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Technical Surveillance and Countermeasures
This section deals with equipment that has been used (or is currently being
used) for finding clandestine transmitters, covert listening devices (bugs)
and monitoring the frequency spectrum in general. Note that there will be
overlaps with other categories on this website.
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TSCM equipment on this website
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Non-linear Junction Detector
A non-linear junction detector, commonly abbreviated to NLJD,
is a countermeasures device for the
detection of semi-conducting materials, such as the P-N barrier in electronic
components like diodes, transtors and ICs. As most
covert listening devices (bugs)
are built from such parts, it is possible to discover their electronic
circuits, regardless of whether the device is powered or not.
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When a semi-conducting object is illuminated by an RF signal of a
particular frequency f1, the non-linear properties of the object
will cause harmonics of that frequency to be generated, in particular the
2nd and 3rd harmonics (f2 and f3).
By examining the minute f2/f3 harmonic signals
reflected by the object, it is possible to discover the object,
even when it is hidden from sight.
Note that other semi-conducting materials, such as a rusty nail or an
oxidised piece of metal, also
generate harmonic frequencies and may therefore cause an NLJD to generate
a false positive.
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For this reason, modern NLJDs often examine the
ratio between the 2nd and the 3rd harmonic.
With an electronic P-N junction, the second harmonic will generally be
stronger than the third, allowing an electronic circuit
to be discriminated from a rusty nail with reasonable certainty.
The NLJD was invented during WWII
by Charles Bovill, who used it to
discover corrosion below painted surfaces on airplanes.
In 1972, shortly after Bovill had become technical director at
Allen International Ltd. (Westminster, London, UK), the device was renamed
Broom and was marketed as a bug-finder.
The Broom was later marketed by Audiotel in Corby (UK) as the
Scanlock Broom, succeeded in 1990 by the
Scanlock Broom ECM
and in 1995 by the Scanlock Super Broom.
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Non-linear junction detectors on this website
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Known non-linear junction detectors (NLJDs)
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As a countermeasure 1 against an NLJD, professional
covert listening devices (bugs)
of the US Central Intelligence Agency (CIA)
were equipped from 1968 onwards with a so-called isolator.
An isolator is a 3-port circulator of which the return port is
terminated with a resistor, as shown in the image below.
Any energy injected into the bug by an
NLJD will be absorbed by the resistor, resulting in no
(or very little) reflected energy. An example of such a
CIA bug
is the SRT-107.
Another very effective counter-countermeasure, is to plant a plethora
of inexpensive diodes at locations that are likely to be swept with
an NLJD. This will generate so many false positives that it masks the
presence of the actual bug(s). This method was used by the Russians
in the 1980s, during the construction of the (then ) new American
embassy in Moscow. Diodes were mixed into the building's concrete,
making the detection of real listening devices virtually impossible [2].
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As it is a countermeasure against a countermeasure device,
it is also known as a counter-countermeasure.
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© Crypto Museum. Created: Saturday 24 December 2016. Last changed: Tuesday, 19 March 2024 - 16:26 CET.
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