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Bodil B1 →
Bodil B2   33342-2
Passive carrier bug receiver

BODIL (Bulgarian: Бодил) 1 was a Cold War covert listening system (bug) for room surveillance, developed around 1978 in Bulgaria, at a time when the country was part of the Warsaw Pact. 2 The system consists of a BODIL-B1 transmitter and a matching BODIL-B2 receiver, and uses an existing line for the transport of its intelligence, using a 60 kHz carrier frequency. In addition, the B1 transmitter is powered remotely 3 by the receiver. In Stasi terminology, the device is known as a TF-B Sender, in which TF means Träger Frequenz (carrier frequency) and B refers to B-Technik (B technology): acoustic room monitoring (bugging). The BODIL-B2 receiver is described below.

Although the device is suitable for virtually any kind of line, its preferred use was over telephone lines inside hotels, strategic companies and 'special objects'. In those situations, Bodil-B2 was simply connected in parallel with the line.

At the target area (i.e. the object) the Bodil-B1 transmitter was connected in parallel with the telephone set, in such a way that it could pickup any sound in the room. Unlike most other wired bugs, the B1 transmitter was not powered by the voltage on the line, but rather by a 30 kHz signal that was injected into the line by the B2 receiver.
Bodil B2 - Receiver for Bodil B1 bug

As the system uses phase modulation (PM) for the transport of its intelligence, it is insensitive to line damping. Furthermore, it is remotely powered, which reduces the chance of detection. The image above shows the Bodil-B2 receiver. It measures 29 x 24 x 7.5 cm and weights 3000 grams. The intercepted sound can be monitored directly from the receiver by means of a pair of head­phones, or recorded on a (tape) recorder. In most cases through, the output from the receiver was forwarded to a Stasi monitoring station, via a leased telephone line (German: PO-Leitung).

The receiver can be powered in various ways: either from the local mains, a local set of 12V DC batteries, or from the leased line. In addition, it could be controlled remotely – via the telephone line – using an external remote control unit. Bodil was developed in Bulgaria around 1978 and was in production for approx. 10 years. Judging from the date codes on the components inside the device featured here, it was made around 1985. Bodil-B2 was also used by the state security serviceStasi or MfS – of the former DDR (East-Germany), where it was designated 33343-2.

  1. Бодил (Bodil) is the Bulgarian word for Thorn.
  2. In its capacity as a highly-developed technological country, Bulgaria was often referred to as the Silicon Valley of the Eastern Bloc at the time [3].
  3. This means that the transmitter can be categorised as a Passive Element, meaning that it does not have a direct local energy souce. Instead, it is powered by energy provided by a signal from the listening post.

Bodil B2 - Receiver for Bodil B1 bug Bodil-B2, rear side Front panel BODIL-B1 test transmitter Bodil-B2 receiver with B1 test-bug Line connection cable Subscriber line connected to the receiver Subscriber and leased line connected to the receiver
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Bodil B2 - Receiver for Bodil B1 bug
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Bodil-B2, rear side
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Front panel
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BODIL-B1 test transmitter
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Bodil-B2 receiver with B1 test-bug
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Line connection cable
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Subscriber line connected to the receiver
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Subscriber and leased line connected to the receiver

The diagram below shows the front panel of the Bodil-B2 receiver. All connections to the lines and any recording or monitoring equipment are at the front panel. The only connections that are at the rear are for the mains (suitable for the 220V AC mains only) and for an external 12V DC battery. For testing, each B2 receiver was supplied with a B1 transmitter on a short piece of wire, that could be connected straight to the input socket marked ЛИНИЯ (line) at the B2's front panel.

