US1917205A - Antenna system for sleet melting and conductor therefor - Google Patents

Description

l.. c. F. HoRLE 1,917,205

ANTENNA SYSTEM FOR SLEVET MELTING AND CONDUCTOR THEREFOR July 4, 1933.

Filed June 20, 1932 ddnnn o 2.51502- /Q SH Hor-weg Patented July 4, 1933 Lawns-noni e. nente, or

ANTnnnA sYsfrnin FR SLL My invention relates to methods and means for employing` in any system' elf conductors whose normal function is to carry high-frequency currents, the heating eiilect caused hy y'the passage 'of lowlirequency or direct currents through the system, with freedom from interference between the sources ot the several currents and with econoi'ny and maxi-r mum ellectiveness in the performance of the ltwo functions. Y 1

More specifically, my invention is directly applicable to the heating hy electrical current ot systems of elevated conductors, such as radio. antennas, for the purpose or' eliminating the 'eiiect of high humidity or the hazard of iailurel due to .sl-eet l'ornnztion;

Particularly in northern latitudes, antennas are likely to acquire heavy .loadings orp ice or slect. lt is hize, 1y desirable to re- 'iduce to a minimum such ice and sleet loadings, not only because or the risk et 1erealing the antenna conductor and causing the antenna to `tall, but also because a, heavy or sleet loading` is liliely to detunethe antenna,

badly and thus change their ei'i'ective height 'from ground and their f wiective-capacity to ground, and 'secondly hecznisel ice has a dielectric constant olfv about three and the'preslence ot'a considerable layer of such a medium immediately surrrnimling conductor will change its vcapacity to ground.

My invention will he iunior-Mood 'from the following specication' and accompanying 351' drawino. For purposes of* explanation I have described a specilic embodiment but it willhe understood that my invention is not limited thereto, butinay he applied other and ditlerent embedhnents. without d Iilparting from the spirit and principles of inu invention. Y y In the drawing', Figure l shows an antenna system embodying `the principles of my invention, and-Figure 2 shows a cross-section which I employ.

jrs an example of the application of my invention, 1n Figure l there is shown a. conl lirst 1because the antenna conductors may et the composite or non-uniform conductor ventional type of radio antenna which is ingeneral use for hroadcasting,` and other purann connnorosl rnnnnron.

poses. lt will he noted that in this 'l' type' antenna the horizontal portion, or flat top, (todo is connected through the two down leads, cg, and gli, to the source of high-trevquency current Sl, and to the source of lowirequency or directl current S2. included in the circuits of the down leads are, of course, the conventional adjustable tuning inductances L which brought their adjustahility allow for the' precise tuning out of the otherwise present reactance ofic the antenna circuit to the end that the antenna circuit may he made resonant to the fre-v quency of thev high-frequency supply, S1. llhere the frequency of the high-frequency supply is less than the natural vfrequency of the antenna system, the use or" the simple series inductanee here shown will serve for the tuning' of the antenna system while, if

vthe frequency of' the high-frequency supplyy n is greater than the natural frequency of the vantenna a negative or capacitive reactance must be supplied in series with the antenna to bring about resonance. This can he provided either by means oit' a properly cho-sen tuning;- condenser in serieswith the antenna and adjustable tuning inductanee, or in shunt with the tuning inductance, as shown in dotted lines at CL, the condenser-inductanee combination being jointly in series withv the antenna. In either event, however, the ease and economy of provision for adjustahility in aninductance element and the lack of these desirable characteristics in commercially 'feasible condensers requires the use of inductance elements, even where the vreactance required by the antenna system is negative and hence capacitive,

rl`hroupjhout my specification, it will he understood that in using the expression lowfrequency current l intend in each case to includedirect current as current of Zero lremiency. i

lt will he noted that provision must loe made in this system for the cfective isola- .tion of the two power sources, S1 and S2, from the influence of one another,lest, on the one hand, any appreciable portion oi the eX- tremely costly,7 hi gli-frequency power output of source S1 be lost in. the low-frequency source S2, and on the other hand, lest the potentially destructive effects of the large currents of the low-frequency or direct current source S2 be allowed to operate on the structural elements of the high-frequency source Sl. To this end the isolating condenser, Ci., are provided .in series with the down leads, ef and gli, while in series with the connections to the 10N-frequency source are connected the choke coils Lf, which constitute a net work in the connections to S2 to exclude the highfrequency power from S2 by virtue of the coil impedance, or preferably, in combination with condensers Cf, and. tuned to the frequency of the high-frequency supply,

through the extremely high terminal im-A pedance of this condenser-coil combination at this frequency.

