Performance of the Decca Navigator on land

Abstract

After noting some characteristics of the Decca Navigator hyperbolic radio aid to navigation, the paper summarises the performance of the system when used on land (e.g. as a position sensor for automatic vehicle location). Reference is made to early theoretical and practical work on the variation of the phase of the LF signals with range, especially over land paths; on the local effects of inhomogeneity in such paths; and on phase errors caused by reradiation of the signals from nearby tall objects. A note is included on the character and magnitude of systematic errors observed on land. The shortcomings of the conventional Decca position-fixing technique when used close to high buildings and overhead wires are indicated, and it is shown that these can be largely resolved by employing the composite ‘multipulse’ lane identification transmissions as the primary means of fixing position. The results are depicted of position-fixing tests carried out on an airfield, on suburban roads and in city streets.