Installing and operating the B1 transmitter and the B2 receiver is straightforward and requires only limited knowledge of bugging devices. The full instructions are avaialable for download in Bulgarian [A] and German [D]. From left to right, the following controls and sockets are available:

  1. Power indicator (LED)
  2. 3-position power switch: off, remote power, local power
  3. Remote control (via second tone transmitter) when depressed
  4. Subscriber line
  5. PSTN (not used in most situations)
  6. Leased line to central monitoring station
  7. 30 kHz power level (adjust for minimum audio distortion)
  8. Headphones audio level
  9. Line output for recorder
  10. Headphones socket
  • Modulation not dependent on distance (damping)
  • No local power needed for transmitter
  • Low compromising risk
  • Hotels, with and without remote control of the bug
  • Companies and institutions with a local PABX (German: GWN-Alage)
  • Building with a central antenna system
  • ...
Depending on the circumstances, the BODIL system could be used in two ways. The preferred use was inside hotels and 'special objects' which in most cases had a local house exchange (PABX) or a special monitoring room. In such situations, the subscriber line was alread isolated from the public switched telephone network (PSTN) and Bodil-B2 could be connected in parallel to the line:

In this situation, the subscriber line is used as normal and Bodil-B2 provides power to the Bodil-B1 transmitter via a strong 30 kHz signal that it superimposes onto the line. The B1 doubles this frequency and returns a 60 kHz phase-modulated (PM) signal, that is then filtered and decoded in the B2. The decoded audio can be monitored or recorded locally, but it could also be relayed to a central monitoring station via a so-called leased line, in German known as a PO-Leitung. The maximum distance between the transmitter (B1) and the receiver (B2) is approx. 800 metres.

In situations were no local PABX is available and the subscriber line is connected directly to the Public Switched Telephone Network (PSTN), the subscriber line has to be cut and the receiver is inserted between the telephone set and the exchange. In this case, the ATC (АТЦ) socket at the front panel is used for connection to the exchange. This method was not frequently used though.

The security service of the former DDR (East Germany) – the Stasi – also used the central antenna installation (CAI) of an appartment building as the transport medium for BODIL. Especially for this application, a transformer-based modification was suggested, that allowed the B1 bug and the B2 receiver to be connected directly to the coaxial cable of the central antenna system [C]. In such cases the bug was usually placed inside or near the antenna wall socket of the TV/radio set.

Bodil-B2 receiver (described above) Test transmitter Bodile-B1 with 7-pin line connector Cable for connecting to the telephone line(s)
Receiver   B2
The receiver - BODIL B2 or 33343-2, is the core device of the installation. It provides power to the B1 bug and remotely activates it. It also contains a PM demodulator that converts the phase-modulated signal from the bug into an audible signal again. It is described above.

The receiver can not be used with other types of wires carrier bugs. It is the only receiver that is suitable for the reception of the B1 bug.
Bodil B2 - Receiver for Bodil B1 bug

Transmitter   B1
To check the functionality of the receiver, a complete and functional B1 transmitter – wired to a suitable 7-pin plug – is supplied with each B2 receiver. This test bug should be connected to the leftmost line socket (marked ЛИНИЯ).

After connecting the bug, the 30 kHz level (G) must be adjusted for minimum audio distortion. Once satisfied, the test bug is removed and the subscriber line is connected to the socket. The level (G) then has to be adjusted again.
BODIL-B1 test transmitter

Line cables
The receiver has three 7-pin USSR-style sockets at its front panel, for connection of the lines. The line socket (ЛИНИЯ) is always used, as it must be connected to the subscriber (i.e. the line under surveillance). The other sockets are optional.

All three sockets have the same pinout. the image on the right shows a suitable line cable with banana plugs and crocodile clips.
Line connection cable

Bodil-B2 receiver with B1 test-bug Test-bug (B1) connected to the LINE socket Line connection cable with crocodile clips Line connection cable Subscriber line connection to the LINE socket Two lines connected
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Bodil-B2 receiver with B1 test-bug
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Test-bug (B1) connected to the LINE socket
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Line connection cable with crocodile clips
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Line connection cable
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Subscriber line connection to the LINE socket
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Two lines connected

