GNU radio has a very very generic approach to signal handling. However, this brings some somehow troubling (and exciting) expectations for the future. It's only matter of time until the software for TEMPEST receivers will be written. Then the cost of lower-end TEMPEST units will drop down to next to zero, allowign even the smallest police unit to be equipped by one. The good side of it is that the system is likely to be so available that we as the defenders will have the possibility to check if our newly installed shielding doesn't leak. Another interesting application could be a passive radar. Three receiver units with precise timebase, located in a rough triangle, correlating the exact times they heard edges on the signal they receive. The same principle used by Czech passive radar systems Kopac, Ramona, and the most advanced, Tamara. Lockheed is now developing their own ones, rumours say their design is based on stolen and reverse-engineered Tamara. GNU radio units with proper software, timebase receiver using a central timebase transmitter or (if the operation scenario presumes satellite operations will be unaffected) GPS signal, a central computer (or cluster of computers) correlating the data from the receivers in the field, sent eg. over the Net. Any aircraft that's using its onboard radio systems will be visible for such network, which doesn't need any active transmitting components. Using a separate fixed omnidirectional pulse transmitter, it should be possible to broaden the system's function as a "standard" radar, possibly showing even the objects that don't broadcast on their own. Which could allow civilian population to build their own radar system for every city and village. Another possibility (would it work?) is using "natural" signal from some transmitter instead, making even active system seeming like passive one (after all, why we should broadcast our own pulsed signal from a fixed location when we have cellular towers doing it for us for free and without giving us FCC hassles.) An extension of this idea will allow tracking of any broadcasting devices; location of cellphones or personal walkie talkie transceivers or wireless bugs will become very simple. An object guarded with such system will be harder to attack clandestinely; at the moment the adversary uses radio to synchronize their people, their location gets instantly betrayed in machine-readable form. If tuned to the frequency of police transceivers (European systems Tetra and Matra are similar to GSM system, using digital pulse modulation which gives sharp, well-defined pulses easy to spot), could be used to log their position over time, giving the taxpayers instant informations that instead of protecting them in the streets the plods spend 70% of their time in their offices. As any technology, it's a double-edged sword. But seems to give much much more power to Us than to Them. So it seems to be good. And as an added benefit, it's a cool geek toy.