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CIA Bugs RT-3R →
The transmitter is housed in a black metal case that measures
150 x 83 x 33 mm and weights 386 grams. It is powered directly from
the AC mains, for which a fixed cable is present. It can be wired
internally for 115V or 230V AC, so that it can be used virtually anywhere
in the world.
Sound in the room is picked up by a Shure MC-11 dynamic microphone
that was supplied with the set, and transmitted in the VHF-L band via
a short piece of wire that acts as the antenna. The device was usually
hidden behind a ceiling or under a floor, where (switched) AC was available.
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The device has an output power of approx. 30 mW, 2 which gives it an
operational range of 100 to 200 metres, depending on the position of the
antenna and the receiver. This means that the listening
post (LP) had to be in the vicinity of the target area.
A suitable receiver was the SRR-4.
ST-2A was the successor to the ST-2 of 1956.
It is not exactly clear when the ST-2A was made, but given
the state-of-the-art and the date codes on the valves (tubes), it is likely
that this was in 1957, at a time when valves were gradually
being replaced by transistors. In this device, the microphone amplifier
is built with transistors, whilst the oscillator and the RF amplifier
are still built with valves. The ST-2A was succeeded in the early 1960s,
by the solid state RT-3 (SRT-3). 3
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In this context, hybrid means that the device contains transistors
as well as valves (tubes).
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Initially the power output was specified at 50 mW, but this caused
the valves to die prematurely [3].
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At this point the CIA switched from 2-letter prefixes to 3-letter
prefixes, so the nomenclature is not clear.
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The diagram below gives an overview of the connections of the ST-2A,
and the accessories that came with it. At one of the short sides
is a fixed cable for connection to the local AC mains, which can be
115V or 230V (internally configurable).
At the opposite side is a socket for connection of the
antenna, which was usually a piece of insulated wire of 101 cm
(depending on the
selected frequency). A coloured triangle in the corner of the same
side, specifies the frequency range.
At the front is an SMA-socket for connection of the microphone, which
was usually a SHURE MC-11, connected via a long cable. A small removable
lid at the front right – held in place by a single screw – gives access
to two tuning points: one for the oscillator and one of the doubler/amplfier
stage. Both tuning coils can be adjusted with a special tuning tool that
was supplied with the kit.
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The ST-2A units are colour-coded with a triangle at the side of the
antenna socket. The center frequencies, as listed in the manual,
are given below. Each unit has a tuning range of ± 4 MHz. 1
The actual frequencies of the blue- and white-coded units in our
collection are shown in red.
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Green 60 MHz ± 4 MHz Blue 70 MHz ± 4 MHz ← 74.9 MHz White 80 MHz ± 4 MHz ← 78.4 MHz Green ?
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The manual
erroneously states that the tuning range is ±4 kHz,
which does not make sense for a free-running wideband FM transmitter.
It should read: ±4 MHz.
In reality the tuning range is ±4-5 MHz.
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The actual transmitter is housed in a black metal enclosure
and has a fixed power lead. There was usually no plug at the end of
the power cable, as the device was commonly connected directly
to the wiring behind a ceiling or under a floor. It is shown here
with regular banana plugs.
The transmitter was available in three frequency ranges, each
identified by a coloured triangle on the side of the antenna socket.
The one shown here is marked with a blue triangle (70 MHz).
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A piece of wire of approx. 101 cm, acts as a ¼λ antenna.
According to the manual, Amphenol No. 14-500 cable should be used
for this, but any other type of wire will work just as well.
The wire antenna should be connected to the Amphenol Sub-Minax
socket at the right side of the transmitter. The RF output power
of the transmitter is approx. 30 mW into a 50 Ω load.
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Each transmitter was supplied with a
Shure MC-11 dynamic microphone,
that has an impedance of 1000 Ω and a frequency
response of 400 to 4000 Hz. It is shown here with a short lead,
but was usually supplied with a much longer one, to allow the
microphone being placed at a convient location, away from
the surveillance transmitter.
It should be connected to the SMA socket at the front of the
transmitter. When placed in the vicinity
of the transmitter, it picks up hum from the mains transformer's
stray magnetic field.
➤ More about Shure microphones
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The ST-2A transmitter was available in three frequency bands
(roughly at 60, 70 and 80 MHz), that could be fine-tuned with
the cores of the coils
in the tuned circuits of the oscillator and
the doubler/amplifier. These tuning coils are accessible through two holes
in the transmitter's case, that are
covered by a small metal panel.
A special tool, such as the one shown in the
image on the right, was supplied for adjusting the cores.
After removing the panel,
The tool can be inserted through the holes in the case
and the frequency can be adjusted over an 8 MHz range.
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Each ST-2A transmitter came with a numbered copy of the
operating and instruction manual, shown in the image on
the right.
The manual contains instructions for setting up the device,
adjusting the frequency and carrying out regular maintenance.
For repair, detailed circuit descriptions and a
full circuit diagram are present as well.
➤ Download the manual
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The signal from the ST-2A can be picked up by any
Wide-Band Frequency Modulation (WBFM)
communications receiver
that is suitable for reception of the VHF-L band (56 - 84 MHz).
A good example of such a receiver, which might actually have
been used by the CIA in this case, is the
SRR-4 surveillance receiver,
shown in the image on the right.
➤ More information
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Accessing the interior of the ST-2A is straightforward.
