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The transmitter has the approximate size of a One Euro coin.
It is a so-called Passive Element (PE) in the sense that it does not have
a direct local power source. Instead, the bug is powered by a 35 kHz
signal that is injected into the line.
The 35 kHz signal is generated by the receiver, which is connected to the
same (telephone) line, somewhere outside the target area. This signal delivers
just enough energy for the 1-transistor transmitter, which is in fact just
a microphone amplifier that causes load on the 35 KHz signal, thereby
effectively amplitude modulating it (AM).
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The receiver is able to treat the variations in its load as an AM signal
and convert it back into an audible signal.
At present, we only have the circuit diagram of the transmitter, which is
available for download below. Any additional information about these devices
is most welcome. Crypto Museum are also looking for a complete Pchela/Peperuda
system for its collection. Any help will be much appreciated.
Until that time, this page acts as a placeholder for future information.
➤ Contact Crypto Museum
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Pchela (ПЧЕЛА) is the Bulgarian word for bee,
sometimes transliterated as Pschola or Ptschelja.
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Peperuda (ПЕПЕРУДА) is the Bulgarian word for butterfly.
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33020-10 Transmitter (standard version as shown above) 33020-11 Transmitter built inside a telephone connection box
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Below is the circuit diagram of the 33020-10 transmitter. At the right is
the (telephone) line. The 35 kHz activation signal that is superimposed on
the line, is rectified in an AA118 diode and used as power for a
Knowles BT1751 electret microphone,
and a BCW60 one-transistor amplifier.
The sensitive microphone picks up the conversation in a room and its output
is amplifier by the BCW60 transistor. The output of the amplifier, is connected
directly to the power rail (i.e. the kathode of the AA118 diode) and causes
a load that varies in the rythm of the intercepted audio.
This effectively results in a form of Amplitude Modulation (AM) of the
reflected signal.
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Document from BStU archives [2],
kindly supplied by Detlev Vreisleben [1].
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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: Saturday 20 October 2018. Last changed: Monday, 16 November 2020 - 22:01 CET.
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![Pchela transmitter next to a one-Euro coin. Photograph by Detlev Vreisleben [1].](img/33020-10_large.jpg)
