Abstract: A radio antenna for mounting in the lid of a water meter box and forming part of a remote meter reading system comprises an annular conductive plate and a circular conductive plate which are coaxial with and parallel to each other and spaced apart to define a slot, the circular plate serving as a ground plate. The antenna has an input in the form of a conductive pillar interconnecting the two members, with a drive input at a selected point along the length of the pillar and a second input on the ground plate. A variable tuning capacitance is disposed between the plates diametrically opposite the conductive pillar. The ground plate also serves for locating the lid in undergrowth or under snow using a metal detector.