The TCM-03 is an advanced unit for testing cables for the presence of
microphones and/or carrier-type eavesdropping transmitters (bugs),
developed and produced by Audiotel in Corby (UK) around 1992.
It is suitable for testing mains power cables as well as other types
The device is powered by internal batteries that are recharged
automatically when the unit is powered from the mains. Protection of the
mains power lines is done through the device's own mains socket.
As most mains lines consist of three wires (Live, Neutral and Earth),
a selector at the rear is used to select the required pair.
The TCM-03 can also be used to check other types of cables and wires,
such as telephone lines, intercom systems, PA systems, alarm cables, etc.,
for eavesdropping devices. For such cables, a special break-out cable
The TCM-03 allows mains power lines and other cable types to be monitored
permanently. Some of its functions can also be found in other Audiotel
equipment, such as the Scanlock 2000
and the Scanlock ECM.
Please note that the version of the TCM-03 shown here is quite different
from the later TCM-03 Mark II which is much better built and has
significantly more features. Amoung other things, it offers AM and FM
demodulation and was available
from Audiotel until 2013.
The TCM-03 was housed in a non-shielded plastic enclosure with a sloped
front panel, that should be placed horizontally an, say, a table. Most of
the controls and adjustments are at the front panel, with the exception
of the main wire-pair selector and the audio attenuator.
Also at the front panel is a 6mm jack socket for a pair of headphones.
The SELECT switch (2nd from the right) is used to select the required
mode of operation. The black rectangluar window at the left,
is a digital volt meter that is used to monitor the voltage on an
analogue telephone line.
All connections to the mains and to any other cables under test are at
the rear of the unit. The mains should be connected to the 3-pin Euro
socket, wilst the wire-pair to be monitored for carrier-type bugs
is selected with the rotary switch marked CARRIER SOUCE to its right.
Any other cables should be connected to the 5-pin 270° DIN socket at
the left. A break-out cable with crocodile type clips was supplied for this.
A recorder can be attached to the sockets at the centre.
The TCM-03 can be used for the following tasks:
- Check for audio signals
Setting the SELECT knob at the front panel to 'AF' allows the cable
under test to be checked for Audio Frequent (i.e. LF) microphones.
- Check for audio devices that need power
Some eavesdropping devices 'steal' a little bit of energy, needed for
their operation, from the cable they are connected to. If the regular devices
on this cable are switched off, the bug won't operate. By supplying a low
voltage to the cable under test, bugs of this type will be activated and,
hence, will become detectable.
- Activate remote controlled devices
A built-in tone generator can be used to active bugs that are
single-tone operated. Once these bugs are activated, they can be detected.
- Check for carrier bugs
Rather than using LF signals (audio), many sophisticated bugs modulate
their audio signal onto a carrier of, say, 200 kHz. Bugs of this type can
normally not be detected without special devices. The TCM-03 can demodulate
carrier bugs automatically by setting the SELECT knob on the front
panel to CARRIER.
- Voltage checks
A built-in digital volt meter can be used to monitor the voltage on
a cable, such as a telephone line. Tampering with the line, e.g. when
placing a bug, will often show significant changes in voltage.
- Line jamming
An automatic tone generator inside the TCM-03 can be used to jam
voice-activated telephone taps automatically.
- Off-hook signalling
An LED indicator on the TCM-03 front panel will show when the telephone
line becomes engaged. This allows the operator to detect unauthorised
use of the line, for example by a recording device or a timed device.
TCM-03 Mark II
The TCM-03 shown above was clearly a gap-fill solution that was rushed
onto the market in the late 1980s in response to an increasing demand
for wire-tap detectors.
Looking at the interior,
reveals that the plastic case is not shielded
and that the PCB
contains many modifications.
Many of the vital components of the unit are spread around the case
and some are just glued together, making it
doubtful whether it would withstand any stafety approval test today.
Nevertheless, it was a very effective device.
Shortly after the introduction of the TCM-03, Audiotel engineers started
the development of an improved version with even more features.
In 1992, TCM-03 Mark II was introduced. It was housed in a different case
and was much better built. Furthermore, it
added the detection of AM and FM radio bugs to the list of features.
The image above shows the improved TCM-03 Mark II as it was pictured on
the Audiotel sales datasheet [B]. The Mark II had an extremely long lifespan.
Although it was introduced in 1992, it was only discontinued in 2013;
a service life of more than 20 years! As analogue telephone lines are less
common today, and more and more telephone services are running over digital
lines (e.g. ISDN, IP, VoIP, etc.), the device has now become obsolete.
The functions of the device have been superceeded by the
Audiotel's latest bug tracing receiver and cable checker.
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© Crypto Museum. Created: Sunday 19 May 2019. Last changed: Sunday, 17 February 2019 - 16:30 CET.