van Eck-style Radiation Interception Experiments


There are alot of rumors and alot of con artists and nuts in the field of "van Eck Phreaking" (raster analysis).  

Back in 1985, Wim van Eck wrote two papers entitled Electromagnetic Radiation from Video Display Units: An Eavesdropping Risk? and Electromagnetic Eavesdropping Machines for Christmas?  This opened the public to the fact that stray electromagnetic radiation from a computer and/or its monitor could be subject to interception and decoding by an external party.  This has been known to the military and intelligence agencies since at least World War One, when it was used to help break mass-murdering, genocidal, Eurosavage encryption codes.  The Peter Wright book Spycatcher also contains several fascinating stories from the Cold War-era on similar techniques.

There is nothing really groundbreaking about designing or implementing TEMPEST shielding to prevent such intercepts.  Charlatans, petty con artists, and Wikipedia nutcases will mention that the info is secret, but this is just "BBS speak" for "I'm full of shit."  Ham radio operators have been enclosing RF circuits with metal and tying it to a single ground for over 80 years.  Yawn...

Also, changing your fonts, like the dumb German says, won't really do that much either.  If fact, you can even get this method to work without a monitor even connected!

Although far from an expert, I do understand the hardware concepts of van Eck phreaking and have also gotten it to work under "lab" conditions.  The following will be a detailed explanation of a starting setup to help you in your experiments.


This is an overview of what is required to perform a van Eck-style interception.  You essentially point a wideband, log-periodic directional antenna at your TARGET computer and/or monitor, amplify the recieved signal (usually the pixel clock - 28 MHz or so), then demodulate it to get a new video signal.  This new video signal is then applied to a HOST monitor, while generating your own horizontal & vertical synchronization signals.

Hardware Tools

One tool you may find useful is a Video Breakout Box.  This is just a standard 15-pin VGA connector with the red/green/blue video and horizontal/vertical synchronization signals running to BNC connectors.  This is helpful for routing any signal you need via short BNC patch cables.

Another tool, which is mandatory, is a Video Synchronization Signal Pass-Through Box.  This is required to allow a separate video card to generate the needed VGA horizontal & vertical synchronization signals.  We then apply our new "intercepted" video signal on either the red, green, or blue video inputs.

Here is a picture of both the Video Breakout Box and the Video Synchronization Signal Pass-Through Box.  They are built out of old Apple II power supply cases.  You can salvage the needed video cables from old thrift store monitors.  Note the Video Synchronization Signal Pass-Through Box has a female DB-15 jack for easily connecting the HOST monitor.

Antenna & Feedline

Spend all your money on the antenna and feedline.  Seriously.  Your antenna and feedline are the most important parts in a radio reciever.  Use only the best possible antenna and mounting hardware and the lowest loss, highest quality feedline coax.

For your antenna, a salvaged TV reception antenna will work fairly well.  Be sure to get one which will allow you to easily change polarities (horizontal to vertical), if needed.  Also, be sure it has good low frequency response, down to 50 MHz or so (TV channel 2).  Some antennas are for VHF/UHF only - try to avoid those.

If you do use a TV antenna, most will required a 4-to-1 transformer & balun to match to your coax (75-ohm, unbalanced).  TV antennas are typically 300-ohms, balanced.  We need to avoid using balanced feedline due to the interference it can receive.  Your antenna will probably include a little plastic matching transformer.  It may look like a little "bullet" with the words "300-to-75 ohm Matching Transformer" written on it.  Throw it away!!  To save a couple of pennies, manufactures avoid impedance matching properly.  Here is a good example.  This "matching transformer" was just a pass-through.

Here is a better 4-to-1 Matching Transformer schematic using a CoilCraft TTWB1040 surface mount, wideband transformer.

The antenna(s) used for this experimental setup where a Grove Enterprise's Scanner Beam (good but large) and a Ramsey Electronics LPY2 (poor but small).

For a proper impedance match to the antenna and the CATV distribution receive amplifiers, you'll need to use high quality 75-ohm coax.  RG-6QS (quad-shield) is probably the best you'll find locally, though 1/2" 75-ohm hardline will be best for longer feedline runs.  You can often get 75-ohm hardline scraps from cable TV repair people, provided they are not communist bastards - like AOL/Time Warner - then just steal it.

