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Telsy TDS-2004M
Mobile voice encryptor

The TDS-2004M was a mobile voice encryption device, introduced by Telsy in Turin (Italy) around 1978. It was part of the TDS-2000 series and is the mobile version of the TDS-2004. It is compatible with other members of the TDS-2000 family, such as the briefcase TDS-2003.

The TDS-2004M was the mobile version of the TDS-2004 desktop encryption device and was housed in a military-grade case, complete with shockmount base-plate. The image on the right shows a typical TDS-2004M, mounted on its base-plate with 2 catches on either side.

The TDS-2004M has two modes of encryption: time division or 2-dimensional coding (time and frequency division) and the cryptographic key determines which mode is used. A total of 9 keys can be preset and the key selector at the front is used to select the key compartment.

Setting the key can be done on the front panel. When setting the key, the mode selector (right) has to be set to SET KEY (INS COD). Then set the key selector (left) to the number of the required key compartment and toggle the middle knob to CLEAR (CHIARO) in order to purge the current key. Next, enter between 1 and 8 digits, by rotating the key selector to the required number and toggling the middle knob to CRYPTO in order to enter the digit. When doing this, you need to remember which digits you have already entered. The TDS-2004M does not have the visual aid of a display, like the TDS-2003. Finally, set the mode selector to SPX (simplex) or DPX (duplex).

The TDS-2000 range appeared to be very successful and thousands of units were sold to the Army, the Police and even to the corporate sector. As a result, the TDS-2004 remained in production well into the 1990s. The image above shows a typical TDS-2004M that was produced in 1991, close to the end of its life-cycle.

TDS-2004M TDS-2004M front panel TDS-2004M front panel TDS-2004M front panel Releasing the locks Pulling-out the interior TDS-2004M interior Extracting the analogue board

All connections to the TDS-2004M are at the front. The leftmost socket, marked TCVR (transceiver) is for the connection to a simplex or duplex radio set. The 12V-DC power source for the unit is also supplied here. It is a standard military 10-way male socket. The pins are marked A-K and are wired as follows:

  1. +12V-DC in
  2. Speaker out
  3. Remote key selection (for 2 keys)
  4. MIKE OUT (to radio)
  5. GNF
  6. MIKE IN
  7. RX IN (from radio)
  8. Relay out (bypass)
  9. not present
  10. Reverse signalling/PTT
  11. RX OUT (earphone)

The rightmost connector, marked MICROTEL, allows an external remote control unit (or other accessories) to be connected to the TDS-2004M. It is a standard military 10-way female socket. The pins are marked A-K and are wired as follows:

  1. +12V-DC out (for accessories, 400mA max)
  2. PRIVATE remote control
  3. CLEAR remote control
  4. CRYPTO remote control
  5. GND
  6. MIKE IN
  7. CLEAR remote LED
  8. Reverse signalling/PTT
  9. not present
  10. CRYPTO remote LED
  11. RX OUT (earphone)
The TDS-2004M is housed in a robust green military-grade case. The electronics are easily extracted from the case, by releasing the 4 locking-knobs at the corners of the front panel. Rotating them counter-clockwise, releases the unit. Once all 4 locks are released, the front panel can be pulled out of the case. All electronics are mounted in a frame behind the front panel.

The TDS-2004M contains two main PCBs: an analogue board at the top, and a digital board at the bottom. They are both inserted from the back and are slotted into a card-edge connector. A sturdy metal frame keeps the PCBs in place.

The image on the right shows part of the digital board with the Z-80 processor at its heart. Considering the fact that the TDS-2004M was designed in 1978, just two years after the introduction of the Z-80, it must have been one of the first designs with this processor. The unit shown here was built in June 1991.
Z-80 processor and peripheral chips

The digital board also contains a number of custom chips that can be recognized by their golden caps. They were manufactured by American Microsystems Inc. (AMI) in their production facility in Austria. The custom chips all carry ID-numbers starting with TY to show that they were built especially for Telsy. Three such custom chips are used on the digital board.

The other PCB contains the analogue circuitry. At the heart of this board are two FX-309 Delta Modulators by CML (UK) [3]. This was a later generation of the FX-209 that was used in the earlier TS-500 voice encryptor. The large white/black chips, marked TY2521-2524, are thick film circuits with OpAmp-based active low-pass filters. They were also custom-built for Telsy. The same analogue and digital boards are also used in the TDS-2003 and in the TDS-2004.

Releasing the locks Pulling-out the interior Top view of the interior showing the analogue board Extracting the analogue board Analogue board Digital board CML FX-309 delta modulators Custom circuits on the analogue board

Damage control
When we received the TDS-2004M featured on this page [1], we immediately opened the unit in order to check it for leaking batteries. Although the device looks brand new, it was manufactured in the early 1980s and a battery that was installed at that time, might be leaking by now.

Leaking batteries can cause serious damage to the interior. When released, the liquids from the battery can 'eat' away copper tracks from the PCB and even complete components. The toxic gasses that are released when the battery comes apart, can even damage components at the other end of the unit, by causing oxidation.

The image on the right shows the interior of the TDS-2004M featured on this page, when we first opened it. Many years of storage have exhausted the battery as a result of which it started leaking. The damage is illustrated in the images below.
Damage caused by leaking backup battery

Although the unit in the above image may appear beyond repair, this was not the case. Careful removal of the damaged parts and cleaning of the PCB has brought the unit back to working condition. The rightmost image below shows the corner of the PCB after cleaning.

With older equipment it is always important to check for leaking batteries. In most cases, it is advisable to remove them as a preventive measure. It may then be replaced by a newer alternative, but that will require maintenance is due course as well. Another possibility is to replace it with a so-called super-cap (a very large capacitor) or leave it out altogether as the device will probably work without the battery (settings will be lost when the unit is switched off).

Damage caused by leaking backup battery Digital board with leaking battery in the top right Close-up of the damaged battery The damaged battery after cleaning it somewhat Damaged components Damaged components Damaged components PCB after cleaning

  1. Telsy S.p.A., TDS 2004M - THANKS !
    Device featured on this page kindly donated by Telsy. February 2012.

  2. Telsy S.p.A., TDS 2004M Instruction Manual
    February 1983.

  3. Consumer Microcircuits Ltd., FX-309 Datasheet
    Continuous Variable Slope Delta Modulator (CVSD).
    Date unknown. Retrieved February 2012.
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Crypto Museum. Last changed: Thursday, 03 May 2012 - 13:17 CET.
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