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TSCM
The internal NiCd batteries are automatically charged when the device
is connected to the mains.
Signals can be picked up with the built-in telescopic antenna, or by
an external antenna that is
connected to the miniature antenna socket
at the front panel. Judging the interior, the device is more or less
a copy of the Scanlock Mark 3, for which
Lee Tracey had failed to register a patent.
The device was developed and marketed by Bonaventure in London,
a company – led by Mr. John Herbert – that was widely known for its
portfolio of counter-terrorism devices, such as electronic stethoscopes
and optical probes. TRACER was part of Bonaventure's portfolio
of equipment for
Technical Surveillance and Counter-Measures (TSCM).
It was also sold by other companies, such as Mercks and Hollander.
According to a label found inside the unit, the device shown here
once belonged to Brent Electronics & Communications Ltd. in Cleethorpes
(Lincolnshire, UK), at the time a supplier of surveillance equipment
to the MoD. Brent Electronics was dissolved in 2009.
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The image below shows the clear and well-arranged controls and readouts at
the front panel of the device. At the left is the integrated telescopic
antenna. At the right is the field strength meter. The device is immediately
ready after switching it on, and locks as soon as it detects a signal
that exceeds the threshold level, in which case the
signal level will be visible on the meter.
The telescopic antenna does not have a knee-joint, which implies that
it had to be used straight up.
In most cases, the use of the built-in telescopic antenna will be sufficient,
but in cases where the bug is difficult to find, a separate 'magic wand'
antenna could be connected to the
external input at the top left.
In addition, locating a bug is assisted by SONIC LOOP and LOCATE,
two features that have been copied straight from the
Scanlock Mark 3.
The device is only suitable for fully automatic scanning and does not have a
manual mode, like the later Audiotel Scanlock Mark VB.
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The TRACER scd auto can be used in a variety of modes and with
various types of modulation,
depending on the type of bug, the method of searching
and the time available to do the sweep. The following modes are available:
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- Automatic mode (AM/FM)
In this mode, the device searches fully automatically for bugs in the
room and locks itself onto the strongest signal that it finds, with a lock
sensitivity of 1mV up to 1.5 GHz. In earas with strong broadcast transmitters,
it may be necessary to move the receiver around the room whilst searching.
- Sonic Loop
In this mode, the device emits a continuous (audible) tone, that changes
to an intermittent tone when the receiver detects itself (i.e. if it hears
its tone through the bug).
This mode should be used as a last resort, as it is likely to alert the
eavesdropping party of the fact that a bug-sweep is taking place.
- Locate mode
When the LOCATE button is depressed, the device provides an audible
tone with a pitch that is proportional to the strength of the acquired
signal. Starting off with a low frequency ticking sound, the pitch gets
higher when approaching the bug. In this mode, the use of a pair of
headphones is advised, as otherwise the eavesdropping party might become
aware of the fact that a bug-sweep is taking place.
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TRACER scd auto is suitable for reception of the following types
of modulation:
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- AM
This is for bugs that use Amplitude Modulation (AM).
Not many bugs are of this type. It is generally used with low-frequency
transmitters (below 80 MHz).
- FM
This is for the most common type of bugs that use
Frequency Modulation (FM). These bugs generally operate at frequencies
from 80 MHz onwards. Most of the cheaper commercial and homemade bugs
are of this type.
- Subcarrier
With some of the more sophisticated bugs, the audio is modulated onto
a non-audible subcarrier. As a result, the bug appears to be sending a
silent carrier (or hum or noise), whereas in reality it carries the
sound it picks up in the target area. In this mode, the device automatically
detects and locks onto the bug's subcarrier frequency as well.
➤ More information
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Operation of the device is remarkably simple. All you need to do
when first scanning a room for potential bugs (sweeping) is to ensure that
all buttons are up (out) when the unit is switched on. Next press the FM
button to search for the most common type of FM bugs. The device will now
automatically lock onto the strongest signal in its vicinity, as illustrated
below:
With the receiver in location A, it will probably lock immediately
onto a strong broadcast station that is nearby. Such broadcast stations are
generally much stronger than a potential bug in the room. When the TRACER
is moved around the room however, it will continue to scan and lock onto
the strongest signal. When the receiver is in location B it will
intermittently switch between the broadcast station and the bug, but when
it is moved closer to the bug (C) the RF signal from the bug will dominate
over the broadcast station and the bug will be heard.
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The TRACER scd auto is based on
Lee Tracey's design of the Scanlock locking
staircase receiver of 1962. As Scanlock was the first locking receiver
of this type that was commercially marketed, it is generally
referred to as the original Scanlock. The device uses the following
principle:
There is no preselection other than a filter that allows only frequencies
above 10 MHz to pass by. The 10 MHz output of the first local oscillator
is fed to a so-called comb generator. This is effectively a non-linear
junction (i.e. a diode) that causes harmonics of the fundamental frequency
to be generated. It produces signals at 10 MHz, 20 MHz, 30 MHz,
40 MHz, etc.
The output of the comb generator is then mixed directly with the antenna
signal, resulting in many frequency segments of 10 MHz each, being superimposed
on top of each other. The problem of sweeping the entire spectrum between
10 MHz and 4 GHz has now been reduced to sweeping just a single small segement
of 10 MHz, by sweeping all superimposed or stacked segments simultaneously.
The output of the 2nd IF stage is fed to three demodulators (AM, FM and
SC), By using a sweeping oscillator in the 2nd IF stage, the resulting
10 MHz segments can be swept in less than a second. The receiver locks onto
the strongest signal found.
In Sonic Loop mode (SL), the speaker produces a continuous 1800 Hz
tone. The output of all demodulators (AM, FM, and SC) is checked
for this tone by applying it to a sharp 1800 Hz filter. When this
particular frequency is detected, the tone is changed into an
intermitted one.
Note that frequencies below 10 MHz are not covered by this receiver.
Although it is unlikely that bugs operate below 10 MHz,
it is possible to use these low frequencies, e.g. when using them as a
carrier. The later Scanlock 2000
contained a extra detector to find
mains carrier bugs (MC) and the Scanlock ECM
even had a separate VLF receiver to cover the 10 kHz to 10 MHz section.
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The interior of the TRACER scd auto can be accessed by removing two screws
from the bottom of the case, after which the font panel can be extracted from
the case shell and the interior is exposed. All internal parts are fitted
to an aluminium frame that is fitted to the front panel.
Although the circuit appears to have been copied from the
Scanlock Mark VB, the layout of the printed
circuit board (PCB) is much cleaner and is silk-screen printed
with the IDs of the com
ponents.
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- Nico van Dongen, Bonaventure TRACER scd auto - THANKS !
Crypto Museum, donated April 2023.
- Michael Dewar, Weapons and Equipment of Counter-Terrorism
Arms and Armour Press Ltd., 1987. ISBN 0-85368-841-9.
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© Crypto Museum. Created: Sunday 30 April 2023. Last changed: Tuesday, 25 March 2025 - 10:59 CET.
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