US2881428A - Antenna for automotive vehicles - Google Patents

Description

April 7, 1959 J. B; BATCHELOR, JR 2,881,428

' ANTENNA FOR AUTOMOTIVE VEHICLES Filed Jan. 5, 1956 r 2 Sheets-Sheet 1 A ril 7, 1959 'J. B. BATCHELOR, JR

ANTENNA FOR AUTOMOTIVE VEHICLES Filed Jan. 5, 1956 2 Sheets-Sheet 2 the loadingcoil is wound;

United States Patent ANTENNA FOR AUTOMOTIVE' VEHICLES Joseph B. Batchelor, In, Monroe, Ga., assignor, bymesue assignments,.to Central Electronics, Incorporated, Chicago,-Ill., a corporation of Illinois Application January' 5, -1956, Serial No. 557,588.

2'Claims. (Cl. 343-714) The present invention rel'atesin general to antennas for transmitting radio signals, and in'particular'to adjustable inductance devices for tuning-"antennas used on automotive vehicles or othermobile equipment. The terms automotive vehicles is to be taken in its broadest sense inasmuch as antennas embodying the invention are advantageously employed on passenger automobiles, trucks, tanks, small boats and any other-moving conveyance.

It is the general aim ofthe invention. to provide an improved loading' or 'tuning inductance for antennas used on automotive vehiclesand which may-be .conveniently adjusted for substantiallyoptimum performance in any of a number of frequ'ency' ranges, while at the same time beingfihighly efiicient in: its operation and small in sizeas well as simple-in construction.

Another object of thea-invention' is the provisionof such a-device which may be adjusted. for xoperationin diflferent' frequency ranges by means operable: from -a. .remote location, for example, the:driver-s:seat:of an. automobile.

A further object is :to-"create :suchran :antenna in: which a loading coil, progressivelyshorted."forsioperationfof the antenna in different frequency ranges,is.so located as to give high transmission eificiency with"regard to signal strength at distant points,1yet havingua coil. and switching assembly of such compact size :that'it may be located in the position'required'withoutan unduly large and heavy supporting structure;

It is still another object toprovide :ansantenna loading coil andswitch means .for adjusting the :same which are not only smalland compact, .but which successfully prevent arcing across ropeniswitchcontacts; present. negligible capacitance between .open switchrcontacts which might otherwise adversely affect the operation; and which drastically reduce the undesirable eflects of mutual coupling between active -r-and.:.shorted.r coil portions.

Other -objectsxandtadvantages ofrthe invention .will become apparent as. thefollowingdescription proceeds, taken in conjunction with theaccompanyingdrawings, in which:

Figure 1.is a.partial'side'elevation..ofa-:typical automotive vehicle having an antenna embodying, the features of the inventionmounted thereon;

' Fig. 2 is .an enlarged fragmentaryview, partially in section, of the antenna shown by. Fig.. 1;

Fig. 3 is a detail elevation-taken substantially along the line 3-3 inFig. 1;

Fig. 4 is a vertical section .showinga coil andfswitching assembly'employedin the antenna;

Figs. 5 and..6 are horizontal sections takem substantially along the.lines .55.'.and 6-6, respectively, ,in Fig. 4;

Fig. 7 is an enlarged fragmentary .section corresponding to a portion of Fig. 4 and illustrating. the manner in which Fig. 8 is a vertical section. taken through the'lower portion of the antenna; and

Fig. 9'isan enlarged view-corresponding to a part of pacitive impedance.

tical matter to make'the antennaequal in physical length 2,881,428 Patented Apr. 7, 1959 While the-invention has been shownand is described in some detailwithreference to a'particular'embodiment thereof,there is no intention that itAthus-be limitedto such detail. On thecontrary, it is intended here to cover all alterations, modifications; and equivalents falling within the spirit and scope of theinvention'as defined by the appended claims.

