Generate AM Radio Broadcasts With Your Monitor

tessellation writes: "Tempest for Eliza is a program that uses your computer monitor to send out AM radio signals. You can then hear computer generated music in your radio." Here is your big chance to disrupt free thinking radio programs in your neighborhood.

This isn't the first

[recursiv]

This isn't the first time something like this has appeared on slashdot. Way back in the day ('99) there was an article [slashdot.org] about a guy who was using the radio interference from his motherboard to do the same sort of thing.

Van Eck phreaking

[jasonzzz]

For many years during the cold war, the NSA had
been nervous about natural radiations emanating/broadcasted by VDTs and electrical wiring. So much so that many government sites were constructed with TEMPEST safeguards with thick concrete walls, wiremesh shielding and isolated electrical works. Even then, VDTs, type writers, phones, and other electrical devices were never placed close to walls adjacent to the outside of the enclosed space.

Read the Van Eck document.
http://www.shmoo.com/tempest/emr.pdf

Read the TEMPEST page
http://www.eskimo.com/~joelm/tempest.html

Re:Done it...

[Kymermosst]

With a crappy radio, it had to be fairly close 5 feet to make it out... my monitor doesn't put out that much rf... it's a low-rad type.

Now, putting my ham radio at 5 watts about 10 feet away does interesting things to my monitor, I can tell you that!

Old News... My TRS-80 does this already :)

[Chmarr]

Eh... old news. My TRS-80 Model I had a game who's instructions read:

For sound effects, place an AM radio next to your monitor

It was a car racing game... the sound effects made a kind of sense... except they didnt stop when you crashed the car :)

Re:weird, its not working - but it does! :))

[leibnitz27]

But I've been in one of Ross Andersons lectures where him and Markus demonstrated tempest working against a laptop. Just using LCD won't protect you, see Here [google.com] (google cache - page seems to be missing) and Here [eskimo.com]

Good description of van Eck

[English Guy]

Good description of van Eck phreaking in Cryptonomicon by Neal Stephenson or in this article [shmoo.com] (which is quite a large pdf)

Re:Just one little detail

[CProgrammer98]

All this program is doing is modulating the EXISTING rf that's coming out of your monitor in a more useful way by calculating and displaying an image that will cause the modulation to be at a particular musical frequency. It ISN'T causing your monitor to emit any more radiation than it already was, it's just "un-randomizing" it.

harumph. Another Johnny-Come-Lately

[hawk]

While remembering the 8bits and their tricks is impressive, it was hardly new. This was done on IBM's and others at least in the 60's, and possibly the late 50's.

Additionally, line printerss played Jingle Bells . . .

hawk

Re:Legal issues

[dattaway]

Oh, there are a few ways to increase the output of your monitor by many watts too. These require the case to be taken off and willingness to turn your screwdriver on parts connected to the B+ chassis (about 2000 volts.) Uplugging the computer during this process is optional. Voiding your monitor's warranty and making it a potential fire hazard is your destiny with this procedure.

Brightness is one good way. Want to vaporize some phosphor off the screen? Well, look at that funny transformer with the thick red wire going to the picture tube's top. No, don't put your fingers under that red cap as you'll discharge 30,000 volts. The capacitance stores enough current that it may jump start your heart into transporter mode to a higher (or lower) place in the heavens. Anyways, look back on the transformer where one or two or more small screwdriver adjustments are provided. One should be the focusing voltage for the electron voltage. All this adjustment will do is make your picture tube require prescription glasses when things get fuzzy. The other adjustment dangerously raises the drive voltages of your homebrew particle accelerator into x-ray producing levels. Enjoy.

The other tasty method to injure personal health is to max out horizontal drive voltage. Your adjustment of choice is on the main circuit board that is a minefield of tempting adjustments. The one I am talking about is an adjustable inductor, when tinkered with will lose the monitor's calibration for the horizontal picture width. Its the one adjustable inductor that stands taller than the rest and its frequency is so high, its design require the turns of wire to be a bundle of stranded wire. Yes, remove the powdered ferrite slug out of this coil. Current will now saturate the picture tube's yoke coils. Electronic devices and radios around the house will now bow to your monitor's new elite status.

There you go. Not only have you voided your monitor's warranty, you have just demonstrated why picture tubes are evil particle accelerators. They should be banned.

Re:Beeping remote?

[ocelotbob]

Yes, I know most remotes are IR. However, the phenomena I'm talking about is fairly well documented; there are several faqs floating around on the internet discussing the subject. Because of how AM radios work, any localized source of radiation of sufficient strength, no matter what the frequency, will cause interference. Its similar to how a thunderstorm will cause pops when listening to the radio.

Re:Only Radio?

[jacklf]

Since you brought it up... [from the CBM-PET FAQ [6502.org]]:

WHAT IS THE 'KILLER POKE' AND SHOULD I WORRY ABOUT IT?

This is THE POKE of computer lore, the command that WILL physically break a
computer! Of course other commands and methods are known that can
potentially cause damage (usually to disks, hard drives or other mechanical
units), but this is the most notable mainly because it was a command somewhat
commonly used and it affects solid-state circuitry.

History of 'the killer poke'
When the first PETs (small 9" screen) models came out, the display wasnt all
that fast.

The old PETs were slow because the print character ROM routine
waited for the interval between screen scans before updating the screen
memory. This reduced conflicts over the screen RAM which would have resulted
in random pixels (snow) being illuminated on the screen. There was an input
on one of the I/O chips which was hooked up to the video circuitry and told
the routine when to access the video RAM.

It wasn't too long before someone learned they could impove the
character display speed via a poke to location 59458; which would set the
video controller to update more readily. It was a noticible improvement of
speed on programs using PRINT often, it was kind of like a free upgrade.
It was mentioned in a few publications and used in many programs that relied
on printing to the screen. I had learned of the poke through Cursor Magazine,
a monthly tape-based publication. They printed the command in one of the
'newsletter' flyers included with an issue which you could insert into their
game "joust" to make it play faster.

Later on, when Commodore released the larger display (14") PETs, they had
improved the display controller which made that POKE unnecessary. An
unfortunate side effect was that the POKE to 59458 affected a different
register which adjusts one of the newer screen display capabilities, which
could result in damaging the PETs video curcuitry when left running. I
discovered it by accident after our school received some large-screen 4016s.
When active, the screen starts to warp after about the third line and the
display stops around the fifth, the keyboard is also unresponsive. When a PET
is in this mode, the only solution is to turn it off, FAST! Fortunately none
of the school's PETs were damaged due to this POKE. Later Cursor Magazine
published a 'fix' that would allow older PETs to use the poke and keep the
large-screen units from frying. Unfortunately there are still many programs
that do not have this fix.