Frequencies emited by Windows Computer

It is a lot harder to read a modern LCD display than it was in the old days of CRT tubes which literally radiated enough information to be reconstructed at a distance. Tempest proofing defeats it for a price.

The various main clock frequencies (and harmonics) inside it and the free run frequency of the SMPSU are generally a pretty good guide. Any basic scanner will latch on to the various frequencies.

Back in the very old days an AM radio in the computer room could be used to listen in on a computation and decide if it was possibly stuck in an infinite loop. The ear is quite good at repeating patterns.

The trend for stupid ones with internal lights and Perspex windows makes things a lot worse. A sealed metal can isn't too bad provided that the holes in it are all very much smaller than a wavelength.

--
Regards, 
Martin Brown

"Martin Brown"

** Back in the 1980s I was easily able to view the monitor of the PC in the unit above mine - with a portable B&W TV set !!! ** But extract no info whatever.

.... Phil

Google TEMPEST.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

Oh, was it all the radiation that caused the shipwreck?

I'm thinking that Caliban is somehow behind Windows.

George H.

He's the inventor of DLL Hell and the FAT filesystem. ;)

Full fathom five, thy filesystem lies; Of its tracks are garbage made, Those are knurls that were its lines, Nothing of inodes that fadeth not...

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

A sniffer on 144MHz is good for finding computers, since USB is based on

72MHz and the sniffer gets the 2nd harmonic.

Beter to measure more, like measure magnetic field emissions. Metal housings pretty much block the electical activity, but those mag-fields 'punch' through and their patterns quickly reveal computer activity. You can see things like clocks [of course], bus activity [of course], and watch software exercising all as bursts [that was expected, but really gave you a signature to look for to see if a specific type app was running].

The thing about USB is that people plug nice antenna into the sockets.

Those mag fields drop off as distance cubed, not squared. They would be useful if you already know where the computer is, but then you don't need to find it.

Years ago, I designed a 'sniffer' sensing emanations, specifically tilted towards looking for the mag-fields from current, that looked for the characteristic signatures of a computer - with various processing to look for simultaneity of operation. I approached a family owned Nevada Casino with the presentation that you can mount this inexpensive device at each gaming table, look for signatures patterns, alert security, and evict abusers of their 'no computers allowed' policy.

The Manager was ecstatic at the concept and wanted to work with us for further development, put them in. However, the grandson of the owner was not enthusiastic at all, and squelched any deal, wouldn't even discuss it further. Only later did I realize that the manager was responsible for P&L so he wanted any tool to help him maximize returns, but the grandson was probably skimming and did not want any monitoring going on. Thus, another 'business' education in the electronics world.