Professional radio bug
The S-35 was a small professional crystal-based
eavesdropping device (bug),
developed and made in the early 1990s by ATET
in Turin (Italy).
The device was intended for use by governments world-wide,
but was also sold to authorized private customers.
It was succeeded by the S-353.
The image on the right shows the bare S-35 transmitter. It is housed
in the metal case of a large crystal. At the top are the antenna socket
and a screw that hold the unit together. At the bottom is a 4-pin connector
to which the 9V DC power and the microphone can be connected.
The S-35 is suitable for a variety of applications, ranging from
body worn covert operations to eavesdropping (bugging) and even tracing
of a person or object (homing). It can be powered by a battery, an
(optional) transformer or (with a special adapter) the 12V battery
of a car.
The S-35 is driven by a crystal which makes the transmitter extremely
stable. The audio signal from the sensitive electret microphone with
built-in pre-amplifier is fed into the modulator. The modulated signal
is mixed with the crystal oscillator and multiplied to the desired frequency.
The signal is then amplified and filtered before it leaves the transmitter
through the antenna. The transmitter has a bandwidth of approx. 25 kHz and can
be received with a professional intercept receiver,
such as the Rohde & Schwartz EB-100.
The S-35 was succeeded by the S-353, which is still available from
ATET today (2013).
The image below shows the S-35 as seen from the front side.
At the left is the antenna socket and the screw that keeps the
case closed. At the right is the 4-pin male connector to which
the various cables and adapters can be connected. Above this
connector is the internal microphone.
The S-35 can be used in the following applications:
Battery operated bug
A standard 9V block-type battery can be connected by using the S-35-B
cable. This is the basic mode of operation of the S-35 in which the
internal microphone, located aside the connector, is used. The internal
microphone is looped back with a link in the connector.
Car battery operation
The S-35 can be powered by the 12V battery of a car by using the S-35-AU
adapter cable. The adapter converts the 12V battery voltage to 7.5V DC
for the transmitter. In this mode, the unit draws approx. 100mA.
Rather than eavesdrop on a conversation, the S-35 can also be used
to follow or trace a vehicle, using the transmitter as a homing device.
Being connected to the car battery, the S-35 can be powered for a virtually
unlimited time. The car can be traced using a professional
Body worn operation
Instead of the sensitive internal microphone, the S-35 can also be used
with the S-35-M external microphone. This small unit connects to the
4-pin connector of the S-35 and has a 55cm lead with a small electret
microphone at the end, plus a short lead with a 9V battery clip.
If Voice Operated Transmission (VOX) is needed, the small S-35-VX
adapter can be connected in between the S-35 and the S-35-M.
The S-35 can be connected directly to an analogue telephone line for
eavesdropping on phone conversations, using the S-35-AT adapter.
In this mode, the S-35 uses the telephone line for three purposes:
alongside the conversation, it 'steals' power from the line and uses
it as antenna at the same time.
The ATET S35 is housed in the metal casing of a large crystal.
The case shell is held in place by a single screw on the top surface (i.e.
the same surface that holds the antenna socket). After this screw is removed,
the case shell can be taken off,
revealing a tiny printed circuit board (PCB).
The PCB has electronic components on both sides and is fitted to the black plastic
bottom of the enclosure. The image on the right shows one side of the PCB,
on which the quarz crystal and the Knowles microhone
are clearly visible. Also visible in this image is an LM358 dual OpAmp.
The other side of the board holds the actual transmitter,
which consists of various coils, capacitors and transistors. Wherever possible,
surface-mount components (SMD) are used. Power and accessories should be connected
to the 4-pin header at the plastic bottom plate.
Considering its age, the ATET S-35 is very well built, with first-class
professional components. Unlike many of its competitors
however, it does not feature audio masking,
which makes it less suitable for government-type
covert listening operations. As it features continuous wave (CW) transmission
only, it can easily be detected with professional
bug tracers, such as the
Spurious< 30 dB
Frequency150-174 MHz (105-250 MHz on special order)
Microphoneinternal and (optionally) external
Dimensions18 x 20 x 8 mm
S 35 BBattery
S 35 ALTransformer
S 35 AUAdapter for car battery
S 35 MExternal microphone
S 35 ATTelephone adapter
S 35 VXVoice operated transmission (VOX)
ATET is an electronics company that develops, manufactures and sells
equipment, systems and solutions in the field of communications and security,
for both private and government use. The company is based in Torino
and Rome (Italy) and sells to customers in Italy and world-wide.
Since 1960, ATET has specialized in the development and production of
miniature and subminiature transmitters for surveillance and covert
listing, mainly intended for use by the Army and Goverment Agencies.
Products like the S-35 were produced during the 1980s and were sold by
the Security Division of ATET. ATET is still in business today and
its Security Division is selling the lates generation of remote controlled
programmable radio bugs. Information about such devices is available only
to authorized customers.
- ATET S-35 Operational Manual
- A.T.E.T. website
Retrieved April 2013.
- A.T.E.T., Operational Manual S-35
7-page instruction manual with drawings. Date unknown.
Any links shown in red are currently unavailable.
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© Crypto Museum. Created: Monday 29 April 2013. Last changed: Sunday, 17 February 2019 - 16:08 CET.