US 3916413 A
An improved remotely tuned conductive-body antenna system is provided which gives superior signal coupling between the low impedance conductive body and the associated radio-frequency circuits with minimum loss of selectivity or "Q" in those circuits by increasing the inductive reactance of the coupling means insofar as the associated radio-frequency circuits are concerned without mis-matching the input to the coupling means and the low impedance conductive-body signal source.
Description (OCR text may contain errors)
Davis Oct. 28, 1975 REMOTELY TUNED CONDUCTIVE-BODY ANTENNA SYSTEM Inventor: Ross Alan Davis, 724 Ala Moana Primary E.vaminer-Eli Lieberman Attorney, Agent, or FirmBruce L. Birchard Blvd., Honolulu, Hawaii 96813  Appl. No 427,259
An improved remotely tuned conductive-body antenna system is provided which gives superior signal U-S- coupling between the low impedance conductive Cl. and the associated radio frequency circuits mini- Fleld 0f Search 712, 713, 856 mum loss of selectivity or Q in those circuits by in- I v creasing the inductive reactance of the coupling  References ('lted means insofar as the associated radio-frequency cir- UNITED STATES PATENTS cuits are concerned without mis-matching the input to 2,750,590 6/1956 Phelps 343/856 the Coupling means and the low impedance Conduc- 3,717,876 2/1973 Volkers et al. 343/712 y Signal Source- FOREIGN PATENTS OR APPLICATIONS 5 Ch'fims, 13 Drawing Figures l,949,828 4/1970 Germany 343/712 1e l9 l I be 2| '2;
l l 82 28 I '28 9Q US. Patent- Oct. 28, 1975 Sheet 1 of4 3,916,413
5.1 qpL US. Patent 00:. 28, 1975 Sheet 2 Of4 3,916,413
US. Patent Oct. 28, 1975 Sheet 4 of4 3,916,413
'high impedance of the input circuits of the radio appa- REMOTELY TUNED CONDUCTIVE-BODY ANTENNA SYSTEM RELEVANT COPEN DING APPLICATIONS Application Ser. No. 427,258, filed Dec. 21, 1973, 5 now abandoned, by this inventor and entitled Antenna System Utilizing Currents in Conductive Body. Application Ser. No. 430,095 filed Jan. 2, 1974, by this inventor and entitled Improved Radio Frequency Transformer.
BACKGROUND OF THE INVENTION In US. Pat. Nos. 2,923,813; 2,971,191; 3,007,164 and 3,066,293 the present inventor described several approaches to utilizing as antennas conductive structures such as automobile bodies. Because of the very unusual characteristics and extremely difficult problems encountered in extracting usable R.F. signals from existing conductive structures, the state of the art has developed only gradually through the years. This has been particularly true for the extraction from conductive structures, such as car bodies, of signals at lower frequencies in the region of the AM broadcast band. New and unique techniques have been required to extract a maximum of these elusive signals (correspond ing to the-magnetic component of incident electromagnetic fields) from existing discontinuities and particularly from the limited discontinuities formed in the fabrication of car bodies. Until recently, the art, even that developed by this inventor, could not properly meet this challenge.
To fully appreciate the many steps of painstaking progress and the many trials and errors involved in achieving the advancements in the art represented by the invention shown and claimed herein, it is desirable to trace the problems faced with the systems described in those patents and how those problems were solved.
As is well known, radiated electromagnetic signals comprise two components, the electrical component and the magnetic component. The signal component relied upon in the operation of the subject invention is the magnetic component, as it was in the earlier-issued patents. The impedance looking into a discontinuity in an existing conductive structure at radio broadcast frequencies is extremely low when such a conductive structure is that of a car body, the inductance being the major part of that impedance with an average maximum of only 2 micro-henries. Because of the relatively ratus coupled to the discontinuity in the conductive body it was considered impracticable, (prior to the work of the inventor), to couple radio broadcast signal energy efficiently out of a conductive body into associated radio apparatus, as for example, into an associated radio receiver.
