US2824306A - Antenna - Google Patents

Description

Feb. 18, 1958 PFAFF 25824 306 ANTENNA Filed Oct. '4, 1950 2 Sheets-Sheet 1 INVENTOR. 5 T Z/ FHFF Feb. 18, 1958 E. R. PFAFF 2,824,306

ANTENNA Filed Oct. 4 1950 2 Sheets-Sheet 2 INVENTOR. fan cs?" I? FFFFP BY I Patented Feb. 18, 1958 ANTENNA Ernest R. Pfaflt, Chicago, Ill., assignor to Admiral Corporation, Chicago, 11]., a corporation of Delaware Application October 4, 1%0, Serial No. 188,375

1 Claim. 01. 343--7 88) This invention relates to improvementsin radio re-, ceivers, and more particularly to an antenna system and the method of designing the same.

As is wellknown to 'those versed in the art, it is common practice and desirable to provide a suitable antenna fora radio receiver whereby the station signals may be intercepted and utilized to audibly reproduce the desired signal. It is also desirable that such an antenna system be one that can be installed in the receiver itself, thus eliminating the necessity of unsightly structures disposed outside the building, as well as the lead-in or transmission line necessary to connect the antenna to the receiver per se; this being desirable from the standpoint of eliminating the fire hazards due to lightning as well as the difliculty of conducting lead-in wires through existing building structures to the receiver itself. Furthermore, in the case of portable receivers, a self contained antenna is most highly desirable.

Heretofore, the most common method of providing a self contained antenna was effected by the provision of a so-called loop antenna. Loops usually consist of a number of turns of wire, usually wound in close proximity to each other and which could be wound as a fiat coil, or the turns can be wound in the conventional helical form. Usually, the entire loop is of a size to conform to the size and shape of the receiver, and the loops may be actually,

asfrequently happens in thecase of portable receivers,

wound around the outside of the cabinet or they may be, and frequently are, supported on a fiber insulating form which may be supported on the rear of the chassis or.

secured to the back of the cabinet.

Regardless of the particular form the loop may take, there are certain characteristics that are undesirable, of

which the main characteristic is that'they are not the most elficient means for intercepting desired signals and do have an ability to intercept undesired radiant energies. Their inefiiciency in connection with the interception of the desired signals is due to the fact that their factor of merit or Q is low. The Q of itself is further lowered due to the proximity of the antenna to the radio chassis.

The ability of the loop to pick up desired signals is proportional to the (a) number of turns, (b) the area.

of the loop, the Q of the loop, and (d) the permeability of the loop which is ordinarily that of air.

The figure of merit of a loop is:

Thefpickup desired is electro magnetic in character.

The number of turnsis jlimited because ,of the large diameter of the turns; and since the inductance per turn of such a loop is high, only a few turns can be tolerated and still enable the receiver to be resonated over the desired frequency spectrum. Because the pickup of the desired signal is predicated on the number of turns, it can be seen that it is desirable to have as many turns as possible. The distributed capacity between the turns, however, limits the range over which the loop may be resonated. The area of the loop is, of course, limited due to space limitations in the cabinet.

The Q of the loop depends on the size of the wire, the dielectric material used, the manner of support, its proximity to the chassis, or other objects including the supportitself, and the form factor of the loop.

The Q of the loop depends on the size of the wire, the dielectric material used, the manner of support, its

" proximity to the chassis, brother objects including the sup- ,been provided which has much greater acceptance of the desired electromagnetic waves, together with a greater rejection of the undesired electrostatic waves.

In the drawings, wherein I have illustrated one form of antenna assembly, particularly useful in a so-called table model type of receiver:

Fig. 1 is a plan view of a complete antennaj Fig. 2 is an elevational view thereof;

Fig. 3 is a view of modified structure;

Figs. 4 and 5 are diagrammatic views of diiferent types of rods that may be used; and Fig. 6 is a diagram illustrating the manner of spacing I the antenna parts.

The improved results, previously cited, are largely obtained by increasing the Q of the loop While actually dethe area encompassed by the loop ability of the loop.

Decreasing the area reduces effectiveness for magnetic as well as electrostatic pickup. The reduction in size, however, is greatly overcompensated for, by the increase in permeability which provides a much greater magnetic pickup than the larger loop because of the enormous increase in effectiveness of the area, but still does not increase the electrostatic pickup.

Increasing the permeability of a coil increases the inductance and enables a reduction in size of the coil. In a loop that has a permeability of 1, because its core is air,

if the permeability is increased to 50 so that magnetic flux is conducted through the core fifty times as good, a coil ,4 as large could be used and still have the same elfe'ctive efiiciency as the larger coil.

