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STU-III/R
Secure voice and data gateway · Remote

STU-III/R is a 3rd generation secure voice and data terminal with remote control interface (RCI), developed around 1991 by Motorola in Seguin (Texas, USA). The device is compatible with STU-III and STU-II (KY-71) terminals and uses a KSD-64A as the Crypto Ignition Key (CIK). When used in STU-II compatible mode, a KEY can be loaded by means of a KOI-18 or KYK-13 key loader.

The device is similar in function to STU-III phone equipment and to the Motorola SECTEL family of secure phones, but its purpose is different. The STU-III/R has no handset or display and is not intended for direct operation by a user. Instead, it should be controlled by an External Remote Controller (ERC), which in most cases will be a secured PBX (exchange), called a RED SWITCH.

The STU-III/R will usually be mounted in a rack. The PBX communicates with it, via a serial RS232 interface, whilst audio signals (transmit and receive) are analogue (600 Ω terminated).
  
Motorola STU-III/R

When mounted in a 19" rack, two STU-III/R units can be mounted side-by-side. Speech from the secured PBX is digitised by means of an LPC-10 vocoder. It uses very little bandwidth, allowing it to be used over a standard analogue PSTN line, at the cost of reduced illegibility. The data is then encrypted by means of an NSA Type 1 algorithm. In STU-II compatible mode, this is SAVILLE.

Likewise, the encrypted LPC-10 data from the telephone line is first decrypted using the same NSA Type 1 algorithm, and then used to reconstruct (sythesize) the original speech again. The device has strict RED/BLACK separation, which is necessary to avoid RED (unencrypted) data from leaking to the BLACK (insecure) network. The price of a STU-III/R in 2005 was US$ 8227 [2].

MISSING — Crypto Museum has two STU-III/R units in its collection, but from both devices the crypto unit (key generator) is missing. These have probably been removed as part of the declassification procedure. For this reason, we are not able to bring the devices back to working condition. We are still looking for two suitable crypto boards for the restoration of these devices, so that they can be demonstrated again.  Contact us
Motorola STU-III/R
Front panel
Rear panel
Backup battery and zeroize switch
FILL connector and CIK receptacle
STU-III/T with KSD-64 CIK
Zeroizing the KEY memory
Backup battery install date
A
×
A
1 / 8
Motorola STU-III/R
A
2 / 8
Front panel
A
3 / 8
Rear panel
A
4 / 8
Backup battery and zeroize switch
A
5 / 8
FILL connector and CIK receptacle
A
6 / 8
STU-III/T with KSD-64 CIK
A
7 / 8
Zeroizing the KEY memory
A
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Backup battery install date

Controls and connections
The image below shows the front panel of the STU-III/R. It holds all controls plus a receptacle for the Crypto Ignition Key (CIK) and a socket for connection of a DS-102 fill device, such as the KYK-13 or the KOI-18. The latter is only needed when the STU-III/R is used in STU-II (KY-71) compatible mode. The unit is powered by an external Power Supply Unit (PSU) that is connected at the rear. Power is enabled with the Power switch at the front panel. When the unit is in operation, the internal KEY memory is retained by a backup battery that can be accessed from the front panel. It is installed behind a removable cap. KEY memory can be purged (ZEROIZED) at all times.


At the bottom right is a receptacle for the KSD-64 key storage device. This is also known as a KEYCEPTACLE. In STU-III compatible mode, the KSD-64 should be supplied with a valid Seed KEY (by registered courier). With the Seed KEY, the user can dial into a secret 800-number at NSA to have it converted into an Operational KEY. The Operational KEY is then split into two parts, one of which is stored inside the STU-III/R. The other part is stored on the KSD-64 which will then become the Crypto Ignition Key (CIK). From then on, the STU-III/R and the CIK are 'paired'.


All connections to external devices are at the rear (with the exception of the KEY FILL device, which should be connected at the front). At the bottom centre is a 9-pin DE-9/M receptacle marked J1 for connecting the external PSU. To its left is an RJ14 socket marked J6 for connection to the analogue PSTN line. At the top centre is a DB-25/S receptacle J4 with the Remote Control Interface (RCI). It carries digital control lines (RS-423A) and in/out analogue audio lines (600Ω) for connection to a secured local exchange (PBX). The Red Digital receptacle (J3) should also be connected to the PBX, if it can process digital in/out data directly to/from the LPC-10e vocoder.

