From: pzs@ficus.webo.dg.com (Peter Z. Simpson)
Subject: Re: CATV monitoring, Tempest screening (was Re: FCC Call letters)
Date: 7 Apr 92 14:40:19
	<1992Apr1.192907.3046@e2big.mko.dec.com>
	<1992Apr3.115836.28499@cunixf.cc.columbia.edu>
	<1992Apr4.204833.1572@lsl.co.uk>
Organization: Data General Corp., Westboro, MA

>>>>> On 4 Apr 92 20:48:33 GMT, robin@lsl.co.uk (Robin Fairbairns) said:

> 2: the military (I think it's NATO-wide at least) have this thing about 
> tempest-shielding of VDUs that will hold sensitive information.  This is 
> a form of Faraday caging of the VDU that is (was?) to prevent the wicked
> USSR spies sitting in large black vans outside the base perimeter
> reading what's on the screens.  Now I've always poo-poohed this idea, 
> but whenever I've done it in the presence of someone employed by the 
> military, they've always `been shown the equipment in use' by a security 
> officer.  

    It's true. I've seen it. I work at a computer company. I had a CGA
display on my IBM PC. Sweep rate is same as TV sweep rate. We had a
small LCD TV in the office to watch the space shuttle take off that
morning. As we brought it near the window (to better receive the TV
station in a steel building), we also brought it near the CGA monitor,
which was at that time displaying the log-on banner for our
timesharing system. I was amazed to see a faint image of the logon
banner appear on the LCD TV. It was tunable, too. That is, you had to
tune the TV to a particular channel to see it (sorry, don't remember
if the channel was live or vacant). Note that it was an LCD TV, so
there were no sweep coils on the (nonexistent) CRT. It may have been
magnetic fields coupling onto the PC board traces, but the reception
range was 3 feet or so, and I suspect the Russkies could do better.


> Well, if it's all true, on the basis that what a USSR spy had yesterday 
> any self-respecting CATV firm probably had the week before last, I'ld 
> say: IF YOU'VE GOT ILLEGAL CATV EQUIPMENT, I'LD GIVE IT UP NOW.

    The *white* van was in my neighborhood a couple of weeks ago. It
had a long low antenna on the roof. I knew exactly what it was. Now,
I'm not saying whether or not I steal cable TV, but I haven't had a
phone call from them yet. They're looking for leaks of their 100 Mhz
test signal, which is the strongest signal on their cable. They have
to keep these under control, per the FCC, so they don't interfere with
other over-the-air services like police & fire, which use the same
frequencies for their radios that the cable company uses for Let's
Make a Deal. If you were to add extra boxes or whatever, and do it in
a haphazard, poorly shielded way, your efforts would be detectable. If
you have a clean system, no problem. Even if you have a legal system,
and it's leaky, you'll probably get a call. My contract says I have to
let them in to work on their equipment, but only at a mutually
convenient time. Let's just say that it's unlikely it'll be convenient
for me if they just knock on the door without first calling for an
appointment. :-)

Pete "don't use zip-cord for that extra box" Simpson, KA1AXY


--
 ==============================================================================
  Peter Simpson                 (508) 870-9837 voice
  Data General Corp.            (508) 898-4212 fax
  4400 Computer Dr. E132
  Westboro, MA  01580           INTERNET: pzs@ficus.webo.dg.com
 ==============================================================================