US2299785A - Radio antenna - Google Patents

Description

Oct. 27, 1942. L, TT 2,299,785

RADIO ANTENNA Filed May 16, 1940 2 Sheets-Sheet 1 Twcwzys Oct. 27, 1942. BARRETT 2,299,785

RADIO ANTENNA Filed May 16, 1940 2 Sheets-Sheet 2 L 4 0, L3. Vi 10/ i RADIO 857' (/ITTo Qugys Patented Oct. 27, 1942 RADIO ANTENNA Edward L. Barrett,

corporation of La Grange, 111., Barrett Engineering Company, Ch

Illinois assignor to lease, 111., a

Application May 18, 1940, Serial No. 335,589

18 Claims.

The invention relates to radio antennas, devices embodying the present invention being particularly adapted to meet the exigencies of use in automobile installations.

One object of the present invention is to provide an antenna embodying a plurality of elongated tubular elements telescoped one on the other, together with a novel motor actuated arrangement for projecting and retracting the same.

Another object is to provide a radio antenna of the type embodying a plurality of telescoped tubular elements in which the problem of transmitting the forces (from a motive power source) requisite for projecting and retracting the tubular elements, is solved by utilizing as a transmission element a tightly spiraled wire helix led through the tubes and hidden from view in them, the wire helix being sufliciently flexible to be coiled up in a small space when drawn in to retract the antenna, and yet sufliciently stifl to withstand without buckling the compression forces applied to it when pushed outward to project the antenna.

Another object is to provide a novel drive mechanism suitable for use in an antenna of the character indicated in which a motion transmission member, in the form of a laterally flexible tightly spiraled helix of wire, is threaded in the tapped interior of a hollow motor shaft so as to form a direct driven-screw connection with it, thereby obviating the necessity of a speed-reduction gearing or other connecting elements between the motor and the transmission element.

Another object is to provide a motor driven antenna of the type indicated embodying a novel control arrangement for automatically correlating the operation of the antenna projecting and retracting drive with the operation of the radio set.

Another object is to provide a radio antenna embodying power actuated means for projecting and retracting it and which is characterized particularly by its low cost and simplicity of construction, as well as its safety and ease of operation,

Still another object of the invention is to provide a motor driven antenna having an extremely low capacity coupling with ground from its various actuating parts, together with a high leakage resistance to ground.

A further object is to afford an antenna of the type indicated having an actuating mechanism form as to make possible complete and adequate shielding w e still retaining small overall dimensions for the entire apparatus.

The invention also resides in various improvements and simplifications in the construction of the power actuating and control switch arrangement for the antenna by means of which low cost and eiiiciency of operation are combined.

Further objects and advantages of the invention will become apparent as the following description proceeds, taken in connection with the accompanying drawings, in which:

Figure 1 is a fragmentary view of an automobile fltted with an antenna embodying the present invention.

Fig. 2 is a side elevation, with a portion broken away, of the antenna apparatus.

Fig. 3 is a longitudinal sectional view of the tensible wave-receiving structure of the antenna, shown in substantially retracted position.

Fig. 4 is an enlarged vertical sectional view taken substantially along the line 4-4 in Fig. 2.

Fig. 5 is a longitudinal sectional view of the antenna actuating mechanism, with the flexible transmission element partially reeled out rather than fully reeled out as in Fig. 6.

Fig. 6 is a detail sectional view of the takeup mechanism showing the tail end of the flexible transmission element when it is fully reeled out.

Fig. 7 is a transverse sectional view along the line in Fig. 5.

Fig. 8 is a detail perspective view of a drive bushing included in the power actuating mechanism of the antenna.

Fig. 9 is a schematic wiring diagram of the control system for the antenna actuating mech anism,

Fig. 10 is a sectional view, similar to Fig. 6, of a modified form of take-up container.

Fig, 11 is a schematic wiring diagram of a modified form of control system.

While the invention is susceptible of various modifications and alternative constructions, I have shown in the drawings and will herein describe in detail the preferred embodiment, but it is to be understoodthat I do not intend to limit the invention but intend to cover all modifications and alternative arrangements falling within the spirit and scope of the invention as expressed in the appended claims.

Referring more particularly to the drawings,

whichis sufllclently compact and of such general the invention has been shown herein as embodied in an automobile installation (see Fig. 1). In such an installation the antenna is exposed to extreme variations in temperature, and to rain, sleet, snow, and'the like, as well as to strong vibrations and jouncing. Furthermore, in the event that the electric actuating motor 1 for the antenna is driven from the conventional storage battery in the car, and that is the only convenient source of current for such a motor, it must be capable of operation despite extremely wide variations in voltage of, for example, 50% above to 50% below normal, such as are frequently encountered in the output of conventional storage battery systems of automobiles. Although the presently disclosed antenna is expressly adapted to meet theexigencies of such an environment, as will more fully appear below, it is manifest that antennas embodying my invention may also be used in a variety of other installations.