The means for increasing the permeability in this in-v stancecomprises the substitution of some material having a greater permeabilitythan air. 'This indicates a magnetic or like material.

One such material i s a crystalline, chemical composition of various metallic oxides having ferr'o-magnetic properies of which several materials are in the market under the name of Magnetic Ferrites or Terami'c's as sold by 0 um. :They have extremely high volume resistivityiand high permeability,

a highdielectric constant; this can beconsidered as an;

undesirable feature because itincreases the; distributed capacity when a coil; is-placed on this type-of matenal, which would result in thereduction-.oftherange-offrequencies to whichsuch a combinationcould be resonated.

One of the. most important undesirable; characteristic; Suc

is .the fact that it hasa high dielectric absorption. a combination. would cause-losses in -the.coil, resulting in a lowering of the Q and resultantradio frequency losses.

I have discovered that theundesirable effects of dielectric absorption maybe greatly, reduced by:

(a) Spreading theturns ofithe' coil,

(b) Spacing the winding, from the core material.

The two above appear to be the most important factors toward making an effective and operative device.

Spacing of the turns decreases the flux density in any, given part of the rod and allowsa greater number of turns to be used, which increases the magnetic pickup. If the turns were closer, the mutualinductance would increase, making it necessary to decrease the number of turns.

The spacing' of the wirefrom the rods is an important feature because it reduces distributed capacity, which is a factor; but more important, the dielectric absorption (losses) are reduced, which in turn increases the Q of.

the combination. Asstated'above, the pickup, is directly proportional to-the Q.

I have discovered, however, that the spacing factor; of the rod from thecoil, isa critical proposition, simply for the. reason. that if thespace is too-far, permeability is reduced, i. e., more airis in the coil core. Again, if the space is too close, dielectric absorption, takes over.

I have found that the spacing may be determined to provide a spacing where the greatest advantages are realized. A formula may be evolved for this spacing wherein a constant,. which maybe readily determined for. any material, is present, which enables anyone versedin the art to, quickly and-efficiently design an antenna system operable within the desired limits, such as the broadcast band. a

This formula may be stated as follows:

D" (2) SY S=space between the rod and the insidezofithe" winding D=diameter of rod' K=constantwhich is determined empirically for particular' types ofmaterial For instance, a rod'No. 1, Fig. 6, having. a diameter D of .225' inch is determined empirically to have a correct spacing S for optimum performance, of .0092 inch between.the outside of the rod and the inside of the coil. A second rod having a diameter of .325 was found to require'a spacing of .0275 inch for best performance.

Dfor rod No; llbe comes .0114" D 'for rod No. 2 becomes .034ii 1.24 being. the constant'for the particular material under consideration I 1.24 in this instance is obtained from empirical tests made. The twotestsvimeachinstance show thatfonrod No. 1,

n @225 i-K T66-L24 In-the caseot rod number 2,

Thereform having: determined in: two' instances that the ratio of (diameter of rod) to the spacingfrom the coil was 1.24 for that particular material, thereafter for any,

rod of this material the spacing can be determined by -t will be appreciated that the factor K could be obtained by making one test-only, but usually it is desirable to make more than one test to make sure that no errors in recount were made.

The Wire of the antenna may be comprised of"Litz""' of the legs 4 of the U-brackets is provided with openings,

through which the ends of the ceramic iron rod 5 extends. Theextremity of the rod abutting the other legof the U.

The Bakelite tube 7 is disposed with its ends abutting,

the innermost legs of the U.

The wire 8 is wound on the Bakelite, tubing. Preferably, the wire is coated with a suitably. moisture proofed cement or wax. The ends of the wire, are secured, to solder lugs 10 riveted to the end of the U brackets.

It isalsopreferable that the zone toward the ends 1 iscoveredwith a suitable cellulose tape, as indicated at 11, to'prevent strains placed on the end leads from unwinding thev wire and to also enable turns of the wire to be removed when aligning the receiver during assembly, without disturbing the main body of the winding.

It. will be noted that the antenna may be mounted at the top of the board where it has the least capacity to the chassis of a receiver. The wire winding terminates wellshortof the ends of the ceramic iron rod, it having been found that if the wire is wound to the ends, the end.

turns have less effect than if the rod extends well beyond the ends of the winding; preferably the rod should extend beyond the winding a distance at least three times the diameter of the rod.

