It is currently unknown why the CIA needed a 'chinese copy' of an existing
inferior 1 bug that could easily be discovered by a professional sweep team,
but it is clear that they wanted to hide its true origin. Although the
NRP managed to duplicate every aspect of the bug, they managed to
improve several characteristics, such as temperature range and stability,
in a completely invisible manner.
The peripheral equipment was fully developed by the
NRP from scratch.
It is currently unknown how long the SRS-153 system was used, but it was
in production until at least 1985.
In this context, 'inferior' means that the CIA had access to
far better technology, consisting of bugs with a far better performance
and superior audio-masking schemes that were much more difficult to detect.
SRS-153 system components
Click any of the items above for further information
The diagram below shows a complete setup of the SRS-153 system.
The SRT-153 transmitter
is installed at the target area (TA) at
the bottom right. It is powered by two strings of
five Mallory mercury cells each, under control of the
QRR-153 switch-receiver at the top right.
At the listening post (LP), which is generally located across the
street from the target area, is the
QRT-153 activation transmitter,
which can send two carriers (one for the ON command and one for OFF)
via a frequency in the 70 MHz band. It has presets for controlling
up to four QRR/SRT-153 sets simultaneously. Once activated, the
signal from the SRT-153 transmitter can be picked up by the
SRR-153 surveillance receiver
at the bottom left. The latter can also be replaced by an
SRR-90 receiver which has been modified for
the reception of subcarrier-modulated transmitters.
In early 1977, the CIA approached
the Dutch Radar Laboratory (NRP) with
the request to analyse a bug that had been discovered inside a wooden
drawer divider in the desk of an ambassador. The bug had already been
analysed by an undisclosed third party, but the findings were inconclusive.
Although the redacted analysis  does not tell us where the bug was found,
it reveals this:
The transmitter/Switch-Receiver was concealed in a desk drawer divider
resembling those of the Ambassador's desk. It was discovered lying at the
bottom of the right-hand bottom desk drawer along with another divider.
The bug's concealment was fabricated to replicate the size, shape, appearance
and finish of the existing wooden dividers, so it is likely that one them
was 'borrowed' while the concealment was being made. It measures
36.8 x 10 cm and is between 5 and 7 mm thick. The concealment is made
of linen-based phenolic that has been milled out to snugly fit the components.
The exterior is covered by a thin layer of wood veneer that closely resembles
the wood of the original divider.
The low-grade image above was taken from the original report submitted by
the CIA . It shows the internal layout of the device after the outer wooden
venier layers and the protective phenolic sheets had been removed. The brown
colouring was added by us, to show the wooden frame that surrounds the inner
linen-based phenolic block. The layout of the bug is further clarified below.
The image above shows what is inside the concealment. At the bottom is a row of
Mallory RM822 mercury cells, of which the middle one is used to power
the receiver. The remaining cells form two parallel strings of five cells
each that are used to power the transmitter, under control of the receiver.
In order to save power, the receiver is turned ON ever 1.5 seconds for just
It is estimated that, under normal condiditions, the batteries allowed one
full year of operation. After that, the bug had to be replaced
or was considered 'dead'.
A magnetic reed switch controls the power to the switch-receiver. A magnet
can be used to switch the entire device OFF to save power once manufacturing
is complete. It is removed after installation at the target area.
According to the report of the initial analysis , it was not the first time
that a bug of this kind had been discovered. It describes the differences in
components and manufacturing techniques between this one and earlier versions.
Nearly all parts had been sourced in Europe, mainly in Germany and France,
and were covered in a sticky white silicone paste. The only American part was
the miniature Knowles 2501 microphone
that was commonly used in hearing aids of the era.
Although the construction of the switch-receiver
is similar to that of the transmitter,
there are significant differences in
manufacturing and construction techniques, indicating that the two devices
may have been manufactured by different suppliers.
The report also describes an earlier version that was much larger and was housed
inside a hollowed-out piece of wood. Such transmitters were generally identified
as Stick Transmitters, and were often customised to fit under a desk
or table, allowing quick and easy installation and removal by an operative.
An example of a Stick Transmitter is given in a separate report .
Similarly concealed bugs were developed during the Cold War by the Czechoslovakian
Intelligence services, such as the Štěnice
that is described elsewhere on this website.
A similar Czech remote controlled transmitter in a wooden stick
is shown by H. Keith Melton in his book Ultimate Spy. 
It was the CIA's intention to do an extended analysis, improve the bug's
behaviour and copy it. Copy not only the bug's circuits, but also its enclosures,
materials, markings, etc. This might seem a bit strange at first. Although the
discovered bug features audio masking, it is
by no means secure, as its subcarrier masking scheme
is no match for the bug tracers
of the era.
It makes you wonder why the CIA wanted to use an insecure device
that was easy to find, when they had accesse to superior equipment,
such as the SRT-91,
that consumed far less energy.
