The European space agency (ESA) has spent the summer tracking down radio signals broadcast in the same frequency that Galileo, Europe's satellite navigation system, will use. Radio signals broadcast by other users in the Galileo frequency band could interfere with reception in some areas. ESA has been touring airports, military installations and similar venues where radio signals within the frequency band allotted to Galileo are sometimes used for legitimate purposes, such as helping aircraft to land safely. When operational in 2008, Galileo will consist of 30 satellites in circular orbits around 24,000 kilometres above the Earth. The satellites will broadcast signals from which users with Galileo receivers will be able to tell the precise time and determine their positions with greater accuracy than every before. Some signals will be used for public services, such as the emergency services, while some will be received by the operators of commercial services, such as road traffic information services. Some signals will be used to preserve safety, at aircraft control centres for example, and some will be used for mass market applications for anyone with a hand held receiver. Unexpected signals picked up by ESA could have come from a number of sources. Some could have come from malfunctioning equipment designed to transmit at a different frequency, while others could have been generated by illegal transmissions. The tour has now been completed and the results are being analysed. Conclusions will be presented to Galileo project specialists at a workshop in December.