To help solve this problem this inventor conceived and successfully reduced to practice a unique voltage and impedance transformer usable at radio frequencies and comprising a one-turn conductive sheath or tube acting as the primary of an auto-transformer, the secondary being formed by a conductor passing through the inner opening of the sheath or tube 8 or 9 times (when used at AM broadcast frequencies) and, hence, being very tightly magnetically coupledto the single turn primary of the auto-transformer. This unique design reduces unwanted electrostatic signals and noise in the transformation process. Further reduction of noise can be achieved by using a double-walled sheath, the inner wall providing electrostatic-shielding, as described hereinafter. To further improve the coupling between the single-turn primary and its secondary and to increase the inductance of the single-turn primary to a level such that it matches the inductance of the discontinuity in the conductive body, and, also, to further shield the transformer from extraneous electrical signals, a series of ferrite, high-permeability beads is applied so that it covers completely the one-turn primary sheath or tubing.
To simplify the discussion which follows, reference will be made frequently to a car body as the conductive body which acts as the antenna for this system. It should be understood that any conductive body, stationary or mobile, having an electrical discontinuity therein either solely for the purpose of this system or performing other functions as well, may be used in this system. In a car body, in addition to desired signals there are many undesired noise signals produced by the ignition system and various other electrical equipment found in cars today. These noise signals are in common conductive paths with the desired signals. Those noise signals have, in a majority of cases, a large electrostatic component and, in early systems designed by this inventor, the interference they produced made acceptable reception of desired signals most difficult without extreme diligence in isolating and eliminating the noise signals from the desired signal currents in the common conductive structure. One method for raising the level of the desired signals with respect to the undesired, or noise signals (beyond that accomplished by the use of the R.F. auto-transformer described herein), is to resonate to the desired-signal frequency the signal source (the conductive body), as is shown and described in copending application Ser. No. 427,258, filed Dec. 21, 1973, by this inventor. A second method is to tune the secondary of the auto-transformer to the frequency of the desired signal. In both cases the inductance is very low and the size of the capacitor required to resonate the inductances at broadcast radio frequencies is very large and the range of capacitance variation required to tune across the broadcast band is very large (9 to 1) making the use of conventional variable capacitors generally impracticable. This inventor then devised a system utilizing banks of small capacitors switched in or out in single step fashion through a multi-fingered sliding contact device which was ganged to the variable inductance or slug tuner in the radio and maintained the approximate value required for resonance of the associated inductance. Unfortunately, the number of switching contacts required was excessive in parallel resonating the auto-transformer secondary and the switching noise produced in the radio input circuits was a problem that required regular service to maintain quiet operation of this tuner. As a result, in the early systems, fixed tuning was the only available solution and it provided less than optimum performance. Further work by this inventor resulted in the development of a simplified, variable, series-resonant tuner that was used in the tuning of the low-impedance primary of the auto-transformer to achieve maximum coupling of energy from a conductive body discontinuity into associated radio apparatus. With this series capacity tuning, step switching was usable because of the low impedance in the primary. Switching noise was not objec tionable even in high-gain car radio input circuits adapted for use with the subject car body antenna system. However, such tuning of the low-impedance primary, by itself, left much to be desired both in selectivity and signal voltage gain. Signal voltage gain is particularly important when the source is a low impedance conductive-body discontinuity, as it is in this case. Attempts to increase the voltage gain in the autotransformer by conventional means, such as by loosening the primary-secondary coupling (to reduce inherent inter-winding capacitance) and increasing the number of primary and secondary turns were not entirely acceptable. Further development work by this inventor was necessary to achieve the required voltage gain and Q in the circuits (and a better L/C ratio, particularly in the low impedance input transformer used to further isolate troublesome noise problems); and, finally, to permit a more simplified tuning of the antenna system remotely, as from the radio receiver in the car, simultaneously with the tuning of that receiver, all without adversely affecting voltage gain and signal selectivity in the receiver.
