Excolex X, also known as Ecolex 10, is a military online/offline
encryption/decryption device
for synchronous and asynchronous telegraphy (telex),
introduced in 1972 by Philips Usfa in Eindhoven (Netherlands)
as the successor to Ecolex IV and Tarolex.
Developed for the Dutch armed forces, it is partly based on the earlier
TROL and Tarolex developments.
The device is also known by its Philips designator UA 8040 and
— in the Royal Dutch Army — as VOT or KL/TGA-3572.
Rather than using One-Time Tapes (OTT),
like its predecessor Ecolex IV,
the Ecolex X uses a built-in key stream generator. 1
This was done to overcome the typical key-tape distribution problems
of mixer class cipher machines (OTT).
The machine is housed in a heavy metal 19" rackmount enclosure.
In vehicles it was typically placed on a shock-absorbing base, as shown
in the image on the right. At the front is a lockable shielded door
behind with the controls and the 36 key-setting thumbwheels are located.
They allow the selection of 836 (2108) different keys.
Development of the machine was started in 1965, but was delayed several times,
due to a delayed order, ambiguous specifications and
TEMPEST problems.
Finally, after a series of additional
developments and modifications, it was released in 1972.
In total, 388 machines were built, the majority of which went to the Dutch Army.
A few machines went to the Dutch Ministry of Foreign Affairs [2].
Ecolex X was superseded in 1977 by Mucolex — a trunk encryption
device (TED) — and in 1982 by Aroflex.
Nevertheless, some of the machines remained in use until approx. 1992.
The main unit contains the actual encryption/decryption device, which uses a
secret proprietary encryption algorithm developed by Philips in cooperation with
the NLNCSA — the Dutch cipher authority.
The device is powered from the AC mains, and the only control at its front
panel is the ON/OFF switch at the top left. There are three sockets for connection
to the mains, the remote control unit and the telex line respectively.
The cryptographic KEY is set by means of 36 thumbwheel selectors, that are located
behind the locked TEMPEST-proof door at the right. Move the mouse over the image
below to reveal which settings and controls are located behind the door.
Behind the heavy door are the key settings, which comprises 36 thumbwheel
selectors, each of which can be set between 0 and 9. Note however, that only
the settings 0-7 are relevant (3 bits). Setting 8 is equal to setting 0, and
setting 9 is equal to setting 1. By convention, all
switches must be set to 7 when the device is not in use.
The key settings compartment also holds configuration selectors, plus a
set of ALARM controls for testing the individual sub-circuits.
Once the key has been set, the Ecolex X is entirely controlled from the
remote control unit (Dutch: Afstandsbedieningskast, or ABK), which is
connected to the main unit (VOT) by means of a thick cable with 32-pin
connectors at either end. This cable carries the data signals as well as
the 230V mains. A Siemens T-100 teleprinter
is connected to the terminals at the top right, and is powered from the
mains socket at the left. The front half of the ABK holds the tape reader
and controls.
The five brightly coloured indicators are labelled in Dutch. The diagram
above shows the English translation. Inside each of the coloured caps is
a light bulb. Furthermore, the rightmost four are also push-buttons.
They can be pressed to enter a certain state or MODE of the device.
The initial version of the Ecolex X was designed with circuit blocks
from ELCOMA — Philips' component division. These circuit blocks are very similar
to the FLYBALL modules used by the NSA in devices
like the KW-7 cipher machine.
Very few machines of this type were made – perhaps five to ten – before it was
decided to redesign the device with modern flatpack ICs.
The machine shown in the image on the right has serial number 005.
Intermediate version
UA-8040/01
Assuming that the numbering scheme used for the different versions
of the Ecolex X is contiguous, there must have been an UA-8040/01
variant. It is likely though, that this was just an engineering version
for evaluation purposes, that was never taken into production.
It is unlikely that there are any surviving specimen of this version.
As a result, the introduction of the machine was delayed significantly,
and all TEMPEST tests had to be carried out again.
The new version, designated UA-8040/02, was introduced in 1972
and a total of 338 units were manufactured.
This version is fully compatible with the UA-8040/00.
The diagram below shows the most basic setup of the Ecolex X. The device
consists of two units: the actual cipher machine (VOT) and a remote
control unit (ABK). Only the VOT is powered from the mains. The
ABK and the Siemens T-100 teleprinter
at the left, ar both powered from the VOT.
In most cases, a TH-3676 FSK modem
(or similar) is needed for connection to the telex line.
