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DF
Covert
Datong
  
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D-903
Tracking beacon

D-903 is a 1 Watt tracking beacon, developed around 1992 by Datong Electronics Ltd. in Leeds (UK). It was used by intelligence and law enforcement agencies, for following suspected vehicles, persons and money. It supports continuous and pulse operation modes, and was commonly used in a combination with a suitable direction finder, such as the Datong DF-4 or Datong DF-5. The device can (optionally) be controlled remotely by means of a CMD-2 or CMD-3 telecommander.

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.
  
Datong D-903/TRSI beacon with antenna

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].

  1. The antenna contains a miniature 10K resistor that is connected in parallel. This resistor enables the device.
  2. For example: locking the doors of the vehicle under surveillance.

Datong D-903/TRSI beacon with antenna
Datong D-903/TRSI beacon
Neodyne magnets
A
×
A
1 / 3
Datong D-903/TRSI beacon with antenna
A
2 / 3
Datong D-903/TRSI beacon
A
3 / 3
Neodyne magnets

Features
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.

Remote control
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
  
CMD-3 telecommander with helical antenna




Click to see more

Interior
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.

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).
  
Interior

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).

Interior
Disassembled D-903 beacon
Switch board
Motion detection board
Microcontroller board
Receiver board
Transmitter board
Transmitter
Battery compartment
Backplane
Terminal block (solder side)
Screw terminals for controlling external device(s)
Close-up of the screw terminals
Close-up of the screw terminals and the PCBs
Datong D-903 beacon with the 5 PCBs removed
B
×
B
1 / 15
Interior
B
2 / 15
Disassembled D-903 beacon
B
3 / 15
Switch board
B
4 / 15
Motion detection board
B
5 / 15
Microcontroller board
B
6 / 15
Receiver board
B
7 / 15
Transmitter board
B
8 / 15
Transmitter
B
9 / 15
Battery compartment
B
10 / 15
Backplane
B
11 / 15
Terminal block (solder side)
B
12 / 15
Screw terminals for controlling external device(s)
B
13 / 15
Close-up of the screw terminals
B
14 / 15
Close-up of the screw terminals and the PCBs
B
15 / 15
Datong D-903 beacon with the 5 PCBs removed

Specifications
  • 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
  1. The antenna has a 10K resistor connected in parallel to enable the beacon.

Receiver   option R
  • Sensitivity
    -118 dBm
  • Modulation
    FSK
  • Deviation
    4 kHz pp
  • Addresses
    16 (24)
Modes of operation
  • Sleep
  • Continuous
  • Pulse 1
  • Fast-pulse 1
  1. In this mode the beacon uses only 10% of the power needed for continuous transmission.

Options
  • T
    Transmitter
  • R
    Receiver
  • S
    Motion sensor
  • D
    Dual motion sensor
  • I
    High-current switch
Documentation
  1. D-903 Leaflet
    Datong, date unknown.

  2. User Guide for Beacon System model D903
    Datong, 19 February 1992. Issue 1.1.
References
  1. Anonymous, D-903/TRSI tracking beacon - THANKS !
    Received December 2020.

  2. Original order confirmation 1
    30 September 1993. In Dutch language.
  1. Confidential document. Not for public release.

Further information
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Crypto Museum. Created: Monday 25 January 2021. Last changed: Monday, 06 September 2021 - 13:42 CET.
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