GB2046529A - Base loaded antenna - Google Patents

Abstract

An aerial 10 has a base loading coil 22 the inductance of which can be varied by means of a conductive ring 14 movable relative to coil 22. <IMAGE>

Description

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

The invention also relates to tuning devices for electromagnetic oscillations; and more particularly to turning devices for antennas and R.F. transmission lines.

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 capacitauce 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 translated, 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 antenna that the frequency of an antenna can be changed by atmospheric conditions, as for example, when precipitations 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.

A problem exists, for example, with quarter wave length antennas that are installed on vehicles, by reason of the fact that the surrounding metal structure has a pronounced capacitive effect which can drastically change the antenna's frequency from that of its uninstalled condition. With quarter wave length antennas, a quarter wave of each oscillation must occur in the transmission line or structure to which the antenna is electrically connected. In addition, metal structures close to the antenna produce a capacitive effect on the antenna to change its tuned frequency. A need therefore exists for a simple way of tuning the antenna after it is installed. In some instances the surrounding structures may have an effect on the tuning device itself, and for such environments a need exists for a tuning device that is substantially unaffected by its environment.

An object of the present invention therefore is the provision of a new and improved variable inductance tuning structure which must be moved from a point outside of its housing.

A further object of the present invention is the provision of a new and improved impedance tuning device of the above described type having a primary inductance coil and an external electrically isolated tuning loop in which a parasitic electromagnetic field is produced which opposes the field of the primary inductance coil with a minimum capacitive effect and minimum resistance losses.

Another object of the invention is the provision of a tuning device for an antenna having a single tuning loop which when adjusted both changes the inductance of a loading coil forthe antenna so that it has the correct electrical length to oscillate efficiently at a new frequency, and simultaneously changes a series tuned circuit so that it is tuned to pass the newfrequency efficiently.

Afurther object of the present invention is the provision of a new and improved device of the above described type wherein the environment has substantially no effect on the device's adjustment of its transmitted frequency.

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.

Figure 1 is a side elevational view of an antenna embodying 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; The drawing(s) originally filed was/were informal and the print here reproduced is taken from a later filed formal copy.

Figures 8 and 9 are an exploded view and an assembly respectively of another embodiment of the invention, Figure 10 is a cross sectional view of a tuning device embodying principles of the present invention, Figure 11 is an exploded view of the device shown in Figure 10, and Figure 12 is a schematic view of a device similar to that shown in Figures 10 and 11 but differing principally therefrom in that the tuning ring is a conductor which leads to a variable resistance device that is remotely located.

The antenna shown in Figure 1 is generally what is called a base loaded, electrical quarter wave length whip antenna, and comprising 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 14 which 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 receving 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 24 to 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 threading 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 against the bottom end of the tuning sleeve 60 to hold the sleeve 60 in its adjusted position.

The embodiment shown in Figure 5 is generally similar to 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 10b 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.It will 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 longtiudinally 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 10b. 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 not 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 articles 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.A terminal pin 120 of the diameter used in commercial coaxial cable connectors extends through the insulator tube 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 insulatortube 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 connector. The sidewalls of the shield 126 are slotted longitudinally opposite the coils 116 and 122 to provide windows 128 and 13U respectively. The outside surface of the shield 126 is threaded to receive tu ning nuts 132 and 134 adapted to be positioned lon gitudinally with respect to the coils 116 and 122 respectively. The bottom end of the coil 122 is sol dered 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 connectorto 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 of which passes through the annular insulator core 114, and the other half of which passes outwardly of the coi 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 down wardlyto 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 a field 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 struc tureswill not change the set frequency of the tuned antenna.

Figures 8 and 9 show a tuning assembly embodying 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 terminals 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 fiberglass rod and thetubularterminal 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 214 when 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 223 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 thatitwill pass through and centertheantenna 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 be 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 provided means for minimizing losses in the coupling to the transmission line for the antenna.

The tuning device shown in Figures 10 and 11 is adaptad to be used either at the base of a whip antenna (not shown) or in a R. F. transmission line.