Apparenty, the CIA wanted to deploy bugs that, when discovered by a sweep
would likely put the blame on another country's spooks. It is also possible that
the bugs were used as a bait. In such cases, the agency hides several
bugs of a different nature in the same target area, in the hope that one of them
is found and will satisfy the sweep team. The remaining bugs will then
still provide useful intelligence. 1 To quote the unwritten law of the
Counter Measures trade (TSCM):
For every bug that is found in a target area,
there are three more that have not been discovered.
was asked to do an extended analysis and fill in the missing bits of
the earlier report submitted by another contractor .
This was done by reverse-engineering
the samples of the bug that had been provided by the CIA.
During the course of 1977, various concepts were tried,
resulting in a development proposal in November 1977 [B].
The CIA subsequently gave the green light for development of what
was then called SRS-53. 2
The NRP spent most of 1978 on the development of the various parts
of the system, whilst simultaneously fine-tuning the analysis.
In February 1979, the NRP was ready and submitted the final version of
their extended analysis in a 28 page report, complete with full circuit
diagrams and descriptions . In addition, the origin of most components
of the original bug has meanwhile been established, and the NRP is
ready to take the various devices into production. The performance and
stability of the
and the QRR-53 switch-receiver have
been improved, and a suitable activation transmitter is ready in April 1979.
For the time being, a modified version of the
SRR-90 was used for reception.
In 1980, the name of the system was changed from SRS-53 to SRS-153,
probably because it was conflicting with other CIA projects.
The names of the sub-components were changed accordingly. In September
1981, the dedicated SRR-153 receiver was added to the range,
so that the modified SRR-90 was no longer needed,
making the SRS-153 a complete and fully self-contained system.
In August 1984, the UVK-153 Transmitter Tester was added to the system.
It is suitable for testing all subcarrier-modulated bugs that were used
by the CIA at that time, including the
and the SRT-105.
The SRS-153 system was in production until at least 1985.
It is also possible that the CIA wanted to use copies of the bug for
lower level targets that were less aware of the possibility of being
bugged, and that had no means to carry out a proper bug sweep.
The system was later renamed SRS-153.
The letters SRS stand for Surveillance Radio System.
- XSRT/XQRR-53 Operating Notes
NRP, October 1977. CM302627/A.
- Proposal for Prototype SRS/QRS-53
NRP, November 1977. CM302627/B.
- Concise Operating Instructions for QRT-53 Actuator
NRP, March 1979. 2 pages. CM302627/C.
- Manual for QRT-53 Actuator
NRP, April 1979. CM302627/D.
- Environmental Test Report on XQRT-53 Actuator
NRP, July 1979. CM302627/E.
- Environmental Test Report on XSRT-53 Transmitter
NRP, August 1979. CM302627/F.
- Environmental Test Report on XQRR-53 Receiver
NRP, August 1979. CM302627/G.
- Operation and Test Manual for SRT-153 & QRR-153
NRP, April 1980. CM302627/H.
- Operation and Test Manual for SRT-153 & QRR-153
NRP, May 1980. CM302627/I.
- Operation and Test Manual for SRT-153 & QRR-153 (draft)
NRP, September 1980. CM302627/J.
- Concise Operating Instructions for Transmitter Tester
NRP, 23 April 1981. CM302627/K.
➤ follow up 26 August 1981
- Preliminary Partial Manual for XSRR-153 Receiver
NRP, 7 May 1981. CM302627/L.
- Environmental Test Report on XSRR-153 Basic Receiver
NRP, July 1981. CM302627/M.
- Operation and Test Manual for SRT-153 & QRR-153
NRP, September 1981. CM302627/N.
- Operating and Test Manual for XSRR-153 Receiver
NRP, September 1981. CM302627/O.
- Manual for QRT-153 Actuator
NRP, September 1981. CM302627/P.
- Operating and Test manual for SRR-153 Receiver
NRP, November 1983. CM302627/Q.
- Environmental Test Report on SRR-153 Receiver
NRP, November 1983. CM302627/R.
- Operation and Test Manual for UVK-153 Transmitter Tester
NRP, August 1984. CM302627/S.
- Environmental Test Report on UVK-153 Transmitter Tester
NRP, January 1985. CM302627/T.
- NRP/CIA, Collection of documents related to SRS-153
Crypto Museum Archive, CM302627 (see above).
- Various manual drawings and notes on SRS-53 / SRS-153
NRP, April 1977 - March 1979. CM302627/x.
- Final Report on the Analysis of the
Unknown author (via CIA). Date unknown but probably early 1977. 35 pages. 1
Crypto Museum Archive, CM302634.
- Analysis of the Stick Transmitter/Receiver
Unknown author (via CIA). Date unknown but probably mid-1970s. Incomplete. 2
Crypto Museum Archive, CM302633.
- Extended Analysis of Example Transmitter/Switch Receiver
NRP, February 1979. CM302624.
- H. Keith Melton, Ultimate Spy
ISBN 978-0-2411-8991-7. Page 115.
This document has been redacted by the CIA, hence the appearance of
in the title. It marks the position of words that
have been removed. This document is otherwise not marked as confidential.
Exact title, date and origin unknown (redacted). Not marked as confidential.
Any links shown in red are currently unavailable.
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