When the Ecolex X is connected to a radio set, such as the
Philips RT-3600, an additional radio adapter
is needed, such as the Telefunken TH-4179,
shown in the diagram below at the bottom right. The adapter is connected
between the handset and the radio. It takes
over the function of the push-to-talk (PTT) switch, allowing the Ecolex X
to switch between transmit and receive.
When a later version of the FSK modem (TH-3676B) is used instead of the
TH-3676 shown here, the TH-4179 radio adapter is not needed as it has
an integrated PTT feature. The TH-7376B was used for example with
the SSB radio [G]. A more detailed wiring diagram can be found here.
This is the actual encryption/decryption device
(Dutch: Versleutel-Ontsleutel Toestel (VOT)).
It is powered from the mains and forms the central hub of
the system. The heavy hinged door at the right gives access to
the key setting selectors.
The device is connected to the mains and the telex line, and is
controlled from the remote control unit (ABK, see blow).
Remote control unit (ABK)
UA-8041
The Ecolex X is controlled from a remote control unit (RCU)
(Dutch: Afstandsbedieningskast (ABK)) that also contains
a tape reader. The ABK is connected to the main unit by means
an 32-pin cable that also carries the mains voltage.
The local teleprinter – in most cases a Siemens T-100 –
was connected to and powered by the ABK. When the ABK was
in transit, the control panel was protected by a metal cover. When the
unit was in use, the metal cover was
stowed on top of the accessory box.
Accessories
UA-8048
All accessories for the Ecolex X are stowed in the metal container
shown in the image on the right (here shown without the top lid).
Inside the container are several cable assemblies (see below) and a
box with spare parts.
The accessory box consists of two metal shells. When it is
closed, the transport cover
of the ABK can be stowed on top of it.
Interconnection cable
UA-8042
Cable assembly VOT/ABK (UA-8042) is needed to interconnect the
two main components:
The cable carries the data signals to and from the tape reader and
the front panel controls, but also the 230V AC mains.
Mains power cable
UA-8043
This cable is used to connect the main unit (VOT)
to the mains power network. In most cases this was 220V AC.
Note that the device can only be powered from the mains. When used
in a mobile environment, an external 220V AC power generator was used.
This cable is used for connecting the Ecolex X (VOT) to
the line terminator (i.e., the modem). In most cases, this was
a TH-3676 or TH-3676A.
When the TH-3676B modem is used, the UA-8050 cable
should be used instead,
Special line cable
UA-8050
This line cable (VOT/SRV) is nearly identical to the one above,
but has two additional wires and can be used to control the push-to-talk
(PTT) of the attached radio. In practice, this was often the
Philips RT-3600 radio.
The two additional wires are connected either to the TH-3676B modem,
the TH-4179 radio adapter or an external send/receive switch box.
For 3rd echelon repairs, further spare parts were available, such as
fuse holders, switches and coloured indicator caps.
Line terminator with modem
TH-3676
For connection of the Ecolex X to a telecom line or to a radio, the
teleprinter connection device (TCD)
shown in the image on the right was used.
The local teleprinter was connected – via the Ecolex X – to this
device, in 4-wire configuration. The device was then connected, also in
4-wire configuration, to the radio.
When connecting the Ecolex X to a simplex two-way radio,
via the TH-3776 modem (above), the additional
TH-4179 radio adapter shown here
is required. It allows the Ecolex X to switch between
transmission and reception by taking over the PTT function
of the radio and its handset.
When the TH-3676B modem is used (instead of the TH-3676(A)),
the TH-4179 is not required.
Two versions were available: TT-4230, with tape puncher, and TT-4231,
with a tape puncher at the left and a reader at the right.
The device shown in the image on the right is of this type.
When the Ecolex X was used in a moble environment, it was often connected
to the Philips RT-3600 VHF/FM radio shown in the
image on the right. Depending on the version of this radio, it allowed
secure line-of-sight (LOS) operation up to a distance of 30 km.
The RT-3600 has two U-229 receptacles
at the far right for connection of a handset. Note that this connector uses a
non-standard pinout.
Development of the Ecolex X started in 1965, in a move to depart from
One-Time Tape (OTT) cipher machines, on to self-permuting systems.
As it soon became clear that its development would take at least five
years, it was decided to introduce Tarolex as a gap-fill solution.
It consisted of an external key generator that was connected
to a modified Ecolex IV one-time tape (OTT) cipher machine.
The key generator effectively replaced the rearmost tape reader of the
Ecolex IV. The KEY was set by means of a short piece
of punched paper tape that was
installed in a static tape reader
behind a door.
