Unitel 225 →
The device is housed in a grey/black metal enclosure that measures
260 × 165 × 63 mm, and is shaped in such as way that it can be
placed on a table, with all controls at the front panel easily accessible.
All connections, with the exception of the earphones, are at the rear.
As it has the same form factor as its predecessor – the RX-905 –
the RX-1000 was intended as a drop-in replacement, albeit with added
functionality like freely programmable frequencies and up to 60 channels,
all under control of in internal 8031 microcontroller — a variant of the 8051.
As the device has a rather poor large-signal behaviour — a strong signal
in the vicinity of the receiver easily overdrives the input stage —
it is less suitable as a general purpose surveillance receiver, unless
it is used with an (adjustable) attenuator. It is currently unknown when
the RX-1000 was first introduced, but based on the design of the PCB
and the choice of components, it is likely that this was around 1990.
The device shown here was manufactured around 2000. 1
A spin-off from this receiver is the Unitel 225 intelligence kit
— basically a portable listening post.
Based on date codes on the electronic components.
The image below provides a quick overview of the controls and connections of
the RX-1000. All controls are located at the
which consists of
a horizontal and a vertical plane. The horizontal plane holds the volume and
squelch controls, plus an LCD with push-buttons. The vertical place holds
an output socket (3.5 mm jack), an output selector to control the level,
and an (optional) selector for the descrambler. Provisions are present for
All connections are at the rear of the device,
which the exception of the
output socket, which is at the front. The device can be powered from the 115V
or 230C AC mains, configurable with a slide switch at the rear.
A fairly large speaker is located under the black grille at the top.
At present, no instruction manual is available, but fortunately,
short-form instruction are printed at the bottom.
The interior of the device can be accessed by removing four screws from the upper
case shell — two at the left and two at the right — after which the
case shell can be removed. To get full access to the PCB,
it will be necessary to remove the black front panel cover as well.
The is done by removing two screws at the front, plus the two knobs of the volume and
The devices in our collection had probably been unused for a number of years,
before they were obtained from a government sale. This means that it was likely
that they had not been powered up for at least 10 years. First of all, we had
to set the voltage selector at the rear to 230V AC.
Next, we thoroughly inspected the interior to check for any damaged parts.
Apart from a loose descrambler board
in one of the units, that was easily
refitted, everything seemed to be in good shape.
But when the device was powered up, it immediately blew the mains fuse
in the house.
As the AC transformer checked out OK, this problem was likely caused by
the mains filter, which consists of
two 10nF/1000V capacitors
that are soldered directly to the mains socket at the rear of the device.
The two capacitors were temporarily removed to see if they
caused the problem.
As this resolved the problem, this means that one of the two capacitor
(or both) had not survived. After
replacing the capacitors with new 1nF variants,
the receiver powered up correctly. The volume and squelch controls appeared
to work as expected. Next, a suitable frequency was programmed into one of
the channel memories, and a known good
covert body transmitter was used
as a test device. The signal came through loud and clear, which means that
the device is OK.
DeviceDigital surveillance receiver
PurposeBug reception, frequency monitoring
ManufacturerAudio Intelligence Devices (AID)
MethodDigital, freely programmable
ModulationFM narrow band
Mains110V or 230V AC (switch selectable)
Dimensions260 × 165 × 63 mm
5001Crypto Museum 1
This version does not contain an EPROM. Instead the software is stored
in a one-time programmable microprocessor.
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© Crypto Museum. Created: Tuesday 16 January 2024. Last changed: Sunday, 21 January 2024 - 16:57 CET.