Referring now to the drawings, an antenna'10 constituting a preferred embodiment of .the invention'has been shown in Fig. l as mounted. on' an automotive vehicle '11 which in this instance happens to be a 1 conventional passenger automobile. The antenna-10 may be viewed as made up of first and second elongated "electrically conductive: sections which maybe-designated as the base section 12 and=the whipx14. Physically interposed between the base'12 and whip 14 is*a 'loading-assembly 15 which, as explained in detail below, includes -an'inductance element orloadiiig coil connected inseries with the two antenna sections. Assembly-15 may include a water-tight protective casing 16 coated onthe inside with a suitable insulating material 17 to reduce the possibility ofinadvertent electrical contact with the enclosed coil.

As shown best-in Fig. 2, the base 12 of the-antenna "is made as a tubular steel member and is fixed in-a vertical position to, while insulated from, the vehicle 11. Forthis purpose, a support fitting "18 is made fasttoa-panel"11a of =thevehicle by a plurality of bolts or. screws 19' which pass through insulating bushings --20="-inserted intomounting holes within thehousing; The screws 19 also pass through an insulating ring .21 which may be made. of plastic or'other suitable insulating'material Sothat-the fitting 18*and 'the antenna lllsupported thereby are'both insulated from the-vehicle itself. The-lower-end of-=the base :section 12 isinserted'vertically dQWnWar-dintothe fitting 18 and retained by suitable means such as set screws 22" (Fig. 3) threaded through the fitting-andengageable in openings 24 drilled in the base: An arcuate cover plate 25 through which the *base 12is'inserted'closes'the'top opening in the fitting 18 and is 'drawntightly against the latter by an annular nut 26- engaged with threads-cut onthe base itself.

For'feeding radio frequency"-'energy-to the antenna, a sheathed coaxial cable 27 leads fromwithin theinterior of the vehicle through an opening-27a cut in the'panelllh, the center conductor '27b being electrically: connected to the "base '12. The cable 27 may lead from :a transmitter (not shown) located.elsewhereiin thevehicle. For a purpose to be described, a rotatable torque transmitting cable 28' is extended from within the vehicle through the insulating ring 21 'and an opening-' 30 in'the-fitting itself.

Merely for purposes of illustration, it may b'e assumed that the antenna 10 is to-be-oper-ated at signal: frequencies in the '10, 15 20, 40, and meter bands; As is well known, the antennashould, when operating in each band, approximate 'series'resonance or substantially correspond to someodd multiple ofa quarter-wavelength. Under these :conditions, maximum power is, drawn from the transmitterbecause the antenna presents a low'impedance and also matches theiimpedance of the connecting coaxial cable. It is':possibleto -makethe antenna approximately-v physically equal to. an oddmultiple of a quarter-wave length .in' the highest frequency range, .i.e., in-the- 10 meter band, but "asthe operatin'g frequency-is lowered, the'antenna presentsa progressively higher 'ca- Of course, it is impossible asapracto a'quarter-wave length in the lowest'frequency -range, i.e., in the 160 meter'band. And 'withrthe antennasubstantially less than aquarter wave length in-the lower frequencyranges; the capacitive impedance: which it :presents is so very' high that little power is drawn fronr'the transmitter, and still less is radiated'into space;

g It is well known that operation at the lower frequencies can be obtained by placing a coil in series with the antenna which has an inductance of proper magnitude to substantially resonate with the antennas capacity.-- A difierent value of inductance is needed for operation in each frequency range, and in some cases for operation in different portions of one frequency range. This has led .in the past to the use of a plurality of coils which might be substituted one for the other, or suitable coils having taps or contacts which could be adjusted to short out different portions.

In these prior arrangements, it was necessary for the operator to stop the vehicle, disembark, and then either substitute coils in the antenna or adjust the tap of a coil mthe antenna, the latter steps often requiring assembly .and disassembly of parts, by the use of tools.

Before considering that aspect of the invention which permits adjustment of a loading coil from a remote locationand thus eliminates the inconveniences referred to, it will be appropriate to treat a second feature of the invention which concerns the physical location of a loading coil longitudinally of the antenna. It will be helpful ,to note first that all radiation in the communication frequencies is both electrostatic and electromagnetic in nature. The electrostatic radiation is commonly known as the ground wave and takes place through minute ca- ;pacitive coupling between the antenna and foreign ob ects, such as receiving antennas, located at remote points.

