Covert RF listening device
31217-132 — codenamed Botond 1 — is a medium power radio frequency (RF)
covert listening device (bug),
developed between 1975 and 1980 in Hungary.
It operates in the 940 - 980 MHz range (band V) using plain FM.
It is concealed
as a triangular piece of wood,
that can quickly be fitted covertly
as an inconspicuous part of an existing piece of furniture,
e.g. under a table .
The device consists of a machined piece of fibre-strengthened phenol
formaldehyde resin, that has milled-out compartments for the batteries,
a power switch, the transmitter and its antenna.
The structure is closed with a triangular lid,
and is plated with wood veneer that is finished with great
precision to make it look like a solid piece of wood.
It has two strong embedded nails
to allow quick fitting – for example
under a table – plus a hole for a more permanent fitting screw.
At the bottom is another hole
through which the built-in microphone picks up sound in the room.
The device is largely built with components from West-European
and American manufacturers.
It is typically powered by two 1.5V AAA-size batteries and has a range
of 100 to 150 metres. It is activated by
removing a pin from the short side.
Once activated, it transmits for approx. 5.5 days [A].
Alternatively, it can be powered by a single AAA-size battery (using a
dummy to replace the other one), in which case
it lasts for approx. 14 days, albeit with a reduced maximum distance.
Botond was developed in the late 1970s, probably for the
Hungarian intelligence service BAS, 2 but was also used by the repressive state security
service of the former DDR (East Germany)
– the Stasi – where it was assigned
technology number 31217-132 . Although it is part of the Stasi's
31217 family of devices,
it is based on a different circuit than DDR-developed devices
like the 31217-1, 31217-100 and 31217-111. Other Botond members are
31217-131 and 31217-133.
Botond is an Hungarian male name, that first appeared as the name
of a brave solder in an Hungarian legend. It also appears as an
Hungarian family name. Literally translated,
it means stick or mace.
From 1959 to 1990,
BAS (Belügyminisztérium Állambiztonsági Szervek)
was the Hungarian State Security Department of the Ministry of Interior,
also known as Belügyminisztérium III (Ministry of Internal Affairs III).
Botond measures 111 x 60 x 14 mm and weights 54 grams (without batteries).
It has a removable lid that is held in place by three recessed screws at
the corners. The device has two strong nails
that protrude the lid.
With these nails, the device can be attached quickly to a piece of
furniture. The diagram below shows the bug with the triangular lid removed
and the internal parts visible.
Along the longest side is the actual Botond bug. It is housed in a rectangular
silver-plated brass case that measures 50 x 9 x 7 mm, with the antenna
sticking out at one end. The microphone is located at the bottom of the far
end of the bug, and picks up any sound in the room through a hole at the
bottom. A microswitch
is connected in series with the power line from the
batteries to the bug, allowing the device to be turned OFF by
inserting a 0.9 mm pin
through a hole at the side. In the image above, a paperclip is
used to keep the device deactivated until it is needed.
Due to the nature of the design, the frequency of transmitters like
Botond has the tendency to drift over time, subject to temperature, battery
voltage and any (moving) objects in the vicinity of the device. For this reason,
the receiver used for monitoring the signal, must have an Automatic Frequency
Correction (AFC) with a wide tracking range. The following receivers
Information about these receivers will be made available in due course
The interior of the concealment can be accessed by removing three recessed
screws at the corners of the wooden lid and taking it off. This reveals a
strong fibre-strengthened phenol formaldehyde resin structure with
machined compartments, as shown in the diagram above.
The structure accomodates up to two AAA-size batteries, a micro-switch
to enable the device, and the actual Botond transmitter.
The latter is housed in a silver-plated
brass enclosure that measures 50 x 9 x 7 mm, with a curved silver-plated
antenna sticking out at one of the ends.
The antenna is curved to make the transmitter more omni-directional.
Furthermore, it is pre-shortened to compensate the dielectric effects
of the resin body. At the other end of the bug is a
Sennheiser MM-301 dynamic microphone,
that has its pin-hole sound port at the bottom side.
Because of the high frequency, the circuit is built onto a ceramic substrate
at the bottom of the case. Some tracks are soldered
directly to the side of the enclosure (which carries the positive side of
the battery voltage) for maximum RF shielding. The RF transistor is roughly
placed at the center, with a stripline inductor running to the end of the
case. The antenna is soldered directly to the 50Ω impedance point of
the stripline. The length of the stripline, and hence the resonance frequency,
is determined by the position at which the grey 30 pF parallel capacitor is
Below is a provisional circuit diagram of the Botond transmitter (bug),
created by observing the miniature structures inside the device.
As we do not want to take the device apart or otherwise damage it,
the value of most components could not be determined.
The design of the transmitter is straightforward and is very similar
to that of contemporary designs for other frequencies.
At the left is an AF transistor (T1)
that is used as a preamplifier for the signal from the built-in
Sennheiser MM-301 dynamic microphone.
At the right is the oscillator (T2) that resonates at a frequency of
approx. 940 MHz. The tuned circuit consists of a short stripline with a
30 pF capacitor to ground, soldered at an arbitrary position to determine
the transmission frequency.
The circuit oscillates by the virtue of a
short piece of wire
from the emitter of T2, that is placed in the vicinity of the stripline.
Simple free-running unbuffered oscillators like the one featured here,
inherently suffer from the so-called hand effect, which means that
the frequency may drift if an object (or a hand) is placed near the bug
or its antenna. For the given application, this was not considered a problem,
as receivers with a wide AFC tracking range were used for its reception.
Document obtained from BStU  and kindly supplied
by Detlev Vreisleben .
Full name: Bundesbeauftragte für die Unterlagen des Staatssicherheitsdienstes
der ehemaligen Deutschen Demokratischen Republik
Federal Commissioner for the Records of the
State Security Service
of the former German Democratic Republic (GDR) —
officially abbreviated to BStU.
In this document, Botond is erroneously called Botonel.
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© Crypto Museum. Created: Wednesday 19 September 2018. Last changed: Friday, 22 November 2019 - 14:00 CET.