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TCD Ecolex IV Ecolex X
Teleprinter connection device with FSK modem
TH-3676 1 is a military
teleprinter connection device (TCD) with built-in
FSK modem, developed around 1964 by Telefunken
in Germany. The device was used by the Dutch and German armies for interfacing
a 2-wire or 4-wire military teletypewriter
to the civil (public) 2-wire or 4-wire FSK
telex network of the Dutch PTT
and the German DBP. It was also used for connecting the
Philips Ecolex X (Ecolex 10)
cipher machine to a SSB radio set.
Also known as NSN 5805-17-036-0253.
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The device converts standard current-based teleprinter signals into
tone-modulated FSK signals and vice versa.
It is housed in a ruggedized military enclosure that measures
150 × 300 × 283 mm and weights 11.5 kg. All connections,
controls and indicators are at the front panel,
which can be covered with a sealed lid.
A mains power cord can be stowed inside the lid.
The image on the right shows the TH-3676A, which is slightly different from the
standard TH-3676, in that it is suitable for the FSK networks of
the Dutch and German telecom providers.
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The advantage of using FSK over current-based telegraphy, is that
FSK is far less sensitive to distortions on the line, as a result of which it
can be used more reliably on bad quality lines. In addition, FSK
enables the use of Telex-Over-Radio (TOR) via HF radio, and also via
VHF/UHF Line-of-Sight (LOS) links.
In circuit diagrams, the TH-3676 can be depicted by the following symbol:
In The Netherlands, the TH-3676 was first used with the
Ecolex 4 cipher machine (1964), in particular
in mobile setups.
The special versions TH-3676A and TH-3676B were later developed for use
with public PTT and DBP networks, and with the
Philips Ecolex X encryptor.
The device is sometimes erroneously
referred to as Deksel Kast (Lid Case) after the
label on the case lid. 2
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There are three versions.
On this page, the notation TH-3676(A) means TH-3676 and TH-3676A.
TH-3676A/B means TH-3676A and TH-3676B.
TH-3676(A/B) means all versions.
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The actual model/serial number label
is at the right side of the enclosure.
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The image below shows the front panel of the TH-3676A. The device consists
of 5 functional blocks, or modules, designated A, B, C, D and E respectively.
Mains power is connected to the 3-way receptacle at the left (A).
Ensure that the mains voltage selector (S4) is correctly configured.
The local device is connected to the jack socket(s) on the rightmost module
(E). For 2-wire setup, only the upper jack is used. For 4-wire setup, the
lower two jacks are used. Select the appropriate local line current with the
rotary knob (S3) of the Local Current Source (B). The line (or radio) is
connected to the 4 banana sockets at the far right.
The Line Mode (FSK) is set with selector S1.
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- TH-3676
Standard version, suitable for local devices with single-current only,
in 2- or 4-wire configuration. The line (FSK) can be 2- or 4-wire, but can
also be connected to an external field telephone, whilst the device is
disconnected from the line. In 2-wire mode, the device also provides
echo-cancellation.
- TH-3676A
Special version suitable for connection to the Dutch PTT or the German
DBP. Local devices can be 2- or 4-wire, with single- or double-current.
The device featured here is of this type.
For further information see
Instruction Card IK11-519/3
[E].
- TH-3676B
This version was made especially for connecting the
Ecolex X encryptor
to a SSB radio. In particular module (E) is different. It has a 10-way
connector for the SSB radio, and a relay contact for the Ecolex X.
For further information see
Instruction Card IK11-519/4 [F].
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Switch S1 on module E is used to select the Line Mode.
The following settings are available:
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4-wire
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2-wire
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Field telephone connected to the line (device disconnected)
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The mode of operation of the locally connected teleprinter is selected with the
rotary switch (S3) on module B. The following settings are available on TH-3676:
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2-wire
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4-wire
On the TH-3676A (featured here) and TH-3676B — both of which are always in
4-wire mode — this switch has a different function. It has three positions:
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Single current 40 mA
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Double current 12.5 mA
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Double current 20 mA
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Below is the block diagram of the TH-3676. At the left are the
local connections. At the right are the line connections.
The upper branch is the transmitter. It converts the single-current signal
from the teleprinter first to double-current and then converts it to an FSK
signal that is sent to the line.
The lower branch is the receiver. It converts the
FSK signal from the line into a double-current signal. This is
then converted to a single-current signal and sent to the teleprinter.
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TH-3676 in 4-wire line mode. Move the mouse over the diagram to see 2-wire line mode.
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Switch S1 sets the line mode. It has three positions: (1) 4-wire, (2) 2-wire
and (3) field telephone. In the latter case, the field telephone is connected
directly to the 2-wire line, whilst the device is disconnected from the line.
S1 is shown here in the 4-wire line mode, as illustrated below:
Move the mouse over the diagram, to see S1 in 2-wire line mode.
Switch S3 set the local mode. It has two positions: (1) 2-wire and (2) 4-wire.