  1. Power switch in the upper position (local power)
  2. Remote control button (ДК) not depressed
  3. Connect subscriber line (with Bodil-B1) to socket (1)
  4. Adjust 'Level' for undistorted audio signal
  • Local AC mains network (220V AC)
  • Local 12V DC battery (connected at the rear)
  • From exchange (local power)
  • From leased line (remote power) (25 mA)
Remote control
  • Remote control button (ДК) depressed
  • Inject 4-10 mA into the line
Remote power
  • Power switch in the middle position (remote power)
  • Inject 25 mA via the leased line (PO-Leitung)
Block diagram
The receiver is connected directly to the subscriber line, as shown at the bottom of the block diagram below. At the left is the 30 kHz generator that delivers the activation signal for the bug. The returned modulated 60 kHz signal is filtered, demodulated, amplified, filtered again and compressed, and is then fed to the headphones and/or a recorder. Alternatively, the signal can also be delivered directly to an external state security listening post via a leased line. The receiver can be powered from the mains, by internal batteries, or from the (optional) leased line.

Block diagram of the BODIL-B2 receiver)

The block diagram below shows how the transmitter works. At the far right is the telephone line from which the 30 kHz activation signal is received (sent by the receiver). This signal is filtered and then rectified, creating just enough DC voltage to power the circuit and the microphone.

Block diagram of the BODIL-B1 transmitter

The 30 kHz is also doubled to 60 kHz and fed to the modulator, where the amplified sound from the microphone is added, resulting in a phase-modulated 60 kHz carrier signal that is injected into the telephone line. The 30 kHz and the 60 kHz signals are way above the audible range, so that they can pass the cable unnoticed. Yet they are sufficiently low to pass the existing cables and junction boxes, especially if the distance between transmitter and receiver is not too large.

 More about the Bodil-B1 transmitter

The interior of the BODIL-B2, seen from the top

The receiver is housed in an universal aluminium enclosure 1 consisting of a strong frame with two (blue coated) aluminium case shells, each of which is held in place by two recessed screws. After removing the recessed screws, the case shells can be taken off and the interior is exposed.

Inside the device are four printed circuit boards (PCBs), mounted to the frame roughly in the middle, with the components visible from the top of the device. At the bottom, the solder side of the PCBs is visible, along with the 220V mains transformer and an additional line filter, which was known as ТОПОЛА (TOPOLA = magnolia).

At the front left is the power supply unit (PSU) with provides three internal voltages, two of which are stabilized. It gets its power from the mains transformer at the bottom, an external 12V battery, or via the leased line (when used).
Crystal-based 30 kHz oscillator

At the rear left is the 30 kHz sine-wave generator that delivers the power for the BODIL-B1 bug which is connected in parallel to the subscriber line. The 30 kHz generator board is shown in the image above. This PCB is normally shielded to avoid interference with the PSU and other circuits.

At the rear right is a large circuit board that holds a high-quality 60 kHz band-pass filter and trans­formers for connecting the subscriber line (in parallel to the 30 kHz generator). The output of the filter board is passed to the demodulator / audio board, which is located at the front right.

The demodulator board has the same size as the filter board, but is the most densely populated of the four boards. It holds a three-stage amplifier-limiter, followed by an FM/PM demodulator, built around an RCA CD4046 phase-locked loop (PLL) integrated circuit (IC) — here visible at the top.
PM demodulator

The output from the CD4046 is passed through a 5 kHz low-pass filter – so that only the speech spectrum remains – and then amplified and compressed in a small hybrid circuit, which is cast in a red compound. The compressor output is amplified for the headphones and for the leased line, using UA741 ICs. The large coil at the right in the above picture, is the leased line transformer.

  1. The enclosure is very similar to the one used with the Chech intercept receiver Přístroj, and was apparently a universal product in the former Eastern Block countries.