In Figure l, it will be noted that the antenna conductors and the terminal cross connections are so arranged that there are continuous paths for the low-frequency current which constitute substantially the entire antenna conductor.

It will be noted that the isolatingl condensers C1, may be made to serve the dual function of isolating the high-frequency source from the low-frequency current and to supply a negative reactance for tuning the antenna system when the remainder of the antenna system is positive in its reaetance. l/Vhere, however, the antenna proper is, itself, negative in reactance, the isolating` condensers, Ci, must be chosen of suiiiciently high capacity (low reactance) to supply negligible reactance to the antennaJ system. ln either event, however, it will be found that the low-frequency reactance of these isolating condensers will be of such a high order of magnitude that substantially complete isolation of the high-frequency source from the effects of the low-frequency current will be provided.

Similarly, the inductanee of the filter chokes, Lf, may be employed for assisting in the tuning of the antenna circuit although practical. considerations dictate the wisdom of avoiding the interdependence of these several reactive elements through the tuning of the cliches by condensers Cf, as shown, in order that the filter systems may present a purely resistance impedance to the high-frequency currents and thus make the tuning of the antenna system substantially independent of the constants of the filter system and the adjustment of its elements, and, simultaneously, reduce the high-frequency power loss in the low-frequency source to a completely negligible magnitude.

Since in any of the commonly employed forms of antennas except the so-called loop or coil antennas` the path of the high-freguency current in the circuit of the antenna is closed through the capacity of the antenna and is thus effectively open circuited to lowfrequency currents such as would be economically useful for heating the antenna, special arrangements of the conductors of the antenna system must be made to provide a closed circuit for the heating currents. ln the T type of antenna shown in Figure l, this is accomplished by constructing both the down lead and the flat top portions of the antenna of at least two conductors and interconnecting them so that the low-frequency current will flow through substantially all parts of the antenna conductors and thus provideA heating power throughout the antenna circuit. The use of two conductors properly insulated to'low-frequency current placed closely adjacent will, in general, not serve because of the high thermal insulation inherent in materials of acceptable electrical insulating properties and the consequent need for relatively high temperatures in the conducting portion of such a conductor and aecause also, of the necessarily great highfrequency dielectric loss that is inherent in such conveniently available insulating materials would give acceptable low-frequency insulation. Y

lt is desirable to provide generous spacing between the conductors of the antenna for purposes of low-frequency insulation between the severalportions which are adjacent but at considerable difference in low-v frequency potential and to provide spreaders, 0o and db and cg of insulatingk between the two low-frequency paths pro vided by the flat-top flowing from g to c to a to e and from g to d to b to e thus in effect, putting the two portions, of the fiat-top, gea@ and gdb@ effectively in parallel to the lowfrequency current. The two heating currents join at c and pass down the down lead cf to the low pass lilter and thence to the low-frequency source, S2.

The path of the high-frequency currents is quite different from that of the low-frequency currents. Thus, the twovdown leads, hg and fc. as well as the two sets of tuning elements, C, and Lt, are effectively in parallel by their attachment to the high-frequency source through the isolating condensers Ci, and, as a result the high-frequency currents divide between the two down-leads in flowing into the flat-top portion of theA CII iig dividing between gc and gd while the current in fe. divides between ea and eb, thus placing gc and gol in parallel and similarly placing @a and e?) in parallel to the high-frequency currents from the down leads.

The return paths for these high-frequency currents are by displacement current through the capacity of the antenna conductors to ground and back to the high-frequency source.v v y Because of the symmetry of the conducting circuit of the antennastructure the points c and a and likewise the points Z) and d are at the same high-frequency potential so thatnoy high-frequency current flows through the the antenna as here described is not present and where the consequent asymmetry of highfrequency .potential distribution must not be disturbed by the required continuity to the low-frequency current, such vcross connec-v tions las .are required by this latterv condition maybe supplied in the form of low-pass filters," such as are shown in Cf and Lf.

lnsuch anantenna system as is here shown it is vitally important that, in the interest of radiation eilicieney, the olnnie resistance at high frequency of the conductorsconstituting the antenna be of acceptably small value as compared with the radiation resistance and that the cross-section of the conductors be of correspondingly large value.

F or a solid homogeneous non-magnetic conductor, the resistance at 60 cycles varies inversely with the square of the radius, whereas, at a radio-frequency the resistance varies inverselyv lwith the lirst power of the radius at least to `a first approximation. With solid copper conductors the wirer required to get a proper value of radio-frequency resistance is so large that its resistance vand heat dissipation at 60 cycles are.

quite small.