This inventor then hit upon the idea of connecting the secondary tuning condenser in the electrical center of the secondary winding of the auto-transformer with its tightly coupled, low-impedance primary and higher impedance secondary. By locating the secondary tuning condenser in the electrical center of the secondary, (whether that secondary is lumped in the matching transformer or distributed along the border of a discontinuity), the effective distributed capacity of the secondary is reduced sharply and the number of turns on that secondary may be increased for a given desired frequency of operation, thus permitting greater voltage gain in the transformer and permitting the remote location of the secondary-tuning capacitor through extended shielded cables. It should be noted that in the lumped auto-transformer the secondary is contained within (and is electrostatically shielded by) the single turn tubular primary. An additional tube or sheath may be provided for electrostatic shielding. Further, the primaryis encased with ferrite material to produce a primary inductance which is matched to the source of signal; viz., the conductive body discontinuity, so that maximum signal current flow may be produced in the single turn primary. (The full voltage available from the discontinuity is applied across this one-turn primary).
To further advance and simplify this body (magnetic) signal technique and at the same time make it fully adaptable to todays standard high impedance car radio inputs (with a minimum of required changed and increased costs), a very practical combination of car body magnetic signals and electrostatic signals from a conventional antenna has been made. This combination simplifies adapting this inventors car-body signal techniques to use with standard radio receiver input circuits. This combination further reduces the need for dual magnetic signal input to the associated radio receiver so that a single conductive-body-signal input may be used when properly combined with a high impedance electrostatic antenna input. Also additional performance features have been gained over both the electrostatic and magnetic systems, which are not available from either separately. This added signal input can be derived from the simple addition of an insulated fine wire antenna imbedded in the windshield (or rear window) as is currently being done in both American made and American imported cars. The magnetic conduc tive-body signal may be derived by magnetic induction from the perimeter of the same windshield or rear window to reduce costs and simplify manufacture. Or, as
described in patent application Ser. No. 427,258 of this inventor, the car-body magnetic signal may be taken from a structural element adjacent the windshield or rear window. One of the unusual assets gained in this combination of electromagnetic and electrostatic signals is that further noise reduction can be achieved when R. F. noise from the two sources is properly phased and balanced as shown and described herein. Further greater extended signal range can be now accomplished by this combination, thus increasing the practicability of the insulated windshield wire antenna which is known for its limited ability to function in poor signal areas. The electrostatic antenna also suffers from sharp signal attenuation in structural, overpass and mountainous areas. To further enhance this combination of signal sources, a functional switch can be added to allow switching in either system separately or in combination. This switching capability is also useful in demonstrating the superior performance of the carbody antenna with respect to the insulated wire electrostatic antenna in varied situations.
Another method for improving the coupling of the signal from the body source to the relatively high impedance receiver input circuits is the double-ended driving of the extended primary of a transformer having a correspondingly larger secondary winding, as described hereinafter.
It should be noted that the antenna system described herein may be used equally well in the transmitting 35 mode as in the receiving mode.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a representation, partially as an elevational view and partially as a schematic diagram of an antenna system according to the present invention;
FIG. 2A is a representation, partially in elevation and partially in schematic form of a second antenna system incorporating the present invention;
FIG. 2B is a schematic representation of a variation in the antenna system of FIG. 2A;
FIG. 3A is a representation, partially in elevation and partially in schematic form of a third form of antenna system incorporating the present invention;
FIG. 3B is a schematic diagram of a variation of the antenna system of FIG. 3A;
FIG. 4A is a schematic diagram of an additional variation of an antenna system according to the present invention;
FIG. 4B is a circuit diagram showing variation of the antenna system of FIG. 4A;
FIG. 5 is a diagram, partially in schematic form, of an antenna system for deriving dual tuned signals from a single discontinuity;
FIG. 6 is a partially schematic diagram of an antenna system according to the present invention utilizing existing functional elements of an automobile for disguising the antenna coupling element;
