The device measures approx. 254 x 154 x 55 mm and weights 1608 grams including
Alkaline batteries. It is powered by four internal 1.5V C-size dry battery cells
that are installed behind a large circular screw-terminal at the right side.
It has a 4 x 40 character liquid crystal display and is suitable for text-based messages, which can optionally be encrypted.
It is suitable for connection to virtually any brand and model of
and supports baud rates from 75 to 1200 baud. The version 2 shown
here, has a 10-pin socket for connection to a SPIDER radio.
The device is intended for use in combat net radio and field wire 3 systems.
It features Forward Error Correction (FEC) and has an RS-232C interface
(available on an NF-7 socket) for connection to a portable printer.
It also features burst transmissions
to reduce the probability of interception
and network traffic load.
The version shown in Jane's of 1988 , is probably the final design, made
of aluminium, as it weights 1.75 kg, whereas the one shown here has a plastic
The MED was developed at HSA around 1987, at the same time as the
SPIDER VHF military radio set.
Given the small number of SPIDER radio sets
that were manufactured, it is believed that only a few MEDs were ever made.
As the device shown here has serial number 0 MODEL S1009 it is likely
that it was part of a prototype series — or null-model — intended for
HSA Huizen – informally known as SIGNAAL or SIGNAL
– was formerly known as
Philips Telecommunicatie Industrie (PTI).
It was taken over in 1990 by Thomson,
which has since been renamed Thales.
The device does not require the CRYPTO option to be installed in the
SPIDER. When available, the encryption was performed by the MED.
Transmission via 2-wire line at 1200 or 2400 baud.
The diagrams below give an overview of the controls and connections on
the body of the MED. At the top is a large window, behind which a 4 x 40
character LCD display is located.
The window is shielded by means of a metal grid, to avoid any unwanted
In front of the LCD is a 30-button
recessed keyboard, of which most keys have a double function. At the left
is the 3-position POWER switch. In the center position, the device is OFF.
In both other positions, the device is ON. If the left position is used,
the backlight of the display is switched ON as well.
Also at the left – at either side of the POWER switch –
are the terminals to the 2-wire interface. It allows two MED devices to be
connected directly via a regular WD-1/TT field wire line.
At the right are the sockets for connection to a radio — in this case
the SPIDER —
and an (optional) printer. When unused, these sockets should
be covered by the protective caps. Also at the right is a large circular
threaded cap, that gives access to the internal cylindrical
The diagram below shows the simplest possible setup for communication
between two MED terminals. The two devices are linked via a standard
2-wire field line (WD-1/TT), with a length of up to 3 km. As each MED
has its own local battery source, communication is possible without any
additional equipment, at
1200 or 2400 baud, subject to the length and the quality of the line.
In most cases however, the terminal will be connected to an HF or VHF
radio via the radio (audio) interface. In this case, the internal modem
will be used to generate FSK tones that can be transmitted over a regular
audio (voice) channel. The diagram below shows a setup with SPIDER radios.
When used in combination with a VHF FM radio (like SPIDER), baud rates
of 75, 150, 300, 600 and 1200 baud are possible. When used in combination
with a narrow-band HF radio, the baudrate will be limited to 75 baud.
The internal modem generates the necessary FSK mark/space tones.
The device featured here is a prototype, which differs from the
final version. It is believed that the final product was housed in an
aluminium enclosure, whilst the green case shown here is made of plastic.
Furthermore, the final version has text labels near the connectors and the
The control panel is held in place by 20 screws around its circumference.
With the prototype these screws are inserted from the bottom side,
whilst on the final version they are inserted from the top .
After removing these screws, the top panel – which holds the display
and the keyboard – can be separated from the case shell.
Inside the top panel are the display electronics
– probably provided by Hitachi – and the
processor board (CPU).
The CPU is built around a 80C31 micro-controller made by Harris,
with 8KB static RAM and a 32KB EPROM that holds the firmware.
The display board is connected to the CPU by means of fixed wiring.
The CPU board is connected to the keyboard by means of a
17-pin header that
protrudes the top panel. After removing the four screws in the corners of
the board, the CPU board
can be lifted from the keyboard connector.
Inside the case shell are two further PCBs.
The one that is visible immediately after opening the case,
is the interface board (I/F)
with its solder side up.
It is connected to the processor board
by means of fixed wiring (i.e. 26 individual wires)
and is held in place by 4 screws at the corners.
It holds a single-chip FX409 FSK modem,
made by CML in the UK [A],
and an RS232 interface
After removing these four screws, the I/F board can be taken away,
revealing the power board
at the bottom of the case. Note that the
I/F board is connected to the power board with a header.
At present, the operation of the MED is not known. Furthermore, it is unclear
whether the current firmware supports encryption and decryption of the text.
If you have any information about this device, such as circuit diagrams and/or
operating instructions, please contact us.
When starting the device after it has been switched OFF for several hours
(to ensure that the supercap has been discharged completely),
it starts with the following text on the display:
Once the device has been configured (i.e. all questions have been answered
and valid parameters have been entered), the current settings are retained
in static RAM. A supercap, which is placed on the power board, preserves the
contents of the static RAM when the batteries are removed.
MED has a 10-pin CANNON NF10 socket that has the same pinout as the
10-pin NF10 socket on the front panel of the SPIDER radio.
Use a 10-way 1:1 wired cable to connect
the two devices. A 180kΩ resistor inside the MED (connected
between H and ground) informs the radio that an MED is connected.
Below is the pinout of the NF-10 socket on the SPIDER (looking into
NOGO'NOGO' information (active low)
ADRPeripheral address 1
PWR+12V supply for peripheral
DATA'Data mode' information (active low)
A 180 kΩ 2% resistor between this pin and ground, informs
the radio that an MED is connected.
The MED has an RS-232C serial port which is intended for connection
of a (portable) printer. It is available on an NF-7
socket at the right side of the device. The pinout of this connector
is currently unknown.
At the left side of the device, at either side of the POWER switch,
is a spring-loaded push-in terminal for connection of a 2-wire field
line. This wiring does not have a specific polarity.
Power6V DC (4 x 1.5V C-size dry battery)
Baudrate75 — 2400 baud ➤ see list
Display4 x 40 character Liquid Crystal Display (LCD)
Dimensions254 x 154 x 55 mm
Weight1.75 kg (including batteries)
- Jane's Military Communications 1988, Message Exchange Device (MED)
Jane's Publishing Company Ltd. ISBN 0-7106-0856-X. p. 428.
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© Crypto Museum. Created: Tuesday 18 December 2018. Last changed: Saturday, 21 November 2020 - 10:31 CET.