Here is a little additional note on using 75-ohm cable TV hardline in your system.

You probably also be forced to use F-connectors if you use RG-6QS.  These connectors and crap and make me want to kill Europeans.  Stick with the higher quality ones and be sure to install them right.  The center conductor shouldn't stick out too far.

Here are a couple pictures of my antenna setups, the Grove Scanner Beam (too big to be fully expanded) and the little Ramsey LPY2 (wrong frequency range).

Receive Amplifers

Not just any RF amplifier can be used for reception.  Only wideband, fairly low-noise, and high dynamic range amplifiers will work.  Fortunately, these already exist in the form of cable TV (CATV) distribution amplifiers.  These exist to help overcome the losses from long coax runs, so they are cheap and easy to find.  Like always, the quality will vary.  The best possible source is the actual CATV distribution amplifiers that the cable TV company uses.  These can often be had by digging through the dumpster behind your local cable TV company office, or if it's those commies at AOL/Time Warner - just steal them from the poles (those little silver boxes with hardline going in-and-out).

For this setup, a Winegard DA-8150 82-Channel Distribution Amplifier is used feeding a generic "V-26274" amplifier.  Each has around 17 dB of gain at VHF frequencies.  Both also have 75-ohm input and output impedances.

Here is a 20 - 70 MHz Band Pass Filter schematic.  Experiment with different front-end filters on the receive amplifers to limit their exposure to interference from AM/FM/TV broadcast stations.  A tracking generator plot of a homebrew 40 - 70 MHz band pass filter, similar to the above 20 - 70 MHz filter schematic.  Yes, I made the tracking generator also, its output is relative - and not calibrated.

This is a commercial CATV distribution amplifier which was used with good results:

Bridger - Model 4-B300 - Picture 1  40 dB of gain from 40 - 400 MHz

Bridger - Model 4-B300 - Picture 2  Replaced the F connectors with BNC connectors.  Voltage requirements are +24 VDC at around 500 mA.

Bridger - Model 4-B300 - Picture 3  Internal view.  Yellow core inductor is part of the output bias-T.

I don't know who the manufacture is, but it was probably built during the 1980s and uses the TRW CA2201 and CA623 hybird modules for amplification.  Its outside case is labelled "BRIDGER" and "MODEL 4-B300".  There are adjustable potentiometers for both gain and slope.  Leave the slope adjustment alone, unless you know what you are doing.  The only modifications made was replacing the original push-on F connectors with BNCs, adding a voltage "bias-T" to allow DC to be placed on the coaxial output for external power, replacing some of the old leaded capacitors with new surface mount versions and an overall cleanup for the circuit board.

The output voltage bias-T is made using a 1000 pF/50 VDC ceramic capacitor in series with the output RF connector.  A 30 µH ferrite inductor then connects from the output RF connector to the postive power line.  Be sure the capacitor and the inductor can carry the fairly high voltage and current.

Video Demodulation

A quick-and-dirty hack to demodulate the received RF signal is to use a cable TV tuner which gives baseband video output.  For this setup, a slightly modified Olson Technology OTD-3000.  The frequency synthesizer was removed and a manual tuning 100 k potentiometer was added, along with a 36-volt tuning range.  This allows for quickly scanning the bands and easier, manual frequency adjustment.  I also tapped the divide-by-64 prescaler output so I can verify the exact local oscillator frequency with a Radio Shack frequency counter.


Prescaler output frequency is 1.651 MHz.  Multiply this by 64 to get 105.664 MHz.  Then subtract the 45.75 MHz IF offset to get a final receive frequency of 59.914 MHz.

The new OTD-3000 tuning ranges are as follows:

Band Switch
1	2	3	Prescaler Output (MHz)		Tuning Range (MHz)

1	1	1	1.36 -                          42 -
1	1	1	2.26                            99        (VHF Low)

0	1	1	1.97 -                          81 -
0	1	1	4.09                            216       (VHF Mid)

1	0	1	3.05 -                          150 -
1	0	1	6.57                            375       (VHF High)

1	1	0	6.06 -                          342 -
1	1	0	13.48				817       (UHF)

Here is Chapter 17  (1 M PDF) of the book Standard Handbook of Video and Television Engineering.  It covers television reception and tuner functions in detail.