FIG. 7A is a schematic diagram of a first doubleended primary drive for the transformer in an antenna system according to the present invention;
FIG. 7B is a schematic diagram of a variation in the coupling system utilized in FIG. 7A;
FIG. 8 is a schematic diagram of a transformerless double-ended signal coupling circuit according to the present invention; and
FIG. 9 is a schematic diagram of a dual source coupling system according to the present invention.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS In FIG. 1 conductive body 10 has opening 11, therein. For purposes of convenience body 10 is shown as a car body and opening 11 may be a front or a rear window therein. Opening 11 is bounded by conductive edge 12 along which radio-frequency currents flow when body 10 is exposed to a radio-frequency energy field. As a result of such current flow a radio-frequency potential difference exists between points 13 and 14 along edge 12. Further, because of the close proximity of conductors 15, 16, 17 and 18 to edge 12 (they may actually be hidden under the trim which normally covers edge 12 for aesthetic purposes) that portion of edge 12 between points 14 and 13 on the side proximate to conductors 15, 16, 17 and 18 is inductively coupled to those conductors and may be considered, along with exciter lead 19, to be the primary of an autotransformer of which conductors 15, 16, 17 and 18 constitute the secondary. This secondary is tapped by means of conductors 20 and 21 more or less at its center point. The tapping point may vary from the exact center point without departing from the essence of this invention. As conductors 20 and 21 emerge from shielding sheath 22 they are coupled across variable condenser 23. Variable condenser 23 may be ganged with main variable inductance or slug tuner 25 which is shunted by trimmer 24. Slug tuner 25, has coupled thereto winding 26 which transfers energy to or from associated electrical circuits for receiving or transmitting radio-frequency signals. Coupling condenser 27 may, by reason of the central tuning of the secondary comprising conductors 15, 16, 17 and 18, be from 20 to 100 pico-farads without destroying the selectivity of the tuned circuit comprising condenser 24 and inductor 25.
Padding condenser 29, which may be of a magnitude of 0.01 micro-farads is coupled between end terminal 30 of the autotransformer made up of conductors through 18, and edge 12 in the region of point 14. The relative capacitance of padding condenser 29 and cou pling condenser 27 determines the portion of the total signal voltage introduced into slug tuner 25. In addition to the signal picked up from the R. F. currents flowing in edge 12, a separate sense antenna 31 may be provided. This is essentially an electrostatic pick-up device which may be embedded in the glass placed in opening 11. The signal from this antenna is carried by conductor 32 to terminal 33 of a two-pole triple-throw selector switch including fixed contacts 33, 34, 35, 36, 37 and 38 and movable contacts 39 and 40. With the selector switch in the position shown both the car body signal and the sense-antenna signal are fed through noise filter choke 40' to the radio receiver input tuned circuit. With the selector switch moved to the left in FIG. 1, i.e., with movable contact 39 connected to fixed contact 35 and movable contact 40 cooperating with fixed contact 36, only the car body signal is coupled to the receiver input circuit. With the selector switch moved to the right, i.e., with movable contact 39 connected to fixed contact 33 and movable contact 40 connected to fixed contact 38, only sense-antenna 31 is in use. In some situations the combination of the signals from the sense antenna and the car body gives optimum results. Sometimes the best signal is derived from the car body alone. Occasionally it may be desirable to use the sense antenna alone. The switching system of FIG. 1 permits the selection of optimum signal strength.
The size of the wire used for conductors 15 through 19 can be varied between 18 and 40 gauge with the criteria being minimal obstruction of vision through opening 11 and minimum resistance in the secondary comprising conductors 15 through 18 In FIG. 2A the secondary of the auto-transformer is disposed in both halves of opening 11. Conductor 200, in combination with edge portions 201, 202 and 203, constitutes the primary of a first half of the secondary comprising conductors 207 and 208, and conductor 200, in combination with edge portions 204, 205 and 206, constitutes the primary of a second half of the secondary comprising conductors 209 and 210. The method for tuning the inductance appearing between center-tap conductors 211 and 212 and for coupling into and out of associated radio apparatus is the same as that described in connection with conductors 20 and 21 of FIG. 1, and need not be repeated here. Early experiments have indicated that the secondary disposition described in connection with FIG. 2A may reduce noise signals arising from local sources, such as the automobile ignition system. Sense antenna 213 is provided for the same purpose and with the same results described for sense antenna 31 in FIG. 1. It is coupled through conductor 214 to a selector switch comprising fixed contacts 215 through 220 and movable contacts 221 and 222. This selector switch performs the same function as the selector switch of FIG. 1.
