Usually, antenna selection is determined by working frequency.
If you're looking for video signals, you'll need something on the order of what the video bandwidth is. Usually this is in the low MHz. Which isn't very sensical for antennas at much of any range. I don't remember what exactly TEMPEST is supposed to be watching; for analog television, internal signals (IF, LO, chroma..) are possibilities, two of which are high frequency, and one of which is limited bandwidth (NTSC chroma is something like 3-5MHz). Digital monitors (CGA and EGA) would generate harmonics from internal logic/buffering and maybe from the video output drivers, but I wouldn't expect much content over 50MHz.
CRTs are your most likely candidates, following a simple raster, and with deflection signals apparent (either by gaps in the video, or by picking up the lower frequency signals themselves). In the modern era, who knows.
Plasma panels throw off all kinds of shit, though as far as I know, they don't do a simple raster scan, so you'll need a scan converter circuit. LCD and OLED I think are going to be scanline driven, too. Internal signals will be nicely visible in the 100s MHz range thanks to fast clocks and serial data paths, but obtaining a useful signal from that (HDMI, or encoded or decoded MPEG, or frame buffer traffic, or..) isn't necessarily straightforward, or likely.
Anything you can find in the literature, of course, will be very useful.
Tim
I would need to know(at minimum) the lowest frequency to give good advice. There are plenty of ultrawideband antennas available but they get big with low cut off frequencies.
When you get to electrically small antennas you can chiise bamdwidth or efficiency but not both. For very low frequencies a small loop antenna might be a good option.
For weak signals an LNA can really be useful to get the most out of those older spectrum analysers.
So it would be nice to be able to demonstrate demodulating something simple, but it doesn't have to be done for every target I do. I'm trying to limit scope a bit because this is, after all, a project for a class and I have research I have to be doing as well to get my MS.
So it would be nice to be able to demonstrate demodulating something simple, but it doesn't have to be done for every target I do. I'm trying to limit scope a bit because this is, after all, a project for a class and I have research I have to be doing as well to get my MS.
RF eavesdropping of modern, well shielded, high frequency electronics is very, very tough task. Better demonstrate conducted EMI attack - by monitoring PSU current or voltage variations of small computing device like RaspberryPI or small laptop/tablet. Other option would be to craft "RF transmission software" on purpose so it is much easier to receive/demodulate known transmission: https://en.wikipedia.org/wiki/Air_gap_malware. [edit] All you need to show - that computer without any wireless adapter is able to transmit keystrokes