Audio-based RF retro reflector
- under construction
LOUDAUTO is the codename or cryptonym of a
covert listening device (bug),
developed around 2007 by the US
National Security Agency (NSA)
as part of their ANT product portfolio.
The device is an audio-based RF retro reflector that should be
activited (illuminated) by a strong continuous wave (CW) 1 GHz 1
radio frequency (RF) signal, beamed at it
from a nearby listening post (LP).
Although the device is activated by an external illumination signal,
it should also be powered by local 3V DC source – typically provided by two
button cells – from which it draws just 15µA. In this respect, it
is a semi-passive element (SPE).
Room audio is picked up and amplified by a Knowles miniature microphone,
that modulates the re-radiated illumination signal by means of Pulse Position
Modulation (PPM). The re-emitted signal is received at the listening post
– typically by a CTX-4000
or PHOTOANGLO system –
and further processed by means of COTS equipment.
LOUDAUTO is part of the ANGRYNEIGHBOR
family of radar retro-reflectors.
In this context, the term radar refers to the continuous wave
activation beam from the listening post, that operates in the 1-2 GHz
The processing and demodulation of the returned signal is typically
done by means of a commercial spectrum analyser, such as the
Rohde & Schwarz FSH-series,
that has been enhanced with FM demodulating capabilities.
In many respects, LOUDAUTO can be seen as a further development of
EASY CHAIR passive elements,
combined with later active
like the SRT-52
which also used Pulse Position Modulation (PPM).
Information about LOUDAUTO was first published in an internal
Top Secret (TS) NSA document on 1 August 2007, that was available to
the so-called five eyes countries (FVEY) 2 only. Although it was scheduled for
declassification on 1 August 2032 (25 years after its inception),
it was revealed to the public in 2013 as part of the
According to a product datasheet of 7 April 2009, the price of a single
LOUDAUTO device was just US$ 30.
According to that document, the end processing
— presumably the demodulation — was still under
development in 2009 .
The device should be activated with an RF signal at a frequency
between 1 GHz and 2 GHz.
USA, Canada, UK, Australia and New-Zealand.
The diagram below provides an educated guess of how the LOUDAUTO device
probably works. At the left is a standard subminiature microphone with
built-in pre-amplifier, made by Knowles.
The analogue signal from the
microphone is fed to the input of a Pulse Position Modulator (PPM), which
might have been implemented in software in a small industry-standard AVR controller.
The microphone and the PPM modulator are powered by a local 3V DC source,
rather than by DC power derived from the activation beam. This means that
the activation beam can be far less strong than with the
CIA's EASYCHAIR devices,
where energy from the activation beam was used to power the
entire circuit. In that respect it can be seen as a battery-assisted
passive element, or semi-passive element,
similar to the battery aided variant of the
EASYCHAIR Mark III-A.
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© Crypto Museum. Created: Thursday 07 November 2019. Last changed: Thursday, 07 November 2019 - 20:25 CET.