It is shown here in 4-wire mode. In this mode, the teleprinter
does not produce a local copy of the outgoing text, as TX and RX
circuits are fully separated. In that case, the only way to get a local copy
is to set the line (S1) to 2-wire mode.
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Note that the above block diagram
is for the TH-3676, which is different from the TH-3676A, in particular as
far as S3 is concerned. On the TH-3676A – which has a different local
interface – the local side is always in 4-wire mode, whilst S3 is a 3-position
switch, used to select the current:
In position (1), the unit works in the same way as the TH-3676, but locally
only in 4-wire mode, whilst the required current for TX and RX are
provided by the internal PSU. In settings (2) and (3), only the current for the
TX side is provided by the PSU, whilst the current for the RX path
is provided by the line. As the local interface is always in 4-wire
configuration, the only way to produce a local copy is to set the line (S1)
to 2-wire mode. When used with an encryption device like the
Philips Ecolex X,
both interfaces must be in 4-wire mode, as a local copy would produce garbage.
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The rightmost board holds the rest of the receiver
circuitry. The two large cans towards the right are transformers or inductors
and may be part of the tone decoding circuit.
This board holds an indicator lamp (La3),
which lights up when the RX level is low or idle.
Spare indicators lamps are
stowed inside a compartment
inside the case lid. It also holds a
plastic tool for removing and inserting the lamp.
It allows a broken lamp to be replaced without opening the module.
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The TH-3676 has an unusual and rare power receptacle at its
front panel. It is made by Souriau
and has 3 pins.
It accepts a female cable part, such as the Souriau 84725F547N002
or Souriau 8400.90.
Below is the pinout when looking into the receptacle.
➤ Souriau catalogue
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- 220V AC (1)
- 220V AC (2)
- GND
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At the far right of the front panel are four vertically aligned banana sockets.
These sockets are used for connection of the subscriber line or a radio. They
can be used in 2-wire or 4-wire mode. Note that, when connecting to a radio,
the line interface must always be used in 4-wire mode.
In 2-wire mode, the upper two banana sockets are used for connection to the
line, whilst the lower two sockets can be used for the connection of an
(optional) field telephone. When switch S1 is in the centre position, the
teleprinter is connected to the line. When S1 is set to 'telephone', the
field telephone is connected directly to the line, whilst
device and teleprinter are disconnected.
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Three 6 mm jack sockets are available for connection of the teleprinter or an
encryption device. These sockets are located on the rightmost module (E), just
left of the banana sockets of the line interface. In 4-wire mode (see below),
the teleprinter is connected to the lower two sockets:
In 2-wire mode — which is only available on the TH-3676 and not on the A
and B versions — the teleprinter should be connected to the upper socket
as shown in the diagram below.
Note that the upper two jack sockets are connected in series and that
these sockets are shorted automatically when the plug is removed. This
allows an additional device, such as a tape reader, to be connected in
series with the transmitter contact of the teleprinter.
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When connecting the Ecolex X encryption/decryption device (Dutch: VOT) to
the TH-3676(A), the two jacks from the cable of the Ecolex X should be
connected to the lower two jack sockets of the device, as shown in the
diagram below. In this example, the local interface (i.e. the four banana
sockets at the right) are used in 2-wire mode. This means that only the
upper two sockets are used to connect the device to the subscriber line,
or to a TH-3676(A) at a different location.
In this configuration, it is possible to connect a regular (analogue) field telephone
to the lower two banana terminals. This telephone can be used for verbal
liasion with the exchange, by placing the mode-selector on module (E)
in the telephone position (i.e. fully clockwise). This connects the telephone
directly to the line, and disconnects the TH-3676 completely.
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Device Telex Connection Device (TCD) and MODEM (FSK) Purpose Military wired and wireless telegraphy (telex) Model TH-3676 (see below) Manufacturer Telefunken Country Germany Year 1964 ~ NSN 5805-17-036-0253 Users Germany, Netherlands Network PTT (Netherlands), DBP (Germany) Line 2-wire, 4-wire Local 2-wire, 4-wire (TH-3676)
4-wire, single-current 40mA, double-current 12.5/20mA (TH-3676A) FSK Mark: 1325 Hz, Space: 1225 Hz Power 11, 127 or 220V AC ±10%. 47 - 63 Hz Dimensions 150 × 300 × 283 mm (HWD) Weight 11.5 kg
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TH-3676 (1964) Standard version (local: single current only, 2- or 4-wire) TH-3676A (1975) PTT/DBP version (local: single/double-current, 4-wire) [E] TH-3676B (1976) Same as A-version, but with 10-way connector for SSB radio [F]
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5 NG 62 Power Supply Unit (PSU) 5 Trs 626 Local Current Source 5 Trs 624 FSK Transmitter 5 Trs 625 FSK Receiver 5 Trs 621 Line Interface
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Document kindly provided by Bart Wessel [1].
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Document kindly provided by Kees Raaymakers.
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- Kees Raaymakers
- Paul Reuvers
- Marc Simons
- Bart Wessel
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© Crypto Museum. Created: Wednesday 27 September 2017. Last changed: Monday, 13 January 2025 - 23:04 CET.
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