In general, the antenna of Fig. i'comprises an extensible wave-receiving structure It and an actuating mechanism, housed in a casing II, for projecting and retracting the same. The casing II is desirably mounted in the rear portion of the well of a front fender I! on the car, as indicated, so that it is completely hidden from view, yet occupies an otherwise waste space so that it neither mars the appearance of the car nor interferes with its other parts. when the antenna is retracted it extends only a few inches above the surface of the fender so that its presence is practically unnoticeable. On the other hand, when the antenna is projected to the operating position shown in Fig. 1, it affords an ample length of wave-receiving structure, free of the car bodyso that it functions without interference or shielding from the car. As is hereinafter described in greater detail, the actuating mechanism housed in the casing II is controlled from the interior of the car so that the user need not manually pull the antenna out or retract it, or, in fact, give any spect to the 'outer tube II. The collar l8 is fashioned in the form of a flanged cup with an open bottom so that it constitutes a stop for the inner end of the tube ID.

The rod II has on it an enlarged head ll of decorative shape which forms a stop connection between it and the tube [5. The outermost section or tube I1 is stationarily mounted in an insulating bushing I8 (Fig. 4) fixed within a threaded sleeve or bushing 19.

with the arrangement of telescoping elements described above, the entire series can be projected or retracted by correspondingly pushing or pulling on the rod l4. Thus, to retract the wavereceiving structure, the rod I4 is pulled inward until its head ll strikes the nose of the tube I5. Thereafter continued inward motion of the rod It brings the tube I! with it and when the latter's inner end strikes the cup l8 on the tube It the latter is also drawn inward, the retractive motion of the sections l4, I5 and I6 being continued until they are withdrawn almost completely within the outermost tube I I in the final position shown in Fig. 2. Similarly, to extend the wave-receiving structure, the rod I4 is thrust longitudinally outward. After' the rod It has been moved to project a major portion of its length from tube IS, the enlarged inner end por-.- tion ll on the rod (see Figs. 3 and 4) strikes the necked portion li of the tube [5, thereby drawing this tube outward with it. Next the collar 15 on the tube l5 engages the neck l6 on the tube It so that the latter tube is moved on outward. The outward sliding motion of the tube It is finally limited, to prevent complete separation of the sections, by engagement of its collar It with the neck I I on the tube H.

To form a concealed motion transmission con- I nection between the hereinafter described power special attention at all to the antenna. This unitary assembly or construction of the antenna permits it to be easily handled and attached as a unit, thereby greatly simplifying its installation, servicing and merchandising.

The wave-receiving structure It is made up of a series of telescoping elements or sections including, as the innermost, a slender, stainless steel rod 14 (Figs. 2, 3 and 4). Telescoped over this rod and on each other are the next successive sections, in the form of seamless brass tubes I5, |6 and l1. Each of the tubes l5, l6 and i1 is necked in at its outer end, as indicated respectively at l5, l6 and [1 in Fig. 3, to form a snug sliding fit with the next adjacent one of the telescoping elements. To aid freedom of movement the sliding surfaces are customarily oiled but in case of very cold weather when such oil becomes sticky or in the event that the antenna becomes coated with sleet or ice, it will be appreciated that the force required in projecting and retracting the telescoping sections is greatly increased and consequently any drive mechanism for them must be able to take care of, without loss of efficiency, such heavy loads.

To guide the telescoping sections against side sway, collars I5 and Ill are fixed tothe tube l5, respectively, at its inner end and at an intermediate point so as to space its inner portion from the encircling tube It. Similarly spaced collars l6 and 5 are fixed respectively to the inner end and to an intermediate portion of the I tube It so as to guide its inner portion with reactuator in the casing H and the telescoping sections of the wave-receiving structure I0, I utilize a slender, flexible member I9 led up through the nested tubes l5, l6 and I1 and anchored to the butt end of the rod I4 (Figs. 3 and 4). This member l9 must meet a number of peculiar, and in some respects antithetical, requirements. First of all it mustbe flexible enough to permit its being coiled or reeled up in a compact storage space when the antenna is retracted. Also it must be capable of transmitting sufficient tension to effect retraction of the telescoping elements. 0n the other hand, the member I9 must be rigid enough that it can transmit sufficient compression, without buckling, to project the telescoping elements even when their sliding surfaces are sticky or heavily loaded. It should be observed that buckling of the member l9 must be avoided not only because it might cause jamming of the cooperating driving parts but also because such buckling would cause the member to rub against the side walls of the encircling tubes, this added friction drag thereby increasing even further the compression load on the member I9. I have found that a member suitable to meet the requirements noted may be made by fashioning a tightly spiraled helix of tinned piano wire. This wire is spiraled so tightly that its adjacent convolutions are abutting and may, for example, in the particular mechanism shown, be 0.025 inch piano wire spiraled in a helix of 0.078 inch outside diameter. This optimum ratio of about yet has the necessary characteristics of stiffness when wound in the configuration noted. The use of tinned wire is desirable because of the marked reduction in friction which such a finish accomplishes in the event that the wire helix is threaded in a tapped driving bushing, as is the case in the hereinafter described actuator mechanism.

In accordance with another aspect of my invention an electric motor type of actuating mechanism is provided such that the wire helix I9 constitutes the driven element of a speed-reduction screw drive. In other words, the convolutions of wire are themselves used as screw threads. This provides, at very low cost, a long member which is in effect screw threaded and which is of very desirable character, even aside from the standpoint of economy, because it can so readily be coiled down in such a small space when reeled in for retraction of the antenna.