In FIG. 2B the extraction of desired magnetic signals from the car body is accomplished by means of inductive coupling from edge portions 230 through 233, which constitute the primary of a transformer, of which conductors 234, 235, 236 and 237 constitute the secondary. This combination differs from the structure of FIG. 2A in that there is no direct connection to the boundary of the discontinuity 238. The advantage of this configuration is that the conductive noise currents which might be mixed with signal currents in the body and are conductively isolated from the radio input circuits, because only inductive coupling transfers signals from the primary to the secondary. A single ground point for the input circuits further limits and conductively isolates these troublesome noise currents. The secondary is balanced as in FIG. 2A, and similarly has a figure-eight configuration. Central tuning of the secondary is accomplished, remotely, in the fashion de scribed in connection with the antenna system of FIG. 2A utilizing condenser 239 coupled through conductors 240 and 241 to the R. F. transformer secondary made up of conductors 233 through 237. The leads to the remote circuits are shielded from noise pick-up by conductive sheath 241'. Sense antenna 242 may be provided and functions as described in connection with FIG. 2A.
In FIG. 3A the secondary tuning concept of this invention is shown applied to an antenna system of the type disclosed in co-pending application Ser. No. 427,258 entitled Antenna System Utilizing Currents in Conductive Body and filed by this inventor on Dec. 21, 1973.
In FIG. 38, column 300 in a conductive body has an impedance discontinuity therein produced by severing the column, using ferrite in and around the column or increasing its resistance in a region, resulting in the appearance of an electrical potential across points 301 and 302. Sheath 303, of copper or other conductive material is connected at its extremes 304 and 305 to points 301 and 302, respectively, and acts as the primary of an auto-transformer for which conductors 306 and 307 form the secondary. The secondary is split at points 308 and 309 and is coupled by means of connectors 310 and 311 to tuning condenser 312 which may be ganged with variable inductance 315. lnductance 315, in turn, is shunted by trimmer 313. This coupling network functions in the same fashion as that described in connection with FIG. 1 and need not be described further here.
Ferrite material 314 may be applied to sheath 303 to provide magnetic shielding and to increase the coupling of the primary and secondary portions of the auto-transformer. Sheath 303, its ferrite covering 314 and the conductors 306 and 307 may be made aesthetically more attractive by incorporating them in a mirror, for example, mounted on column 300, taking care not to short circuit the desired impedance discontinuity in column 300.
In FIG. 3B auto-transformer 320 is located remotely from the discontinuity in the conductive body but is coupled thereto by coaxial cable 321 having central conductor 322 and conductive sheath 323. Central conductor 322 is connected to point 324 and conductive sheath 323 is connected to point 325 on opposite sides of discontinuity 326 in column 300. Thus, the full R.F. potential appearing between points 324 and 325 is applied across coaxial cable 321. While a coaxial cable has been found to perform best in this coupling directly to the low impedance signal source, strictly speaking a coaxial cable is not required but merely an internal conductor insulated from an outer conductive sheath may be used when of good design for R. F. en-
ergy transfer. The outer sheath, in either case minimizes noise signal pickup from surrounding noise sources when correctly grounded at both ends.
In FIG. 3B, auto-transformer 320 functions as does the auto-transformer described in connection with FIG. 3A. However, it is often inconvenient to mount the auto-transformer at the body discontinuity. This inventor has found, surprisingly, that the remote location of auto-transformer 320 not only performs an effective impedance and voltage transformation but also produces a significant noise reduction by reason of the shielding and electrostatic isolating effect of outer tubing or sheath 327 which also constitutes the one-turn primary of auto-transformer 320. The remote location of transformer 320 also allows conductive isolation from undesirable noise currents flowing with the desired signal currents in the conductive structure. Additional shielding sheath or tube 328 provides further noise suppression by isolating the primary and secondary portions of transformer 320, electrostatically, from each other. This system has proven in tests to be very effective in cars with high levels of locally generated noise. The remainder of the circuit of FIG. 38 operates in the same fashion as the circuit of FIG. 3A.
