Re: Laptops and TEMPEST

["Timothy C. May" <tcmay@got.net>]

At 2:03 PM -0700 12/5/96, C. Kuethe wrote:

>Here's some more about that.  I use both the Texas Instruments ti85 and
>Hewlett Packard HP48 graphics calculators.  I was playing tetris on my ti85
>one day and had the radio on.  every now and then this funny noise would
>come out of my radio.  After a while I noticed it was sync'ed with a
>keypress on my calc.  So I tried some experiments, and I found that doing
>just about anything would emit a detectable signal.  Keep in mind that I was
>using a cheap radio, tuned to a 100kW radio stn and still could tune in a
>calc.  I tried
...
>and they all sound different.  My favorite was the for loop.... sounds like
>a diesel engine.  Maybe that's why my calc is running so slow.  it's only
...

Back in the Olden Days, we used to use these signals as sound output for
our computers. For example, on my Sol 20 computer (bought and soldered
together in 1978, in case anyone's interested).

There were various BASIC programs that ran various loops, thus generating
crude tones on nearby radios. And the games that were available had
routines which used radios as crude sound devices.

(None of which could hold a candle to my 1968 "amateur transmitters": neon
sign transformers, sending Morse code to my friend a mile or so away...it
was detectable on all AM bands! I never got a visit from the FCC, but I
only "transmitted" a few times.)

--Tim



Just say "No" to "Big Brother Inside"
We got computers, we're tapping phone lines, I know that that ain't allowed.
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Timothy C. May              | Crypto Anarchy: encryption, digital money,
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