In the instant construction the actuator mech anism comprises an electric motor designated generally at 20. (Figs. 4 and 5) having a stator 2| and rotor 22. Desirably the motor 20 is adapted to operate on a direct current of low voltage so that it can be supplied from the conventional six volt storage battery of an automobile. The armature 22 is carried by a shaft including an outer tubular steel jacket 23 journaled in self-alining, self-oiling bearings 24 of well known form and which are mounted in the motor casing 25. The motor 20, being of the direct current type, alsoincludes the usual commutator 26 and brushes 21. This motor has stator or field windings 2I and an armature winding 22, the motor being reversible by changing the relative polarity of potential supplied to the rotor and stator windings, respectively.

In order to form a drive connection, of the general character indicated above, between the motor and the flexible wire helix I9,- the latter is led through the hollow motor shaft and the latter is constructed to present interior screw threads mating with the convolutions of the helix I9. In this manner the convolutions of the wire helix are themselves used with screw threads so that the member I 9, which is fixed at its tail end to hold it against rotation, constitutes a driven screw which is moved lengthwise by rotation of the motor shaft, the direction of axial movement for the member I9 depending of course upon the direction of motor rotation. For this purpose a tapped or interiorly threaded bushing 28 (Fig. 5) is fixed in the tubular shaft jacket 23 and the wire helix or shaft I9 is threaded in it. Desirably the bushing 28 is made of hard bronze and its exterior is circumferentially grooved and knurled (see Fig. 8). The tapped bushing 28 is iorce fitted in an insulating bushing or sleeve 29 i Fig. 5) which is in turn force fitted in the tubular shaft jacket 23. The roughened exterior of the tapped bushing 28 insures it against rotation with respect to the insulating sleeve 29. It will be observed that the longitudinal bore in the sleeve 29 is tapered outwardly toward its respective ends, from the ends of the tapped bushing 28, so as to insure clearance from the helix i9. At the respective ends of the sleev 29 additional bushings of electrical insulating material are forced in the ends of the motor shaft jacket 23. The sores in these bushings are tapered inwardly so as to form guide throats loosely engaging the member I9 which passes through them. It should also be noted that the outer ends of the bushings 39 are turned outwardly to form oil-thrower surfaces which will, by centrifugal force, throw out any oil or other liquid falling on them and thus prevent its entry into the interior of the motor shaft.

The novel screw type drive effects, with high emciency, a large speed reduction, without the necessity of interposing expensive and noisy speed-reduction gearing. By way of example, if the helix I9 ha forty turns per inch and the motor 20 revolves at 2.000 R. P. M. the speed reduction is great enough to require ten or twelve seconds to project or retract the antenna, a nice speed for the purpose. The high efficiency of the drive connection, which is about per cent, results in a large measure from the minimization of friction between the drive bushing 28 and the helix I9. To minimize this friction, the bushing threads are cut with a special tap which shapes them to conform with the rounded cross section of the outer sides of the helix turns which mesh with them. The tinned finish 0n the helix I9, heretofore noted, also materially reduces the friction. Still another factor in the minimization of friction is the small length of the drive bushing 28. In the present instance it is only long enough to mesh with about nine convolutions of the helix I9.

Despite the high efficiency and low friction noted just above, the drive is highly resistant to reverse operation. In other words, it is practically impossible to rotate the bushing 28 as a driven member by pushing endwise on the helix I9 as a driver. Incidentally, this type of reversal is, of course, to be distinguished from a mere reversal of direction of motion for the parts in which the bushing 28 still remains the driver and the helix I 9 the driven member. The latter type of reversal is readily accommodated by the present drive mechanism. Inability of the helix I9 to perform as a driver in the system is a highly necessary characteristic since the jouncing and vibration of an automobile tends to cause the telescoped sections of the antenna to move inadvertentiy to collapsed position. As will hereinafter appear, however, the switching arrangement of the present antenna is such that the antenna is automatically grounded and, hence, rendered inoperative, as soon as the retraction motion of the helix I9 starts. Hence, if the drive connection permitted even a small endwise creep of the helix under the conditions noted, the antenna would become grounded, so it is imperative that the driv should automatically lock against reversal of the driving and driven elements. 01 the common forms of drive available, as distinguished from the novel one herein disclosed, about the only one which has such a locking characteristic is a worm and worm wheel drive. In it, however, the eificiency is only about 20 per cent. This very great reduction in efficiency, as compared to 35 per cent for the herein disclosed drive, is extremely bad in an installation of this type because either an almost prohibitively large and expensive electric drive motor must be used or else the system will stall under overloads encountered in cold or bad weather conditions or when the supply voltage from the automobile storage battery becomes low.

The casing ll not only houses the motor 20 described above, and its associated control switches hereinafter described, and electrically shields the various parts housed in it, but also forms a take-up chamber 3| (Fig. 5) into which the fiexible wire helix I9 is coiled when the wavereceiving structure I 0 is retracted. To this end the casing comprises a tubular sheet metal body portion 32 in the intermediate portion of which the motor casing 25 is fixed. The opposite ends of the body 32 are closed by removable sheet metal caps 33 and 35. To the outerend cap 33 (see Fig. 4) is fixed the threaded mounting bushing l9. To'secure the unitary antenna structure in place on an automobile fender, as shown in Fig. l, the bushing i9 is projected through a suitable hole M on the fender l2 (Fig. 2) and lock nuts 35 are threaded on the bushing, holding the assembly in place with the casing ii hidden beneath the panel or fender and with the wavereceiving structure it projecting freely from the other side.