Spectrum Analyzer

A RF spectrum analyzer is very useful for determining the frequency of any electromagnetic radiation from your computer.  This tool displays an entire frequency range in one view and will allow you to "zoom" in on a particular frequency for further scrutiny.

Yes, I built my own 0 - 1000 MHz Spectrum Analyzer.  If you are up to a challange, build Scotty's Spectrum Analyzer.  It's DDS/computer controlled - very nice.

HOST Computer

We are now ready to piece everything together.  Here is a picture of my demodulation setup (front panel close up).    The ammo box to the lower right contains a 12-volt lead acid battery, and the speaker is connected to the audio output jack of the OTD-3000.  This is helpful for verifying TV or FM broadcast interference.  Note the frequency counter reading 1.651 MHz.  This equals a received frequency of 59.914 MHz.  It was probably receiving the second harmonic of the pixel clock, for my TARGET monitor, which is around 28 MHz.  The OTD-3000 is unable to tune below 42 MHz.

This is the display on the HOST computer monitor, a 15" original DEC C10E monitor.  In the picture, it's displaying random noise from the OTD-3000 video output going to the monitor's blue video input.  I used the blue video input 'cuz it looks pretty.

The computer to the left, a Compaq DP4000 with a Matrox Mystique PCI video card, is generating the horizontal & vertical synchronization signals.  The operating system is RedHat 9, and the computer is in command line mode running the vgaset command.

Here is a close up picture of the Video Synchronization Signal Pass-Through Box in operation.

The specifications for the HOST computer's monitor are:

  Vertical Sync = 70.216 Hz
Horizontal Sync = 31.527 kHz 
    Pixel Clock = 28.38 MHz

Those are found via the clockprobe command.

TARGET Computer

This is the display on my TARGET monitor.  It's a 17" CTX 1765 with a Matrox Mystique PCI video card (Compaq DP4000).  The computer was in DOS-mode, with a DIR of the C:\WINDOWS directory.  The receive antenna was resting on top of the monitor, so much for the reading-your-monitor-from-miles-away-myth.

I don't know the TARGET computer's monitor specifications because Microsoft is run by freakin' retards.

It Works!!!

Sort of.

You can see the results here.  The text was was actually a little crisper than the picture shows, but just barely readable.  The monitor's picture is "rolling" from right-to-left because the horizontal synchronization signals were not matched prefectly.  This resulted in the picture being "smeared."  Here is another example of the horizontal rolling.

The maximum reception range I was able to achieve was only a few inches.  Mind you, this is with a crappy antenna, cheap receive amplifiers, and no modification of the OTD-3000's video demodulation circuitry.

Extending the Range

The only true way to extend the range of "van Eck phreaking" is to hide the antenna, receive amplifiers and video demodulator somewhere near the target area.  You then take the raw video output and transmit that, via a high power transmitter back to your hidden receiver location.  A 20 Watt amplifier and good antennas will easily go 10 miles in the 1.2 GHz amateur radio band.  To receive (and demodulate) this signal, you only need an old C-band satellite tuner, without the block downconverter.

There is an article on the construction of a homebrew 1.2 GHz ATV Video Transmitter and the amplifiers which will work for this method.  The Ramsey LPY2 antenna will work very well as the 1.2 GHz transmit and receive antenna.  Be sure to keep your antenna feedline cable (LMR-400 or RG-8) runs as short as possible.

It also appears possible to record the raw demodulated video signal to tape via a standard VHS VCR.  Most VCRs need to see the proper sync signals before they'll start recording, but my experiments showed this is not always the case.  The only major problem is the VCR will try to "fix" the signal by adding its own sync signals.  This will distort the signal as needed.

Pictures from the VCR record experiment.  VCR was a Sharp VC-A303U piece of junk:

VCR Record Experiment - Picture 1  Output video signal from VCR.  The HOST VGA monitor and the VCR use different sync rates, hence the distortion.

VCR Record Experiment - Picture 2  Intercepted text via the radiation from the TARGET monitor - the quality is very poor.

Transmitting Video Signals

To re-create a TARGET's video signal exactly, without any noise interference, you'll need to transmit the raw video signal to a remote location.  This isn't as hard as it sounds, and it is covered under this section, GBPPR VGA Video Monitor Transmitter.

