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Remote controlled transmitter
Pager Bug 1 was a remote controled
covert listening device (bug), consisting
of a mains-powered crystal-controlled transmitter with electret microphone,
and a commercial Motorola
pager [2] that acted as a switch receiver,
made during the 1980s by a Dutch group of skilled hobbyists, known as
Counter Observation Team (COT)
[1].
It was used by criminals in the Amsterdam underworld.
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The disadvantage of most radio bugs that use continuous wave (CW) transmission,
is that they are easy to trace when active. Battery operated devices have the
added disadvantage of limited battery life, reducing the bug's effectiveness.
The bug shown here, overcomes both issues. It has a built-in mains
power supply unit (PSU) that gives it a virtually unlimited life,
and is remote-controlled by means of a pager, so that it can be switched
OFF when it is no longer needed. This is the case when no conversation is taking
place (e.g. at night) or when a sweep-team is in action.
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The pager – normally powered by an internal 1.5V AA-size battery –
is also powered by the bug's PSU, so that its standby time is no longer
limited to a few days. The bug is activated by sending a special code to the
pager via the public telephone network,
and can be deactivated with another code. When active, the radio transmitter
has an operational range between 200 metres and 2 km, depending on obstacles
and circumstances. When inactive, the device is virtually undetectable. 2
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The real name of this device is unknown, but as it is remote controlled by
means of a Motorola pager, we have nicknamed it Pager Bug.
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Except when a
Non-Linear Junction Detector (NLJD)
is used by a skilled operator, but this was little known at the time,
and certainly not common practice.
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The diagram below shows how remote-controlling of the bug worked. At the centre
is the target area with the actual bug. At the right is the nearby listening post,
where a regular telephone set (or a phreaked mobile phone) is used to dial out
the pager's subscriber number and the numeric message (1).
The call is passed by the public network
(PSTN) to the
Semafoon paging service (2).
At the Semafoon service, the message is queued for transmission (3).
As soon as the network is free, the message is broadcast nationwide via
a network of cell towers (4). When the message reaches the pager,
it is decoded (5), and the transmitter is enabled.
When the bug is active, its microphone picks up the sound in the room,
and transmits it to the nearby listening post (6).
When bugging is no longer required, another message is sent to deactive
the transmitter again.
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The actual bug is housed in a standard black plastic enclosure, the interior of
which is shown in the diagram below. At the front is the actual transmitter.
It was probably an off-the-shelf part, that was modified to make it fit.
One of the corners has been removed, and the quarz crystal is mounted at
an angle. The electret microphone – with built-in pre-amplifier – protrudes
the case.
Behind the transmitter is a home-made decoder/switcher. It takes the signal
from the (modified) Motorola pager, and converts it into an ON/OFF signal.
At the far side is the mains power supply unit, which consists of a
miniature transformer, a stabilising circuit and two voltage regulators.
The Motorola pager is used here as a remote control unit,
or switch receiver,
for the transmitter (bug). It was a standard device that could be purchased
in a telecom shop, and could be activated from the national paging network
(Dutch: Semafoon netwerk). A message was sent by calling the pager's
subscriber number (in this case: 06-59565008) 1 followed by the numeric message
that had to be displayed on the pager's LCD screen; in most cases,
the number that had to be called.
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The Semafoon paging network is no longer operational, and the 06-59... numbers
have since been reused for the GSM telephone network.
Similar paging services still exist today however (2020).
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- Anonymous donor, Switched FM radio transmitter with Motorola pager - THANKS !
Received January 2020.
- Wikipedia, Pager
Retrieved February 2020.
- Wikipedia, Semafoon
Retrieved February 2020 (Dutch).
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© Crypto Museum. Created: Tuesday 04 February 2020. Last changed: Sunday, 03 May 2020 - 09:44 CET.
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