GB2329526A

GB2329526A - Helical antenna

Info

Publication number: GB2329526A
Application number: GB9720029A
Authority: GB
Inventors: Andrew Jesman; Christopher Jesman
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-09-19
Filing date: 1997-09-19
Publication date: 1999-03-24
Also published as: GB9720029D0

Abstract

A radio antenna comprising a helical wire spring 2 encapsulated in a sheath 1 of synthetic plastics material, is provided with means at its base for electrically engaging a spigot 4 which forms part either of an antenna terminal of a radio set or an adaptor for making a connection to a conventional antenna terminal. The antenna fits over a smooth upper portion 4a of the spigot and is screwed onto a lower portion 4b having a complementarity screwed surface to make physical and electrical contact.

Description

IMPROVEMENTS IN AND RElATING TO HELICAL RADIO AWTEIQbZAS Helical radio antennas that comprise a helical spring encapsulated in a plastic sheath are well known. Such antennas have the merits of being relatively compact, flexible and impervious to moisture. However, although the antenna can be constructed relatively easily by injection molding the encapsulating material around a wire spring, the antenna element is required to be connected to a tçrminating adaptor, and this has significantly increased the cost of manufacture.

It is accordingly an object of the invention to provide a helical antenna of the kind referred to, wherein the construction is simplified in order to reduce manufacturing cost.

In accordance with the invention there is provided a radio antenna comprising a helical wire spring encapsulated in a sheath of synthetic plastics material, the said sheath having an opening at one end of the spring that communicates with a hollow cylindrical passage extending axially of the helices of the wire spring, and the arrangement of the wire spring and the synthetic plastics sheath at said open end being such that the spring and sheath can be resiliently distended by the insertion of an electrically conductive spigot dimensioned to be a fit within the helices of the spring whilst making electrical contact therewith. Preferably the antenna is associated with such a spigot that has a screw threaded portion dimensioned to be a force and screw fit within the helices of the spring whilst making electrical contact therewith.

In the antenna according to the invention, the need for a terminal connector of the conventional kind is avoided, since electrical connection to the antenna can be made via a simple spigot fitted within the spring.

Advantageously, the helices of the spring, at least in the region of said open end, are of uniform pitch and diameter, in order that an antenna blank can be tuned to a desired frequency by cutting down the open end of the sheath until the wire spring attains its optimum frequency, and then inserting the spigot to provide mechanical and electrical connection of the antenna to a radio apparatus.

Further preferred features and advantages of the invention will have become apparent from the following description taken in conjunction with the drawings, in which: Figure 1 is a diagrammatic side elevation of an antenna in accordance with one embodiment of the invention, partially fragmented to show internal detail, Figure 2 is an end view of the antenna of Fig. 1 taken in the direction of the arrow A, Figures 2A and 2B are diagrammatic views illustrating the attachment of an antenna according to Fig. 1 to a mounting provided on a radio set, and Figures 3A to 3C are views similar to Fig. 2 showing the attachment of the antenna to a radio set via an intermediate adaptor.

Referring to Fig. 1, there is shown a side elevation of a helical antenna comprising an external sheath 1 of resilient synthetic plastics material that is formed by injection molding around a helical wire spring 2 illustrated diagrammatically in broken lines and in the sectional view. The sheath 1 is closed at its upper end 1A in order that the antenna is rendered impervious to moisture, and at its lower end 1B has an opening 3 communicating with a hollow cylindrical passage extending axially of the helical spring 2.

The helical spring 2 is preferably of constant diameter, at least in the region of the open end 3, and the turns of the spring are spaced apart at a regular pitch, as shown. Thus in the region of the open end 3, the helical spring 2 and the sheath 1 are sufficiently resilient that they can be distended by the insertion of a spigot into the cylindrical bore defined by the internal diameter of the spring 2.

As shown in Figs 2A and 23, this characteristic of the antenna enables it to be fitted in a simple manner to a terminating conductor comprising a cylindrical spigot 4 having a narrow portion 4A corresponding to the diameter of the opening 3, and a wider threaded portion 4B that is dimensioned to be a good screw fit within the spring 2.

The spigot 4 extends from a mounting base 4C.attached within a surrounding casing 5, provided for example by the casing of a radio set of which the spigot 4 forms an antenna terminal. The casing 5 has a cyclindrical recess 6 dimensioned to receive the base of the sheath 1. As shown in Fig. 2A, the portion 4B of the spigot 4 is spaced from the mounting base 4C to leave between itself and the base 4C a narrow section 4D having the same diameter as the section 4A.

Thus, as shown in Fig. 2B, the antenna can be mechanically and electrically connected to the radio set simply by forcing the open end 3 of the sheath 1 over the spigot section 4A until the open end reaches the top of section 4B. The antenna is then screwed down over section 4B until the sheath 1 reaches the base of the recess 6. The lowest turn of the spring 1 snaps into the recess formed by the section 4D and thus serves as an extra retention mechanism to keep the antenna in position.

If desired, instead of providing the spigot 4 as a fixed terminal connection within a radio set, it can form part of a threaded adaptor for screwed attachment to the terminal of a radio set, in conventional manner.

Thus, as shown in Fig. 3A, a terminal adaptor may incorporate an insulated sleeve 7 performing the function of the casing 5 of Fig. 2, and the method of attachment to the antenna is identical to that shown in Fig. 2 with exception that the spigot 4 has a screw threaded extension 4E for engagement with a threaded electrically conductive terminal 8 (Figs. 3B and 3C) provided in the casing of the radio set.

Thus it will be seen that an arrangement in accordance with the invention provides a helical antenna of simple and inexpensive construction. Moreover, a single antenna blank of the kind shown in Fig. 1 can simply be adapted to a desired frequency by cutting down the base of the antenna until the helical spring 2 is at the correct length for a given resonant frequency.

Claims

CLAIMS:

1. A radio antenna comprising a helical wire spring encapsulated in a sheath of synthetic plastics material, the said sheath having an opening at one end of the spring that communicates with a hollow cylindrical passage extending axially of the helices of the wire spring, and the arrangement of the wire spring and the synthetic plastics sheath at said open end being such that the spring and sheath can be resiliently distended by the insertion of an electrically conductive spigot dimensioned to be a fit within the helices of the spring whilst making electrical contact therewith.

2. An antenna as claimed in Claim 1, wherein the helices of the spring, at least in the region of said open end, are of uniform pitch and diameter.

3. An antenna as claimed in Claim 1 or Claim 2, wherein the spigot has a screw threaded portion dimensioned to be a force and screw fit within the helices of the spring whilst making electrical contact therewith.

4. An antenna as claimed in any preceding Claim, wherein the opening is co-axial with the cylindrical passage.

5. An radio antenna substantially as described herein with reference to the Figures of the accompanying drawings.