The electrostatic orground wave radiation is normally effective for only short distances in the order of 3 to .miles and it is produced as the result of voltage varia- .-tions on the antenna giving rise to a radiating electrostatic field. The electromagnetic radiation, on the other hand, is produced by current flow within the antenna generating a changing magnetic field which isradiated in --space. This is commonly called the sky wave and it is effective for extremely great distances depending upon .the atmospheric conditions.

In the loading coil for the antenna were located at its very base, or perhaps inside the body of the vehicle, it is possible to tune" the antenna to series resonance and thus properly load the transmitter. However, the result- ;ing current flow is primarily confined to the loading coil and is shielded by the vehicle body so that only a high voltage is present, for practical purposes, on the exterior portion of the antenna. This produces then, a relatively strong electrostatic radiation or ground wave, and a -.correspondingly weak electromagnetic radiation or sky wave. This has been proven by actual tests and found unsatisfactory for transmission of signals over appreciable distances.

- On the other hand, if the loading coil is interposed and ,connected in series with two antenna sections, the coil being located in the mid portion of the antenna or near the top thereof, the upper portion of the antenna, for a given over-all length, becomes so short that it has very little capacity. As a result, in order to resonate that capacitive reactance an extremely large inductive loading tively heavy, coil located near the top of the antenna has been found to present structural difiiculties. Either the base must be made unduly large and heavy, or risk of breaking the antenna is present.

, to the lower portion of the antenna, which is capacitively coupled directly. back to the vehicle, that a relatively weak electromagnetic wave is produced. If the loading coil is placed in the upper portion or center of the anstantially-perfectresonance is not readily t fib i vd coil must be employed. Such a large, and therefore rela-' tenna then it must be of higher inductance and since subassneas to the extremely small capacity of the shortened top antenna section, smaller currents flow in the upper section of the antenna and thus produce a relatively weak electromagnetic wave.

Accordingly, it has been my discovery proven by experiments that an electromagnetic or sky wave" of maximum strength, for a given antenna length and transmitter power, may be obtained by locating the inductive loading coil approximately mid-way between the center of the antenna and its lower end. Stated another way, I have found that appreciably better radiation for long distance transmission can be obtained by making the combined length of the antenna base section and the loading coil approximately one-third as long as the upper antenna section, e.g., by making the'base 12 and loading assembly two feet long and the whip 14 six feet long.

It has been my discovery that in order to obtain high transmission efiiciency, the capacitive coupling between the upper portion of the antenna and the base or vehicle body must be maintained very low in relation to the capacity between the upper antenna portion and free space. In other words, stray capacity back to the vehicle body or the antenna itself which shunts radio frequency energy must be minimized in order that substantially all of the radio frequency energy will be radiated, i.e., transmitted through the capacitance between the antenna and free space. For no matter how perfectly the antenna is tuned to resonance and how well it loads the transmitter, it is the strength of the transmitted signal which determines the success of the antenna.

Inputting this principle to advantageous use, a loading coil assembly is constructed in a manner such that the stray capacity between its adjacent turns is minimized, and switching means are provided which present very little capacity across open contacts. These, two features result in an antenna having a very small stray capacity between its whip and either the base or the vehicle, so that a greater proportion of the radio frequency energy is transmitted into free space.

In accordance with the invention, there is provided a loading assembly which due to its relatively small size and weight, is conveniently located as described above,

and which affords adjustment of the effective value of the loading inductance by means operable from a remote location. In accomplishing this, an elongated hollow coil form 35, having a central passage 36 therethrough, is physically interposed between the base section 12 and the whip section 14 (Figs. 2 and 4). As illustrated in the drawings, the coil form 35 may be cylindrical in shape and may be made of any suitable insulating material such as a ceramic. For attachment of its lower end to the upper portion of the base section 12, the coil form 35 is counterbored and tapped at 38 to be screwed onto'threads cut in the upper extremity of the base section 12 (Fig. 4). Similarly, the upper end of the coil form 35 is counterbored and tapped at 39 to receive the threaded shank 40 of a plug 41 having large spiral threads thereon. For attaching the whip section 14 so that it may deflect without damage if it should strike an overhead object, resilient means in the form of a heavyhelical spring 42 are employed. The spring has its turns in thread-like engagement with the plug 41, and receives at its upper end an externally threaded plug 44 which is internally tapped as at 45 to receive the threaded lower end of the whip section 14. The base 12, coil form 35, and whip 14 are thus all supported in vertically upright, coaxial relation, the latter having freedom to deflect owing to the resiliency of the spring 42.

