The 31218-1 belangs to the 3rd generation of DDR radio bugs and is based
on the 31217-1,
which in turn is based on the 31216-1. Like the 31217 it
does not have a built-in battery and microphone, but instead features a
two-stage audio amplifier. In addition, the 31218 is fitted with an RF
power amplifier that raises the output power to ~ 100 mW, making the device
suitable for an operational range of ~ 500 metres.
The image on the right shows the basic 31218-1 variant with an external
– permanently fitted – dynamic microphone made by
Knowles 2 (USA).
With the device shown here, the microphone and battery wires have been
taped to the body of the transmitter by means of cellotape. This was
the usual practice at the Stasi.
It was also possible to fit an (optional)
SVM-144 or SVM-145 audio-masking 3
module between the microphone and the
bug, to reduce the chance of accidental or deliberate discovery
of the device and its intelligence.
The device was commonly operated in combination with the special
31215 or 31225 surveillance receiver.
It was part of a family – consisting of the
and 31218 –
and was available in several variants, allowing
it to be used with a variety of microphones and audio-masking 3 units.
It was mainly used in combination with microphones from Western manufacturers
such as Sennheiser and
Knowles 2 ,
commonly ordered under the pretence of hearing aid manufacturing.
Institut für Technische Untersuchungen (ITU) was a covert operation
of the OTS, the Operativ-technische Sektor (Technical Operations
Sector) of the MfS (Stasi).
Not to be confused with the CIA's OTS.
Note that Knowles
was an American manufacturer that supplied
for hearing aids. Ironically, many of their microphones were
developed with funding from the US
Central Intelligence Agency (CIA)
for use with CIA bugs.
In Stasi terminology, audio masking
was known as Sprachverschleierung (speech concealment), or SV.
The diagram below shows the basic setup of an 31218-1 unit.
At the left is the transmitter, which consists of an 31218-1
driver stage (which is actually a 31217-1 transmitter)
and an 31218-ES power amplifier (PA). At the right is the matching
31225 surveillance receiver
for 940-980 MHz.
For specific bugging operations, especially in the vicinity of
the West-German border, the Stasi often chose to use
by means of subcarrier-modulation,
to avoid accidental
or deliberate interception of a conversation. The 31218-14 variant
was made especially for this application. It consists of a 31218-1
from which the audio amplifier has been removed.
In this variant
the RF oscillator is driven directly by an external SVM-44
audio masking unit, which modulates the audio on a 22 or 24 kHz
subcarrier (double FM) and injects a 80 or 100 Hz hum
into the baseband. In German this is known as
Sprachverschleierung mit Maskerator (SVM).
The above solution was also available in a single package
as the 31218-145, which basically consists of a 31218-14 unit
with an integrated SVM-44 speech masking unit. Other variants
were available for connection of electret microphones instead
of dynamic ones.
The diagram above shows how the
The first digit tells us which department was responsible for it. In this
case it is department 33, which was Außenstelle Beucha (Outstation
Beucha). Before 1977, the prefix '3' was omitted, or the prefix 'AB' was used.
The next two digits define the theme and the group within
the theme. The next two digits define the actual project (within the group).
If a device is part of a kit, the number behind the dash specifies the item
number (within the kit). The last two digits are optional, and
specify the version or variant.
Known versions and options
31218-1Basic version for dynamic microphone, with RF PA
31218-11Basic version for dynamic microphone, with RF PA
31218-111Suitable for electret microphone
31218-14For use with audio masking module SVM 144 or SVM 145
31218-145Combined with SVM 144 audio masking module
31218-10200 mW version
31218-20Mains power upply unit (PSU)
31218-SSSteuer-Stufe (driver stage only)
31218-ESEnd-Stufe (power amplifier only)
The 31218-1 bug is housed inside a protective case or sleeve, which
consists of two thin PVC case shells, with cut-outs for the wires at both
of the short sides. The case shells, and in some cases part of the wiring,
are held together
by means of cellotape.
Inside is a silver-plated can.
After cutting through the cellotape, the two
case shells can be removed
and the silver-plated copper can is exposed. The can is close with a
removable cap that is usually soldered in place.
The image on the right shows the enclosure of the 31218-1 after the cap
has been removed from the can. Inside the can are two
ceramic PCBs with miniature components,
each of which takes about half the space. The PCB at the left is identical
to the one inside the 31217-1 bug.
It contains a free-running RF oscillator
(from the 31216 bug)
plus a two-stage audio amplifier.
The PCB at the right holds a single-stage power amplifier (PA) that takes
the signal from the RF oscillator and raises it to approx. 100 mW. The
S-shaped copper track on the rightmost PCB is a stripline filter.
Due to the fact that a PA-stage is present between the RF oscillator and
the antenna, the device suffers less from the so-called hand-effect
than the 31216
and the 31217.
The basic 31218-1 transmitter consists of two parts: a driver stage with
a two-stage audio amplifier and an RF oscillator, and a power amplifier
(PA), mounted together in a single metal enclosure. The driver stage is
in fact an exact copy of the complete 31217-1 transmitter:
This circuit is complemented by an RF power amplifier (PA) which takes the
output from the oscillator at point (X) and raises its level to ~ 100 mW.
The PA also isolates the
RF oscillator (BFS17) from the antenna, so that the unit suffers less
from the hand-effect. The filter in the output circuit (L3 and 1-4pF)
reduces the transmission of harmonic frequencies somewhat.
Transistor (T4) is powered via L5.
Note that the unit has the (+) terminal connected to ground.
If the 31218 was used in combination with an SVM-44 or SVM-45
or speech concealment unit, the two-stage
audio amplifier (T1, T2) was omitted and the bare RF oscillator
was used to drive the PA. This oscillator is known as the 31216-SS
driver stage (Steuerstufe) and is nearly identical to the oscillator
part of the first diagram (31218-1) and to the
In this case, the output of the 31218-SS oscillator (X) is connected to
the input of the 31218-ES power amplifier (X), whilst the signal from the SVM-44 audio
masking unit is provided to the LF input terminal (3). The nominal frequency
of the oscillator is determined by the position of the 4.7pF capacitor on the longest
arm of the stripline transformer (TR).
Power supply9V DC
Frequency940 - 980 MHz (fixed spot frequency in band V)
HF power100 mW @ 9V DC supply
AntennaWire, 11 cm (¼λ)
Audio200 Hz - 8 kHz
Deviation± 75 kHz
Subcarrier22 or 24 kHz, with 80 or 100 Hz hum 1
Dimensions53 x 17 x 8 mm
Only for units with audio masking option (SVM).
Document obtained from BStU  and kindly supplied
by Detlev Vreisleben .
- Detlev Vreisleben, 31218-1, technical description and operating instructions
Personal correspondence, May - August 2018.
- Bundesbeauftragte für die Stasi-Unterlagen (BStU) 1
Federal Commissioner for the Stasi-Records.
- Louis Meulstee, 31218-1 (GDR bugs V)
Wireless for the Warrier, Volume 4 Supplement, Chapter 129 v1.01.
Retrieved August 2018.
- Hinweise fur die Erprobung der Technik 31216, 31217, 31218 1
Recommendations for application of 31216, 31217 and 31218 (German).
MfS, BV Gera OTS 0102. 8 September 1976.
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.
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© Crypto Museum. Created: Saturday 04 August 2018. Last changed: Saturday, 18 December 2021 - 10:32 CET.