At its inner end the casing it presents the generally cylindrical take-up chamber 35 to the adjacent end of the hollow motor shaft and from which end of the motor shaft the flexible wire helix i9 emerges as the telescoping antenna elements are retracted. Means is provided for anchoring the inner end of the helix 19 in the chamber 39 so as to restrain the helix against rotation, as is necessary for proper operation of the drive, also to hold its inner end portion permanently curled in a direction generally circumferential of the chamber 36. For this purpose the end of the helix It is soldered to the free end of a leaf spring '36, anchored to the casing cap 341 as described below, with the helix is extending laterally from the spring 36. It will thus be seen that when a maximum permissible amount of the helix is pulled out of the take-up chamber 36 the remaining tail end portion is curled as shown in Figs. 6 and 7. Hence, when the helix it is fed into the chamber 3!, this initial curl will cause it to coil up neatly and automatically in the chamber without the necessity of providing any take-up reel or the like. The omission of a take-up reel makes possible not only the accomplishment of an important saving in cost but in addition very substantially reduces the capacity coupling to ground for the antenna. As to the latter point it should be noted that if a metal take-up reel is used for the helix E9 or,

similar element the take-up reel must be of the same potential as the antenna element to which it is connected, namely, the helix l9, and hence the entire surface of the take-up reel adds to the capacity coupling to ground.

In order to prevent the electric driving motor 26 from causing undesirable interference noises to issue from the speaker of the associated radio set when the antenna described is used on a radio receiver, a muting switch is provided for automatically silencing the set whenever the motor 29 is in operation. In the embodiment of the invention shown in Figs. 1 to 9, inclusive, this muting switch comprises (see particularly Fig. 6) astationary contact 31 and a cooperating movable contact 38 fixed to the mid-portion of the leaf spring 36. The butt end of the leaf spring is fixed to an insulator supporting block 39 by an overlying insulator block Ml (see also Fig. 7). Hence when the switch contacts 3?, 38 are open the extensible antenna, which is directly connected to the spring 35 as described, is isolated from ground. On the other hand, when the contacts 31, 38 are closed, the antenna structure is connected to ground through them, or in other words, is grounded to the housing H and the automobile body. Such connection of the an- -tenna to ground of course mutes or silences the radio receiving set. Since the leaf spring 36 is attached to the tail of the flexible wire helix IS the contacts 31, 38 are pulled open by the tension exerted by the helix I 9 just as the telescoping 7 antenna sections reach their fully extended position. It will be observed, however, that whenever the motor 2&3 is running to feed the flexible helix l9 into the chamber 3! or to draw it out of the same, there will be a sumcient slack length of the helix in the chamber so that the spring 86 retains the contacts 37, as closed. In other words, the switch mechanism described acts auto= matically to mute the associated receiving set whenever the antenna actuating motor is in operation,- but automatically removes the muting round connection for the antenna when the latter is fully extended. 1

For the establishment of a circuit from the antenna wave-receiving structure it to an ,associated radio set, a bayonet type plug receptacle M is provided (see Fig. 4). This receptacle is fixed in the side wall of the casing H and is connected through a conductor di with the outermost sectionill of the telescoping sections. A suitable plug connector (not shown) may of course be inserted into the receptacle M to complete the connection to the in-put terminal of the radio set. Similarly the supply leads for the motor 20 enters the casing H at a terminal block 52 in its side wall. 7

Electrical control means has been provided for the actuating motor 28 such that operation of a manual switch serves to institute either an antenna-projection or antenna-retraction cycle of operation for the motor, as may be required, and which is automatically terminated at the completion of the desired movement of the extensible antenna. Furthermore, the controls are such that the usual on-off switch on the associated radio set itself may be used to institute these cycles of operation so that the antenna is automatically projected into operative position whenever the radio set is turned on, and automatically drawn in when the radio set is turned ofi.

The wiring diagram for the control system noted above is shown in Fig. 9. Upon reference to it, it will be seen that the conventional storage battery for an automobile, indicated at 33, may constitute the source of power for both a radio receiving set M and the actuating motor 20 for the antenna. The control system also includes a double-pole reversing relay 4%: as well as up and down limit switches it and d1. Incidentally, the relay 55 is mounted in the casing l l on one end of the motor casing 25 (see Fig. 4), while the limit switches 36, W are also mounted in this casing at the respective ends of the motor, the particular construction of these switches being hereinafter described. The reversing relay 45 comprises stationary contacts 58, 49 and 50, as well as movable contacts 5| and 52. The movable contacts are carried by interconnected spring fingers which also carry an armature 53 operated by an energizing winding 54. When the relay is deenergized the movable contacts 5 l, 52 are closed respectively against the stationary contacts 48, 69 and when the relay is energized the armature 53 ispulled down so that the movable contacts engage respectively the stationary contacts 49 and 50,

With the control circuit connected as shown in Fig. 9, closure of the main on-ofi switch 55 of the radio set 44 connects the radio set to the battery 43 and also energizes the relay winding 54 from this same battery through conductors 56, 51. As heretofore noted such energization of the relay causes its pairs of contacts til-49 and 5252 to close, thereby establishing an energizing circuit for the motor 20 (from the battery 43 through 5622*5250.5846-59-2l 49-5l to ground) so that the motor rotates in a direction to feed the fiexible helix l9 upward and project the wave-receiving structure I0.

