In its draft report into the Echelon communications interception network, the European Parliament provided a guide to identifying Echelon listening stations. Most Echelon stations are, according to rapporteur Gerhard Schmid, operated by the US National Security Agency (NSA) or, in the case of the UK, by the Air Force on behalf of the British GCHQ intelligence service. One such installation is RAF Menwith Hill, which is owned by the UK Ministry of Defence, and made available to the US Department of Defence as a communications facility. The station chief is provided by the NSA, and last summer there were 415 US military staff at RAF Menwith Hill, compared with just five UK military staff. The main difference between sites such as Menwith Hill and other installations operated by civilian bodies such as the Post Office, BT, broadcasters or research institutions are that the latter group are open to visitors -- at least by appointment. Interception stations are not. The other important differences lie in the type of antennae used and their size. A military site such as Menwith Hill will have various types of antennae: arrangements of tall rod antennae in a large-diameter circle (Wullenweber antennae), for example, are used for locating the direction of radio signals; circular arrangements of rhombic-shaped antennae (Pusher antennae) serve the same purpose; while omnidirectional antennae, which look like giant conventional TV antennae, are used to intercept non-directional radio signals. But only parabolic antennae are used to receive satellite signals. If the parabolic antennae are standing on an open site, it is possible to calculate which satellite is being received. Most often parabolic antennae are concealed under spherical white covers known as radomes: these protect the antennae, but also conceal which direction they are pointing in. "If parabolic antennae or radomes are positioned on an intercepting station site," says Schmid in his report, "one may be certain that they are receiving signals from satellites, though this does not prove what type of signals these are". Schmid goes on to single out military-run sites that are closed to the public and which have large parabolic antennae, with diameters of around 30 inches. "As far as your rapporteur knows there is no military application for antennae of this size," he says. "Consequently, if they are found on a site [run by the military with no public access], it may be concluded that civilian satellite communications are being intercepted on that site." The reason that the European Parliament's own rapporteur had to work on clues such as the type and size of antennae is that there is still no official statement by the foreign intelligence services of the Echelon global interception system. They can see you... Find out how and why in ZDNet UK's Surveillance News Section. Have your say instantly, and see what others have said. Click on the TalkBack button and go to the ZDNet News forum. Let the editors know what you think in the Mailroom. And read what others have said.