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Mactron bug
Professional radio bug

The Mactron bug was a professional crystal-based miniature transmitter built in the early 1990s by Mactron in Oosterbeek (Netherlands). The device was intended for bugging (eavesdropping on conversations) and for covert operations, primarily by government agencies such as the police.
The device measures 51 x 15 x 16 mm and was often housed in a black box along with a 9V block battery. The circuit consists of a varicap-based modulator, a crystal oscillator and an amplifier that delivers a Frequency Modulated signal with an output power of 150-200mW.

The Mactron bug operates in the 140-170MHz range for which ordinary scanner crystals were used. The device shown here operates at approx. 142 MHz. For eavesdropping on a conversation, a sensitive electret microphone is needed, which should be connected via an external amplifier.
Professional crystal-driven Mactron bug

Thanks to the small form factor, the Mactron bug was suitable for a wide range of applications. It was sometimes used as part of a larger bug, such as the purpose-built telephone bug shown below. It could also be used as a homing device, for example when tracking the vehicle of a criminal in the days when GPS was not yet available. The Mark II version of the Mactron bug was sometimes supplied as a test transmitter with bug tracing equipment like the Scanlock ECM.
Telephone bug
In the late 1990s, a bug was discovered in the telephone exchange of a company in The Netherlands. It was a professionally designed, purpose-built eavesdropping device that was connected to the company's central office line (CO) and transmitted all of its conversations.
At the heart of the telephone bug was a Mactron FM transmitter with a short helical antenna. It was mounted on a piece of full-copper PCB, along with the other components of the circuit.

At the top right is a current transformer that allowed the telephone line to be tapped without drawing any current from it or disturbing its impedance. Furthermore, the bug transmitted only when the telephone line was engaged. For these reasons the device remained undetected for a long time, and allowed many conversations to be recorded before it was finally discovered.
Custom-built telephone bug, based on a Mactron bug

The company involved, became increasingly suspicious after more and more critial information about recent developments had leaked to their competitors. Although the remote line check, that was carried out by the telecom provider, did not reveal anything, investigators later discovered the bug when physically checking the lines and the exchange system. When studying the image above, it becomes clear that the bug was a one-off that was built especially for this purpose. It also becomes clear that the person who built it was a professional who knew what he was doing.
Top view of the Mactron bug Professional crystal-driven Mactron bug Professional 2-transistor Mactron bug Top view of the Mactron bug Mactron bug in operation Custom-built telephone bug, based on a Mactron bug Custom-built telephone bug, based on a Mactron bug Mactron transmitter at the heart of the telephone bug

Mactron bug Mark II
The initial version of the Mactron bug (shown above) was not suitable for the direct connection of a microphone. If it was used for eavesdropping on a conversation in, say, a room, an extra PCB with a pre-amplifier had to be installed between the microphone and the transmitter.
As a result, the Mactron bug was only suitable for applications where a line-level signal was available, such as the telephone bug described above, or when audio was not required, for example when tracing a car or a person.

Especially for bugging rooms with the purpose of recording human voice, an enhanced version of the bug, known as the Mactron Mark II was released. It featured a very sensitive two-stage audio amplifier that allowed virtually any type of microphone to be connected to its input without any further components or adjustments.
Mactron Bug Mark II

The Mactron Mark II was slightly longer than the initial version, but was still small enough to be built inside many different concealments. As these types of bugs are driven by a quartz crystal, they are extremely stable. Furthermore, the RF output of these bugs is remarkably clean.
For simple eavesdropping tasks, the Mactron Mark II was also available in a black plastic case, with space for a standard 9V battery and a wire antenna. This version was also used for training puposes, such as sweep teams that had to be trained on a Scanlock or a Delta-V bug tracer.

The image on the right shows a complete Mactron Mark II bug. As the unit does not have a built-in microphone, an external one, such as the plug-on electret microphone shown here, is always needed. Alternatively, a wired body microphone (e.g. phonak) could be used instead.
Mactron Mark II bug with external microphone

A small external microphone was often used for covert operations and on infiltration tasks. The transmitter was then hidden on the body, safely protected by the operator's clothing, whilst the microphone was installed in a position where it could pick up the sound of the conversation.

The interior of the cased version of the Mactron Mark II is very straightforward; it just contains the Mark II PCB, the 9V battery a switch and a connector for the microphone. To make the circuit more stable and robust, and to protect it from prying eyes, it was covered in hard brown epoxy.
Advanced version of the Mactron bug, with microphone pre-amplifier. Advanced version of the Mactron bug Mactron Bug Mark II Mactron Mark II bug with external microphone Mactron Mark II interior Mactron Mark II interior A bar Mactron Mark II PCB aside a complete unit Marctron Mark II with external Phonak microphone

Mactron Beacon
Although in most cases eavesdropping involves recording or transmitting a (voice) conversation in a room or in a car, this is not always the case. One example is when you want to follow (track) a person or a car, or when you want to retrieve (trace) a package, such as a money transport.
Especially for tracking and tracing applications, Mactron released onother variant of their famous Mactron Bug: the Mactron Beacon. Like the Mactron Mark II it is slightly longer than the original Mactron bug. Instead of the microphone amplifier of the Mark II, a HEF 4010 IC is used to create a timer with a duty cycle of 25% (1:4).

Every four seconds, the transmitter is turned on for approx. one second an is then switched of for three seconds. This was done to save power and allowed the beacon to transmit at full RF power for several days on a single 9V battery.
Mactron Beacon transmitter

As the Beacon's PCB has the same form factor as the Mark II PCB, it can be fitted inside the same enclosures and concealments. When on the air, the Mactron Beacon transmits a silent carrier, making it difficult to trace the transmitter based on the strength of its audio signal. For these types of bugs, the interceptor would normally use a sensitive Single Side Band (SSB) receiver. By tuning slightly off-channel, the receiver produces an adjustable tone (beat). The volume of this tone is a measure for the signal strength of the received signal.
Mactron Beacon transmitter Mactron Beacon (front) and Mactron Mark II bug (rear) Close up of the IC on the Mactron Beacon Four different versions. From front to rear: the original Mactron, the Beacon, the Mark II and a prototype of the Mark III

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Crypto Museum. Created: Monday 29 April 2013. Last changed: Friday, 13 January 2017 - 22:13 CET.
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