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← Telsey Phone
1st generation mobile phone encryptor
The TX-900S was a compact sophisticated duplex voice encryption device
for mobile application, introduced by Telsy in Turin (Italy)
in 1985 as the successor to the simplex TX-800.
It was one of the first devices that were fully digital and used
DSP technology for processing voice signals.
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The TX-900S was housed in a slim-line green metal case and had only two
buttons on its front panel and a single connector at the rear to which all
peripherals were connected. The unit was suitable for simplex and duplex
radio links, making it the ideal solution for integration into 1st generation
mobile phone equipment.
Different versions of the TX-900 were available.
The image on the right shows a typical TX-900S unit.
It measures only 175 x 260 x 27 mm, and contains a single PCB.
Due to its size, it could easily be used in a mobile environment.
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The TX-900M was designed for mobile use in combination with full duplex
mobile radios such as 1st generation car phones.
The complementary TX-900F was used at the other end, where it could be
integrated with a fixed telephone (PSTN) and/or mobile radio network.
All necessary hardware, such as transformers and echo-cancelling circuits,
are included two-fold in each unit.
The TX-900S unit shown here, was a special version that allowed secure
end-to-end communication with automatic key-exchange. It could be used over
ordinary telephone lines (PSTN) as well as over radio links. The unit has only
two push-buttons (marked CLEAR and CRYPTO) and an 8-character
alpha-numerical LED display that is used when setting the key.
The TX-900 was followed in 1986 by the popular
KV-3000 that exceeded all
sales expections.
A smaller (simplex) variant of the TX-900 was the later
TX-1020 that was used for narrow-band
FM radios, such as the ones used by the police.
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- TX-900M
Self-contained mobile unit in rugged metal housing. It connected directly to
the mobile radio via a single connector.
- TX-900
Custom designed single PC-device, mounted inside the mobile radio.
- TX-900F
Fixed unit that was normally installed at the radio-telephone
exchange. Depending on the application, it consisted of 1 or 2 PCBs.
- TX-900S
Self-contained special version, offering end-to-end protection (with personal
key) between two TX-900S units, or 'radio link only' protection when used in
combination with other members of the TX-900 family. The TX-900S can be
connected to a Telsy remote control telephone or to a mobile radio.
This version is featured on this page.
- TX-900S-MS
Multi-standard version of the TX-900S that was used for demonstration
purposes. It could be programmed to simulate the TX-900, TX-900F, TX-900S
and the older TX-800 (simplex version of the TX-900).
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All connections to the TX-900S are via a single 25-way sub-D connector (DB25)
at the rear. A female version of the DB25 connector is mounted on the TX-900,
so a male version of this connector is required for connection to the outside.
The diagram below shows the pinout of this connector.
The connector on the FX-900M is wired identically.
The connector can be used for connection to the radio as well as for
connection of a handset or remote control unit. All signals that are required
for such a connection are present on the DB25.
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Considering its age, the TX-900S was a highly compact beautifully engineered
device, consisting of a single PCB and a minimum of controls.
All that was needed externally, was a 12V-DC power supply
(e.g. the battery of a car) and a communication device
(telephone with PTT line or radio).
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The TX-900S was one of Telsy's first products with DSP technology, featuring
the TMS-320, the first generation DSP by Texas Instruments
(USA). As the unit is suitable for full-duplex,
two identical DSP circuits are present on the board.
The image on the right shows part of the PCB inside the TX-900S.
The Integrated Circuits (ICs) with the golden caps are custom chips that are
built at Telsy's specification by AMI (American Microsystems Inc.) and
Texas Instruments (TI). The line interface consists of two
AM-9701
Subscriber Line Audio Processing Circuits.
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© Crypto Museum. Created: Wednesday 29 February 2012. Last changed: Saturday, 24 February 2018 - 21:16 CET.
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