The only real problem is generating the exact synchronization signals.

Software Tools

There are several useful console tools included in the SVGATextMode package.  These include grabmode, which probes your monitor's current "Modeline", clockprobe, which grabs your monitor's current synchronization rates and pixel clock frequency, and vgaset, which allows you to manually tweak the horizontal and vertical synchronization rates.

Documentation for the grabmode/clockprobe commands.

Precompiled binaries for Linux/RedHat 9.0 :   grabmode and clockprobe

The Estimated pixel clock value (in MHz) which is displayed by running clockprobe on your TARGET monitor should be used as the starting point for tuning your receiver.

Documentation for the vgaset command.

Precompiled binary for Linux/RedHat 9.0 :   vgaset

For X11, use the included xvidtune utility.

Another tool which is useful for directly controlling VGA video card registers is setVGAreg.  To read the registers use getVGAreg.

Documentation for the setVGAreg/getVGAreg commands.

Precompiled binaries for Linux/RedHat 9.0 :   setVGAreg and getVGAreg

National Security Agency TEMPEST Notes / Military Guidelines

Mirror of Cryptome's National Security Agency TEMPEST program notes.  Broken URLs and images have been fixed or noted.

  1. NACSIM 5000  TEMPEST Fundamentals
  2. NSA Specification No. 94-106  Specification for Shielded Enclosures
  3. NACSEM 5112  NONSTOP Evaluation Techniques
  4. NSTISSI No. 7000  TEMPEST Countermeasures for Facilities
  5. NSTISSAM TEMPEST/2-95  Red/Black Installation Guidance
  6. NSTISSAM TEMPEST/1-92  Table of Contents and Sections 1-5
  7. NSTISSAM TEMPEST/1-92  Sections 6-12
  8. NSTISSAM TEMPEST/1-92  Appendix A (TEMPEST Overview)
  9. NSTISSAM TEMPEST/1-92  Appendixes B-M
  10. NSTISSAM TEMPEST/1-92  Distribution List
  11. NSA/CSS Regulation 90-6  Technical Security Program
  12. NSA Zoned Equipment  Products Program
  13. NSA Endorsed TEMPEST Products Program  Procedures Package
  14. NSA Endorsed TEMPEST Test Services Program  Test Services Procedure Package
  15. Emissions from Bank Computer Systems Make Eavesdropping Easy, Expert Says  American Banker, March 26, 1985
  16. Eavesdropping On the Electromagnetic Emanations of Digital Equipment: The Laws of Canada, England and the United States  by Christopher J. Seline, 1989
  17. The Tempest over Leaking Computers  by Harold Joseph Highland
  18. Physical Security Requirements for NSA/CSS Sensitive Compartmented Information Facilities
  19. TEMPEST Glossary
  20. US Air Force Emission Security Countermeasure Reviews
  21. US Air Force EI TEMPEST Installation Handbook  (343k PDF)
  22. US Air Force Emission Security Assessments
  23. Radio Frequency Shielded Enclosures  (MIL-HDBK-1195)  (PDF Version)
  24. TEMPEST Shielded Facilities  Chapter 12 of EP 1110-3-2  (1.2 M PDF)  (Complete Document)
  25. U.S. Air Force Engineering Technical Letter 90-3  TEMPEST Protection for Facilities  (148k PDF)
  26. Emission Security (EMSEC) Information Guide
  27. Navy INFOSEC TEMPEST Training Information
  28. TEMPEST Timeline
  29. RAGEMASTER  NSA's RF retro-reflector that provides an enhanced radar cross-section for VAGRANT collection.
  30. CTX4000  NSA's CW radar illuminator (1-2 GHz) used for VAGRANT and DROPMIRE collection.  It's replacement is PHOTOANGLO (1-4 GHz).
  31. LOUDAUTO  NSA's audio-based RF retro-reflector.
  32. NIGHTWATCH  NSA's display and horizontal/vertical sync generator for processing VAGRANT signals.
  33. TAWDRYYARD  NSA's beacon RF retro-reflector to provide rough positional location.

Notes & Links

Return to Homebrew Military & Espionage Electronics Page