Features
  • High quality voice, and high-speed data at 9600 baud (MRELP)
  • 4800 baud voice communication according to government standard CELP 3.1
  • Interoperable with STU-III
  • Interoperable with STU-II (KY-71) in Net Broadcast Mode
  • External modem connection (black)
  • Black digital alerting capability
  • Emergency ZEROIZE at front panel
  • Clear/secure or secure-only operation
  • Configurable 2/4-wire PSTN interface
  • Red digital voice output for digital conferencing
  • VOX or push-to-talk half-duplex operation
  • Simple user interface for FILL operations
  • Ruggedized enclosure for industrial and airborne environments
  • Wide range PSU (90-250V AC, 50-440 Hz)
  • AUTOVON and IVSN peemption tone detection (4th column DTMF)
Interoperable devices
STU-III Secure Telephone Unit - 3rd generation - any manufacturer
Secure Telephone Unit - 2nd generation (KY-71)
Secure Telephone Unit - 3nd generation - NATO version (KY-71D)
Philips Spendex-40 secure telephone for voice, fax and computer
Siemens/ANT/R&S Elcrovox 1/4
Siemens/ANT/R&S Elcrodat 5/4
Elcrodat
5/4
STK (Thales) TCE-5000
Setup
The diagrams below show the various configurations in which the STU-III/R could be used. In the simplest setup, only a handset with integrated Push-To-Talk (PTT) button could be connected directly to the Remote Control Interface (RCI). It allows secure conversations to be answered in half-duplex and full-duplex mode. It is also possible to use a modified telephone set for this.


In the default configuration however, the STU-III/R would be placed between an analogue subscriber line (POTS, PSTN) and the local analogue PBX inside a building. In this case, the PBX has analogue voice circuits, whilst it controls the STU-III/R via a digital serial RS423 port (RCI).


If the PBX has digital voice circuits, it could be connected directly to the red digital port of the STU-III/R. This would generally provide a better audio quality. In addition to the red digital port, the PBX would also be connected to the RCI port, to control the STU-III via its serial RS423 port. This configuration was also used for a secure teleconferencing setup.


In all of the above configurations, the analogue interface is used at the black side, as it is connected to an analogue PSTN (TELCO). The black signals are also available in digital form however, which can be useful when connecting the STU-III/R to an external MODEM.


In the above example, the STU-III/R is connected to an external modem, which in turn is connected to a RF transceiver (TRX). In most cases, RF links were used in half-duplex mode, which means that the user had to press a PTT button — integrated in the handset — when speaking, or that the PBX needed to have a VOX circuit.


Operation
STU-III compatible mode
In STU-III mode, keys are generated externally by a COMSEC authority, and are transferred to the device on a KSD-64 Key Storage Device.

Once the keys are loaded, the KSD-64 is converted into a Crypto Ignition Key (CIK) which is paired with the device. The CIK has to be installed to enable secure communication. Without the paired CIK, the STU-III/R cannot be used in secure mode.

 More about the KSD-64

  
KSD-64A installed in thge STU-III/R

STU-II compatible mode
In STU-II mode, keys are transferred to the device by means of a DS-102 key transfer device like the KYK-13 or the KOI-18. The image on the right shows the KYK-13 connected to the FILL port of the STU-III/R. The user must press the grey FILL button on the front panel of the STU-III/R to initiate a transfer.

In this mode, the KSD-64 is used as the CIK. The CIK is always paired with the devide and must be installed to enable secure operation.

 More about key loaders

  
Loading keys into the STU-III/R with a KYK-13

Zeroizing
When security is compromised, the keys inside the STU-III/R have to be purged immediately. By convention this is always a two-step or double-action procedure, such as pressing two buttons simultaneously. On the STU-III/R it involves pulling-out the ZEROIZE switch and placing it in the upper position.

To resume normal operation and allow new keys to be loaded into the device, the switch has to be returned to the lower position first.
  
Zeroizing the KEY memory

Backup battery install date
Backup battery with removed cap
Backup battery
B
×
B
1 / 3
Backup battery install date
B
2 / 3
Backup battery with removed cap
B
3 / 3
Backup battery

Block diagram
The diagram below shows how the STU-III/R was integrated in the existing infrastructure. The device consists of three compartments: a black side – connected to the outside world – a red side – connected to the equipment that must be secured – and a compartment that controls the data streams, the vocoder, the key generator and the encryption. A plastic KSD-64A key can be used as a fILL device and also as a Crypto Ignition Key (CIK). In STU-II compatible mode, an external FILL device (KOI-18 or KYK-13) is used to load the keys, whilst the KSD-64A is used as the CIK. After initialisation, the CIK is paired with the STU-III/R and must be installed for operation.