It will be appreciated that the antenna may be mounted in other places, that described being for purpose of illustration. It isnot my intention to be limited as ,to the exactlocation selected.

Withthe foregoing information and formula, it is possible to quickly and easily design, and reproduce in production, antennas for any particular receiver that are highly efi'icient in operation, less subject to interference from static, and are cheap and, economical in construc tion. It also enables-antennas to be provided for the smaller sets which can be, fully concealed within the space limitations of the smallercabinets.

Although thespacing. between the. wire and the form has been described as being obtained by. winding the wire on a form'of'suitable thickness, it" will be appreciated thatthe spacing may be obtainedin-other ways.

5. The rod is secured to the base 1 by brackets 34 having sponge rubber bushings35r that engage the rod over the winding. This provides. a..desirable mounting for the rod since it is quite brittle and subject to breakage.

As can be seen in the drawing, the wire between.the... rods is wound thereon so that theturns are. inspaoed, relation, which is largely determinedby therangeto be.

tuned, the capacity of the tuning condenser, and the, space limitations within the; particular receiver. So far as spacingis concerned, it isnot'critica'l'. T he brackets-with the rubber bushings also serve to clamp the winding in place so that the turns do not shift relative to each other.

It will be noticed that outside of the bracket, as indicated at 36', there are Zones where the wire is closely spaced. This enables the inductance to be readily adjusted by removing or adding turns when needed. The ends of the Wire in this instance are also secured to a trimmer condenser 37, which performs the usual function of such condenser.

It will also be appreciated that the inductance may also be adjusted by dividing the sleeve into two sections, one end section of which may be moved relative to the other as shown by the dotted lines 40 in Fig. 1. In this case, the end section of the inductance may be slid on the rod to vary the inductance.

Throughout this specification, I have described the rod as being a plain cylindrical rod. I have'found, however, that the rod does not need to be cylindrical, neither does it have to be a single rod. For instance, in Fig. 4, I have shown a group of three rods 40 having the wire 41 wound around the group directly on the rods. In Fig. 5, I have shown a single rod 50 which is generally Y shape in cross section with the wire 51 wound on the rod. This rod is substantially the equivalent of that of Fig. 4.

My formulae are also applicable to this type of construction, for the open space between the wire and the rod in each instance may be determined in the same manner as previously described, i. e., with a known cross sectional area of rod, a predetermined amount of space between the rod and wire must be maintained to realize optimum performance.

The area of this space may be determined by determining the cross sectional area of the rod and relating it to the area of a circular rod of equivalent cross sectional area. Then the space for a cylindrical rod applies; the legs of the rod, being of determined length so that the trianglar space between the rod and the wire equals that desired.

As an example, a circular rod having a diameter of .450 inch would require a spacing between the rod and the inside of the wire of .074 inch.

From Fig. 6, D =D+2S=.450+.148=.598.

The area A of rod D (.450 dia.).=.16 sq. in.

The area A used by the periphery of the form this being the ratio between the two areas.

Then the rod having the shape of Figs. 4 and 5 is used. It would be formed to have an area A equal to A or the equivalent area of a rod having a certain diameter would be determined. Then the area A to be enclosed by the wire wound on A would be determined by providing areas such that As stated then, the ratio of areas of (a) the space enclosed by the wire to (b) the space enclosed by the rod can be determined by comparison with cylindrical rods and wire forms of like area and applied to rods of different formation.

One of the advantages of the rods of Figs. 4 and 5 is that, bare or enameled wire may be wound directly on the rod and good results obtained by using my dis covery.

Although I have described the rods as being solid rods, tubular rods are also efiective providing the wall is not too thin.

Having thus described my invention, I am aware that numerous and extensive departures may be made therefrom without departing from the spirit or scope of my invention.

I claim:

An antenna comprising an inductance in the form of a helical winding of conductor disposed about a core of ferrite wherein the conductor is spaced from the core a distance such that the maximum permeability for the helix is retained and dielectric absorption by the core to the conductor is minimized for most efficient operation of the antenna as a receptor of radio waves and wherein the spacing is determined by the formulae where S equals the spacing from the inner periphery of the conductor to the outer periphery of the core; D is the diameter of the core and K is a factor determined empirically by measuring one or more antennas constructed for optimum performance and equals References Cited in the file of this patent UNITED STATES PATENTS 2,191,782 Valane Feb. 27, 1940 2,266,262 Polydorofi Dec. 16, 1941 2,355,969 Schaper Dec. 7, 1943 2,492,772 Van Billiard Dec. 27, 1949

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