This invention relates to a radio beacon device which is activatable to generate radio signals to act as a beacon whereby to assist in the location of lost persons.

In accordance with one aspect of the invention there is provided a radio beacon device comprising a housing with a radio transmitter mounted therewithin, the . housing having at least one coiled antenna which antenna may be uncoiled and conformed to an elongate configuration for use of the device. The antenna may be in the form of a coil of wire of a suitable flexible metal which is capable of being uncoiled by movement of a free end away from the housing, such as axially of the coil, by hand, but is sufficiently stiff to maintain its elongate form when so extended. The device may be formed with cavities at either end, each receiving a separate coil and provided with end caps which close those cavities but which are removable to enable operation of the device. These end caps may be held in position by removable tapes.

such as adhesive tape wound around the casing, or by other releasable means. A switch effective to turn on the radio transmitter may be provided, likewise with in one of the cavities.

The invention is further described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a perspective view of a device constructed in accordance with the invention;

Figure 2 is a perspective view of the device of Figure 1 but with end caps.thereof removed;

Figure 3 is a side view of the device of Figure 1 with antennae thereof extended for use;

Figure 4 is a diagrammatic longitudinal cross section of the device of Figure 1 with one end cap thereof removed ;

Figure 5 is a side view of the device of Figure 1;

Figure 6 is a perspective view of an antenna coil incorporated into the device of Figure 1 and;

Figure 7 is a circuit diagram of a transmitter incorporated into the device of Figure 1.

The device 10 shown comprises a casing 12 having end caps 14, 16 which are removable from the casing 12, but which are held in position by means of adhesive tapes 18, 20 wound around the casing and end caps. By removing the tapes 18, 20 the end caps 14, 60 may be slid off projecting end rim portions 12 a, 12 b of the casing 12.

The two rim portions 12 a, 12b of the casing 12 enclose respective cavities 22, 24 at opposite ends of the device 10. These house respective antennae 28, 30 arranged in the coiled up configuration shown in figures 2 and 4 and are normally closed by end caps 14, 16 to enclose the antennae.

The antennae 28, 30 have free inner ends which extend through transverse walls 29, "32 of casing 12, at the inner ends ov cavities 22, 24, and into a central cavity 40 of the casing. This cavity 40 houses an electric circuit board 42 containing circuitry for a radio transmitter 44, the electrical circuit of which is shown in figure 7.

The cavity 40 also houses a battery such as a lithium battery 46 for powering the transmitter 44. An on/off switch 50 controlling application of electric current from the battery 46 to the transmitter 44 is positioned in cavity 24.

The coiled up antennae 28, 30 may be of the form shown in figure 6 at which the coiled up antenna 28 only is

shown. Each comprises a first helical coil 54, which may contain any desired number of coil turns, and a second helical coil 56 of one or two turns which is positioned with its axis side by side to and spaced from the axis of the coil 54. The two coils 54, 56 are wound from one piece of wire of a suitable soft material, such as soft iron or steel, and the free end of the coil 54 joins to one free end of the coil 56. The other free end of the coil 54 is formed with a lengthwise extending portion 58 extending parallel to the axis of the coil 54. The portions 58 of the antennae 28, 30 respectively extend through openings in the walls 29, 32 of the casing 12 and thence into the cavity 40, for connection to the circuit board 42. The coils 54 are securely anchored to the casing and/or to the circuit board 42 so that, by grasping the coil 56 of each antenna the coil 56 can be moved axially outwardly of the casing 12 to unwind the wire from the coil 54 so that the antennae 28, 30 extend as shown in figure 3 from opposite ends of the casing 12. The wire from which the antennae are formed is sufficiently rigid material to enable the shape to be retained when the antennae are so uncoiled.

At each lateral side of the casing 12, the casing is provided with, a separate pair of bridging pieces 70. These are of similar form and each comprises a thin generally planar portion 70a which extends in closely spaced parallel relationship to the respective side wall of the casing 12, and in-turned end portions 70b by which each portion 70a is joined to the casing 12.

There is thus defined, between the side walls of the casing 12 and each of the portions 70, narrow slots 72. These may be utilized to pass an elastic retaining band 74 therethrough whereby to provide, for example, a neck loop by means of which the device 10 may be worn around a user's neck.

In use, the device 10 is carried by a user and is in an unactua ed condition in the sense that the transmitter 44 is turned off and no radio transmission emenates from the device. In the event that the bearer of the device should become involved in an emergency situation, he may activate the device 10 by removing the tapes 18, 20 to expose the cavities 22, 24, then extending the antennae 28, 30 as previously described, and turning on the transmitter 44 by use of the on/off switch 50. Thus, ^" the transmitter is effective to generate, via the antennae 28, 30, radio signals which may be received and tracked by other parties.

The arrangement described has the advantage that it is relatively compact when in its unactivated condition but that it can be readily converted to a condition for use. Furthermore, once the device has been used, the antennae 28, 30, as extended, cannot readily be folded up again and positioned within the cavities 22, 24 so that reuse of the device is not readily possible, thus, avoiding the possibility that a device selected for use by a person should, through for

example failure to replace batteries after a previous use, prove to be unactivatable when required.

The device 10 has particular application for use as a beacon to enable tracking of lost persons. When used at sea, it may be fitted with a suitable buoyant ring 78 (figure 5) positioned around the casing 12 and located in position say, by a projection 80 which engage grooves 84 formed on the exterior of the casing 12 between adjacent pairs of portions 70. Such a ring may, for example, be formed of resilient material which can be slipped onto the casing.

Further, although the device could be operated by removing the end caps and operating of the on/off switch with the antennae in the packed coiled condition, the range of the transmitter under such a condition would be relatively limited so that such use would be unlikely.

Suitably, the transmitter may have a power output of say, 125 milliwatts and it has been found practicable by employing a lithium battery as above described to operate the device for a duration of 48 hours at 80 milliwatts or 60 hours at 40 milliwatts using frequencies between 100 megahertz and 200 megahertz for transmission. In such a case, the antennae may be about one half a metre in length in the extended conditions.

Although not shown, a switch may also be provided for selecting the power output of the transmitter.

The invention has been described by way of example only and many modifications may be made to the described example without departing from the spirit or scope of the invention.