[6449] in cryptography@c2.net mail archive
Re: beyond what is necessary
daemon@ATHENA.MIT.EDU (Phil Karn)
Fri Jan 21 10:36:01 2000
Date: Thu, 20 Jan 2000 17:06:45 -0800
Message-Id: <200001210106.RAA06815@homer.ka9q.ampr.org>
From: Phil Karn <karn@ka9q.ampr.org>
To: mix@anon.lcs.mit.edu
Cc: cryptography@c2.net
In-reply-to: <20000115204011.25314.qmail@nym.alias.net> (message from lcs
Mixmaster Remailer on 15 Jan 2000 20:40:11 -0000)
Reply-To: karn@ka9q.ampr.org
>>"a.4. Specially designed or modified to reduce the compromising
>>emanations of information-bearing signals beyond what is necessary
>>for the health, safety or electromagnetic interference standards;"
>So, who gets to say what's a standard?
>Some people's standards are higher than the government
>(e.g., varieties of 'organic'; kosher; etc).
This is especially true for radio amateurs (hams) doing "weak-signal"
work on the VHF (30-300 MHz) and UHF (300-3000 MHz) bands. Some of the
propagation modes used include tropospheric scatter; meteor trail
reflection; satellite communications; and the ultimate, EME
(earth-moon-earth, i.e., using the moon as a passive reflector).
Natural background and modern receiver noise levels are all very low
on these bands, so unwanted computer emissions have long been a
serious problem. (Modern CPU clock speeds are now well into the UHF
region). Simply meeting the FCC Class B (residential) emission limits
is not nearly enough. Those regulations were intended to protect
broadcast receivers working with signals considerably stronger than
those involved in amateur weak-signal work.
So ever since the first personal computer appeared in a ham shack,
hams have been trying to shield, bypass and otherwise suppress their
interfering signals. Some approaches resemble those taken in Tempest
equipment: special filters on power and signal lines; metal equipment
cases with insulating paint removed and resealed with finger stock and
copper tape; plastic cases coated with conductive paint; and so forth.
I still have an early-80's clone monochrome PC monitor that I
extensively modified in this way. It's obsolete, but it's quiet. And
it was all "necessary for (my) electromagnetic interference
standards".
Phil