Tarolex became the first Dutch self-permuting cipher machine.
As it was based on TROL,
it could be developed in less than a year, which is incredibly fast
for a top-level cipher machine.
Tarolex development was started in 1966 and went on
in parallel with the Ecolex X development. It was
rolled out in 1967 and a total of 151 machines were delivered to the Dutch Army.
In addition, the same number of existing Ecolex IV machines were
modified for connection to Tarolex.
With the rapid introduction of Tarolex, Philips had bought
itself more time for development of the Ecolex X, which
turned out to be an insightful decision. There were many
hurdles that had to be taken, including a delayed order, ambiguous
specifications and TEMPEST problems.
The image above was taken at the production site at Schouwbroekseweg
in Eindhoven in the early 1970s, and shows how the device was soak tested [1].
Finally, after a series of additional developments and modifications,
the machine was approved and rolled out.
In total, 388 machines were built, the majority of which went to the Dutch Army,
where they gradually replaced the Tarolex machines.
A small number of machines were provided to the
Dutch Foreign Office [2].
Ecolex X was approved for use in NATO
context for messages at the highest level of secrecy.
Ecolex X is suitable for offline and online use, via telephone lines,
as well as over HF, VHF or UHF radio.
When used in online mode, the built-in key generator produces a
constant key stream – even when the operator is not typing any text –
so that an eavesdropper cannot determine the start and end of a
message. This principle is known as Traffic Flow Security (TFS).
Ecolex X was intended for stationary use, but could also be
used in a mobile environment, as shown below.
Mobile secure VHF setup
The image on the right shows a typical setup, installed at the back of a 1-ton
DAF YA-126 truck, with a separate trailer carrying a 220V power generator. At the
centre of the table is a Siemens T-100 teleprinter.
To its left is the Ecolex X remote control unit (ABK).
The machine itself (VOT) is placed under the table at the left.
At the top left is the TH-3676 modem. It is connected to the
TH-4179 radio adapter at the top right, which in turn is connected
to the RT-3600 VHF radio on the table at the right.
Note the TX/RX switch at the bottom right of the modem.
Mobile secure HF/VHF setup
The image on the right shows a similar setup at the back of a DAF YA-126
truck, but in this case a SSBHF transceiver is placed under the table at
the left, whilst the Ecolex X main unit is placed on a shelf at the top left.
To the left of the ABK is a modified TH-3676B modem, which also
takes over the role of the TH-4179 radio adapter.
This truck is also fitted with an RT-3600 VHF radio
which is just visible at the left edge of the picture.
Image taken in 2011 at the Military Communication Museum of Mathieu Driessen
(ON8PO) in Lanaken (Belgium).
The Ecolex X has an advanced built-in ALARM circuit that allows 14
internal functions (cards) to be tested without disassembling the unit.
The ALARM functions are operated with the middle three knobs in the
key settings compartment (marked ALARM KONTROLE). The rotory switch
at the centre (0-8) is used to select one of eight tests. In addition,
the I/II switch allows a second bank of tests to be selected.
This offers another 6 checks (1 to 6 — 7 and 8 are unused).
Any setting other than '0' enables a test. It introduces a fault in
one of the plug-in cards inside the Ecolex X. This causes the yellow
indicator at the front of the remote control unit (ABK) to be lit.
Now press the black push button to the right of the selector.
The yellow lamp should now go off. Now release the black button and
the yellow lamp should come on again. If this is the case, the test
has been executed successfully. Now repeat this for the other 13 tests.
For full details about each test, please refer to the 1st/2nd
Echelon Technical Manual [F].
Interior
Main unit (VOT)
The interior of the main unit can be accessed by releasing 8 Allen screws
around the edges of the front panel, after which the front panel with all
building blocks can be extracted from the case shell. All parts are mounted
to the front panel by means of retaining clips around the edges.
The image below shows the extracted interior, with the front panel facing
down. The largest part is occupied by a stainless steel card holder
with 27 plug-in cards. The rightmost eight cards (marked 'A') are known
as the wheels and form the key generator.
A full list of plug-in cards can be found here.
Detailed circuit diagrams can be found in the 5th echelon documentation [H].
Plug-in cards can be extracted from the card holder after
releasing the horizontal locking bar.
Furthermore, the entire card holder can be taken off by pushing the
release brackets at either side of the assembly towards to the front panel.
This gives access to the remaining parts:
The image above shows the front panel assembly after removing the
card holder. Each of the remaining units — the transformer and the
two filter units — is held in place by means of retaining clips.
