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Telephone microphone radio bug
The phone mike bug was a small radio transmitter that was disguised
as a normal microphone of the handset of a standard telephone set.
It was sold during the 1980s by security shops like the Spy Shop
in Amsterdam (Netherlands). As it was an illegal radio device,
it was 'export only'.
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Back in the 1980s, in the days when the national telephone companies (PTT) had
not yet been privitized, most (if not all) handsets of domestic telehone sets
contained similar microphones and speakers. When the carbon microphone of an old
telephone was broken (which happened rather often),
it could easily be swapped for a new one by unscrewing
the mouth-piece of the handset.
The radio bug shown in the image on the right is built inside the casing
of a standard microphone element, making it virtually indistinguishable
from an original microphone used in those days.
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As all telephone sets of the 1950s though to the mid-1980s used a carbon-based
microphone element, the phone had to provide a DC bias voltage of 8 to 10
Volt for the microphone. When small electret microphones (with built-in
amplifiers) and transmitters became available during the 1980s,
it became relatively easy to exploit
this voltage to power a small radio transmitter.
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The device shown here works in the 100 MHz FM band and has a small screw,
hidden behind one of the circular holes, to adjust the frequency.
It has an operational range of 25 to 50 metres.
One of the great things of the early telephone systems, is that nearly
all telephone sets, world-wide, used a microphone with the same form factor.
As a result, the microphones of all these sets are interchangeable, allowing
the phone mike bug to be used virtually anywhere in the world.
The image on the right shows a typical German W48 phone that was used
in the 1950s.
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Bugs of this type were easily installed in an existing telephone without
any technical knowledge or skills.
They were therefore frequently used
for industrial and private espionage during the 1980s and 1990s.
A standard domestic FM receiver in a nearby room was enough to intercept
any conversion. The transmitter was switched on automatically
when the user picked up the handset. The user would not notice the presence
of the transmitter as the device would act like a normal microphone.
Due to leakage, the transmitter would pick-up
both sides of the conversation.
The Phone Mike Bug can bee seen as a professional radio bug. Due to its
appearance, its high build quality and the fact that it was only on the
air during the phone conversation, the device was difficult to trace.
It was often sold as a test transmitter with professional bug tracing
equipment, such as the
Audiotel Scanlock ECM,
and was used to train bug-sweeping teams.
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- Crypto Museum, Phone mike bug
Date unknown. Inventory number CM300497.
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© Copyright 2009-2013, Paul Reuvers & Marc Simons. Last changed: Tuesday, 30 April 2013 - 14:29 CET
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