Aerial assembly from Sea Watch Major radar beacon, made by GEC-AEI (Electronics) in Leicester, 1968. The "Sea Watch Major" produced a distinctive response on the screen of any 3-cm marine radar operating within its range of maximum 55 kilometres. Separate receiving and transmitting aerials were employed, vertically offset to minimise mutual interaction but otherwise identical. Each consisted of a length of waveguide, slotted back and front, and terminated just above the slots by a movable plunger. Wedge-shaped ‘wings’ gave the aerials an omnidirectional response in the horizontal plane. A plastic ‘radome’ protected the aerials from the weather and was made half a wavelength thick so that cancellation occurred between the reflections generated, in antiphase, at its inner and outer surfaces. The aerials followed a design originated by the Admiralty Signal and Radar Establishment in 1951. Aerial assembly from Sea Watch Major radar beacon 1968