As an active twist, we can also use a separate unit, Illuminating Transceiver (IT), periodically broadcasting a pulse of known characteristics, easy to recognize by the LPs when it bounces from an aerial target. This unit has to be cheap and expendable - it's easy to locate and to destroy by a HARM missile. As a bonus, forcing the adversary to waste a $250,000+ AGM-88 missile on a sub-$100 transmitter may be quite demoralizing. There can be a whole hierarchy of ITs; when one of them
Microwave oven. This has been done in recent years in various theatres.
Even other sources can serve as involuntary ITs. The landscape is littered with cellular base stations and civilian TV and radio transmitters. Just pick the suitable frequency and listen on.
There is enough wideband power in the ether above inhabited areas to make passive detection from reflected EM possible in theory (without any EM emanating from the target.) The space is illuminated, but the "eyes" are not good enough, yet. Signal levels are extremely low, but it's likely that a flying jet reflects back enough from hundreds of cellphone/celltower transmissions to be few dB above the background noise. However, without knowing where to "look" the receiver cannot use typical narrow beam high-gain antennas. What is needed is an array, like an insect's eye, and that will be a sizeable contraption - passive, but not small. In other words, the size of a passive eye is proportional to the wavelength. To get human eye resolution in 10cm band the size gets to 2km across. Big eye. ===== end (of original message) Y-a*h*o-o (yes, they scan for this) spam follows: __________________________________ Do you Yahoo!? Yahoo! SiteBuilder - Free, easy-to-use web site design software http://sitebuilder.yahoo.com