Interior - top view Interior - bottom view High-Q filters Line transformer CD4046 PLL circuit Low-pass filter for connection of outside exchange Top side Bottom side
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Interior - top view
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Interior - bottom view
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High-Q filters
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Line transformer
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CD4046 PLL circuit
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Low-pass filter for connection of outside exchange
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Top side
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Bottom side

When we acquired our BODIL B2 receiver, not much was needed in terms of restoration. It had pencil-written translations in German on its front panel, which were likely not put there by the original owner: the Stasi. We have carefully removed the text from the front panel with a solvent.

The only problem – if you can call it that – was that the device did not always power up when the three-position power switch (A) was placed in the upper position. The reason for this was that the front panel was mounted to the frame a few millimetres too low, and was therefore partly blocking the power switch. This was solved by removing the cover and refitting the front panel.

Apart from this, the receiver worked straight away without any glitches, which is mainly due to the high manufacturing standards and the fact that only first-class components were used.
Front panel with pencil-written German translations

Connecting a BODIL-B1 transmitter to the line socket (ЛИНИЯ) required only the 30 kHz level (G) to be adjusted in order to obtain a noise-free distortion-free signal through the headphones. We assembled several line cables for testing the device on a local analogue POTS telephone line.

Circuit diagram
The receiver is extremely well designed and built, with well-selected components and a good sense of high-quality filtering. Below is the circuit diagram of the device, which has been split into a number of sub-circuits, in line with the block diagram and the original circuit diagrams [A].

The first sub-circuit is the line filter PCB. It contains the line transformer which is connected directly to the subscriber line (a/b) and a multi-section 60 kHz bandpass filter for extracting the signal from the bug. An additional filter (shown in yellow in the diagram below) is mounted at the bottom of the unit. It is only used when connecting the receiver to an external exchange (a'/b').

Filter board with line transformer and 60 kHz bandpass filter

The next circuit is the 30 kHz generator, which provides the activiation signal and the power for the actual bug (i.e. the Bodil-B1 transmitter). The circuit is housed in a shielded enclosure in the corner of the unit, and is built around six BC107 transistors. At the left is the crystal-controlled sine-wave oscillator from which an adjustable level is supplied to an amplifier, or booster. The output from the booster is then injected into the subscriber line via the transformer at the right.

30 kHz generator for activating the remote bug

The output of the filter board (at the top of this section) provides the input for the demodulator board, which is located immediately behind the front panel of the unit. The signal is first passed through a 3-stage amplifier/limiter – built around BC107 transistors – and then fed to a CD4046 phased-locked loop (PLL) circuit, made by the western manfuacturer RCA [E]. It demodulates the phase-modulated signal and recovers the original audio, which is available at the bottom right.


The buffered signal from the demodulator is now passed through a 5 kHz low-pass filter and is then applied to the input of an amplifier/compressor, which in this case is a small hybrid circuit. The output from the audio compressor is available as a fixed-level recording output on the front of the device. It is also passed to the headphones amplifier (at the bottom left) and to a separate amplifier that provides the coupling to the (optional) leased line (visible at the bottom right).

Audio circuits

Both the headphones amplifier and the leased line amplifier, are built around the well-known UA741 operational amplifier (op-amp). The headphones level can be adjusted with the volume control at the front panel, whilst the leased line amplifier is internally adjusted at a fixed level. Note that the line transformer at the bottom right has two diodes that are used when the device is remote-powered (via the leased line). These terminals are connected to the power supply unit.

Power Supply Unit (PSU)

Above is the circuit diagram of the power supply unit (PSU). It consists of a small PCB – located at the front left of the device – and a small transformer at the bottom. The PSU delivers a raw 10V DC plus two stabilized voltages. At the left are the connections for the mains AC network, and for an external 12V DC source. At the top right is the (optional) power supply from the leased line.