For providing the necessary compensating inductance in various ones of the frequency ranges, a coil designated collectively by the character 46 is wound on the coil form 35. For optimum performance, the coil is created from a continuous conductor, or a number of conductor: connected in series, which is wound in multiple'layei .z'between'the turns a :and b, lying'inzthe channel formed "thereby. After the turn is completed,;the wire is crossed ..axially:along the coil form and wrapped in a fourth turn .dudirectly in'contact with the coil form. The wireis 'fthen crossed retrogressively. to form'the fifth turn e which If lies on and :between' the turns b and d. Upon-completion xxtofthe turn e, the wireisledaxially along the coil form ":to creat the turn f, 'andthen idoubled back to-form the tturn g lying overv and between the turns d and, f. The wire is, of course, enamel or otherwise insulated andthe pattern illustrated by Fig. 7 is repeated over and over to create the entire .coil 46.

. Several advantages .have been .found to result from the acoil which is bank-woundas-described. Such-winding :lowers the. capacitive coupling :between adjacent turns,

i.e., the stray capacity across the coil. As .explainedabove, this contributes to the elimination of shunting energy. back to the base 12 or the vehicle 11,so:that more :energy is radiated from the whip intofree space. Secondly, bank-winding increases the mutual: inductance between adjacent turns of the coil so that the coil has a higher inductance'for fewer turns, ascontrasted with a helical coil, thereby permittingit to be smaller in size. Moreover, fewer turns mean that a shorter length .of larger. diameter :coil wire. maybe used in the available :space so that copper-,losses,,i.e., 13R losses,'are consider- :ablyrreduced. As a result of the bank-winding arrange- -:iment,:,ther'efore, azrelatively smallcoil provides a"rela tivelyhighxinductance with littlestray capacityand :resultsdnieflicientoperation since copper losses are con- :siderably reduced.

,Asillustrated in Figs..2 and 4,the composite coil 46 is madenp of a plurality ofv individual "coil portions 5058-which are spaced :axially along the :coil form. The several individual coil portions. spaced apart axially may :be formed by a single conductor or-by a plurality of individual conductors which are connected-together. in .series relation. As noted, each of the coil portions 50-58 .:.is :bank-wound. Merely by way of example, the coil izportion 50 may present sufiicient inductance to correctly resonate the antenna for operation in the 75. meter band.

Likewise, the sum of all of the inductances provided .by the'coil portions 50 through '58 properly'compensates for operation of the antenna in .the low portion of the 160 meter band. It will be observed that the coil poreither the high, medium or low portion of the 160 meter band, while the coil portions 54 and 55 likewise provide for compensating adjustment withinthe 75 ,meter band.

The coil form and coil are maintained relatively small in over-all diameter while provision is made for pro gressively shorting out the coil portions 50-58 to tune the antenna for operation in any of the several frequency bands indicated by way of example. For this purpose, a plurality of taps are electrically connected at spaced points along the coil, and more particularly at junctions in the coil between the successive coil portions. As shown in Figs. 2, 4 and 5, such taps are cre ated by electrically conductive screws 60 which are threaded into a corresponding plurality of radial holes drilled through the coil form 35. The heads of the sev- .:-nect with the .coil conductor in'the' region where .itprogressesfrom one coil'portion toanother, asshown particularly in Fig.2. The taps preferablyinclude resilient .brushes to facilitate :switchingas described below.

In this instance, a small spring 61 of phosphor. bronze vor the like is suitably soldered or welded to the innerend of each screw 60, .the inner, free end161a .of the spring projecting into the passage .36. Electrical connection of thebase section 12 to the lowermostspring 61 and screw 60, therefore, leaves all of the coil portion 50-58 in' series, while electrical connection of the base 12 toal1 of the springs 61 and screws 60 shorts out each vof the respective coil portions 5058, leaving the antenna adjusted for proper operation in the 10 meter band with no compensating inductance.

