[105207] in Cypherpunks
Re: TEMPEST laptops (fwd)
daemon@ATHENA.MIT.EDU (Jim Choate)
Sun Nov 8 17:09:01 1998
From: Jim Choate <ravage@einstein.ssz.com>
To: cypherpunks@einstein.ssz.com (Cypherpunks Distributed Remailer)
Date: Sun, 8 Nov 1998 15:24:31 -0600 (CST)
Reply-To: Jim Choate <ravage@einstein.ssz.com>
Forwarded message:
> Date: Sun, 8 Nov 1998 15:58:39 -0500
> From: Dave Emery <die@die.com>
> Subject: Re: TEMPEST laptops (fwd)
> Lasers are a technology for generating light, not kinds of
> radio waves.
Same damn thing. Photons bouncing between electrons and protons exchanging
momentum. Why they do what they do at different wavelengths is even the same
physics.
> Most microwave ovens incorperate a motorized metallic device
> called a stirrer that sits directly in the beam of energy from the
> magnetron and is designed to reflect microwave energy bouncing around
> the cavity and change the standing wave pattern as it rotates, resulting
> in much more even distribution of energy. Without the stirrer hots
> spots would be much worse...
True, think of it as a moving mirror (optical analog). As the blades rotate
they take the reflected energy and rotate it. It does nothing for the need
to rotate the target for equal energy painting (re rf shadow effects).
You'll still find spots that are dead.
> Difraction becomes very significant for openings near in scale to
> the wavelength of the energy in question, thus the edges of the top will
> act to scatter energy in all directions...
For diffraction to occur the beam must hit the edge, not travel parallel with
it as in my point. There is also the question of relational wavelength
between the hole and the signal. If the hole is less than 1/3 wavelength
there will be nearly no scatter from a longitudinal transit of the hole by
the beam.
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( ( ( ( ( ( ( ( ( ( ( ( ( ( ( (
> This makes no sense whatsoever. The EM radiation takes place
> when changes in the current flowing happen.
If current flows there is a EM radiation, whether it is constant or changing
relates to charge motion.
> Thus radiation occurs only
> when the TTL signal changes state, not during either its high voltage or
> low volage state.
Wrong, they still emit a constant EM field during these periods. The point
is that if that constant field (which the info rides on top of) is such that
when it is actualy switched on or of it nearly saturates the rf input stages
of your reciever you're going to have a hard time getting info off it. In
those situations you need an amplifier that has more dynamic headroom.
So what does this tell us? One way to help mask EM radiations from such
things as laptops and other devices is to create a quickly changing field of
sufficient magnitude to swamp the input stages. This isn't just my
invention, it's behind radar jamming where you send a signal back of the
correct frequency at a radar transmitter (say in an attack aircraft).
Because the radar input stages can't differentiate between its own signal
and the spurious one it is harder to get a lock with the radar. The only
effective ways to defeat this are to increase the dynamic headroom of the
input rf stages or else 'burn-through' with a more powerful radar
transmitter on the aircraft.
> The amplitude of the current step is determined by
> the impedance of the circuit and how fast the logic switches and how
> great the voltage or current swing is , and how effectively it gets
> radiated is determined by the geometry of the conductor and its
> sourounding ohjects. EM radiation results only from changes in the
> magnetic and electric fields, not from their steady state values. Thus
> it is entirely meaningless to talk of the change in steady state values
> as only "3 db" when no radiation results from either the steady high or
> steady low value. And indeed near the conductor, the energy radiated
> from the current step will be 100 db greater than the ambiant (decibels
> are relative units, thus it is meaningless to talk of "radiating a rf
> signal that is 100 db").
Um, that explains why DC electromagnets don't work I guess.....NOT.
Ok, now let's address this dB (spell it right, Bell deserves the respect)
issue you raise. First, the various industries (pysics, electronics, etc.)
agree on standard references or conditions when using the term dB. I'm not
going into those standards. Secondly, *anytime* you speak of *two* signals
it is permissible to treat the lower level of the signal as 0dB, and as a
consequence talk of the second signal being some dB greater or smaller than
your reference. So if I have two signals (1v and 2v) it is perfectly
permissible to speak of the second signal being 3dB larger than the former.
It is exactly the same sort of metric practicality that permits one to say
the second signal is 100% larger than the former as well. In fact one is
saying the *EXACT* same thing either way.
On a completely different topic....
The book that I refered to the other day and said I'd forward a link to
is:
High Speed Digital Design: A handbook of black magic
HW. Johnson, M. Graham
ISBN 0-13-395724-1
~$50 US
Sorry I forgot about it the other day.
____________________________________________________________________
To know what is right and not to do it is the worst cowardice.
Confucius
The Armadillo Group ,::////;::-. James Choate
Austin, Tx /:'///// ``::>/|/ ravage@ssz.com
www.ssz.com .', |||| `/( e\ 512-451-7087
-====~~mm-'`-```-mm --'-
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