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Automatic bug scanner

COMPUSCAN was an add-on for the Audiotel Scanlock Mark VB, developed by Glenn Whidden of Technical Services Agency (TSA) in the US in the early 1980s. It required a special version of the Scanlock Mark VB that had an extra DIN socket (marked COMPUSCAN) at the front panel. The unit was small enough to be fitted inside the accessory pocket of the Scanlock's carrying case.
The Compuscan was designed to carry out most of the functions of the human operator automatically. It was a computer-controlled device that allowed the signals in a room to be compared with a previously recorded 'safe area' that was stored in the Compuscan's memory.

The image on the right shows a COMPUSCAN 1A unit that belongs to a collector in the US. It was used in tandem with a Scanlock Mark VB and is connected with it through the DIN socket at the bottom left of the front panel. A similar socket is available on the front panel of the Scanlock.

Please note that the Compuscan can only be used in combination with a Scanlock that has been modified for it. It can be recognised by the DIN socket marked COMPUSCAN at the front panel, to the right of the 2MHz IF output. There is also an extra ON/OFF switch to enable/disable the Compuscan. It is possible that in the early days, Scanlock units were modified for this in the US by TSA, but a later variant was manufactured in the UK with this connector already present.

The idea behind the Compuscan was developed by Glenn Whidden at TSA, a former technical expert of the CIA. It would later evolve into a series of products known as Glenn's Eagle. Glenn Whidden is also featured in the Channel 4 documentary The Walls Have Ears that is available through the YouTube link below [3]. When the Scanlock Mark 5B was succeeded in 1984 by the Scanlock 2000, the old Scanlock Mark 5B was kept in production especially for the US market, as it was the only model that was suitable for the COMPUSCAN add-on. It was sold by TSA.
COMPUSCAN 1A COMPUSCAN 1A COMPUSCAN 1A Compuscan 1A standing up straight Treshold adjustment and DIN socket for connection to the Scanlock Mark 5B LCD and FINE TUNING control Close-up of the control panel Scanlock Mark 5B with Compuscan on top

All controls, indicators and connections are located on the front panel of the unit. This allows the COMPUSCAN to be stored and used whilst inside the side pocket of the Scanlock Mark 5B's carrying case. It is connected to the Scanlock via a special cable that runs from the 5-pin DIN socket at the bottom left, to a similar socket on the control panel of the Scanlock Mark 5B.

All indicators are nicely arranged at the top of the front panel. There are 6 LEDs and a small LCD display. The MODE of operation is selected by the switches at the center, as is the scanning speed. The ON/OFF switches at the bottom are used to select various features. The most frequently used operational controls, such as the start, stop and recording buttons, and the ability for fine tuning, are all located at the right, so that they can be operated with one hand.
When performing a thorough bug-sweep, the operator would first take the Compuscan to a so-called safe zone; an area away from the target that was known to be free of bugs. Compuscan was then used to record the activity on all frequencies and store this in its built-in memory 1.
He would than return to the target area and perform a full sweep automatically using the Compuscan. As the Compuscan had recorded all activity at the safe area, it knows which stations and frequencies to ignore. As a result, only new signals (i.e. the eavesdropping bugs) are found.

In the Channel 4 documentary The Walls Have Ears, Scanlock inventor Lee Tracey can be seen using a Scanlock Mark VB with a COMPUSCAN connected to it [3]. The image on the right was taken from that program and shows a working Compuscan unit at the top right.
Scanlock Mark VB with a Compuscan on top. Image taken from the Channel Four documentary 'The Walls Have Ears' [3].

When scanning the target area, the Compuscan/Scanlock searches the spectrum in 4096 units with a selectable speed, and autmatically stops when a signal is detected that is not stored in Memory 1 and that exceeds the current treshold as set with the large knob at the left. The treshold knob works similarly to a squelch control. If the operator is away from the unit, any suspected signal can be stored automatically in Memory 2, so that they can be examined later.

The scanning speed is selectable in three steps: F (fast), M (medium) and S (slow). The best results are obtained in Slow mode. In that case a full scan takes approx. 1 minute and 20 seconds. As the Compuscan is powered by the Scanlock via the DIN cable, it reduced the Scanlock's battery life to approx. one hour (when not powered from the mains).
Early model Scanlock Mark VB   Modified for Compuscan
Intially, the COMPUSCAN was connected to a modified - standard - Scanlock Mark VB. The modification was probably carried out by TSA and consisted of the addition of a 5-pin DIN socket and an ON/OFF switch to the Scanlock's front panel, and a small PCB that was mounted inside.

