What's inside a MTS2?

A little story

When I was a kid, my parents had a hard time buying me stuff that ran on electricity. My grandfather once bought me a portable black-and-white TV, to their horror; within a months I had opened it, just to look at what's inside. My cousin gave me an Atari - that too got opened to see what a Microprocessor looked like.In fact I cannot think of any piece of kit I had, up until my early twenties, than didnt get opened for one reason or another.

This fascination with looking at "techy" stuff continues until today, and although I am able to resist opening our flatscreen at home, I'm still curious to look inside radio stuff.

Some Background

A Motorola Dimetra (TETRA) system, consists of a one ore more Mobile Switching Office(s) or MSO. Outside of Motorola, this is known as a SwMI.

The MSO is connected to any number of Base Stations (or RF sites) via IP. There are essentially three models of Dimetra Base Stations: MTS1; MTS2 and MTS4.

I will go into the above in another post some time.

The MTS1 is a self-contained Base Station that can be mounted outdoors; on the wall or on a pole. It supports one carrier. The MTS2 supports 2 carriers and the MTS4 supports 4*.

The MTS2

Below is a picture of the MTS2 with its front door in place:

Removing the front door reveals the internal workings (i.e. the interesting stuff):

This specific configuration here is rather interesting because it has been set up with triple diversity. I can tell because of the choice of components in the RFDS section at the top and because each Base Radio has three receiver cables going to it. Also, somehow they left out the fans when this picture was taken - it's not critical but the RF site where this is installed will need extra cooling (an air conditioned room will do fine).

In the RFDS section above, there are three receiver multicouplers (top left and middle). Each multicoupler is connected to an antenna socket on the top at the back of the cabinet. When installed, this MTS2 will use three antennas (2 RX only and 1 TX+RX).
Each multicoupler provides one receive signal to to each Base Radio - so each Base Radio has three RX inputs.

On the top right is the transmitter combiner. In this case it is a hybrid combiner. The output of the Hybrid Combiner feeds a Duplexer (just below the third Multicoupler) which is in turn connected to one of the antenna sockets at the back.

Since this is a MTS2, there are two Base Radios. As the name suggests, they produce the TETRA signaling and RF signal and receive inbound signals from the radios.

On the front there are three RX connectors; one TX connector and a connection for DC power. There is also three Ethernet connectors - two for the Site Controller and one for service - and status LEDs.
There are two Ethernet connectors for the Site Controller becuase it's possible to have a redundant (backup) Site Controller for each Base Radio.

Since the Base Radios run on DC, there needs to be a Power Supply.

The Power Supply does more than just provide DC power. It also manages the batteries, if connected, and fans. If the MTS2 is supplied with a Auto Tune Cavity, it will also provide power to the stepper motors.

Lastly, the Site Controller manages all on site activities and communicates with the MSO. It also has a GPS antenna since TETRA is very frequency and phase critical and needs a stable clock source (of course if GPS fails, it can generate its own clock but will less accuracy).

Here's a video I made a while back showing a Dimetra Express system. This is based on the MTS2 hardware but the 2nd BR slot is used by the MSO.

What's Dimetra Express? Here's a short overview.