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DF Covert Datong CMD-3 → ← DF-5
The microprocessor-controlled transmitter is housed in a black milled aluminium
enclosure, and can be expanded with a receiver (for remote control), a motion
detector and a high-current switching unit for controlling external
devices.
A complete D-903 unit is shown in the image on the right. It is powered by two 3.6V
lithium cells that are installed insde the slimmer part of the enclosure.
An antenna is connected to an SMA socket at the side. It has an extension coil
and is tuned for the chosen frequency. The device can be attached to a vehicle
by means of magnets.
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It could also be permanently mounted inside a vehicle – powered by the
car battery – in which case the battery pack was omitted. Depending on
the national regulations, the transmitters were manufactured and adjusted
to order. In most cases the beacons operated in the 2 m band (~170 MHz)
or in the 8 m band (~36 MHz), but other frequencies were also used
(e.g. 400 MHz).
The device has no controls. It is activated as soon as the batteries are
installed and the antenna is connected. 1 Furthermore, when the
Receiver Board (option R) is installed, it can be put to sleep and
activated remotely. It can also be woken by the motion sensor (option S/D)
or by an external event. In addition it can control external devices 2 if
option I is installed.
The price of a complete D-903 beacon with all options fitted (D-903/TRSI),
was the equivalent of EUR 1310 in 1993 [2].
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The antenna contains a miniature 10K resistor that is connected in parallel.
This resistor enables the device.
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For example: locking the doors of the vehicle under surveillance.
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The diagram below provides a quick overview of the features of the D-903. The
bare beacon measures 37 x 75 x 37 mm, but when the battery pack is fitted this
becomes 95 x 75 x 37 mm. At one of the short sides of the beacon is an SMA
socket for connection of the supplied antenna. Fitting the antenna will
activate the device. At the other side are 8 screw terminals, covered by
a sealed aluminium lid. When Option I is fitted, these terminals can be used
for controlling external events, such as locking the doors and/or stopping the
engine of the vehicle under surveillance.
In the pictured configuration, the device is powered by two 3.6V lithium
batteries, such as the Saft LSH14. The battery compartment is accessible
via a panel at the bottom, that is held in place by 4 recessed screws.
Alternatively, the device can be powered from the car battery – using a
12 to 7V converter – in which case the battery pack can be omitted.
At the underside of the device (not visible) here,
are twelve strong neodymium magnets, that allow the device to be attached
quickly, covertly and invisibly inside the wheel arch or to the bottom of
the target vehicle.
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When the device has the optional receiver board (option R) installed, it can
be controlled remotely by mans of the CMD-3 telecommander
shown in the image on the right.
➤ More information
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The interior of the beacon can be accessed from the top of the device,
by removing four recessed screws and
taking away the sealed top cover.
This reveals the edges of one or more small printed circuit boards (PCBs).
Depending on the installed options, up to five such
PCBs can be installed.
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The image on the right shows the interior of a D-903 that has all four
options (T, R, S and I) fitted. Each PCB is installed into a 19-pin
header on a common backplane. At the corners or each PCB are small
holes that allow it to be extracted by means of a dental hook or a
similar tool.
From top to bottom are the transmitter (T), receiver (R), microcontroller,
motion sensor (S) and high-current switch (I). The five boards are shown
side-by-side in the diagram above. The only board that is always present,
is the microcontroller PCB. It controls the state of the device and
the pulse sequences of the transmitter (T).
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The enclosure bulges out somewhat to the right of the PCBs. Inside this
'blob' – that can be accessed by removing the four recessed screws in the
corners – are 8 screw terminals to which external devices can optionally
be connected. The terminal block is sealed against water (rain).
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Frequency To order (e.g. 36, 172 or 400 MHz) Output 1 W Impedance 50Ω Harmonics > 55 dBs suppression Antenna Base-loaded whip (tuned to frequency) 1 Modes 3 (see below) Power Internal or external 7 - 8 VDC (typically 7.2V) Batteries 2 x 2.6V Saft LSH14 lithium battery Current 200 µA (sleep), 8 mA (RX), 350 mA (TX pulse) Pre-sleep 10 sec, 10 min, 20 min, 12 hrs Wake-up via telecommander, motion and AUX, motion or AUX Address Configurable on microprocessor board Dimensions 37 x 75 x 37 mm (with battery pack: 95 x 75 x 37 mm) Weight 364 g
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The antenna has a 10K resistor connected in parallel to enable the
beacon.
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Sensitivity -118 dBm Modulation FSK Deviation 4 kHz pp Addresses 16 (24)
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- Sleep
- Continuous
- Pulse 1
- Fast-pulse 1
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In this mode the beacon uses only 10% of the power needed for
continuous transmission.
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T Transmitter R Receiver S Motion sensor D Dual motion sensor I High-current switch
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- D-903 Leaflet
Datong, date unknown.
- User Guide for Beacon System model D903
Datong, 19 February 1992. Issue 1.1.
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- Anonymous, D-903/TRSI tracking beacon - THANKS !
Received December 2020.
- Original order confirmation 1
30 September 1993. In Dutch language.
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Confidential document. Not for public release.
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© Crypto Museum. Created: Monday 25 January 2021. Last changed: Monday, 06 September 2021 - 13:42 CET.
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