There's at least one firm which makes this stuff commercially, their products are available via http://www.appsig.com/prods/index.html. This looks like a one-stop ECHELON shop: you take one or more of their products (pick your type, intended target, and budget), plug as many E1's or E3's or whatever into one side as you can handle (the most impressive one does 16 E3's or 7680 voice/ data channels) and all modem, fax, and voice comms going through the circuit are available on the other side. They have products to do automatic channel/ signal scanning, demuxing, decoding of various data formats, processing of satellite and radio signals ("combines tuning, demodulation, descrambling, decoding, demultiplexing, and output formatting in one chassis"), every kind of mobile phone signal you've ever heard of, digital microwave links, decoding of higher-level protocols like V.42/V.42bis, X.25, HDLC, PPP, every Internet protocol worth doing, etc etc (their terminology is pretty neat, they have for example a 1.5-44.7Mbps "modem for on-the-move applications" :-). Much of the hardware claims to be built to TEMPEST specs. One interesting point is that most of their stuff is for E1's and E3's even though they're a US company. Hmmm.... Peter.