For example, if the antenna is to Vbe employed at the frequencies used-for broadcasting-of the order of one megacycle, 300 meters-the length of the entire lattop of the` antenna would be chosen to be about three hundred feet, while the length o'l' the down lead would be about two hundred feet.` ln such an antenna usingsolid copper conductors the effective radiation resistance would be of the order of lifty ohms, and the choice of the diameter of the conductors constituting the antenna must therefore be made to provide an effective radio-frequency conductor vresistance, as measuredr at th-e base,'of not more than a few pei` cent of the radiation resistanee, in order to provide suitably high radiation efficiency. Such a choice ofconductor sizes will, in practice, result inthe use of No. l0 B. and S; gauge copper wire in the flat top and intheuse ofNo. 7 or No. 8 B. and S. gauge copper wire in the down lead, and in a total eilective conductor resistance somewhat less than one elim. lt'will be realized, however, that any definite statements as 'to electrical Vproperties of antennas must be limited to narrow temperature ranges, and that in practice, particularly in northern latitudes, the variations ol temperature to which an antenna is exposedv are lar greater than exist in mest electrical structures. For these reasons, the specific data which l give are to be consider-ed simply as illustrative examples, and in actual practice the principles of my invention are applicable in accordance with familiar and well-known engineering practices.

However, Vas a result of this choice of conductors oracceptablc eiiiciency of radiation which is mader necessary by the extremely high cost oi,iadio-frequency power, the resistance of the antenna circuit to suoli lowfrequency current as may be employed for heating the antenna is necessarily extremelyv low and, in the case here considered, is ci the order of one-third et an ohm, i'or a solid copper conductor, thus making it necessary to supply the antenna system 'ith exceedinUl lar e currents for the fren-eration of sufcient heat. Experience indicates that for the prevention oi the- 'tormation of sleet on suoli an antennal as this, it is desirable that about ten watts of heating power per foot of antenna conductor he provided, and thus that in this antenna a total of ten kilowatts of heating` pow-er be supplied. There provision visl to be madefior the melting oi any considerable amount of sleet that may have been allowed to form on the antenna conductors, even greater powers per foot must be provided yup' to, and including, thirty watts per foot of conductor, depending, oit course, on the sleet'melting capacity desired and on the size of the conductors employed. ln oi'- der,however, that only the smaller heating power may be supplied, it is, therefore, necessary that the antenna be supplied withv heating current of about 175 amperes ata voltage of about sixty volts.

y The requirement of such high currents asV tlies-e at such relatively low voltages results ductances, LL and Lf, and all interconnecting conductors, oi" very large sizes and costs of copper, .and within the limitations of coil size and cost involve'an excessive temperature rise'and power waste.` In addition,'and

Athe low-frequency heating current While leaving the resistance of the antenna circuit to the high-frequency current substantially unchanged.

The high-frequency current and low-frequency current ivill flow simultaneously through the antenna conductor, with substantially no mutual. interference, and slcet can. be melted from an antenna Which is simultaneously radiating.

rTypical of this type of especial conductor is on-e made up of a core of steel, or highresistance and `ierferabl i'ion-inaenetic` 7 Y *O l alloy completely enclosed in a cylindrical covering of substantially p ure copper. Such a conductor may be prepared by welding or soldering` to a cylindrical billet of steel or other high resistance alloy an outer shell of copper of annular section and then drawing down the composite billet so made to the desired size of wire. i v

Figure 2 shows a cross-sectional View of such a composite conductor, wherein l is a core and it a surrounding` shell.

` Such specially prepared conductors may be employed in all parts of the antenna structure, or only in particular parts, such as in the horizontal elements of the type of antenna shown in Fig. l, retaining a homogeneous conductor, as solid copper, for the down leads, according to the conditions existing in a particular installation. rlhus the downrleads may beof considerable length, and parts of them may be near the ground, for which conditions solid copper may be lmost suitable. The atmospheric conditions may be much less favorable to the formation of ice near the ground than at the top of an antenna. Greater mechanical strength to avoid breaking may be required in the flat top, and hence it may be more important to use the specially prepared conductor iii the top of an antenna than in the doivn leads, to get both greater tensile strength and increased resistivity. 0i, in particular instances, as ovei' swamps,