The device shown comprises a lower, support, connector 10, which in the present instance is a modified male half of a coaxial connector. The lower connector 10 comprises an outer grounding sleeve 12 having external threads 14 on its lower end and an annular recess 16 on its upper end. A tubular terminal pin 18 is supported centrally of the grounding sleeve 12 by means of an insulator sleeve 20 that is firmly supported by the sleeve 12. The lower connector 10 is spaced apart from an upper connector 22 that is identical therewith and includes a corresponding grounding sleeve 24, insulator sleeve 26, and terminal pin 28. A copper wire coil 30 is positioned axially between the terminals 18 and 28 with a wire leading from the top of the coil 30 to terminal 28 and connected thereto by solder.In order that the electromagnetic flux of coil 30 will be intensified without increasing its length, coil 30 is connected to another coil 32 which is positioned internally of the coil 30 and is connected in series circuit therewith. In the embodiment shown, a wire 34 is connected between the lower terminal 18 and the top of coil 32, and the bottom of coil 32 is connected directly to the bottom of coil 30. Atuning capacitive effects exists between the coils 30 and 32, and the amount of intercapitance is controlled by the thickness of a tubular spacer 36 that is positioned over the coil 32 and on which the coil 30 is wound.It will be seen that a concentrated electromagnetic field is provided by coils 30 and 32, which field extends as a torus from the top of the coil externally thereof and then around back through the center of the coils. A nonconductive plastic 38 is injection molded around the coils, between connectors 10 and 22 to rigidly connect the assembly, protect it from weather, and provide the external surface. Threads 40 are molded into the external surface for receiving an internally threaded, tubular electrically conductive tuning loop 42. In the embodiment shown the tuning loop 42 is a metallic sleeve and the threads 40 extend well below the lower end of the coil 30 so that it can be threaded into and out of the magnetic field created at one end of the coil.The flux intercopted by the loop 42 creates a flow of electricity around the loop which in turn produces a magnetic field opposing that of the coil 30. In this manner the inductance of the coil 30 can be reduced from a point outside of the coil without a moveable mechanical connection between the inside and outside of the device. The present invention thereby avoids this possibility of external fields being transmitted through such an adjustment mechanism.

According to further principles of the present invention a tubular electrically conductive shield 44 is positioned over the coils 30 and 32 to isolate them from R. F. fields in the environment. One end of the shield is rolled into the recess 16 to attach it firmly to the connector 10, and the other end of the shield is rolled into the corresponding recess of the connector 22 to firmly attach it thereto. The shield and connec tor 22 are thereby grounded by anything connected to the connector 10. The shield 44 has four windows 46 therein which are spaced around the shield and each of which runs longitudinally between positions sufficiently above and below the coil 30 that flux passes out one end of the windows and in the other end of the windows 46.

By moving the tuning loop 42 upwardly over the windows a counter magnetic field is produced which opposes that of the coils to thereby reduce their inductance.

It will be seen that the coils 30 and 32 provide a capacitance therebetween that is in series with their inductance to provide a series tuned circuit that allows passage of D. C. electricity. As the tuning loop 42 is moved up into the field of the coils, the inductance is reduced, thereby reducing the electrical length of an antenna connected thereto, and increasing the frequency at which the antenna can efficiently oscillate. Simultaneously therewith the tuned frequency of the series tuned transmitting circuit formed by coils 30 and 32 is also shifted upwardly, so that the antenna maintains its Q value at the new higher frequency. It will now be seen that the double coil arrangement provides a capacitive effect to provide a series tuned circuit of high Q whose tuned frequency shifts in the same direction as does the tuned frequency of an antenna connected thereto.

The embodiment shown in Figure 12 corresponds generally to that of Figures 10 and 11 but differs principally in the construction of the tuning loop.

Those portions of the embodiment shown in Figure 12 which corresponds to portions shown in Figures 10 and 11 are designated by a like reference numeral characterized further in that a suffix "a" is affixed thereto. In the embodiment shown in Figure 12, the tuning loop 42a comprises at least one coil of an electrical conductor wire which extends to a remote location where a variable reactance mechanism 50 is installed in series therewith. By varying the reactance, and particularly resistance, the tuned frequency of the device can be changed remotely.