The composite coil 46 is.electricallyinterposed orcon- .nectedbetween the base section .12 and the whip section :13. For this purpose, a conductive metal strap 65 (Fig. 2) is engaged by the top tap 'screw60and a screw '66 which is threaded through the coil form for locking engagement and electrical contact with the shank 40 of the plug 41 (Fig. 4). The .plug 41 is, of course, electrically connected with the whip 13 through the spring 42 and the plug 44.

For the purpose of progressively engaging the coil taps here formed by the springs61 and screws 60, a

conductive, preferably'non-magnetic plunger 70 is disposed within thepassage 36 of the coil form 35 with freedom to slide axially therein. .The plunger 70 is always electrically connected to the base. section 12.regardless of its position, as will become apparent from the following paragraphs. As itshupper end ismovedup- --wardly, it successivelyengages the coil taps and there --load.a transmitter for operation in the 15 meter band,

tions 57 and -58-permit adjustmenbfor' operation in "60.

fore successively shorts out the coil portions 58 through 50. With'the plunger 70 .in-theposition illustrated by Fig. 4, the coil portions 58, 5.7, 56and-55 are all shorted andthe antenna is adjusted for operation in the high region of the 75 meter band. i

It will be observed that the cooperative arrangement of the coil taps projecting inwardly through the coil form and the plunger 70.slidable axially within thecoilform results inanassembly whichis relatively small in diameter. .Other advantages. accrue from the.arrangement-described. By spacing the coil portions 5058 axially apart onthe .coil form 35, the coil taps formed by the screws 60 andsprings '61 are likewise spaced axially apart. Thus. with the upper end ofithe plunger engaging a: given one of the springs-(Slit still is considerably spaced from the next tap spring. there is very'little capacitive coupling between the upper .end' of the plunger 70 andthe next coil tap. Viewing For this reason,

theiplunger. 7i) and'each of the springs :61 as switch'contacts, therefore, the switch contacts have negligible capacity when open. Thus the switchingarrangement min imizes capacitive shunting from the whip and activeportions'of. the coil back to the base. 12. This, as explained above, promotes greater efficiency by eliminating or minimizing shunting of energy back to the base, to the end that most of the radio frequencyenergy is radiated from the whip .into free space.

. Additionally, experience hassshown .that with theappli- .cation' of only 50 watts :ofxradio frequency energy to an :.antenna of this type, the voltage-becomes .so high that it will are approximately one-half inch. I have found it necessary that open switch contacts be separated by something in excess of one-half inch. In the present arrangement, the upper end of the plunger 70 is always separated from the next free coil tap by a considerable distance so that the likelihood of arcing is substantially eliminated. Finally, with the coil portions spaced apart axially on the coil form 35, there is only relatively small mutual coupling between adjacent portions. This becomes important when one considers the effect of shorted coil portions on unshorted coil portions. For example,

-as viewed in Fig. 4, theshorted coil portion 53 has relsmall circulating currents are set up in the coil portion 53 and the power loss in the latter coil portion, which would subtract from the efliciency of the antenna, is

minimized.

- In order to shift the plunger 70 to any of its axial positions, i.e., to selectively short out successive ones of the coil-portions 50-58, motion transmitting means operable from a remote location are provided. In the present instance, the lower end portion 70a of the plunger 70 is circular in shape and externally threaded. The upper end is preferably rectangular in cross section to facilitate electrical contact with the springs 61 and to prevent rotation of the plunger within the coil form. Cooperating with the externally threaded lower plunger portion 70a is an internally threaded nut 74 which has a sliding, journaled contact with the inner surface of the tubular base section 12. The nut 74 is restrained against axial movement within the base 12 by a pair of retain ing rings 75, 76 (Fig. 6) axially restrained inside of the base 12 by suitable means such as inturned beads 12a. It will thus be seen that rotation of the nut 74 in opposite directions serves to move the plunger 70 up or down within the coil form 35. To prevent rotation of the plunger 70, it is passed through a bushing 78 seated in the upper end of the base 12 and having a rectangular hole 78a therethrough mating with the cross section of the plunger 70 (Figs. 6, 8 and 4).

