OsmocomTETRA

The Motorola Dimetra EBTS is a TETRA Base Station design.

We have been able to get our hands on some of them.  This page documents our knowledge about the units, their configuration and how to use them.

== Hardware ==

=== Motorola Dimetra Base Radio (T5931A) ===

The Base Radio (BR) is a modular design in a 4U case, consisting of the following modules:

==== Power Supply (CPN1031B) ====

As the name suggests, it is merely a power supply, converting from the 48 V input to the various voltages required within the radio

==== Controller (CAE010CMX) ====

This is s small PowerPC based embedded system.  It communicates with the TETRA Site Controller (TSC) over 10-Base-2 Ethernet

and controls all the other units of the Base Radio via the backplane of the BR cabinet.

It has the following connections:

 * RS-232 on the back of the BR

 * RS-232 on the front of the BR

 * Site Alarm I/O on the back of the BR

 * 10-Base-2 Ethernet on the back of the BR (BNC)

 * Clock input on the back of the BR (BNC)

==== 3x Diversity Receiver (CTX1090A) ====

This is the receiver.  It has three antenna inputs in order to use antenna diversity for additional signal gain.

The received and demodulated TETRA bursts are forwarded to the Controller via the BR backplane.

==== Exciter (CLN1510A) ====

This is the transmitter.  It receives TETRA frames from the Controler via the backplane and encodes/modulates them.  The output

is fed into the power amplifier over a SMA jumper connection on the back of the base radio.

==== Power Amplifier (CTX1030A) ====

This is a RF power amplifier, used to generate a high-power signal from the output of the exciter.

It has three coaxial connections on the back, which are used as follows:

 * input from the exciter

 * feedback from PA into the exciter

 * actual RF power output (towards antenna)

=== Integrated Site Controller (CLN1480A) ===

This is a unit that interfaces up to 8 Base Radios with the core network of the Dimetra TETRA network (SwMI).

Hardware-wise, it is a PowerPC based system, looking very much like an old-fashioned PC mainboard with

both ISA and PCI slots.

The mainboard houses the PowerPC CPU and it has slots for RAM.

There are some extension cards plugged into the system:

 * Clock generation card (ISA, full length).

  * has an integrated GPS receiver, to which you attach a GPS antenna

  * generates the reference 5MHz clock distributed over Coaxial cable to the Base Radios

 * Ethernet Card using DEC tulip chipset (PCI)

  * This card is what talks to the Base Radios (BR) via 10-Base-2

 * Unknown card with RJ-45 jack (REDUND) on the back.  Might be E1

There are further inputs and outputs on the system:

 * A DB-15 jack for X.21 synchronous serial backhaul (2048Mbps)

 * FIXME

 * A RS-232 serial port for local configuration

=== RF Distribution System (CFX4041A) ===

This is a sophisticated combiner for the high-power output signals of the PA of up to 4 Base Radios.

In order to ensure optimal impedance matching, the combiner is mechanically tuned by electrical motors

which are controlled by some control logic.

The combiner inside the system has the following connections (external connections in '''bold'''):

 * '''4 high-power radio input ports''' (N socket on the front, one close to each motor)

  * this is where the RF signal emitted by the PA of the BR enters

 * 4 RF taps, one for each of the high-power radio inputs

  * they are connected to the controller unit attached to the inside of the front lid

 * 1 high-power radio output port (N socket)

  * this output is connected to a power meter inside the same cabinet

 * 4 stepper motor electrical connections

  * connected to the controller unit attached to the inside of the front lid

 * RS-232 serial line for control+monitoring

  * this is a DB-9 port of the controller unit attached to the inside of the front lid

  * interconnected to one of the Base Radios (typically BR1) inside the rack

The flow of the signals is as follows:

 * RF from the PA enters at the four combiner inputs

 * combined RF output leaves through central output of the combiner, from where

 * it is routed to the FR power meter

 * whose output socket is routed to the transmit antenna (or a duplexer in case of a shared Rx/Tx antenna)

{{{

#!graphviz

digraph G {

  graph [ rankdir = LR  ];

  //{ rank=same; combiner; controller; };

  br1_pa_out -> combiner

  br2_pa_out -> combiner

  br3_pa_out -> combiner

  br4_pa_out -> combiner

  combiner -> power_meter

  power_meter -> tx_antenna

  combiner -> controller [ dir=both color=red ]

  power_meter -> controller [ color=red ]

  power_meter [ shape=box ];

  combiner [ shape=box ];

  controller [ shape=box ];

}

}}}

=== Rx LNA Multicoupler (CRX102A) ===

The purpose of the Rx LNA multicoupler is to amplify the received signal from the antennas, and split

the signal so each Base Radio is attached to each antenna:

{{{

#!graphviz

digraph G {

  graph [ rankdir = LR ];

  antenna1 -> lna1

  antenna2 -> lna2

  antenna3 -> lna3

  lna1 -> multicoupler1

  lna2 -> multicoupler2

  lna3 -> multicoupler3

  multicoupler1 -> br1_rx1

  multicoupler1 -> br2_rx1

  multicoupler1 -> br3_rx1

  multicoupler1 -> br4_rx1

  multicoupler2 -> br1_rx2

  multicoupler2 -> br2_rx2

  multicoupler2 -> br3_rx2

  multicoupler2 -> br4_rx2

  multicoupler3 -> br1_rx3

  multicoupler3 -> br2_rx3

  multicoupler3 -> br3_rx3

  multicoupler3 -> br4_rx3

  lna1 [ shape=box label="LNA 1" ];

  lna2 [ shape=box label="LNA 2" ];

  lna3 [ shape=box label="LNA 3" ];

  multicoupler1 [ shape=box ];

  multicoupler2 [ shape=box ];

  multicoupler3 [ shape=box ];

}

}}}