'the atmospheric conditions may mostffavor the formation of ice on conductors near the ground, in which cases it may be more iinportant to use the specially prepared conductors in the down leads than in the top of the antenna, especially since the stress diagram will show that a foot of sleet-loaded conductor adds more stress on the supports` the eli'ective penetration of the current is not greater than a feiv thousandths 0f an inch, it is possible to provide a composite conductor of the type here described in which suflicient thickness of copper 'surfacing vis provided to carry the high-frequency currents with substantially the same losses as in a homogeneous solid copper conductor of the saine diameter, While, at the same time, the low-frequency currents which distribute themselves substantially uniformly over the crosssection meet with many times the resistance of that of a homogeneous solid copper conductor of the same cross-section. More sp cil'ically, a copper-steel conductor of this type can be prepared very economically to provide a threefold increase of the 'loviT` frequency resistanceivhile giving completely 'gible increase Iin the vhigh-frequency res ance. Further, if the core is made of a suitable higiij-r-esistance alloy the loW-frequency res ance of the conductor may be made as li iga as twenty or more times as great asthat of the pure copper conductor Without material change in the high-frequency resistance. I Y

lt is also possible to employ a conductor Whose cross-sectional resistivity distribution is radially non-uniform with distribution other than. the particular structure which I have here shown in detail, and it Will be,v

somewhat porous core in 'amolten copper bath, preferably in an atmosphere of hydrogen, nitrogen, or other reducin or inert gas. Another Wav is to maire a Wire from an alloy which contains metals which do not readily oxidize, such as any of the higher resistance alloys that are used for heating and furnace Work, and in preparing the alloy for the Wire, adding a generous amount of a material such as the oxide or sulphidel of copper or sliver; then, after draivingthe Wire, reducing'the copper or silver on the surface by suitable reducing agents and further drawing and polishing to make the skin continuous and of low resistance. In these orV 4ll5 paring such a conductor is to immerse a ganese, and 84 per cent copper, and Con-r stantan`alloy, consisting effi() per cent nickel and 60 per cent copper. Sonie compositions of Monel metal, which are iron-free and contain about tvc-thirds nickel and one-third copper will also serve. These alloys have resistivities of from twenty-six to thirty times that of copper, and are practically non-magnetic. That is, their permeabilities are well less than 1.1. In the'cases of some materials, such as Monel metal, it may be desirable to give particular heat treatment as quenching, to obtain low permeability. @ther alloys oi" high resistivity and which have substantially unitypermeability may likewise be employed.

The selection of the materials and crosssectional dimensions ott the conductor in any given case require calculation and in'v stigation to obtain the` optimum combination, and is a compromise in view oi the various factors which must receive consideration.

The range'of high 'frequencies to be employed, and the diameter of antenna conductor required for mechanical reasons, are irnportant considerations. In an iron-core conductor, surrounded by a copper shell not thinner than 0.01 centimeter, and for a conductor not smaller than about No. 8 B. and S., for high-frequency currents of frequency not less than one megacycle, about 99 per cent of the high-frequency lcurrent will be carried in the copper. rI he copper must not be made too thin or appreciable high-frequency current will be forced into the core,- with resultant `ross of the eiqoensive liigh-frequei'icyenergy.

Vith a non-magnetic core such as manganin it is desirableI with the size ot antenna conductor mentioned to employ a copper coating not less than 0.03 centimeter in thickness which will cause over 98 per cent of the highis overcomeby the higher resistance of a manganin core conductor to low-frequency current, and it is simply necessary to see that the copper is not so thin as to force more than, say 2 per cent` of the high-frequency current into the core, nor so thick as to inaterially reduce the low-'frequency resistance.

In general, therefore, the use of a suitable non-magnetic core is to be preferred.

If the copper is made too thin, the process of drawing` the composite wire from the billet is likely to cause the core to be exposed in spots with resultant' more rapid weathering, and this is a limiting condition on the thickness ot the copper. @ne of the most important considerations is to get a large conductor resistance at low frequency without inaterially arllecting the high-frequency resistance. rlhe mechanical requirement 'for the minimum thickness of the copper will usually provide sutiicient thickness of copper even on a conductor with non-'magnetic core, von the specification just mentioned, to avoid having any appreciable amount of high-frequency current flowing in the core.

Thus, when employing this type ot conductor is such an antenna structure as has been` here described, it becomes possible to greatly reduce the value of the low-frequency heating current to avoid the diiiiculties of heating olf the tuning elements and the deterioration of thecontacts in the circuit as well as to conserve the heating power for use only in the elevated portions of the antenna structure.

