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Telsy TDS-2003
Portable telephone encryptor

The TDS-2003 was a portable telephone encryption device, introduced by Telsy in Turin (Italy) around 1980. It was built inside a standard Delsey briefcase and was part of the TDS-2000 series. It featues two-dimensional encryption based on a time and frequency division scrambler.
The TDS-2003 followed hot on the heels of the compatible TDS-2004 and TDS-2004M that were introduced a few years earlier. The TDS-2000 range appeared to be extremely successful and thousands of units were sold to the Army, the Police and even to the corporate sector. They remained in production well into the 1990s.

The image on the right shows a typical TDS-2003 built inside a Delsey briefcase that was commonly used by business men in those days. The unit is powered from the mains which is connected to a socket at the front left.
TDS-2003 ready for use

The TDS-2003 can be connected directly to an analogue telephone line (PSTN), using one of the supplied cables. If a direct line is not available, it can also be used with the built-in acoustic coupler at the right. In that case, an external phone is used as the interface to the PTT line.
The image on the right shows the acoustic coupler in use. The handset of a domestic telephone set is placed over the two rubber pads of the coupler. The transmitter and receiver of the coupler can be adjusted to accomodate virtually any handset, such as this one.

In front of the encryptor is a built-in handset that is used for the voice conversation. It is connected to the main unit via a DB25 socket at the front left. The handset can also be placed outside the briefcase and has a dial that is used when the unit is connected directly to the line.
Using the acoustic coupler

Hidden inside the acoustic coupler is a spare microphone that was commonly used in domestic telephone sets in those days. It is stored under a metal bracket and was used to replace the one in the analogue telephone set that was already used inside the (hotel) room, just in case it was bugged. Although this seems far fetched, telephone microphone bugs were quite common then.
Delsey briefcase with TDS-2003 TDS-2003 ready for use Adjusting the acoustic coupler Using the acoustic coupler Connection for the handset Using the built-in phone outside the briefcase The dial on the handset Spare microphone

Operation of the TDS-2003 is rather straight forward. It is similar to controlling the TDS-2004M, but has the added advantage of a LED display for monitoring the input. The device has 9 key compartments, allowing 9 different keys to be stored in advance. When the unit is switched off, the keys are retained in memory by an backup battery that is mounted on the digital board.
At the center of the control panel is the CODE selector. It is a 11-position switch, marked with the numbers 0-9 and '*'. Position 0 is for private communication, whilst 1-9 are used for the key compartments. In case security is compromized, they can be purged (ZEROIZED) by setting the key dial to the *-position and pressing CLR.

Loading a valid key into a key compartment involves the selector to be set to the appropriate number, pressing of the CLR-button (to erase any previous key) and entering a number between 0 and 99 999 999 (1 to 8 digits).
Entering Key 1

Entering a digit is done by setting the selector to the desired number and pressing CRY. The image above shows the 8-position alpha-numerical LED display when entering the cryptographic key for key compartment 1. The first digit determines the encryption mode: 1-5 is used to select time division only, whilst 6-9 selects 2-dimensional coding (time and frequency division) [2].

To the right of the key selector is a BNC-socket that allows an external key-filler to be connected. The key-filler was used for automated loading of the valid keys without the need to follow the above procedure. It minimizes errors when settings the keys and helps keeping the keys secret.
TDS-2003 inside Delsey briefcase Opening the control panel Revealing the controls TDS-2003 top view TDS-2003 top view TDS-2003 controls Entering Key 1 Selftest On/off switch and push buttons

The TDS-2003 is easily removed from the briefcase by releasing a lock at the right. The entire unit can then be lifted out and placed on the table. The interior of the device is accessible by removing a few bolts from the front and the sides, and then removing the cover.
The TDS-2003 is based on the same electronic design as the TDS-2004. At the heart of the TDS-2003 are the same two PCBs with the analogue and the digital circuitry. These are accompanied by a built-in mains power supply, the control panel and the acoustic coupler.

The image on the right shows the analogue board which becomes visible when the top cover is removed. It is identical to the analogue board of the TDS-2004 and is inserted from the left into a PCB socket. At the front left of the unit is the power supply (PSU).
Analogue board

The digital board is located at the bottom, just below the analogue board. It is also slotted-in from the left and connects to the rest of the electronics via a card-edge connector. Also at the bottom is the control panel and the acoustic coupler. For a more detailed description of the analogue and digital boards, please refer to the description of the TDS-2004M.

When we received the TDS-2004M we discovered that the internal backup battery had seriously damaged the interior. After many years of storage, the battery had desintegrated and its contents had damaged various tracks and components on the PCB. So, when we received the TDS-2003 [1] we immediately opened it in order to removed the backup battery. Luckily, the battery in this device was of another brand (Catalyst) and type (3440) and was still fully functional. Although it was installed in 1987, this Lithium-Iodine cell still supplied its nominal voltage of 2.8V.
TDS-2003 outside the briefcase TDS-2003 interior Analogue board TDS-2003 bottom view Power Supply Digital board Bottom view of acoustic coupler and user interface Close-up of 2.8V backup battery

  1. Telsy S.p.A. TDS-2003 - THANKS !
    Device featured on this page kindly donated by Telsy.

  2. Telsy S.p.A., TDS 2003 Operating Manual
    June 1982.

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Crypto Museum. Last changed: Thursday, 03 May 2012 - 13:17 CET.
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