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CIA NRP EC ← SRN-58
The SRN-59 was made for use in combination with
covert listening devices (bugs),
such as the SRT-107, and is in fact the directional
variant of the nearly identical omni-directional
SRN-58.
Like the SRN-58,
the SRN-59 is a vertical dipole, constructed from two
short brass pipes that are mounted inside a perspex (plexiglass) stick.
It is half a wavelength long (½λ), but is fore-shorted in
order to compensate for the dielectric effects of the environment (the perspex
stick). Unlike the SRN-58 however, the antenna is not placed at the centre
of the stick, but towards one side.
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At the circumference of the perspex stick, opposite the dipole antenna,
is a narrow brass strip that acts as a non-resonant reflector.
It is this strip that gives the antenna its directive property, which results
in an isotropic gain of +2 to +6 dB. It should be clear that this antenna
can only be used in situations where it can be positioned accurately
with respect to the position of the nearby listening post (LP).
If this is not the case, the
omni-directional SRN-58 should be used instead.
The diagram above shows the construction of the SRN-59, seen from its side,
whilst the antenna is in horizontal position. In practice the antenna was
used straight up, with the red arrow showing the direction of optimum radiaton.
For further information, please refer to the SRN-58 page.
➤ More about the SRN-58
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The SRN-58 and SRN-59 were developed at the
NRP between December 1968 and
November 1969, as part of a CIA research contract to investigate the
feasibilty of moving the operational frequency of
covert listening devices (bugs)
from 290 MHz and 350 MHz to the newly allocated 1500 MHz band [1].
For this project, the following new components were developed:
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In September 1969, the first equipment was sent to the CIA for evaluation.
This resulted in an upgraded version of the SRT-56 bug,
of which the SRK-35 RF-module was replaced by the new SRK-145,
making it suitable for 1500 MHz operation.
It was fitted with an SRN-58/59 antenna.
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The Rejected Pulse (RP) audio masking scheme of the SRT-56 was kept,
as it was housed in a separate cylindrical enclosure. The image on the
right shows a complete set as it was discovered by the Russians in
one of their buildings in the USA. It consists of an SRK-145 RF-module,
an SWE-56 video coder and a large Mercury battery array.
At the right is the SRN-58 antenna stick.
The combination shown in the image on the right
was in production from 1971 to 1974,
after which it was succeeded by the integrated
SRT-107, which was
smaller and easier to conceal.
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The SRT-107 was in fact a combination of the
SRK-145 RF-unit and an SWE-56 video coder (i.e. the audio-masking unit),
housed in a single cylindrical enclosure that was approx. 15 cm long.
With the SRT-107, the SRN-58 (or SRN-59) antenna was permanently fitted
to the transmitter.
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The SRN-59 (or the omni-directional SRN-58) was commonly supplied as
an integral part of a transmitter (bug) such
as the SRT-107
shown in the image on the right. In that case the 25 cm
long coaxial cable was fixed to the body of the transmitter.
➤ More information
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The SRN-58 is the omni-directional variant of the SRN-59.
Although it does not provide the +2 to +6 dB isotropic gain of the
SRN-59, it was preferred in most situations, as it makes the positioning
of the target area (TA) concealment and the listening post (LP) much less
critical.
➤ More information
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Device Coaxial dipole antenna Manufacturer NRP Customer CIA Frequency ~ 1500 MHz Gain +2 to +6 dB (isotropic) (in brick environment) Pattern Cardioïdal Medium Plexiglass Impedance 50Ω Length 94 mm Diameter 26 mm
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- NRP/CIA, Manual for 1.5 GHz system
September 1969. CM302484.
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© Crypto Museum. Created: Thursday 23 March 2017. Last changed: Tuesday, 22 November 2022 - 11:49 CET.
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