Jim Choate wrote on 1998-02-10 03:40 UTC:
11MHz base frequency won't produce a clean ring at 125MHz or 210MHz, they're not a whole number multiple of the base. How is this accounted for? What did he calculate the Q at? At what range was he picking up these harmonics as well as the base? The lower harmonic implies a 4MHz beat and the higher a 1MHz beat, how did he account for these signals? Personaly I would be more inclined to suspect the information was riding on the beats. He didn't happen to measure the frequencies to 3 decimal places did he?
You might want to consider to read van Ecks paper yourself: Wim van Eck: Electromagnetic Radiation from Video Display Units: An Eavesdropping Risk? Computers & Security 4 (1985) 269--286 If you don't have C&S in your library, you might also find a scan on <http://www.eskimo.com/~joelm/tempest.html>
If you have only a van Eck style receiver, yes. But as soon as you record the reception over some time and observe the images phases to drift only slightly against each other, you might be able to separate them using similar processing techniques as used in computer tomography.
As I alluded to with the comment I made about integrating the received signals. The easiest way to do this sort of stuff with a small budget is with a flying capacitor integrator.
Please explain! I was more thinking in terms of digitizing everything and solving large per-pixel systems of equations to separate the drifting images, which does not sound much like something equivalent to a single hardware integrator, but more like something that keeps a workstation very busy for a few minutes. Markus -- Markus G. Kuhn, Security Group, Computer Lab, Cambridge University, UK email: mkuhn at acm.org, home page: <http://www.cl.cam.ac.uk/~mgk25/>