It will be seen that applicant has provided a tuning device for antennas and the like which utilizes a predominantly inductive load for tuning in antenna at a low frequency and decreases the inductive load for higher frequencies to provide a system having minimum 12R losses and maximum radiating efficiencies. This is accomplished by variations in the strength of an induced electromagnetic field which opposes that of a completely sealed tuned circuit from a point outside of the sealed unit. In addition the device can be shielded and the tuning accomplished from a point outside of the shielding. In a preferred arrangement the primary inductance producing device is a coil within a coil so that a minimum of heat loss occurs by reason of the electromagnetic field.

While the invention has been described in considerable detail, I do not wish to be limited to the particular embodiments shown and described, and its 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 and which fall within the purview of the following claims.

Claims (1)

1. A variable mutual transductance tuning device, and the like, comprising: a helically wound coil which produces a magnetic field of generally torroidal shape when electricity flows therethrough, first means inside said coil for intensifying said magnetic field, an electrically conductive tuning ring in the field externally of said coil, said ring being electrically insulated from ground and said coil, said ring being constructed and arranged to produce an opposing magnetic field in response to induced electrical flow in said ring, and second means for varying said opposing magnetic field produced by said ring.

2. The variable mutual transductance tuned circuit of claim 1 including a cylindrical body of nonconductive material surrounding and hermetically sealing said coil, said body having external threads thereon, and said second means comprising threads on said tuning ring which engage said external threads of said cylindrical body.

3. The variable mutual tranductance tuning device of claim 1 wherein said second means comprises a variable resistance for varying electrical flow through said tuning ring.

4. The variable mutual transductance tuning device of claim 1 wherein said first means is a core of paramagnetic material.

5. A variable mutual transductance tuning device, and the like, comprising: a helically wound coil which produces a magnetic field of generally torroidal shape when electricity flows therethrough, first means inside said coil for concentrating said magnetic field into said torroidal shape, a generally cylindrical body of electrical insulating material surrounding and hermetically sealing said coil and means inside said coil for intensifying said magnetic field, and an electrically conductive tuning ring around said generally cylindrical body of electrical insulating material for producing a counter electromagnetic field.

6. The tuning device of claim 15 wherein said tuning ring has internal threads which threadably engage the external surface of said electrical insulating material for adjusting its position relative to said torroidal shaped magnetic field of said coil.

7. 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.

8. The antenna of claim 7 wherein said coil is coaxially located with respect to said rod, and said conductor is an annular member surrounding said coil.

9. The antenna of claim 7 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.

10. The antenna of claim 9 wherein said second coil is coaxially located with respect to said rod, and said conductor is an annular member surrounding said second coil.

11. 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.

12. 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 member threadably engaging said external threads of said base for positioning said annular member axially of said antenna rod.

13. 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.

14. The antenna of claim 13 including: an electri cai conductor in the external field of said coil, said conductor affecting the mutual transductance of said coil.

15. The antenna of claim 14 wherein means is provided by means for changing the position of said conductor in said magnetic field of said coil.

16. A new and improved antenna system comprising: an electromagnetic radiator having an oscillatory length that is slightly 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.

17. The antenna of claim 16 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.

18. The antenna of claim l7whereinsaid magne- tic field transmitting member is a ring of larger diameter than said coil and which is adjustable axially of said coil.

19. 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.

20. Atuneableantenna comprising: a projecting electrically conductive radiator, a ferromagnetic core positioned coaxiallywith 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.

21. 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 inputterminal 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 shields 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.

22. A tuning 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.

23. The tuning device of claim 22 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.

24. A tuning 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 metallic tuning ring positionable longitudinally of the window opposite said second coil.

25. A support for antennas and the like compris ing: an inverted generally hollow cup-shaped base the sideswalls 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 cupshaped 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 adjacent internal sidewalls of said cup-shaped base to close off the bottom of the base and hold said slide in said horizontal groove.

26. A tuning assembly for an antenna comprising: 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.

27. The tuning assembly of claim 26 wherein said ferromagnetic member is a core inside of said coil and said electrically conductive ring is externally of said coil.

28. The tuning assembly of claim 27 wherein said ring is adjustable longitudinally with respect to said coil to tune said assembly.

