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AU-015 →
Universal UHF/FM bug · receiver
AU-018 is a miniature two-channel crystal-controlled
narrowband FM receiver,
for the reception of a variety of covert listening devices (bugs),
developed in the early 1990s by an unknown 1 manufacturer. The device works on
two predetermined channels (A or B) in the UHF radio band. 2
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The receiver measures 82 x 50 x 20 mm and weights 94 grams, battery included.
It comes with two antennas: a 63 mm helical
for short range, and a 170 mm ¼λ whip
for longer range.
It is powered by an internal 6V miniature battery
and delivers its audio to a miniature earpiece.
The built-in noise cancellation (squelch) opens
as soon as a signal is detected. At the bottom is a
two-position channel switch,
marked A and B, that selects one of the two built-in crystals.
The formula for calculating the reception frequency is given below,
and will be around 400 MHz.
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The receiver was suitable for the reception of a range of
crystal-controlled covert listening devices (bugs),
such as the AU-015 room bug,
the AU-032 miniature bug
and the AU-026 telephone bug [1].
Depending on the circumstances and the selected transmitter,
it has an operational range between 300 m and 1 km.
Note that the device is unsuitable for free-running bugs
like the AU-020.
The AU-018 receiver was available around 1991 for a price of US$ 485.
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Based on the choice of components, it seems likely that the device was
made in Japan.
➤ More
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Around 400 MHz.
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The reception frequency (fr) can be calculated with the formula below,
in which fc is the frequency printed on the crystal. The crystal
frequency is multiplied by 9 and added to the 10.7 MHz IF1.
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Channel
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Crystal
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RX Frequency
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A
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43.100 MHz
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398.600 MHz
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B
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43.1944 MHz
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399.450 MHz
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The AU-018 receiver is suitable for the reception of a range of
crystal controlled transmitters from the same manufacturer,
that operate on the same frequencies in the UHF band.
The table below provides a list of compatible transmitters and
their prices in 1991 [1].
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Model
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Range
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Description
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Price
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AU-014
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300 m
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Room bug in the shape of a pen
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$485
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AU-015
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1 km
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Standard room bug
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$485
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AU-012
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300 m
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Room bug in the shape of a calculator
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$485
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AU-017
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300 m
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Room bug in the shape of an outlet adapter
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$485
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AU-021
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300 m
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Room bug in the shape of a credit card
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$485
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AU-052
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300 m
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Room bug in the shape of an USB or HDMI cable
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$485
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AU-062
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300 m
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Room bug in the shape of an optical USB mouse
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$485
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AU-032
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300 m
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Miniature room bug
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$485
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AU-016
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300 m
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Room bug in the shape of a telephne splitter
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$485
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AU-026
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300 m
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Telephone bug (for analogue lines)
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$485
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The receiver is housed in a black aluminium enclosure that consists
of two case shells. The rear shell can be removed by loosening the
large bolt at the centre with a screwdriver or a coin, after which
it can be taken off. This is the side when the 6V battery (V 4034 PX)
must be installed.
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The front case shell can be removed by taking out the recessed screw
at the center of the shell. The receiver itself is covered by two
aluminium shields: one at the components side and one at the solder
side, held together with cellotape. The image on the right shows the
components side of the
receiver with the two shields removed.
The circuit is built around a Motorola MC3357P
narrowband intermediate frequency IC
[a]. It has an IF1 of 10.7 MHz and an IF2 of 455 kHz. Note that the circuit
is nearly identical to the
NFM strip of the 1985 Yaesu FRG-9600 receiver
[2].
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The output of the MC3357 is fed to a NJM386 audio amplifier IC
made by JRC in Japan [b]. It is compatible with the western LM386.
Based on the choice of passive components, the transistors and the NJM386 audio IC,
it seems likely that the receiver was made in Japan. In the device shown here,
most of the parts have date codes from 1991, but the Motorola IC is from 1997,
which suggests that the device was in production for at least 6 years and probable
longer.
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Device Crystal-controlled UHF bug receiver Model AU-018 Purpose Room overhearing (covert listening device) Manufacturer Unknown Type Double-conversion FM receiver Band UHF Modulation Narrowband FM (NFM) Channels 2 1 Frequency A: 398.600 MHz, B: 399.450 MHz Range 300 metres to 1 km Power 6V Battery V 4034 PX (4LR44) Dimensions 82 × 50 × 20 mm Weight 94 grams
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A later version had three channels marked A, B and C.
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© Crypto Museum. Created: Monday 04 April 2022. Last changed: Thursday, 22 December 2022 - 08:43 CET.
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