When the latter is fully projected the up limit switch 46 is automatically opened thereby interrupting the energizing circuit set forth above and stopping the motor.

Upon opening of the radio set on-off switch 55 the radio set is, of course, disconnected from the battery 43 and the relay 45 is simultaneously deenergized. Such deenergization of the relay causes its contacts 48, Si and 49, 52 to close thereby establishing an energizing circuit for the motor 20 (from the battery 43 through 5622--52- 49-2l 60-41-48-5l to ground). It will be observed that in this alternative energizing circuit for the motor, the field winding 2l'- is energized with a reversed polarity compared with that in the first instance noted so that the motor 20 operates in the reverse direction to draw the flexible helix IS in and thereby retract the telescoping antenna sections. Upon completion of full retraction of the antenna the down limit switch 41 opens, thereby interrupting the motor circuit previously described and stopping the motor. It should be particularly noted that when the radio set is turned off neither the antenna motor 20 nor its reversing relay 45 draw any current after the antenna is finally retracted so that continued drain on the car battery, when the radio set is not in use, is ob'viated. Furthermore, the arrangement is such that if the current supply lead to the radio set should be broken inadvertently the relay 45 will be deenergized thereby causing the antenna to be drawn in automatically. In other words the system fails safe.

Turning now to the details of the limit switches 46, 41 (Figs. 4 and 5) it will be seen that a very simple and compact limit switch arrangement has been provided especially adapted for use with a drive mechanism of the character set forth. With the exception of the shape of the insulator bushings at their outer ends the two limit switches are substantially identical in construction and accordingly the same reference numbers have been used to designate identical parts, In the case of the down limit switch 41, it comprises a metal tube or housing 6| fixed to the motor casing 25 and axially alined with the motor shaft. In this tubular housing BI is slidably mounted an insulator bushing 62 having a central opening through which the flexible shaft I9 is free to pass. This opening is however sufiiciently small that the enlargement l4 on the inner end of the rod l4 cannot pass through it but will abut against it and force the insulator bushing down from the position of Fig. 5 to that of Fig. 4 when the antenna is retracted. A helical compression spring 63 yieldably urges the slidable bushing 62 to the position of Fig. 5 and in which position it abuts against a second insulator bushing 64 fixed in the outer end of the tubular housing 6|. The center opening in this latter bushing 64 is large enough to permit free passage of the enlargement l4 on the rod I4.

The sliding bushing 62 has an outer end portion of reduced diameter which is encircled by brass ring 65 that constitutes a bridging contact for the limit switch. Cooperating with this bridging contact ring are two resilient contact fingers 66. These contact fingers are mounted on insulator blocks 61 clamped to the exterior of the tubular housing 6| by a strap 68 (see Fig. 7). It will be noted that the bridging contact ring 65 is slightly larger in diameter than the opposed reduced end portion of the fixed bushing 64. Consequently when the ring 65 is thrust upwardly into its bridging position shown in Fig. 5 the contact fingers 66 are spread apart slightly to insure a firm frictional grip of them on the bridging ring so that an eifective elec trical contact will be established. When the sliding bushing 66 is moved down, however, so that the bridging ridge 65 disengages the fingers 56, the latter snap in against the reduced nose of the vfixed insulator 64. The latter is, however, sufiiciently large that the fingers are retained spread apart far enough that there is no danger of their touching or short circuiting on the tubular housing 5| through whose apertured side walls they project.

From the foregoing it will be seen that'the "down" limit switch 41 is positively actuated to its open position by the butt end of the rod l4 when the antenna is fully retracted so as to stop the drive motor 20 automatically at such a point. In connection with the operation of the switch structure it has been found that a fairly strong compression spring 63 should be utilized since a weak spring or none at all at this point permits sufllcient over-running of the parts, due to the momentum of the armature 22, that the helix I9 is likely to become jammed in the drive bushing 28. The spring 63, which is sufficiently long and strong to prevent the sliding bushing 62 from going solid against the end bushing 30 on the motor shaft, prevents any such jamming however.

The up limit switch 46 is identical with the down limit switch described above except that at its outer end it has a stationary bushing 64 with a throat of somewhat different shapethan that of the bushing 64. In the case of the latter its throat or center opening is of cylindrical form and its outer end is shaped to receive the antenna section H. In the case of the bushing 64 of the up limit switch 46, however, the throat in the bushing is flared outwardly in a funnel shape. The shape or the throat serves to guide the helix l9 at a proper angle to coil down smoothly in the take-up chamber 3|. Actuation of the up limit switch 46 is accomplished by means of a bead or enlargement 69 on the helix I9 (see Fig. 6) which is larger than the central hole through the slidable bushing 62 and thus serves to force this bushing upward into switch-open position when it contacts it at the end of the extension travel for the antenna.

The operation of the apparatus will in general be clear from the foregoing. As a brief rsum of such operation it may be noted that to extend the antenna and condition the radio set for operation, it is only necessary to close the radio set on-ofl switch 55 (Fig. 5). Closure of this switch energizes the relay 45 and starts the motor 20 revolving so that the wire helix I9 is screwed axially through it and the set of telescoping elements l4 to I! fully distended. Upon completion of this projection of the antenna the up limit switch 45 opens thereby deenergizing the motor 20. At the same time the tail end of the helix l9 pulls open the muting switch contacts 31, 38 thereby removing the ground connection from the antenna so that the radio set is conditioned for operation, this ground connection having previously muted the set during the operation of the motor 20 so that no unpleasant interference noises would be emitted from the receiver.