29. Atuning assembly for 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 body for connecting an antenna thereto and for making an electrical connection to said second terminal pin.

30. The tuning assembly of claim 29 including an electrically conductive ring around said body and positionable longitudinally of said window.

31. The tuning assembly of claim 30 wherein said second terminal pin has a threaded end for receiving the threaded end of an antenna rod.

32. The tuning assembly of claim 31 wherein said threaded end of said second terminal pin projects out of said tubular body.

33. The tuning assembly of claim 32 wherein said ferromagnetic core is tubular and an insulator extends through said core to rigidly connect said terminal pins.

34. The tuning assembly of claim 33 wherein molded plastic fills said chamber between said terminal pins and coil and said sidewalls of said tubular body.

35. The tuning assembly of claim 34 wherein said body is metallic and an annular insulator body is threaded onto said second terminal pin and into the portion of said body th rough which said second terminal pin projects.

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

37. Atuning device comprising: a generallytubular body having a central chamber therein and with a magnetic flux escaping window in the sidewalls thereof, electromagnetic flux producing means in said central chamber, said means having first and second electrical terminals which communicate externally of said body, an inductance tuning loop externally of said tubular body and crossing over said window, said loop producing a counter electromagnetic flux which opposes the flux escaping from said window, and means for varying said counter electromagnetic flux produced by said loop.

38. The tuning device of claim 37 wherein said inductance tuning loop is an annular ring in which a flow of electricity is produced by said escaping flux, and wherein the function of said last menetioned means is accomplished by changing the position of said ring relative to said window.

39. The tuning device of claim 37 wherein said inductance tuning loop is a loop in which a flow of electricity is produced by said escaping flux, and wherein the function of said last mentioned means is accomplished by varying the resistance to the flow of electricity in said loop.

40. The tuning device of claim 37 wherein said electromagnetic flux producing means is a coil having flux amplifying means located internally thereof.

41. A tuning device comprising: a generally tubular body having a central chamber therein and with a magnetic flux escaping window in the sidewalls thereof, first and second terminals in respective ends of said body, an electromagnetic flux producing coil in said central chamber, said coil being electrically connected between said first and second terminals, means inside said coil for intensifying the electromagnetic flux of said coil, and an inductance tuning loop positioned externally of said body adjacent said window in a position to produce a counter electromagnetic flux opposing that escaping through said window from said coil.

42. The tuning device of claim 41 wherein said means inside said coil is a second coil operatively connected to said first and second terminals to add its flux to that of said first mentioned coil.

43. A tuning assembly 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 terminal pin in said chamber adjacent said one end thereof, a second 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, means inside said coil for intensifying the field produced by said coil and part of which passes through said window, and an electrically conductive ring around said body and positionable longitudinally of said window.

44. The tuning assembly of claim 43 wherein said second terminal pin has a threaded end for receiving

45. The tuning assembly of claim 44 wherein said threaded end of said terminal pin projects out of said tubular body.

46. The tuning assembly of claim 43 wherein said means is a ferromagnetic core.

47. The tuning assembly of claim 43 wherein molded plastic covers said tubular body to seal said chamber and its coil and means for intensifying the magnetic field of said coil.

48. The device of claim 47 wherein the outside of said molded plastic is threaded and the threads of the molded plastic is threadably engaged by internal threads on said electrically conductive ring.

49. Atuning device for an antenna comprising: a coil, an electrically conductive metallic member in the external field of said coil for producing a flow of electricity in said member which opposes said external magnetic field, said member being posi tionable longitudinally of said external magnetic field to change its resistance to said magnetic field, and a metallic shieid between said electrically con ductive member and said coil, said shield having windows opposite said coil and said member whereby positioning said electrically conductive member axially of said coil changes its impedance.

50. 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 over said core, one end of said coil being connected to a transmis sion line terminal and the other end being connected to said exposed length of conductor, a tubular shield surrounding said coil, said shield having field escap ing windows therein, and a ring of electrically con ductive material opposite said windows, 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.

57. The tuning assembly of claim 43 wherein I molded plastic hermetically seals said coil and means inside said coil for intensifying the field pro duced by said coil.