GB1390009A - Method and apparatus for radiating low-frequency radio waves - Google Patents

Abstract

1390009 Aerials WESTINGHOUSE ELECTRIC CORP 3 Dec 1973 [12 Dec 1972] 55910/73 Heading H4A In propagating radio waves of a frequency not exceeding 300 kHz from an aerial which is adapted to be deployed from an aircraft and to be connected toward its upper end to a transmitter, said aerial has length substantially equal to one-fourth of the operating wavelength of the transmitter, and at least part of it is suspended vertically from the aircraft. At the lower end of the aerial are means for providing a lowresistance path to a body of water having a conductivity at least equivalent to the presence therein of 1 part per 1000 of NaCl, whereby it acts as a ground plane. In one embodiment an aerial element 18, Fig. 2B, extends from a helicopter 10 to the sea 21 where it terminates in a drogue 20, which provides a good electrical connection. The aerial element 18 may have a diameter of # to ¢ inch and be made of a mechanically strong material such as steel or fibreglass, with a conductive coating of copper or aluminium. It is lowered from the helicopter by means of a winch, and passes through an insulating bushing 22. One terminal of a radio generator 26 is connected through a coupling unit 24 to the element 18, and the other terminal thereof is connected to the shell of the helicopter. A counterpoise 32, which enables the length of the element 18 to be reduced below #/4, is deployed from the helicopter, one end being connected to the shell thereof, and the other end being terminated in a conductive shell 34 of greater diameter, to reduce corona effects. In another embodiment, the counterpoise is omitted (Fig. 2A, not shown) and in another it is passed through an insulating bushing to one terminal of the radio generator, the other terminal of said generator being connected via the coupling unit to the helicopter shell, to which the aerial element is also connected (Fig. 2C, not shown). The drogue 20, Fig. 4, has a lightweight housing 44 in which is a solenoidoperated door 54 controlled by radio signals from the helicopter for admitting water when the drogue is lowered and for releasing water when it is raised. A conductive coating 62 is provided on the outside of the body 44, and the element 18 is attached via a universal connector 40.