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COT Tracker
ISM band telemetry transmitter

COT Tracker 1 is an animal telemetry transmitter, also known as a tracking bug or tracker, made during the 1990s by an unknown manufacturer. The device operates in the 434 MHz ISM-band, and was used by members of the Dutch Counter Observation Team (COT), for the detection of vehicles that were used by observation teams of the Dutch police and intelligence service BVD.

The bug measures 19 x 10 x 4 mm, and weights just 2 grams. It has two wires (red and blue) for connection of a 3V DC power source, such as a miniature Lithium button battery cell. At one of the short sides is a bended sliver plated wire that acts as a loop antenna for the 434 MHz band.

When powered, the device briefly transmits a carrier (CW) for just 50 milliseconds at three second intervals. This is done to save power, and should be enough to detect the nearby presence of the device. It is basically a simple telemetry transmitter – or beacon – for animal detection.
ISM Tracker

The device consists of a small double-side printed circuit board (PCB), that has components on both sides. One side holds the analogue parts and is bascially a single-transistor transmitter. At the other side is a 144.838 MHz crystal and an integrated circuit (IC) for the interval timing.

Counter Observation Team (COT), was a group of scanner listeners, hackers and students, in the Amsterdam area (Netherlands) that had made it their hobby to observe the surveillance teams of the Dutch police and of intelligence services like BVD, basically to discover their modus operandi.

When the group (COT) discovered that the small animal telemetry transmitters could also be used as vehicle trackers, they started mounting them (covertly) to the cars that were used by the police and intelligence services, so that their presence could be detected during a (covert) operation.
ISM tracker compared o the side of a hand

The cars had initially been discriminated by monitoring the frequencies that were used by these services, and by using radio direction finding (RDF) to determine their location. The fact that the covert teams used encryption on their communication, was an extra indication for the group that something important was going on. More often than not, the group frustrated the service's work, causing police and covert intelligence operations to be aborted on more than one occasion.

The activities of the group did not go unnoticed. Apart from the police, they were also picked up by criminals who were prepared to pay good money to obtain the ability to detect the presence of the police in their vicinity. This was particularly the case in the Amsterdam drugs-related scene. A long list with thousands of licence plate numbers of police and intelligence service vehicles, that circulated in the Amsterdam underworld, was attributed to the Counter Observation Team [2]. 2

  1. This is not the official name of the device, but as the device was used by COT and the original manufacturer is unknown, we have chosen to use it as a nickname.
  2. This was assumed by the Dutch intelligence service BVD, but no actual proof was found [2].

ISM tracker compared o the side of a hand ISM tracker compared o the side of a hand ISM Tracker Crystal and timer Close-up of the analoge parts ISM tracker top side
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ISM tracker compared o the side of a hand
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ISM tracker compared o the side of a hand
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ISM Tracker
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Crystal and timer
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Close-up of the analoge parts
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ISM tracker top side

Block diagram
Below is the block diagram of the tracking device. At the heart is a quartz-controlled oscillator that runs on a 144.838 MHz crystal (in 3rd overtone). The 3rd harmonic of the base frequency is used as the transmission frequency at ~ 434.520 MHz. Despite the fact that a high-pass filter is present between oscillator and antenna, the base frequency of 144.838 MHz is just 20dB down.

The unit is driven by an interval timer with a duty-cycle of 1.6%, as a result of which the battery will last approx. 60 times longer than with a continuously broadcasting transmitter. The timer is built around a low-power HEF40106 hex-inverter, and enables the transmitter briefly every 3 sec.

  1. Wikipedia, ISM band
    Retrieved February 2020.

  2. BVD Maandbericht November 1990, Scannerfreaks
    Binnenlandse Veiligheidsdienst (now: AIVD). 2135137-65. (Dutch)
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Crypto Museum. Created: Tuesday 04 February 2020. Last changed: Friday, 24 April 2020 - 21:19 CET.
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