The device has an internal modem at the black side, which forms the interface between the digital lines to and from the device and an analogue 2-wire or 4-wire PSTN telephone line (J6). The black side is also available in digital form, so that it can be connected to an external modem (J5). The latter is typically used to connect an HF modem which in turn is connected to a radio transceiver.

At the red side, the signals are also available in analogue and digitial form, so that the External Remote Controller (ERC) — typically a secured telephone switch (PBX) — can either use the analogue audio lines (J4) or the digital data directly from the LPC vocoder (J3). The ERC can send commands (e.g. dial codes) to the STU-III/R via a serial RS232 that is line embedded in J4.


Click to see more

Parts
STU-III/R mainframe
Power Supply Unit
PSU
Power cables
Key Storage Device KSD-64 - Crypto Ignition Key (CIK)
CIK
Key FILL device KYK-13
Key FILL device KOI-18
Fill cable for KOI-18
Operating instructions
STU-III/R mainframe
The actual STU-III/R unit measures 324 × 267 × 81 mm and weights 5.7 kg. All controls are at the front, whilst the connections to the outside world are at the rear. When placed in a 19" rack, two units can be mounted side-by-side.

Although the device is intended for use in combination with a PBX, it is possible to wire a telephone unit or handset directly to the RCI connector (J4) for stand-alone use.

  
Motorola STU-III/R

Power supply unit
The STU-III/R does not have an internal mains power supply unit (PSU). Instead, it must be powered by the approved external wide-range PSU shown in the image on the right.

The primary side must be connected to the mains 90-265V AC. The secondary side provides necessary +5V, +12V and -12V DC voltages that should be connected to a 9-pin DE9/S receptable (J1) at the rear of the STU-III/R.

 Pinout of the 9-pin connector

  
Mains PSU

Power cables
The STU-III/R was supplied with two power cables: (1) for connection to the AC mains and (2) for connection to the power socket (J1) at the rear of the device. The latter is a 1:1 cable with a DE9/S connector at one end and a DE9/P at the other end. The cable must be shielded.

The mains cable shown here, is for connection to the AC mains network in Northern America. For other parts of the world, such as continental Europe, a different cable should be used.

  
Power cables

Crypto Ignition Key   KSD-64
To secure the key material inside the STU-III/R, all keys are stored in encrypted form, using an internally generated random key which is stored on a removable KSD-64 Key Storage Device (KSD) that is used as a Crypto Ignition Key (CIK).

Once the STU-III/R is initialised and valid keys are loaded into its key compartments, the CIK is paired with the device. Without the CIK, the device is useless. Furthermore, the CIK cannot be used to activate another STU-III/R device with which it is not paired.

 More information

  
PK64KB (black) and PK256KB (clear)

Key FILL device   KYK-13
When using the STU-III/R in STU-II compatible mode, a valid NET KEY must be loaded into the device by means of a key transfer device that supports 128-bit key material in DS-102 format, such as the KYK-13 shown on the right.

The device has a male and a female connector that are connected in parallel. It can be connected directly to the U-229 socket at the front panel, or via an optional fill cable.

 More information

  
KYK-13 key transfer device

Key FILL device   KOI-18
As an alternative to the KYK-13 it is possible to use the KOI-18 shown in the image on the right. It transfers the NET KEY from punched paper tape directly to the STU-III/R.

The device only has a male U-229 connector, and must therefore always be connected to the STU-III/R via the fill cable shown below.

 More information

  
KOI-18 with open lid

FILL cable
To connect the KOI-18 key transfer device to the STU-III/R, a special FILL cable must be used, such as the one shown in the image on the right. It can also be used between the KYK-13 and the STU-III/R.

The FILL cable consists of a 5-wire cable with a female U-229 connector at either end, wired 1:1. The cable is also used for transferring keys from a KOI-18 to a KYK-13 key filler.

  
FILL cable with two 5-pin U-229 connectors

Operating instructions
Each STU-III/R was supplied with an A5-size ring-bound booklet with instructions on how to setup, use and maintain the device.