The image above shows an Scanlock Mark VB Issue 2 that has been modified for use with the COMPUSCAN. On this version, the built-in telescopic antenna has been replaced by an N-type socket. Furthermore, the red knob that was originally used for manual subcarrier adjustment, is now used for FINE TUNING and the lettering has been change accordingly. The odometer-style tuning knob of the original Scanlock Mark VB is replaced by a more common multi-turn knob.
Later model Scanlock Mark VB   Compuscan-ready
When the COMPUSCAN became successful, also in the UK, Audiotel decided to change the design of the Scanlock Mark VB slightly, so that it became COMPUSCAN-ready. The layout of the front panel was changed, so that the 5-pin DIN socket and the switch fitted in nicely with the rest.

Furthermore, the red knob was replaced by a black one, as it was no longer used for subcarrier adjustment, and was swapped with the VOLUME adjustment. It makes more sense as the FINE TUNING is now aside the TUNING control. The functions of the eight push-buttons at the bottom left are no longer printed on the knobs but are now screen-printed on the front panel itself.
The COMPUSCAN is built inside a standard plastic enclosure that measures approx. 20.5 x 17 x 6.5 cm. It consists of two identical case shells that can be separated by removing two long bolts from the bottom of the unit. After rmoving the upper case shell, the interior becomes visible.
The entire assembly consists of a front panel with all controls, indicators and the main connector, and three printed circuit boards (PCBs) that are stacked togetheras a sandwich.

The bottom PCB is mounted to the bottom of the case with four small screws at the corners. After removing these screws, the entire assembly can be lifted from the case. The three PCBs are bolted together with metal mounting posts, and are inter-connected by means of a ribbon cable at the rear that acts as a backplane. Several flying wires connect the PCBs to the front panel.
Compuscan interior

Contrary to what the name 'COMPUSCAN' may suggest, the device does not contain a computer or a controller of any kind. Instead, it contains a programmable MC145151 PLL, manufactured by Motorola [4], and some computer memory, that is fully controlled by standard CMOS logic ICs. When disconnected, the memory contents are retained by a standard 9V battery at the back.
Compuscan interior Rear view of the interior Compuscan interior seen from the rear Rear view of the Compuscan interior Interior viewed from the left Interior views from the right Close-up of the bottom PCB The bottom PCB removed
Bottom view of the lower PCB Bottom view of the lower PCB Close-up of the backplane Backup battery Motorola parallel PLL An extra capacitor in the power circuit Detail of the rear of the LCD display and some push-buttons Close-up of the rear of the DIN socket

The operation of the COMPUSCAN is bst explained by the block diagram that is presented in US patent 4,368,539, a patent filed on 22 August 1980 by Glenn Whidden in the US. It is the patent on which the Compuscan is based. Please note that the items in the top left are in fact the Scanlock receiver. Although it is an external device, it is effectively integrated with the Scanlock.

Compuscan block diagram. Click for a larger view.

Updated 26 January 2014

We have received a Scanlock Mark VB issue 3, which is the COMPUSCAN-ready version, complete with a working COMPUSCAN unit. Unfortunately, the Scanlock has been 'demilitarized' by people who didn't know that this was never a classified item. In the process of 'demilitarization', most ICs have been removed from their sockets and all wiring has been cut and removed. Some of the components have simply been ripped from the PCBs. One IC has been desoldered from the board.

The PSU board is broken into pieces, probably to get access to the main board below it, and even from this board the ICs have been removed. All wires to and from the front panel controls have been cut and removed whenever possible. Luckily, the special TSA Compuscan modification board is still present. It is our goal to restore this unit and, if possible, bring it back to life again.
All wires to the front panel cut Wires cut from front panel Bottom view of the front panel PCB TSA Compuscan interface board Damaged PSU board PSU transistors broken off IC's removed from the main board. One IC (at the right) has even been desoldered. Power wires from the transformer cut

Related patents

  1. Technical Services Agency, Inc., Compuscan - Operating Instructions
    The TSA Compuscan for use with Mk Vb Scanlock. December 1983.

  2. Technical Services Agency, Scanlock Mark VB Handbook
    Date unknown.

  3. Channel 4, The Walls Have Ears
    Fascinating Channel 4 documentary about The Spying Game - The Walls have Ears.
    1999. Via YouTube. Interviews Glenn Whidden, Lee Tracey, Charles Bovill and others.

  4. Motorola, MC145151 parallel PLL Frequency Synthesizer
    1995. Retrieved January 2014.

Further information

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Crypto Museum. Last changed: Wednesday, 29 January 2014 - 11:44 CET.
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