Today is a recovery day. I spent Sunday scrambling through holly thickets, sinking calf-deep into odoriferous bogs and trying to scale chalk mountains and giant ravines near Salisbury. The cause of this unusual activity was Top Band DFing, a cross between orienteering and amateur radio: two transmitting stations hide out somewhere within the area of a standard Ordnance Survey map, and 20 oddballs armed with special radios try and track them down. It is, by any measure of human behaviour, a rum business indeed. It is impressively hard to stay hidden. Everyone found both stations within a couple of hours or so, despite the considerable physical and electronic efforts made by the transmitters to throw people off the scent. It increases the respect one has for those people who signal from behind enemy lines during wartime, but if it's that easy for amateurs using home-made gear and decades-old techniques how good is the state of the art? A few minutes poking around online reveals the answer: terrifyingly good. Professional radio direction finding is mostly covert business by covert people, so you won't find GCHQ's equipment neatly documented on the Web. But there's enough information out there from manufacturers and the odd throw-away line in official reports to work out that this is reasonably big business. It looks as if there are tens if not hundreds of automated DFing stations in the UK alone, capable of pinpointing transmissions almost anywhere on almost any frequency within, I'd guess, a hundred milliseconds or so. The old memories of vans cruising through darkened streets with loops twisting away on top should be replaced with the idea of a large network of computerised scanners peppered across the countryside, instantly swapping signal strengths and bearings the moment something anomalous pops up. So in some ways, the current worry about privacy and location based mobile phone services is a bit of a red herring. If every wireless device you own is capable of divulging your location the moment it pipes up, you can be tracked even if you take every precaution to control what the mobile phone network knows about you. It also underlines the fact that all those London pirate radio stations blatting away on top of Radio 4 are there because nobody can be bothered -- or afford -- to sort them out. This is the reality of Big Brother: They know where you are. They know what you're saying. They just don't care.