator tube in said opening, an antenna rod having one end seated in said insulator tube, an inductance coil extending around said rod with one end electrically connected to said rod and the other end electrically connected to said base, and a dielectric plastic molded over said coil with one end sealed to said rod and the other end sealed to said base.

6. An antenna comprising; a base having an axially extending opening therein surrounded by external threads, an insulator tube in said opening, an antenna rod having one end seated in said insulator tube, an inductance coil extending around said rod with one end electrically connected to said rod and the other end electrically connected to said base, and an annular memberthreadably engaging said external threads of said base for positioning said annular member axially of said antenna rod.

7. An antenna comprising: an antenna rod, a transmission line terminal, a coil with one end of said coil being connected to said rod and the other end being connected to said terminal, and a ferromagnetic member in the field of said coil.

8. The antenna of claim 7 including: an electrical conductor in the external field of said coil, said conductor affecting the mutual transductance of said coil.

9. The antenna of claim 8 wherein means is provided by means for changing the position of said conductor in said magnetic field of said coil.

10. A new and improved antenna system comprising: an electo-magnetic radiator having an oscillatory length that is slightiy less than an even fraction of a desired wave length for which the antenna is to be used; an impedance coil connected in series with said radiator, said coil producing an electromagnetic field; and a magnetic field transmitting member adjustably positioned in said field so that upon adjustment it changes the impedance of said coil and thereby the tuned frequency of said antenna.

11. The antenna of claim 10 wherein said coil is coaxially mounted with respect to said radiator; and said magnetic field transmitting member is positioned in the external field of said coil.

12. The antenna of claim 11 wherein said magnetic field transmitting member is a ring of larger diameter than said coil and which is adjustable axially of said coil.

13. An antenna comprising: an exposed length of conductor for generating or receiving radio waves, a ferromagnetic axially extending core, a coil of electrically conductive material coiled generally circumferentially around said core, one end of said coil being connected to a transmission line terminal and the other end being connected to said exposed length of conductor, and a ring of electrically conductive material in the external field of said coil, said ring being adjustable axially of said coil, and whereby the inductance of said coil can be varied by changing the position of said ring.

14. Atuneable antenna comprising: a projecting electrically conductive radiator, a ferromagnetic core positioned coaxially with said radiator, a support terminal positioned axially beneath said core, said support terminal having axially extending external threads on its upper end, a tubular metallic sleeve surrounding said core with the lower end of said sleeve being threaded onto the external thread of said support terminal and with the upper end of said sleeve bracing said radiator, said sleeve having windows opposite said core, an electrically conductive coil wrapped around said core with one end of said coil being connected to said radiator and the other end being connected to said sleeve, and an electrically conductive ring positioned externally of said sleeve, said ring being axially positionable longitudinally over said windows to change the inductance of said coil.

15. Atuneable antenna comprising: an axially extending antenna rod, first and second ferromagnetic cores positioned axially of each other adjacent the lower end of said rod; an input terminal pin projecting axially beneath the lower one of said cores; first and second electrically conductive coils wrapped around respective first and second ferromagnetic cores with one end of each coil connected to said terminal pin; a tubular metallic shield positioned around said coils; pin and lower end of said rod with the upper end of said shield laterally supporting said rod; a plurality of windows in said shield opposite said first and second coils; said second coil having its other end connected to said shield and said first coil having its other end connected to said rod; and first and second tuning rings adjustably supported with respect to the windows opposite respective first and second coils.

16. Atuning device for an antenna comprising: a ferromagnetic core, a coil wrapped around said core, and a metallic ring in the external field of said coil, said ring being positionable longitudinally of said coil to change its impedance.

17. The tuning device of claim 16 including a metallic shield between said coil and said ring, said shield having windows opposite said coil and said ring whereby positioning said ring axially of said coil changes its impedance.

18. Atuning device for an antenna comprising: a transmission line terminal, first and second ferromagnetic cores, first and second electrically conductive coils wrapped around respective cores with one end of each coil being connected to said terminal, said first coil having a shield extending there around with a window therein opposite the first coil, said second coil having a shield extending there around with a window opposite the second coil, the opposite end of said second coil being connected to its shield and the opposite end of said first coil being arranged for connection to an antenna, a first metallic tuning ring positionable longitudinally of the window opposite said first coil, and a second metallictuning ring positionable longitudinally of the window opposite said second coil.

19. A support for antennas and the like comprising: an inverted generally hollow cup-shaped base the sidewalls of one half of which are generally V-shaped and the bottom of which is open, said base having a horizontal groove in the inside of said V-shaped sidewalls spaced upwardly of its bottom open end, said sidewalls having a section removed opposite the portion of said V-shaped sidewalls which contain said groove; a generally horizontal U-shaped slide with its upper leg being generally V-shaped and slid into said groove, and with its bottom horizontal leg being spaced below said cup-shaped base for clamping around the edge of a structure on which it is to be mounted: and a plug wedged between said U-shaped slide and the adja cent internal sidewalls of said cup-shaped base to close off the bottom of the base and hold said slide in said horizontal groove.

20. Atuning assembly for an antenna compris ing: a coil having a transmission line terminal at one end and an antenna terminal at its other end, a ferromagnetic member in the field of said coil, and an electrically conductive ring also in the field of said coil for varying the coupling between the coil and ferromagnetic member.

21. The tuning assemblyofclaim 20 wherein said ferromagnetic member is a core inside of said coil and said electrically conductive ring is externally of said coil.

22. The tuning assembly of claim 21 wherein said ring is adjustable longitudinally with respect to said coil to tune said assembly.

23. Atuning assemblyfbr an antenna comprising: a generally tubular body having a central chamber opening into one end thereof and with a magnetic flux escaping window in the sidewalls thereof, a first centrally located terminal pin in said chamber adjacent said one end thereof, a ferromagnetic core in said chamber, a second centrally located terminal pin adjacent the other end of said chamber, a coil in said chamber with respective ends of said coil being electrically connected to respective terminal pins, said first pin at one end of said body forming a coaxial connector, and means on the other end of said generally tubular bodyforconnecting an antenna thereto and for making an electrical connection to said second terminal pin.

24. The tuning assembly of claim 23 including an electrically conductive ring around said body and positionable longitudinally of said window.

25. The tuning assembly of claim 24 wherein said second terminal pin has a threaded end for receiving the threaded end of an antenna rod.

26. The tuning assembly of claim 25 wherein said threaded end of said second terminal pin projects out of said tubular body.

27. The tuning assembly of claim 26 wherein said ferromagnetic core is tubular and an insulator extends through said core to rigidly connect said terminal pins.

28. The tuning assembly of claim 27 wherein molded plastic fills said chamber between said terminal pins and coil and said sidewalls of said tubular body.

29. The tuning assemblyofclaim 28 wherein said body is metallic and an annular insulator body is threaded onto said second terminal pin and into the portion of said body through which said second terminal pin projects.

30. An antenna substantially as herein described with reference to any of the accompanying drawings.