More specifically, the employment of the simple copper-steel conductor referred to above allowsrtlic reduction o'f thc heating current to one hundred amperes and the in-` crease of the supplydvoltage to about one hundred volts, and hence allowing for the direct connection of the' antenna system to the commonly available power supply systems and. the reduction of the power losses in the tuning and filter inductances to one-third the values which are met when employing solid copper antenna conductors. Further, the employment of a composite conductor having a non-magnetic alloy core will even more markedly improve the conditions of operation of this system, making the low-frequency power losses in all parts of the antenna system other than the elevated lconductors completely negligible and usually making it possible to employ the higher voltages of conventional power distribution systems without transformers or other costly and vpower consuming devices.

lVhile I have described specific embodiments of my invention, it will be understood that the principle of my invention is ot' broad scope and applicable to embodiments other than those whichI have described specifically, and I do not intend to impose any limitation upon the scope of my invention except as set forth in thev appended claims.

Having now particularly described my invention and in what manner it is to be einployed,I claim: y y

l. In an antenna system, an antenna conductor consisting of an inner core of comparatively high electrical resistivity and an outer contiguous shell of comparatively low electrical resistivity, and means for deliver'- ing a low-frequency current to two separated points of said antenna conductor, said two points being so located that low-frequency current delivered to said antenna conductor traverses paths constituting substantially the entire' length oi said antenna conductor in passing between said points.

2. ln an antenna system, an antenna conductor consisting et an inner core of comparatively high electrical resistivity and an outer contiguous shell ot comparatively low electrical resistivity, said antenna conductor comprising a plurality of conductor elements connected to form a continuous electrical path, means tor delivering high-frequency energy to said antenna conductor, and means for delivering low-frequency current to two separated points of said antennaconductor which are electrically distant trom each other i'or low-frequency currents.

3. Inan antenna system, a plurality of conductor elements, means ter interconnecting terminal. points of said conductor elef ments for forming a continuous low-trequency path th-erethrougli, means ttor delivering high-'frequency energy to said conductor elements, means ier delivering lowfrequency energy to two separated points oi said conductor elements which are electrically distant from each other ttor lowirequency currents, said interconnect-ing means being connected between points oit substantially the same high-frequency potential, said conductor elements having a cross-sectional resistivity distribution rwhich is radially nonuniform and decreases from thecenter outwardly.

4. ln an antenna system, an antenna con ductor whose cross-sectional resistivity distribution is radially non-uniform, and means tor delivering a low-frequency current to two separated points of said antenna conductor, saidL two points being so located that lowifrequency current delivered to said antenna conductor traverses substantially the entire length of said antenna conductor in passing ,A between said points.

5. ln an antenna system, an antenna conductor whose cross-sectional resistivity distribution is radially nonfuni'form, said antenna conductor comprising a plurality of conductor elements connected to form a continuous electrical path, means for delivering vhigh-frequency energy to said antenna con# ductor, and means for delivering a low-frequency current to two separated points of said antenna conductor which are electrically distant from each other tor lowsfrequency currents.

6. ln an antenna system, an antenna conductor consisting of an inner non-magnetic core of comparatively high electrical resistivity, and an outer contiguous non-magnetic shell of comparatively low electrical resistivity, and means ior delivering a low-frequency currentv to two separated points of said antenna conductor, said two points being so located that low-frequency-current delivered to said antenna conductor traverses paths cronstituting substantially the entire length of said antenna conductor in passing'between said points.

7. ln an antenna system, an antenna conductor consisting of an inner core ofcomparatively high magnetic permeability and comparatively high electrical resistivity, and an outer contiguous non-magnetic shell 0i' comparatively low electrical resistivity, and means for delivering a low-frequency current to two separated points of said antenna conductor, said two points being so 1ocated that low-frequency current delivered to said antenna conductor traverses paths constituting substantially the entire length of said antenna conductor in passing between said points.

8. In an antenna system, an antenna conductor consisting ot an inner non-magnetic core of comparatively high electrical resistivity, and an outer contiguous shell of comparatively low electrical resistivity, said antenna conductor comprising a plurality of Yconductor elements connected to form a continuous electrical path, means tor delivering' high-frequency energy tosaid antenna conductor, and means ior delivering 'a lowrequency current to two separated points of said antenna conductor which'are electrically distant from each other for low-frequency currents.