Upon turning off the radio set 44, the operator need only open the main switch 55, whereupon relay 45 drops out and the motor 20 is energized for rotation in the opposite direction. The motor thus draws in the helix I9 feeding it into the take-up chamber 3| where it is smoothly and automatically coiled down into the container. At the institution of this feeding of the helix into the chamber 3| its pull on the leaf spring 30 is relieved so that the muting contacts 31, 38 close preparatory to the next projection of the antenna. The contraction of the antenna continues until the butt end of the rod I4 opens the down limit switch 41 whereupon the motor 20 is deenergized leaving all of the circuits dead. It will thus be seen that the operation of the antenna is fully automatic and is controlled simply as an incident to turning on and oil the radio set so that the operator need give it no special attention whatever.

The antenna apparatus described above is characterized by its low capacity coupling with ground. The best manually operated automobile radio antennas on the market today have a capacity coupling to ground of about 35 mmf. On the other hand th introduction of an electric driving motor or other power actuated mechanism of the antenna is likely, in the absence of special precaution, to run this capacity coupling up to 500 or 600 mmf. Tests on the present antenna structure have shown, however, that it has a capacity coupling of only 47 mmf. or, in other words, the same order-of magnitude as that for an antenna having no power actuating means whatever. A number of factors contribut to this low capacity coupling in the present appara- I a smallpart of the helix remains in'the chamher so that there is very little surface left for capacity coupling to the chamber walls. Altogether a highly efficient combination of elements has been achieved.

In Fig. 11 I have shown a wiring diagram for a modified form of a control circuit for an antenna apparatus of the general character set forth above but which is such that the antenna can be stopped at will during its projection movement, thus making it possible for the operator to extend the antenna to any length desired. Aside from the control elements the only change in the apparatus required is that the lower end of the casing II be made in th form of an insulating cup 34, as; shown in Fig. 10, rather than in the form of a metal cup. Furthermore, th flexible shaft I9 is now anchored directly to thi insulator cup and a separate muting or grounding switch for the antenna, in the form of a relay I 00 (Fig. 11) is used. Incidentally the tail end of the flexible shaft I 9 is anchored in the cup 34 with the same initial curl as before so that it will coil down smoothly into this cup when the antenna is retracted. The control arrangement of Fig. 11 also illustrates the use of a reversible motor I20 which, though generally like the motor 20 described above, has two separate field windings I 2| and I2l which are alternatively energized for opposite directions of motor rotation rather than a single winding whose polarity is reversed for reversal in rotation. Such a double winding tus. In analyzing these factors it should be borne tively, and varies inversely with the length of air or other dielectric gap between such surfaces. When the present antenna is projected for operation the only parts remaining within the grounded casing II, which are at antenna potential or in other words are themselves parts of the antenna, are the butt end portion of the tub I1 and a portion :of the small diameter helix I9. These are both separated from the grounded casing I I by quite a wide air gap, however, since the casing is of substantially greater diameter than either of them. Furthermore, the helix I9, being of small diameter presents a minimum of external area. The magnetic structur of the motor and its shaft are also at ground potential but they are close to only the short length of the helix I9 which projects through them. Also, the

insulating sleeve 29 in the motor shaft is made a as thick as the dimensions of the associated parts will permit so as to give a maximum air gap between even this short length of the helix I9 and the grounded motor parts. This insulating sleeve. 29 also forms a high resistance barrier between the metal parts of the motor and the adjacent antenna element, namely, the helix I9, so that the leakage path between them is of very high resistance. Another factor, heretofore noted, which very markedly reduces the capacity coupling is the elimination of any take-up reel for the helix I9. Upon reference to Fig. 6 it will be seen that after the helix has been fed out of the chamber 3| to its fully extended position only reversing motor may be controlled by a simpler form of relay shown as I45 in lieu of the more complicated double pole type exemplified by the relay 45 above. Also included in the control system of Fig. 11 is a push button switch IOI arranged to be held in open position by releasable latch mechanism I02, the latch being released by energization of an associated solenoid I03. Other parts of the control system which are identical to those described above have been given the same reference numerals.

Assuming that, in the system of Fig. 11, the antenna is retracted and the radio set off, the operator closes the radio set on-off switch 55 to project the antenna into operating position. Closure of this switch connects the radio set 44 to the battery 43 and at the same time connects the main relay I45 to this battery. Energizationof this relay I45 causes its contacts I 45 to close and its normally closed contacts I45 to open. 'I'hereupon the motor I20 i energized (from the battery 43through a circuit 43---I45*-I0I---I0Ii---4Ii-I2I -422 the antenna in some partially projected position he need merely depress the push button IOI, which may be located at some convenient joint as, for example, on the dashboard of the car. When this push button switch is thus opened it is latched in open position by the latch I02. Since the .push button switch IN is included in the energizing circuit for "up movement of the motor as well as in the energizing circuit for the relay I the motor and relay I00 are both deenergized as soon as the push button switch IN is opened. The projection of the antenna is thus arrested and the muting ground connection for it opened.