In order to effect rotation of the nut 74, it is rigidly socketed into the upper end of an auxiliary tube 80 which is coaxially disposed within the base 12 and which coaxially surrounds the plunger portion 70a. The tube 80 is journaled at its upper and lower ends by the retaining ring 76 and a bearing ring 81, respectively. Disposed in the lower end of the tube 80 is a plug 82 having a non-circular opening therethrough which receives a non-circular or flattened end 28a of the cable 28, thus effecting a driving connection between the cable and the tube 80.

The cable 28 as shown in Fig.) extends into the interior of the vehicle 11 and may be rotated by any suitable means such as a hand crank, or power means such as a motor. As here shown in Fig. 2, an electric motor '85 is located inside the vehicle and serves to drive the cable 28 through a suitable speed reducing gear box 86.

The motor may be controlled for starting and stopping and as to its direction of rotation by appropriate switch means (not shown) located, for example, at the drivers seat. Through this arrangement, therefore, the operator of mobile radio transmitting equipment carried by the vehicle equipped with the antenna may adjust the latter for operation in any one of a number of frequency ranges simply by controlling the rotation of the cable 28 and thus vertically positioning the plunger 70 so that it engages a proper number of the tap springs 61 to short out the proper ones of the coil portions 50-58. Yet, despite the convenience afforded by this inductance-adjustingarrangement, the inductive coil and swich means are themselves so very compactly constructed that they may be mounted, as indicated, physically interposed between top and bottom antenna sections. An especially high value of inductance is realized for a given size of the coil form and length of coil wire by bank-winding the wire to create the composite coil 46. Such bank-winding substantially reduces capacitive coupling between adjacent coil turns, at the same time increasing mutual inductance between turns so that the over-all inductance of the coil portions is high relative to their physical size. The particular switch means consisting of taps projecting inwardly from the coil to the interior of the coil form and cooperating with an axially movable plunger, results in a switching means which leaves the coil assembly small in diameter but yet which presents negligible capacitance between open switch contacts, and spaces those open contacts sufficiently to prevent arcing when the antennais driven with relatively high power.

I claim: t

1. For use with an antenna having two conductive sections, one of said sections being hollow and rigid and having means for attaching the same in a vertical position to and insulated from an automotive vehicle, the combination comprising a hollow elongated coil form of insulating material rigidly fastened in vertical position to the upper end of said one section, spring means fastening the other of said antenna sections in vertical position to the upper end of said coil form, a coil comprising wire bank-wound on said coil form in serially connected portions spaced apart axially of the coil form, means electrically connecting the extremities of said coil respectively to said two antenna sections, a plurality of coil taps connected respectively with the wire between successive ones of said coil portions and extending inwardly to the interior of said coil form, a conductive plunger having electrical connection with said one antenna section and slidable axially within said one section up into said coil form to contact said taps and successively short out said coil portions, means rotatably disposed within said one antenna section and connected with said plunger for shifting the latter axially, and a flexible drive connection leading from the exterior of said one section to said rotatable means for turning the latter.

2. For use with an antenna mountable on an automotive vehicle, the combination comprising a base section of tubular metal, a hollow cylindrical coil form of insulating material and means fixing it in coaxial relation to one end of said base section, a coil made up by a conductor bank-wound upon said coil form in series connected axially spaced portions, a plurality of taps ex tending through said coil form and electrically connectec' to said coil intermediate the successive portions thereof, 2 conductive r'od slidably extending through said coil torn and adapted to engage said taps, the lower end of saic rod projecting into said hollow antenna section and hav ing threads thereon, a nut disposed within said hollov antenna section and threadably engaged with the lowe end of said rod, and means including a flexible elemen extending from the interior of the exterior of said hollov section for relatively rotating said nut and rod, so that th! rod may be moved axially to progressively contact sail taps and short out successive ones of said coil portions.

Hefele Sept. 14, 194 ElllS Oct. 4, 195

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