The booklet contains full pinouts of the various connectors and provides some hints on the commands that can be used via the RCI port (J4).

 Read the manual

  
STU-III/R manual

Complete STU-III/R setup
Motorola STU-III/R
Mains PSU
Power cables
KYK-13 key transfer device
Loading keys into the STU-III/R with a KYK-13
KOI-18 with open lid
Loading keys into the STU-III/R with a KOI-1
C
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C
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Complete STU-III/R setup
C
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Motorola STU-III/R
C
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Mains PSU
C
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Power cables
C
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KYK-13 key transfer device
C
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Loading keys into the STU-III/R with a KYK-13
C
7 / 8
KOI-18 with open lid
C
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Loading keys into the STU-III/R with a KOI-1

Interior
The STU-III/R is housed in a ruggedised black die-cast aluminium enclosure, which consists of a compartmented frame with removable top and bottom lids. The identical top and bottom panels are held in place by 7 black screws each, plus two long screws that extend from top to bottom. At the bottom, these two screws are sealed to provide evidence that the case has been opened.

The bottom section, shown in the image on the right, is completely shielded off from the rest of the device. The main compartment contains one large PCB of which the solder side is visible here.

This board contains the TELCO interface, which connects the device to an analogue PSTN line. It also holds the LPC-10 vocoder. The board is connected to the PCBs at the top side, via a shielded DB25 connector in one of the corners. In the other corner is a small compartment that contains the receptacle for the KSD-64 CIK. At the center of the front is the red on/off switch.
  
Interior - bottom side

All other electronic circuits are at the top side of the device, shown in the image below. There are two large PCBs of which the upper one is visible here. It holds a microprocessor with RAM and firmware in EPROM — responsible for handling the RCI — plus the RED analogue audio interface.

The RED analogue signals and the digital RCI interface (RS232) are available on the DB25/S connector (J4) at the rear centre of the board. It is intended for connection to the local PBX.

The far side of this board also holds part of the BLACK digital interface, which is available on a DB25/P connector (J5) at the rear. It is physically separated from the RED and RCI interfaces to avoid side channel leakage. The upper board is connected to the other PCB — mounted below it — and to the rest of the device via several flat­cables and flying leads at the edges of the PCB.
  
Interior - top side

Note the tamper switch, which is located just behind the front panel, towards the centre. The switch is engaged as soon as the top panel is removed, and ensures that all cryptographic material held inside the device's CMOS RAM is purged. It has the same effect as ZEROIZING.

The upper board is held in place by 10 black screws around the edges plus the 4 retaining screws of the RCI and BLACK digital connectors. After removing these screws and disconnecting the various cables around the edges, the upper board can be removed as shown on the right.

The lower board is slightly smaller than the upper one. It holds the RED digital interface and the encryption unit. Towards the front of the PCB is a large 64 pin socket into which normally the key generator is installed. Unfortunately this unit has been removed from the device shown here.
  
Red digital board with removed crypto board (missing)

This means that this particular device cannot be used or demonstrated anymore. The missing key generator is a small daughter card that is similar (but not identical) to the key generator of the Motorola STU-III shown here. The card should be fitted in the large 64-pin socket on the lower board and is held in place by two screws: one at the centre and one next to the connector.

Note that the lower board is almost identical to the lower board inside the Motorola SECTEL 2500 (STU-III) desktop telephone set, which suggests that the products were developed more or less simultaneously. 1 In the STU-III/R, the board is rotated by 90° compared to the SECTEL STU-III.

  1. It is likely that the STU-III/R hardware is a spin-off from the STU-III hardware development.

Removed serial number
Broken seal
Interior - bottom side
Wire modification (additional ground)
Interior - top side
Interior - top view
Black digital / Red analogue interface board - solder side
Wire modification
Several modifications in the black interface
Black interface with several wire modifications
Main processor with RAM and EPROM memory
Red analogue interface
Various modifications in the black interface
Black digital / Red analogue interface board - solder side
Wire modifications at the bottom
Red digital board with removed crypto board (missing)
FPGA and firmware on the red digital board
Crypto board removed
Hitachi processor with firmware
Shielded red digital wiring
Tamper switch in the top section
KSD-64 receptacle in separate compartment
Key generator - component side
Key generator board - solder side
D
×
D
1 / 24
Removed serial number
D
2 / 24
Broken seal
D
3 / 24
Interior - bottom side
D
4 / 24
Wire modification (additional ground)
D
5 / 24
Interior - top side
D
6 / 24
Interior - top view
D
7 / 24
Black digital / Red analogue interface board - solder side
D
8 / 24
Wire modification
D
9 / 24
Several modifications in the black interface
D
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Black interface with several wire modifications
D
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Main processor with RAM and EPROM memory
D
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Red analogue interface
D
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Various modifications in the black interface
D
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Black digital / Red analogue interface board - solder side
D
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Wire modifications at the bottom
D
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Red digital board with removed crypto board (missing)
D
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FPGA and firmware on the red digital board
D
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Crypto board removed
D
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Hitachi processor with firmware
D
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Shielded red digital wiring
D
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Tamper switch in the top section
D
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KSD-64 receptacle in separate compartment
D
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Key generator - component side
D
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Key generator board - solder side