In turning off the radio set 44 the operator opens the radio set switch 55 whereupon the relay I is deenergized so that its contacts I 05 open and contacts 5 close. Closure of these latter contacts connects the motor I20 for rotation in a direction opposite to that heretofore described (from the battery 43 through 5 IIIM"I03I22 to ground) so that the motor rotates to draw in the antenna. This rotation continues until the down limit switch 01 opens, thereby arresting further rotationof the motor. It will be observed that the energizing circuit just set forth for the motor includes the solenoid I03 so that whenever the motoris energized to draw in the antenna the latch I02 is automatically moved toits disengaged position thus permitting the push button switch IM to snap back out to its initial closed position, in the event that it has been previously opened, thereby conditioning the circuit for a subsequent initiation of an antenna-projection cycle.

I claim as my invention:

1. An extensible radio antenna comprising, in combination, a plurality of elongated metal antenna sections arranged in telescoping relation to each other, at least the outer. one of said sections being of hollow tubular form, a transmission member extending longitudinally into the interior of said outer section from the base end of the latter and operatively connected to the innermost element of the series, said transmission member comprising a wire tightly spiraled in a long slender helix of substantially smaller diameter than the interior diameter of said outer antenna section, an electric drive motor having a hollow shaft with interior screw threads, and means for restraining said helix against rotation, said helix of wire being threadably engaged by said threads in the motor shaft to screw the helix lengthwise and thereby project or retract said telescoping sections upon rotation of said motor.

2. An extensible radio antenna comprising, in combination, a series of telescoping antenna sections including a slender metal rod as the innermost element of the series and a plurality of seamless metal tubes telescoped one over the other and over said rod, a transmission member extending longitudinally into the interior of said series of antenna sections from the base end of the outermost one and anchored to the butt end of said rod, said transmission member comprising a resilient and flexible wire tightly spiraled in a helix of a diameter substantially three times that of the wire itself, an electric drive motor having a hollow shaft with a tapped longitudinal bore, and means for anchoring said helix against rotation, said helix of wire being threaded in said tapped shaft bore to effect a screwing of the helix lengthwise through the bore and thereby a projection or retraction of said telescoping antenna sections upon rotation of said motor.

3. In a radio antenna for an automobile installation or the like where the apparatus is subjected to strong vibration during use, the combination of a series of tubular telescoping antenna sections, an electric drive motor, and

means forming a drive connection between said motor and antenna sections which is self-locking against a reverse action in which said motor is rotated by force applied to the antenna sections, said last named means comprising a hollow shaft for the motor presenting interior screw threads in which a long, slender, and laterally flexible screw member, anchored against rotation and connected in driving relation with the antenna sections, is threaded for endwise movement.v through the same upon rotation of the motor. i.

4. In a radio antenna, the combination with an extensible wave-receiving structure including a closely spiraled helix of wire, and means for restraining the helix against rotation, of an electric drive motor therefor having a hollow drive shaft through which said wire is led and presenting interiorly located screw "threads mating with the convolutions of said wire to feed the same axially through said shaft upon rotation of the latter.

5. In a radio antenna, the combination of an electric motor having an armature shaft comprising a tubular metal jacket with a bushing of insulation fixed in it and an interiorly threaded metal bushing fixed in said insulating bushing, an extensible wave-receiving structure including a closely spiraled helix of wire screwed in said threaded bushing, and means anchoring said helix against rotation, whereby said helix is shifted endwise by screw action upon rotation of the motor shaft. 6. A radio antenna comprising, in combination, an extensible wave-receiving structure, means including an electric drive motor for projecting and retracting said structure, said motor having a hollow drive shaft presenting interior screw threads, and power transmission means connecting said motor in driving relation with said extensible structure comprising a flexible helix of wire led through said shaft and screwed in said threads.

7. In a device of the type described, the combination of a plurality of elongated metal elements arranged in telescoping relation to each other, at least the outer one of said elements being of hollow tubular form, a transmission member extending longitudinally through the interior of said outer element from the inner end of the latter and operatively connected to the innermost element of the series, said transmission member comprising a wire tightly spiraled in a helix of substantially smaller diameter than the interior diameter of said outer element with successive convolutions of the wire abutting solidly against each other and capable of transmitting both compression and tension forces requisite to project and retract the series of telescoping elements without substantial lateral distortion of said member, the ratio of the diameter of the wire to that of the helix which it forms being approximiately one to three, and means operatively connected to said transmission memher for coiling and uncoiling the portion thereof projecting from the inner end of said outer element to retract and project the telescoping elements.

8. In a device of the type described, the combination of a plurality of seamless metal tubes telescoped one over the other, a slender metal rod telescoped in the innermost tube, the outer ends of said tubes being necked in to a sufllciently small diameter to form a snug sliding fit with the next adjacent telescoping element, a tightly said wire projecting from the tubes for coiling and uncoillng the same to retract and project the telescoping elements.

9. In a device of the type described, the com- I bination of a plurality of elongated metal elements arranged in telescoping relation to each other, at least the outer one of said elements being of hollow tubular form, a transmission member extending longitudinally through the interior of said outer element from the inner end of the latter and operatively connected to the innermost element of the series, said transmission member comprising a wire tightly spiraled in a helix of substantially smaller diameter than the interior diameter of said outer element with successive convolutions of the wire abutting solidly against each other and capable of transmitting both compression and tension forces requisite to project and retract the series of telescoping elements without substantial lateral distortion of said member, the ratio of the diameter of the wire to that of the helix which it forms being approximately one to three.

