Antenna foot for movable antenna and method for the manufacture hereof.

0001The invention relates to an antenna foot of the kind disclosed in the preamble to claim 1.

0002This type of antenna foot is used to a great extent for movable antennae in connection with radio and/or radio telephone antennae for cars. With the known types, the side facing the car roof is covered with a cap of plastic or rubber, thus preventing the roof of the car from being scratched or damaged in any way when the antenna is mounted, taken off or moved. It is necessary for the protective cap to be rela­tively thin on the side facing the car, hereby ex­cluding the formation of too great a gap between the magnet poles and the metal roof of the car, which would otherwise reduce the magnetic forces which se­cure the foot of the antenna to the car roof.

0003In practice, the known types of protective caps have proved to be easily damaged, in that the downwards­-facing edge of the antenna foot's dish-shaped metal holder penetrates the cap, thus giving rise to the possibility of direct contact with and consequent damage to the car roof, especially if the antenna is moved or removed without due care, e.g. by pulling on the antenna cable.

0004The object of the invention is to provide an antenna foot of this kind which is arranged in such a manner that damage to the roof of the car is excluded, re­gardless of the way in which the antenna with the an­tenna foot is removed or mounted on the car roof.

0005This object is achieved by configuring the antenna foot according to the invention as disclosed and characterized in claim 1. The permanently secured protective element ensures that the downwards-facing edge of the antenna foot's dish-shaped holder can never come into contact with the roof of the car, and at the same time determines the distance of the antenna foot's magnet poles from the metal roof. The protective element is configured as an annular, flexible or yielding item of half-hard material which is incapable of scratching or damaging the car roof. The distance between the metal parts of the an­tenna foot and the car roof is thus not established by these parts being separated by a thin membrane of rubber or plastic. Moreover, the permanent securing prevents any ingress of water in between the protec­tive element and the holder.

0006The permanent securing ensures that the antenna foot is always provided with the protective element, and one avoids the frequent situation with the known constructions, i.e. the protective cap gets lost and, for reasons of lack of time, it is necessary to use the antenna foot without the protective element and with consequent damage to the roof of the car.

0007When the antenna foot according to the invention is configured as disclosed and characterized in claim 2, maximum security is achieved against damage to the car roof in connection with the use of the antenna foot.

0008The antenna foot according to the invention is pref­erably configured as disclosed and characterized in claim 3, whereby increased securing possibilities for the protective element are achieved, hereby enabling it to surround and adhere to the full extent of the edge of the dish-shaped holder.

0009If the antenna foot according to the invention is configured as disclosed and characterized in claim 4, a number of advantages are achieved from the view of production technique, in that the manufacture of the antenna foot can be simplified, and one and the same material is used for both the assembly operation and the formation of the protective element, and these operations can therefore be effected simultaneously. It is a considerable technical simplification and a cost-reducing advantage to be able to assemble and join all of the parts together in one operation, e.g. in an injection moulding operation.

0010Other embodiments of the invention, particularly with regard to the configuration and securing of the pro­tective element, are disclosed and characterized in claims 5-7. The embodiment desired for use can, for example, depend on the type of production equipment at disposal, and also on the technology over which one has most control. For example, with the embodi­ment disclosed and characterized in claim 6, the antenna foot can be provided with a surface of non­-magnetic material over the dish-shaped holder, and with the embodiment disclosed and characterized in claim 7, one completely avoids having to undertake an external surface treatment of the dish-shaped holder, which is covered and protected by the pro­tective element. A completely finished product is obtained via one injection moulding process. More­ over, the holder can be manufactured with less pre­cision, in that the moulding equalizes production tolerances and conceals marks and irregularities which arise in the production of the dish-shaped holder.

0011A preferred practical embodiment of the invention is disclosed and characterized in claim 8. The annular slots with binding materal ensure that the magnetic circuit becomes completely as desired, i.e. with the main part of the field opposite the underside of the antenna foot so that strong magnetic fields are est­ablished through the metal roof of the car. The same securing element secures both the magnet yoke and the antenna itself, which simplifies both the construc­tion and the assembly hereof.

0012The invention also relates to a method for the manu­facture of the antenna foot according to the inven­tion. The method is preferably as disclosed and characterized in claim 9, i.e. all of the individual parts of the antenna foot are disposed and positioned in an injection mould arranged for this purpose, after which the moulding is effected so that at one and the same time the moulding is carried out of the protective element and a casting of the magnet item during the centering and formation of distance slots.

0013After the preliminary work on the antenna foot accor­ding to the invention has been completed, the magnet item is magentized. This is preferably a ring magnet which is magnetized so that the one pole faces to­wards that side of the dish-shaped holder which is in direct contact with the ring magnet, and the other magnet pole faces away from the underside, i.e. down towards the car roof.

0014The underside of the antenna foot according to the invention can be finished in the final working as disclosed and characterized in claim 10. The coating can be an application of lacquer, paint or other coating, or be a foil, for example a self-adhesive foil, which is applied so that the product is given an area printed with information for the user, ad­vertisement etc.