Restoration
When we received our two STU-III/R units in January 2023 [1], they were in the state visible in the images. That means that no restoration or cleaning was required for the time being. However, when inspecting the interior, we discovered that the crypto hearts (i.e. the key generators) were removed from both units, probably as part of the declassification procedure. This means that we are unable to test and demonstrate the units, until we find two STU-III/R key generators. 😢


Connections
At the rear of the device are 4 sockets for connection to the outside world, marked J1 and J3 - J5. Another connector is at the front panel, and is used for connection of a key fill device when the device is used in STU-II compatible mode. The wiring of the connectors is specified below.

Power   J1
  1. SSB
    Internal control bus for diagnostic monitoring
  2. +5V
    +5V, 2.5A
  3. +5V Sense
  4. +5V Sense
    Return (ground)
  5. -12V
    -12V, 300 mA
  6. +5V
    +5V return
  7. GND
    Ground
  8. +12V
    +12V 400 mA
  9. ±12V
    +12V return
Red Digital   J3
This connector carries the digital output from the internal LPC-10e vocoder, which may be passed to a PBX capable of handling digital voice data from an RS232 port. The connector also carries a digital input, so that the PBX can send its digital data straight to the STU-III/R without converting it to the analogue domain first.

  1. AA
    Protective Ground (GND)
  2. BA
    Transmitted Data (TXD)
  3. BB
    Received Data (RXD)
  4. CA
    Request to Send (RTS)
  5. CB
    Clear to Send (CTS)
  6. CC
    Data Set Ready (DSR)
  7. AB
    Signal Ground (GND)
  8. CF
    Data Carrier Detect (DTD)
  9. DB
    Transmitter Signal Element Timing
  10. DD
    Receiver Signal Element Timing
  11. CD
    Data Terminal Ready
Remote Control Interface (RCI)   J4
The Remote Control Interface (RCI) allows the device to be controlled remotely. This connector is typically wired to an external secured PBX which can use the STU-III/R to encrypt and decrypt calls to and from the outside world. The connector carries a serial port through which the PBX can dial out, similar to operating the keypad on a telephone set. It also holds the analogue voice in/out lines and a couple of control signals.

  1. AA
    Protective Ground (GND)
  2. BA
    Transmitted Data (TXD)
  3. BB
    Received Data (RXD)
  4. CA
    Request to Send (RTS)
  5. CB
    Clear to Send (CTS)
  6. CC
    Data Set Ready (DSR)
  7. AB
    Signal Ground (GND)
  8. CF
    Data Carrier Detect (DTD)
  9. PTT
    Push-to-Talk
  10. LPCIN
    LPC Input Enable
  11. TXPAUD
    Transmit Audio
  12. RXAUD
    Receive Audio
  13. CD
    Data Terminal Ready (DTR)
  14. RXAUDRET
    Receive Audio Return
  15. TXAUDRET
    Transmit Audio Return
Black Digital   J5
This connector holds the digital in/out signals of the BLACK side. It bypasses the internal modem and can be used to connect an external one, such as a HF modem for communication via radio.