The device is housed in a black welded aluminium enclosure.
It has a lid at the top, which is held in place by two
screws at the short sides of the transmitter. After
removing these two screws, the top panel can be lifted off.
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Inside the enclosure are two pertinax side panels
– along the long sides – with slots for the four PCBs,
each of which can be removed vertically.
At the left is the mains transformer, which can be hard-wired
for either 115V or 230V AC. Instructions on how to change
the wiring are given in the manual [A].
The transformer has secondary windings for the
filaments of the valves (2.5V), the transistor circuits (5V)
and the anodes of the valves (65V). The filaments of the
two valves (1.25V each) are connected in series.
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All internal wiring, including the wires to and from the mains
transformer, have teflon insulation, which makes them heat resistent.
From left to right, the four printed circuit boards (PCBs) are assigned
as follows: lower-voltage board (5V), high-voltage board (65V),
AF board and RF board.
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The 1AD4 valves have 5 contact pins that are fitted in suitable
contact sockets on the PCB, with a bended metal spring-clip to hold the
valve in place. The image above shows a
TUNG-SOL 1AD4 valve that has been
removed from the frequency doubler/amplifier.
From eye-witness accounts,
it is known that early production batches
of the 1AD4 valve had problems with the filaments, that would lose emission
after 50 to 100 hours of operation, but still measured as conducting [2].
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When we received the two ST-2A transmitters featured on this page,
we carefully checked them before connecting them to the mains power,
as they had probably not been operated for several years. First of
all, the primary side of the transformer was rewired for the
European 230V mains.
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This was done by
desoldering the primary transformer wires
of the two units from the ceramic solder points at the side panel.
As one of the mains cables had become brittle over the years
(and was missing from the other unit),
it was decided to replace them at the same time.
The image on the right shows the transformer wiring of the unit with
the highest serial number (299),
in which twisted red teflon wires are used.
It should be noted that the earlier unit (with
serial number 227)
had grey untwisted wiring.
This indicates a small manfufacturing change.
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As we wanted to connect the transmitters to a local wall socket
for testing, two banana plugs were fitted at the end of each of the
power leads. Before switching the units on, the circuits were carefully
removed from the pertinax frame and inspected for broken wires and shorted
contacts.
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No short circuits were found, but in one unit the black teflon ground
wire from the RF board was broken at the case edge. As the other end
of the wire was about to break as well, it was decided to replace it with
a 'new' era-correct teflon wire.
Once both units had been inspected thoroughly, it was decided to power
the first one up. This was done gradually by means of a VARIAC, to allow
the electrolytic capacitors to reform themselves. Once the mains
voltage was raised to the desired 230V, reception of the estimated TX
frequency was checked on a WBFM VHF receiver.
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After some searching, the signal was found. Initially there was a
strong 50 Hz hum on the signal, but this soon turned out to be the
stray magenetic field of the mains transformer that was picked up by
the microphone. It was solved by moving the microphone away from the
transmitter. The transmitter produces a clear signal and has an
adjustable deviation, allowing any sound in a room to be picked up
easily. The second unit worked as well, after gradually raising the
mains voltage.
It was discovered that the transmitter suffers slighly from the so-called
hand-effect, which means that the transmission frequency changes slightly
when the antenna is placed near an object. This is to be expected from
a transmitter that is based on a free running oscillator. The
RF amplifer somewhat reduces this effect, but cannot eliminate it
completely. Furthermore, the transmission
frequency is ~ 300 kHz lower whilst the top lid is removed.
This should be considered normal.
The following restoration work was carried out:
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1AD4 is a subminiature filament type, fully-shielded sharp-cutoff pentode
valve (tube), designed for RF and AF applications in portable equipment.
It has five wire leads that can be soldered onto a PCB directly,
but can also be cut and inserted into a suitable socket,
as is the case in the ST-2A.
Suitable equivalents for the 1AD4 are: PF62, CV2237 and DF652.
➤ More about the 1AD4
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Device Covert listening device Purpose Room overhearing Developer CIA, TSS User CIA Frequency VHF-L band 56 to 84 MHz (3 channels, see above) Modulation FM Deviation 5-50 kHz/100µV signal input (adjustable) Output ≥ 30 mW into 50Ω Power 115V or 230V AC, 50-60 Hz Consumption 1.3W at 190V AC, 2W at 230V AC, 2.5W at 250V AC Microphone Shure MC-11, or equivalent 1000Ω reluctance microphone Response 400 to 3500 Hz Antenna 101 cm wire Dimensions 150 × 83 × 33 mm Weight 386 g Quantity 300 (est.)
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- WBFM receiver 56-84 MHz, e.g. SRR-4
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The following numbers are known.
Please report additional serial numbers and colour-code.
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227 White Crypto Museum 299 Blue Crypto Museum
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The serial number can found on a
label inside the enclosure, close to the
transformer's mains connection. It is currently unknown how many ST-2A
transmitters were made, but it is clear that the two units in our
collection (227 and 299) are from different production batches or from
different manufacturing, as the wiring from the transformer and the
S/N labels are different.
It is certain however, that at least 300 units were made, as our
manual
is 'COPY 35 of 300' [A].
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© Crypto Museum. Created: Monday 21 September 2020. Last changed: Monday, 28 August 2023 - 14:36 CET.
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