In FIG. 4A the signal potential produced between points 401 and 402 on opposite sides of discontinuity 403 in column 404 is applied to conductors 405 and 406 of coaxial cable 407. Sheath 406 is grounded at the receiver end, as shown. Center conductor 405 is coupled through series tuning condenser 408 to primary coil 409 of input transformer 410, the secondary 411 of which is core or slug tuned. Condenser 408 and the movabie core which tunes secondary 411 may be ganged. Noise transfer from primary 409 to secondary 411 is prevented by electrostatic shield 412. Inherently however, because of the low impedance of the network including coaxial cable 407 and primary 409, little noise is picked up in that network.
In FIG. 4B, signals appearing across points 401 and 402 are coupled to primary 409 through a balanced system as contrasted with the unbalanced system of FIG. 4A. Conductive shield 413, which is grounded at the receiver end as shown, prevents noise pickup in the coupling between the signal source and the receiver primary 409. Series condenser 408 series resonates the circuit including primary 409, as described in connection with FIG. 4A. Electrostatic shield 414 reduces noise coupling between primary 409 and secondary In FIG. 5, two signals having differing directional characteristics are derived from a single discontinuity in a car body and remote tuning of the dual antenna system is provided.
Conductive sheath 500 is connected to the boundary of the opening at points 501 and 502 and, as described in connection with earlier embodiments, constitutes the primary of an auto-transformer, the secondary of which comprises conductors 503, 504 and 505 and 506 which pass through the primary and are tightly coupled thereto. In some applications the car body trim itself may act as the primary of the auto-transformer and the conductors may pass through that trim. The conductors pass diagonally across opening 507 in returning for passage through the primary. The size of the wires is such that they do not obstruct vision through the opening, which may be the rear window. The secondary is center-tapped and the leads come out at conductors 508 and 509 to permit center tuning of the secondary of the auto-transformer by condenser 510. Padding condenser 511 is coupled between low-impedance antenna output lead 512 and ground. Conductor 512 is coupled to the receiver input circuits.
Similarly, signals are picked up between points 513 and 514 along the boundary of discontinuity 507 and are transformed in voltage, upwardly, by the autotransformer action of primary 515 and secondary conductors 516 through 519 passing through the primary.
Output signals are taken from conductor 519, as shown. The secondary of this auto-transformer is tuned at its center by condenser 520 which is remote, as at the radio receiver, and may be ganged with the main tuning device of the radio receiver.
It should be noted that the car body surrounding the discontinuity 507 acts as a shield for this antenna system against many electrostatic noise signals.
In FIG. 6 the concepts set forth in connection with FIGS. 1 through 5 are embodied in an otherwise functional portion of the car body. In the disclosed embodiment the primary 600 of the auto-transformer bounds a portion of the perimeter wind-wing assembly 601 and may be a hollow conductive sheath or tube through which the secondary windings 605, 606 and 607 pass. The potential difference between points 602 and 603 on the car body edge 604 is used to drive this longer portion of this low impedance primary. The secondary of the auto-transformer is tuned remotely by condenser 606 which may be ganged with the receiver main tuner 617. Instead of incorporating the auto-transformer in the wind-wing assembly it may be incorporated in a rear-view mirror mounted between conductive body driving points 602 and 603, with the balance of this primary being used to support the external mirror.
The structure shown and described in FIG. 6 may be duplicated on the opposite side of the vehicle to obtain multi-directional signals and provide nearly omnidirectional reception. Switching, automatic or manual, may be provided, as shown using fixed contacts 607 608, 609 and 610 and movable contacts 611 and 612. Energy from the second auto-transformer, not shown, is brought to the switch through coaxial cable 613. Condensers 614 and 615 are coupling condensers bringing signals to the receiver input circuits. Condensers 614 and 615 act as padding condensers to apply the optimum signal to the receiver input circuits including trimmer condenser 616 and core tuned inductance 617.