  1. AA
    Protective Ground (GND)
  2. BA
    Transmitted Data (TXD)
  3. BB
    Received Data (RXD)
  4. CA
    Request to Send (RTS)
  5. CB
    Clear to Send (CTS)
  6. CC
    Data Set Ready (DSR)
  7. AB
    Signal Ground (GND)
  8. CF
    Data Carrier Detect (DTD)
  9. DB
    Transmitter Signal Element Timing
  10. DD
    Receiver Signal Element Timing
  11. CD
    Data Terminal Ready
TELCO   J6
At the rear of the device is a 6-pin RJ-25 (6P6C) modular socket for connection to a 2-wire or 4-wire subscriber line. When connecting to a 2-wire line, an RJ-11 connector can be used, as only the middle two contacts (3 and 4) are needed. The pinout is as follows:

  1. TIP
    Line (A)
  2. RING
    Line (B)
When connecting to a 4-wire line, the pinout is as follows:

  1. T1
    TX analogue to provider (A)
  2. R1
    RX analogue from provider (A)
  3. R2
    RX analogue from provider (B)
  4. T2
    TX analogue to provider (B)
The TELCO socket (J6) can also be wired to an 8-position RJ-45 (8P8C) interface by using an optional adapter. In this situation all 6 contacts of the RJ25 socket are used. Note that the extra pins (1,2, 5 and 6) can only be used when RJ45 and MI/MIC are enabled in ERC.

  1. Resistor to pin (6) to adjust the output level 1
  2. MI/MIC (off-hook detection) 2
  3. TIP
  4. RING
  5. MI/MIC 2
  6. Resistor to pin (2) 1
  1. Adjust output level between 0 and -12dBm into 600Ω. This option requires RJ-45 to be enable in ERC.
  2. Pins 2 and 5 are shorted when the handset is off-hook. This option requires MI/MIC to be enabled in ERC.

FILL interface
At the top right of the front panel is a 5-pin socket for an U-229 connector. This is a standard DS-102 FILL interface used on NATO and other military communications devices. The pinout is specified when looking into the receptacle.

 More about the U-229 connector
 More about the DS-102 fill standard
  1. GND
    Ground
  2. -
    unused
  3. ACK
    FILL request acknowlegment
  4. DATA
    Serial fill data into STU-III/R
  5. CLK
    Serial clock into STU-III/R
Specifications
  • Device
    Secure voice and data gateway
  • Purpose
    PBX encryption/decryption, secure conferencing
  • Manufacturer
    Motorola
  • Country
    USA
  • Users
    US Government, NATO
  • Encryption
    NSA Type 1, SAVILLE
  • Modes
    STU-III, STU-II
  • CIK
    KSD-64
  • FILL
    DS-102
  • Backup
    3V 1/3N Lithium (at front panel) - 2 years
  • Approval
    USA, Belgium, Germany, UK
  • Temperature
    -20°V to +70°C
  • Storage
    -55°C to +85°C
  • Humidity
    95% non-condensing
  • Altitude
    35,000 feet
  • Dimensions
    324 × 267 × 81 mm
  • Weight
    5.7 kg
  • Price
    US$ 8227 in 2005 [2]
Modem
  • V.32
    4800 and 9600 baud with Echo Cancelling
  • V.26
    2400 baud with Echo Cancelling
  • Input
    +6 to -43 dBm
  • Output
    0 to -12 dBm (adjustable)
Secure data transmission
  • Async
    70, 110, 300, 500, 1200, 2400, 4800, 9600 baud
  • Sync
    2400, 4800, 9600 baud
  • Data
    RS232C compatible
Speech processor   Vocoder
  • 2400 baud, interoperable FED-STD-1015
  • 4800 baud, interoperable FED-STD-1016
  • 9600 baud, Motorola proprietary
Interfaces
  • Black
    Analogue: PSTN 2- or 4-wire TELCO or Autovon
    Digital data: RS232C
  • Red
    Analog voice: 4-wire balanced 600 Ω
    Digital voice: RS-232C
  • Remote
    RS-423A
Power supply unit
  • Input
    90 to 265 C/AC, 50 to 440 Hz
  • Current
    305 mA at 117V
  • Fuse
    GMC 1A/250V
  • Dimensions
    165 x 114 (140) 1 x 64 mm
  • Weight
    528 grams
  1. Including mounting tabs.



Documentation
  1. STU-III/R, Operation, Installation and Maintenance Manual
    Motorola Inc., March 1991.

  2. STU-III/R Interface Control Document — WANTED
    Doc. No. 5983-B004-001.
References
  1. Anonymous, STU-II/R terminals - THANKS !
    January 2023.

  2. TSG, Approved Telephones - Pricelist
    TSG Standard 6, July 2005.
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Crypto Museum. Created: Wednesday 04 January 2023. Last changed: Saturday, 11 February 2023 - 23:39 CET.
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