10. A radio antenna comprising, in combination, an extensible wave-receiving structure including a long and closely spiraled wire helix, an electric motor having a shaft with an elongated bore presenting interior screw threads, said helix being led through said shaft bore and the convolutions of the helix mating with said threads, a take-up container presenting a generally cupshaped chamber to one end of said shaft, said helix being led into said chamber, and means anchoring the end of said helix in said chamber to -the container with the tail end portion of the helix permanently curled in a direction circumferential of the interior of the chamber, whereby as the shaft is rotated to screw the helix into the chamber, the helix will coil down in the chamber.

11. A radio antenna comprising, in combination, an extensible wave-receiving structure including a long and closely spiraled wire helix, an elongated cup-shaped sheet metal container, an electric motor having a stator and a rotor, said stator being fixed in the central portion of said container and said rotor being carried by a hollow shaft extending longitudinally of said container, said shaft presenting interior screw threads, said helix being led through said shaft with the convolutions of the helix mating with said threads, said helix being led into a chamber defined between the closed end of the container and said motor, and means anchoring said end of the helix in said container in position to curl the tail end portion of the helix in a direction circumferential of the interior of said chamber, whereby as the shaft is rotated to screw the helix into the chamber the helix will automatically coil down snugly in the chamber.

' 12. A radio antenna comprising, in combination, an extensible wave-receiving structure including a long and closely spiraled wire helix, an electric motor having a shaft with a longitudinal bore presenting interior screw threads, said helix being led through said shaft bore and the convolutions of the helix mating with said threads, a take-up container presenting a generally cupshaped chamber to one end of said shaft, said helix being led into said chamber, means for anchoring the end of said helix in said chamber to the container in position to permanently curl the tail end portion of the helix in a direction circumferential of the interior of the chamber, and means located at the end of said shaft adjacent said chamber to form I an outwardly flaring funnel-shaped guidethroat through which said helix passes.

13. A radio antenna apparatus of the ty e described comprising, in combination, a cylindrical metal casing having closed ends, an aperture in one of said casing ends, a tubular member insulatingly mounted in said aperture and disposed coaxially with the casing, a plurality of telescoping antenna sections projectibly mounted in said tubular member, an electric motor housed within the mid-portion of said casing and having a hollow shaft coaxial with the casing and alined with said tubular member, said shaft presenting a set of interior screw threads, a flexible wire tightly spiraled in a helix of very small diameter as compared to that of the casing, said helix being led through said hollow motor shaft with the convolutions of the helix threaded in said screw threads, the outer end of said helix being fixed to the innermost one of saicltelescoping antenna sections and the tail end of said helix being led into the chamber formed between the motor and the closed end of the container opposite said tubular member, said tail end of the helix being anchored with a permanent curl in such portion of the helix in a direction circumferentially of the interior of the container.

14. The combination with an electric driving motor having a hollow shaft presenting interior screw threads, and a long slender helix of flexible wire threaded in said screw threads for movement axially through said motor shaft upon rotation of the latter, of a take-up container shaft through wihch said screw member is led and presenting interior screw threads mating with said screw member, whereby said screw it member is threaded axially through said shaft upon rotation of the latter, a pair of stationary tubular housings fixed to opposite ends of said motor and axially alined with opposite ends of the motor shaft, insulator bushings slidably mounted in respective ones of said housings and freely encircling said screw member which is also led through said housings, limit-switch contacts on said bushings and cooperating stationary contact elements, helical springs received in said housings and yieldably urging said bushings outward to engage said movable contacts with said stationary contacts, and means including abutments fixed to said screw member at spaced points along it for engaging corresponding ones of said bushings to push the same inward in its housing against the bias of its abutting spring to open the associated set of contacts.

16. In a radio receiver antenna installation, the combination of an extensible antenna comprising a long flexible wire, a take-up container adapted to receive the wire when coiled up in storage position, means including an electric motor for feeding said wire out into extended wavereceiving position or coiling it into said container, and means including a normally closed switch for grounding said antenna wire when closed, said switch being connected to the inner end of said wire and pulled open thereby by the tension exerted on it by the wire when the latter is in fully extended position.

17. In a radio receiver antenna installation, the combination of an extensible antenna comprising a long flexible wire, a take-up container adapted to receive the wire when coiled up in storage position, means including an electric motor for feeding said wire out into extended wave-receiving position or coiling it into said container, a grounding switch in said container comprising a stationary contact and a movable contact on a leaf spring normally urging the movable contact into engagement with said stationary contact, and the inner end 01' said wire leading into said container being fixed to said leaf spring, whereby when said wire is fed out 01' the container into wave-receiving position said leaf spring will be pulled to open said contacts by the final tug of said wire as it reaches its limit position of extension.

18. In a radio antenna apparatus of the type described, the combination of an electric drive motor having a hollow drive shaft presenting interior screw threads, an extensible antenna comprising a long, slender, laterally flexible helix of wire led'through said motor shaft with the convolutions of the helix threaded in said screw threads, a cup-shaped take-up container presented to one end of said shaft with the tail end portion of said helix leading into it, an antenna grounding switch comprising a leaf spring mounted in cantilever fashion to extend diametrically across the inner face of the end wall of said container, and means anchoring the tail end of said helix to the free end portion of said spring at a point laterally displaced from the axis or said shaft and with the fixed end portion of the helix extending transversely across said spring,

EDWARD L. BARRE'I'I.

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