There is provided a high voltage blocking device for a manpack antenna. More precisely there is provided a high voltage blocking device for a manpack antenna, the manpack antenna having a radiation element that is designed to be in electrical contact with a radio transmitter.

A manpack radio transceiver normally has an antenna attached that protrudes upwardly from the transceiver that often is carried on the back of the operator.

The antenna with its radiating, electrically conducive element is subjected to come into contact with overhead active electric wires. Such contact may result in fatal electrocution of the operator.

The purpose of the invention is to overcome or reduce at least one of the disadvantages of the prior art.

The purpose is achieved according to the invention by the features as disclosed in the description below and in the following patent claims.

There is provided a high voltage blocking device for a manpack antenna, the manpack antenna having a radiation element that is designed to be in electrical contact with a radio transmitter, wherein a capacitor is connected in serial between the transmitter and at least a part of the radiation element.

In this document the term "high voltage" includes voltages that may be detrimental to a person at mains frequency.

The working principle of the invention is to design the capacitor to allow the transmission of a relatively high current at radio frequencies, but only let a safe impulse of current pass at mains frequency. If the antenna should come in contact, for instance with non-insulated overhead mains or high voltage cables, this feature will save the operator from receiving fatal electric impulses.

In some security devices for use on 230 V mains supply at 50 or 60Hz, the device will trip at for instance 30 mA. This level is considered to be safe. An antenna will however be fed with say one Amp at radio frequency.

Tests have been undertaken showing that two 15kV 470pF capacitors connected in series work satisfactory for the purpose. Capacitance of between 200 -lOOOpF are considered to give the wanted safety.

There may be more than one capacitor connected in series. Thus, as the voltage is divided between the capacitors, potential voltage across each capacitor is reduced . Thus readily available, relatively small capacitors may be used.

The manpack antenna may be equipped with an antenna matching unit and the capacitor may be connected between an antenna matching unit and the radiating element.

The radiating element may be equipped with at least a spring or a goose neck and the capacitor may be connected between the antenna matching unit and the spring or goose neck.

The manpack antenna may have a section on its outside that is able to resist a leakage current. As the high voltage from the radiating element may reach the operator through the outside surface of the antenna, it may be necessary to secure that at least a section of the outside surface has a resistance to leakage current.

The outside surface may, if the material of the actual section is unsuitable, be treated for instance with a painted layer or be covered by a shrink tube.

The treatment of the outside surface may be a layer of epoxy, polyurethane, polytet- rafluoreten or any other suitable material that exhibit sufficient resistance to leakage current. When a salty atmosphere is present, polytetrafluoreten that is marketed as "Teflon" by DuPont, has proved to be well suited .

The high voltage blocking device according to the invention may contribute to reduce the loss of lives due to electrocution.

Below, an example of a preferred device is explained under reference to the enclosed drawing, where: Fig. l shows a simplified electrical circuit diagram of a manpack antenna according to the invention; and

Fig.2 shows a principal drawing, partly sectioned, of the manpack antenna according to fig. 1.

On the drawings the reference number 1 denotes a manpack antenna that is connected to a radio transmitter 2 by a cable connection 4. As shown in the circuit diagram of fig. 1, the manpack antenna 1 comprises an antenna matching unit 6 and a radiating element 8. A capacitor 10 is electrically connected in series between the antenna matching unit 6 and the radiating element 8.

In the manpack antenna 1 shown in fig. 2, the radiating element 1 has a spring 12 that is removably fixed to an antenna base 14. The antenna matching unit 6, as well as the capacitor 10, here in form of two capacitors 10 that are connected in series, are placed inside the antenna base 14.

The antenna base 14 has a section 16 that on its outside is treated with a leakage current resistive material in the form of a painted layer 18, such as polyurethane. The axial length 20 of the section 16 is calculated on the basis of the material properties of the chosen surface material. Some actual materials have a surface dielectric strength of 3000 - 5000 V/cm.

In an alternative embodiment a shrink tube 22 is put over the section 16 and shrunk onto the section 16. As stated in the general part, polytetrafluoreten has proved to be well suited in salty atmospheres.

In yet another embodiment, the spring 12 may be exchanged for a gooseneck 24.