9. ln an antenna system, an antenna conductor consistino oi an inner core of comparatively high magnetic permeability and comparatively high resistivity, and an outer contiguous shell oi comparatively low electrical resistivity, said antenna conductor comprising a. plurality of conductor elements connected to ltorina continuous electrical path, means for delivering high-frequency energy to said antenna conductor, and means for vdelivering a low-frequency current to two separated points of said antenna conductor which are electrically dist-ant from each other for low-frequencycurrents. i

l0. n an antenna system, an antenna eenductor consisting o1y an inner core of comparatively l'iigh electrical resistivity and an outer contiguous shell oit comparatively low electrical resistivity, said antenna conductor comprising a plurality of conductor elements connected to form a continuous electrical path, means for delivering highsfrequency energy to said antenna conductor, means for delivering low-frequency current to two separated points oit said antenna conductor which are electrically distant from each other for low-frequency currents, and means for electrically isolating said means for delivering high-frequency energy from said means for delivering low-frequency current, whereby high-frequency current and low-frequency current can circulate simultaneously in said antenna conductor without mutual interaction of said means.

11. In an antenna system, an antenna conductor consisting of an inner core of comp-aiatively high electrical resistivity and an. outer contiguous shell of comparatively low electrical resistivity, said antenna conductor comprising a plurality of conductor elements connected to form a continuous electrical path, means for delivering high-frequency energy to said antenna conductor, and means for delivering direct current to two separated points of said antenna conductor which are electrically distant froin-each other for lowfrequency currents.

12. In an antenna system, an antenna conductor comprising a pair of substantially parallel wires, conductive cross connections at the ends of said wires, a pair of leads attached to said wires substantially at the midpoints thereof, a source of high-frequency current, means for excluding low-frequency current and passing high-frequency current connected between said leads and said source of high-frequency current, a source of lowfrequency current, means for vexcluding highfrequcncy current and passing low-frequency current connected between said source of lowfiequency current and said leads, said antenna conductor consisting of an inner core of comparatively high electrical resistivity and an outer contiguous shell of coinparatively low electrical resistivity, whereby high-frequen cy current and low-frequency current circulate'simultaneously in said antenna conductor and leads without interaction of said sources.

13. In an antenna system, a pair of similar sets of conductor elements symmetrically -arran-ged with reference to a plane, said conductor elements being cross connected at terminal points thereof symmetrically disposed with relation to Asaid plane, in such manner as to constitute substantially the entire length of said pair of sets of conductor' elements a continuous low-frequency current path, means for delivering high-frequency energy to sai-d conductor elements, and means for delivering low-frequency energy to two sepa.

' low-frequency currents, said conductor elements having a cross-sectional resistivity distribution which is radially non-uniform.

14. In an antenna system, an antenna conductor composed of two different materials, one of said materials being of comparatively low electrical resistivity and being principally disposed in an outer shell, the other of said materials being` of comparatively high electrical resistivity and being principally disposed in an inner core, said materials betribution is radially non-uniform and continuous, said antenna conductor comprising a plurality of conductor elements connected Ato form a continuous electrical path, means for delivering high-frequency energy to said antenna conductor, and means for delivering a low-frequency current to two separated 'points of said antenna conductor which aie electrically distant from each other for lowfrequency currents. Y

16. In an antenna system, an antenna conductor comprising a pair of substantially parallel wires, conductive across connections at the ends of said wires, a pair of leads attached to said wires substantially at the midpoints thereof, a source of high-frequency current, means for excluding low-frequency current and passing high-frequency current connected between said leads and said source of high-frequency current, a source of lowfrequency current, means for excluding high.- i frequency current and passing low-frequency current connected between said source of lowfrequency current and said leads, said antenna conductor and said leads consisting of an inner core of comparatively high electrical resistivity and an outer contiguous shell of comparatively low electrical resistivity, whereby high-frequency current and lowfrequency current circulate simultaneously in said antenna conductor and leads without interaction of said sources.

In testimony whereof, I aiiX my signature.

LAWRENCE C. F. HORLE.

Certiicate of Correction Patent No. 1,917,205. July 4:, 1933.

LAWRENCE C. F. HORLE It is hereby certied that error appears in the printed specification of the abovenumbered patent requiring correction as follows: Page 1, line 59, for brought read through; page 2, line 6, for condenser read condensers; and line 26, for C1 read 0,; page 4;, line 126, for sliver read silver; page 5, line 85, for is read in; and page 7, line 98, claim 16, for across read cross; and that the said Letters Patent should be read With these corrections therein that the same may Conform to the record of the case in the Patent Office.

Signed and sealed this 17th day of October, A. D. 1933.

[SEAL] F. M. HOPKINS,

Acting 00mm/wiener of Patents.

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