They are connected to the card holder by means of several (arrays of)
connectors.
The modular design allows for quick repairs by 3rd echelon technicians,
simply by swapping modules and/or cards, whilst component level repair is
left to 4th and 5th echelon engineers.
The construction of the remote control unit (ABK) is very similar
to that of the VOT, except that in this case all internal parts are
mounted to the top panel. Loosen the four screws in the corners of the
top panel to extract the entire interior from the case shell, as shown
in the image below.
The ABK comprises three functional blocks: the tape reader (right)
and two filter units (left) each of which protrudes the front panel
and is held in place by means of retaining clips. The tape unit is
unshielded as it has no direct connections to the outside world.
It can be removed in its entirety by
releasing 4 retaining clips. This part also holds
the five coloured push-buttons.
The Ecolex X featured on this page, has not yet been tested,
and restoration of the machine and its accessories therefore hasn't
started yet.
Related equipment
Tarolex
Since development of the Ecolex X took a rather long time, it was decided
that a separate key stream generator would be developed as a gap-fill
solution. In 1966/67, the so-called Tarolex 19" was developed
for use with a modified Ecolex IV machine. Like the
Ecolex X, Tarolex was based on the earlier
TROL developments.
Approx. 150 Tarolex units were
delivered to the Dutch Army and an equal number of existing
Ecolex IV machines was modified for them
[2].
Following the success of the Ecolex X, Philips developed its successor,
Ecolex 20, 1
in the mid-1980s. Although the design was completed
and was even listed in Jane's Military Communications of 1986, it was not
taken into production.
It did not meet the requirements of the era and development of the all-new
ZODIAC integrated communication
system was already underway.
Below is an overview of the connections that must be made when the
Ecolex X is connected to an RT-3600 VHF/FM simplex radio.
When the device is used over fixed telephone lines, the TH-4179 radio adapter
is omitted and the TH-3676 modem is connected directly to the telex line.
With external PTT switch
Below is the same setup, but with an additional TX/RX switch added at the
bottom right. This switch controls the push-to-talk (PTT) line of the radio and
allows the automatic PTT-contact from the Ecolex X to be overruled.
It is likely that this was an aftermarket upgrade (1975) as the switch
is not painted green and does not have a NATO stock number (NSN) or any other
designator. It is only
shown in Instruction Card IK11-529[E] and is visible in
this photograph.
Mains power
The mains power input is at the top left of the front panel of the Ecolex X.
Below is the pinout of the 10-6P connector, when looking into it. This connector
accepts a 10-6S cable part. 220V AC mains power is applied to pins A and D.
Ground should be connected to pin B. When a shielded cable is used (needed
for TEMPEST reasons) the shield to be connected to pins
C, E and F.
PWR
220V AC (1)
GND
Ground
GND
Shield
PWR
220V AC (2)
GND
Shield
GND
Shield
Other connector wirings
The wiring of the individual connectors of the Ecolex X is specified in the
4rd/5th Echelon Technical Manual [H pp. 5-1 to 5-5].
For the other connectors, check the relevant pages on this website where
the corresponding devices are described.
Specifications
Complete set
Device
Telex encryption device with Trafic Flow Security (TFS)
IK11-519/4, Instruction card 4 (Dutch) 1
Describes connection of the TH-3676 to an SSB radio.
CM-300668. Dutch Army, 9 April 1979.
Replaces IK11-519/4 of 27 September 1976.
Ecolex-X Technical Manual 1/2 (Dutch)
Technische handleiding vercijfer- ontcijferuitrusting KL-TGA-3572.
1e en 2e echelons bediening en onderhoud.
CM-300669. 1/2TH11-959. Dutch Army, 26 January 1973.
Ecolex-X Technical Manual 3 (Dutch)
Vercijfer- en ontcijferuitrusting KL/TGA-3572.
3e echelons technische beschrijving en onderhoud.
CM-303239. 3TH11-959. Dutch Army, 12 September 1973.
Ecolex-X Technical Manual 4/5 Wiring Diagrams (Dutch)
Vercijfer- en ontcijferuitrusting KL/TGA-3572.
4e en 5e echelons onderhoud. Bedradings- en montagegegevens.
CM-300287. 4/5TH11-959/2. Dutch Army, 5 October 1976.
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Crypto Museum. Created: Sunday 16 June 2013. Last changed: Tuesday, 18 August 2026 - 09:04 CET.
![Ecolex-X machine under soak test. Photograph courtesy Philips Usfa [1].](img/301322/000/full.jpg)