0015The invention will now be described in more detail with reference to the drawing, in that <ul id="ul0001" list-style="none"><li>fig. 1 shows an antenna foot according to the inven­tion according to a first embodiment,</li><li>fig. 2 shows the same antenna as in fig. 1 but seen partly in section,</li><li>fig. 3 shows an antenna foot according to a second embodiment, and</li><li>fig. 4 is a sketch of the moulding tools for use in the manufacture of the antenna foot according to figs. 1 and 2, and for use in the manu­facture of a third embodiment.</li></ul>

0016In figs. 1 and 2 is seen a preferred embodiment of the antenna foot according to the invention. The an­tenna foot consists of a dish-shaped holder 1 formed in 1-3mm thick iron plate with a central threaded hole through which a screw 2 secures an antenna 3 on the top of the holder. In the normal position of use, the dish-shaped holder 1 is thus open down towards that surface, e.g. a car roof, on which the antenna is to be placed. The screw 2 also secures and centres a central soft-iron yoke 5. Around the yoke 5 there is disposed a ring magnet 4, separated by a concen­tric mass 12, and thus an annular slot exists between the yoke 5 and the magnet 4. Around the magnet 4 there is also an annular slot filled out with a bind­ing material 11 which, as shown in fig. 2, extends over into an annular outer profile 6 via an area 10 running under the lower edge 7 of the dish-shaped holder 1, and thus the whole of the annular edge on the holder 1 is covered. In order to increase the stiffness of the annular profile 6 and to increase the adherence to the holder 1, its outer edge can be configured with an annular groove 9 or a similar arrangement, e.g. a series of annularly-extending holes, which will increase the adherence.

0017The underside of the antenna foot is covered with a foil 8, e.g. a self-adhesive foil. In fig. 2 it will be seen that the lower edge 7 of the holder 1 will normally be slightly raised in relation to the lower edge of the ring magnet 4 and the foil 8, and that the lower edge of the annular profile 6 is slightly lower than the underside of the foil 8.

0018The moulding or binding material, which comprises the protective element 6 with underpart 10 and the annu­lar distance slots 11 and 12, is configured, for ex­ample, of thermoplastic rubber, artificial rubber or synthetic resin, for example Perstorp Dryflex type DF, DFG or mixtures hereof; Akzo - Armitel injection moulding plastic; Polyurethane - the elastomer Elast­ogran or similiar materials.

0019In fig. 3 is seen a second embodiment of the inven­tion, where a further cap 13, e.g. of metal, is used instead of a groove 9 to secure the annular protec­tive element 6, which can be in one with the annular moulding material between the magnet 4 and the holder 1, but which as shown can also be configured as an independent, encircling profile ring secured to the outer side of the holder 1 and reinforced and secured by the outer cap 13. The protective element 6 is thus an independent, encircling profile ring which is mounted and secured after the rest of the antenna foot has been produced in the normal manner by cast­ing of the magnet item. In this embodiment, the pro­file ring 6 can be produced of the same material as the binding material 11 or of another material with other characteristics.

0020It is also possible to configure the encircling pro­tective element in such a manner that it surrounds the whole of the outer side of the holder 1, whereby a large contact surface is achieved and herewith a particularly strong adherence to the outer side of the holder 1, see right-hand half of fig. 4. This embodiment is described in more detail later in con­nection with the method for the manufacture of the antenna foot.

0021It will also probably be sufficient to have an en­circling protective element 6, e.g. as shown in fig. 2, and also without the element extending in under the lower edge 7 of the holder 1, in which case an extremely careful securing is required around the whole of the edge, and in such a way that it is en­sured that the edge 7 is held at the desired distance from the car roof.

0022The left-hand side of fig. 4 shows a sketch of a tool for use in the assembly of an antenna foot ac­cording to the invention and of the kind which is shown in figs. 1 and 2 of the drawing, and in the right-hand side is seen a sketch of a tool for use in the assembly of an embodiment where the moulded material completely surrounds the outer side of the antenna foot. Firstly, the bolt 2 is screwed through the yoke 5 firmly into the threaded hole in the hol­der 1, thus securing the yoke firmly in place cen­trally in the holder. A ring magnet 4 is then mount­ed as shown, positioned with an annular distance slot in towards the yoke, and similarly so that an annular distance slot arises between the magnet and the edge of the holder. The parts are now placed in the mould part 14 as shown, and the mould parts 15 and 16 are closed against the part 14, whereby the ring magnet 4 is secured in place. A normal injection moulding can now be carried out with a suitable bind­ing material through an inlet hole 17 in the mould part 16. In one operation there is hereby moulded both the encircling protective element around the edge of the holder 1, and the annular distance slots are formed around the magnet 4, which is hereby se­cured in the dish-shaped holder.

0023With the tool in the right-hand half, the outer side of the holder 1 is also covered with a layer of moulding material 18, for example 1.5 mm thick, ex­ cept for the area blocked by the ring mandrel 19 where the antenna is subsequently mounted. As shown, it is possible to provide blow holes 20 in the holder 1, so that the moulding material fills out the mould cavities more quickly and effectively. With this con­struction, it is possible for the annular groove 9 in the holder 1 to be dispensed with.

0024The underside of the antenna foot can hereafter be finished if necessary, and covered with a coating 8 which, for example, is a self-adhesive foil, and the magnet item 4 is excited.

0025It will be obvious to those familiar with the art that the mould can be arranged otherwise than shown in fig. 4. Normally, the mould will be arranged for the moulding of several units simultaneously, pos­sibly in different sizes so that optimum use is gained from the injection moulding machine.