Interior - top view Shielded 30 kHz oscillator Crystal-based 30 kHz oscillator 30 kHz crystal Line transformer and filters Line transformers Power supply unit (PSU) Mains transformer
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Interior - top view
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Shielded 30 kHz oscillator
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Crystal-based 30 kHz oscillator
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30 kHz crystal
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Line transformer and filters
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Line transformers
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Power supply unit (PSU)
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Mains transformer

  • Carrier
    60 kHz
  • Modulation
    PM (phase modulation)
  • Mains
    220V AC +10%/-20%
  • Battery
    12V DC ± 1V (external)
  • Current
    ≤ 40 mA when powered from the mains
  • Current
    ≤ 40 mA when powered by a 12V battery
  • Current
    25 mA when powered from a leased line
  • Impedance
    ЛИНИЯ (LINE) 150Ω
  • Damping
    ≥ 4dB
  • Recording
    250 kΩ, 100mV ± 3dB
  • Leased line
    600 kΩ, 500mW ± 2dB
  • Distortion
    1000 Hz ≤ 6%, 5000 Hz ≤ 3%
  • Noise
    ≤ 800µV (recording)
  • Dimensions
    290 x 240 x 75 mm
  • Weight
    3000 grams
GWN   Großwählnebenstelle
German expression for a local Private Automatic Branch Exchange (PABX).
PO   Postmietleitung im Ortsnetz
Local leased telephone line.
POTS   Plain Old Telephone System
Common expression for an old analogue telephone network, based on twisted pair copper wiring and electromechanically or electronically switched subscriber lines, with analogue signalling and pulse or tone (DTMF) dialling. Also known as Plain Old Telephone Service.
PSTN   Public Switched Telephone Networks
Common expression for an automated switched telephone network – which can be analogue as well as digital – for exchanging telephone calls between subscribers.
Telephone line   ЛИНИЯ - АТЦ - ЦЕНТЪР
The Bodil B2 receiver has three sockets for connection of telephone lines at its front panel: ЛИНИА for connection of the subscriber line (with the B1 transmitter connected in parallel to the telephone set), АТЦ for connection to an outdoor exchange 1 , and ЦЕНТЪР (center) for the (optional) leased line to a Stasi monitoring station (CEKO).   

  1. Not used in most situations.

Tape recorder   МАГН
  1. Line out
  2. GND
  3. Line out
  4. not connected
  5. not connected
  1. БОДИЛ Б (BODIL B), Technical manual and operating instructions
    Bulgaria, 1979. Original manual in Bulgarian/Russian language.
    BStU, 21 pages marked BStU 0178—0199. 1

  2. Bodil, Beschreibung
    DDR, date unknown. Hand-written description (German).
    BStU, 10 pages, marked BStU 0223—0232. 1

  3. Bodil Anpassung, Beschreibung des Vorslages
    Hauptmann Bräunig, Suggested modification (German).
    Date unknown. BStU, 2 pages marked BStU 0221-0222. 1

  4. Information Linie B, Nr. 1/86. Kennblatt 'Bodil' 33343-1, 33343-2
    Bodil technical specifications (German). January 1986. 6 pages marked BStU. 1

  5. Texas Instruments, CD4046 Datasheet
    2003. Retrieved January 2014.
  1. Document from BStU archives [2], kindly supplied by Detlev Vreisleben [1].

  1. Detlev Vreisleben, BODIL, technical and historical documentation
    Personal correspondence, July 2018.

  2. Bundesbeauftragte für die Stasi-Unterlagen (BStU) 1
    Federal Commissioner for the Stasi-Records.

  3. Wikipedia, Bulgaria
    Retrieved, May 2018.

  4. Erprobungsbericht System 'Bodil B'
    Oberstleutnant Sillmann, Test report System 'Bodil B' (German).
    Berlin (DDR), 17 June 1981, BStU, Abt. 26 Nr. 1551. 1
  1. Full name: Bundesbeauftragte für die Unterlagen des Staatssicherheitsdienstes der ehemaligen Deutschen Demokratischen Republik (DDR) — 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: Wednesday 02 May 2018. Last changed: Friday, 22 February 2019 - 14:05 CET.
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