In FIG. 7A oppositely phased signal voltages appearing at points 70 and 71 on column 72 are fed to opposite extremities 73 and 74 of conductive sheath or tube 75 which acts as the primary of an impedance and voltage step-up transformer 76 through which a secondary terminating in leads 77 and 78 passes. Because primary 75 is being driven in push-pull fashion with its center grounded its length may be doubled for better matching of the impedance of the source and, at the same time, greater signal step-up may be realized in the secondary. Ferrite beads 79, which surround sheath 75 assure increased primary-secondary coupling and permit direct parallel tuning of the secondary of transformer 76 by condenser 80 which is ganged with receiver input circuit tuning inductor 81. Signals are injected at the high potential end of that inductor through coupling condenser 82 which may have a capacitance of pico-farads. Input to the first receiver translating element is through secondary 83.
In FIG. 7B push-pull (or double-ended) driving of primary 84 occurs, as with primary 75 in FIG. 7A. However, the method of coupling signals from the secondary winding of step-up transformer 85 through leads 86 and 87 to associated radio apparatus is different from the method in FIG. 7A. Series tuning of the cicuit including the secondary of transformer 85 and coupling inductances 88 and 89 is accomplished by capacitance 90 which is ganged with input tuning inductor 91 to assure optimum performance of the antenna system at each setting of the tuner in the associated radio apparatus. Again, the antenna tuning element is located remotely from the conductive-body signal source.
In FIG. 7B the signal source is shown as being points 92 and 93 on column 94 in which there is a discontinuity. A second signal may be derived from a second source, not shown and supplied through cables 95 and 96, to which terminals 97 and 98 of primary 84 may be points 800, 801 and 802, 803, respectively, by operation of slide switch 804. This is a balanced system with remote tuning of the antenna system accomplished by series condenser 805 which may be ganged with variable inductance 806. Coils 807 and 808 may be wound in layers, one on the other and connected in aiding fashion. Their self and mutual inductance may be increased by using a ferrite core. In fact, it is possible to design the tuning core for inductance 806 so that it has a portion always within coils 807 and 808 despite the controlled entrance of that core into inductor 806 for tuning purposes.
In FIG. 9, signals may be coupled into and out of discontinuities 900 and 901 which may be between the header 908 and body 909 of an automobile. Omnidirectionality in transmission and reception may be approached by proper coupling of energy into and out of the conductive body through cables 902 and 903. Tuning of the combination of the body inductance and primary inductance 904 to a desired frequency is accomplished by capacitance 905, which may be ganged with variable tuning inductance 906 in associated radio apparatus. Signals into and out of the system may be taken through coupling coil 907. This circuit has been used very successfully at 27 magaherz.
While specific embodiments have been described, modifications may be made within the scope of the invention. The following claims are intended to cover such embodiments.
What is claimed is:
1. A vehicle body antenna system, including:
a windshield opening having a conductive perimeter and being responsive to a radio frequency field to produce at points across the perimeter a potential at said radio-frequency;
radio frequency circuits remote from said discontinuity and forming a part of associated radio apparatus;
coupling means including a secondary winding directly connected to at-least-one point of the conductive perimeter and juxtaposed t0 at-least-one portion thereof to form therewith a transformer with a single turn primary; and,
tuning means coupled to said transformer and physically positioned remote from said discontinuity and proximate to said radio frequency circuits.
2. Apparatus according to claim 1 in which said secondary winding is connected at its other end to a capacitor which, in turn, is connected to a point on said conductive perimeter opposite said at-least-one point.
3. Apparatus according to claim 2 in which the magnitude of said capacitor is in the order of 0.01 microfarads.
4. Apparatus according to claim 1 in which said secondary winding comprises first and second sections each having a winding direction opposite from the other section and each section juxtaposed to a different portion of said conductive perimeter from said other section.
5. Apparatus according to claim 1 in which said radio frequency circuits includes tuning apparatus, said tuning apparatus being mechanically coupled to said tuning means.