Converting signals for transport

Once AAVS1 was completed, it became clear that there were many disadvantages to having a signal aggregation unit (the APIU) in the middle of the antenna field, and that their hybrid power and signal cables were needlessly complex. However, the early signal conversion to fibre remained a necessary part of the SKA-LOW system, so a new component was required to bridge this gap in functionality. Engineers from INAF and CIRA worked in collaboration to design what is known as the SMART boxes.

These 'Small Modular Aggregation and RFoF Trunk' devices convert coaxial cable RF signal to RF over fibre. With the SMART box, RF signal from each individual antenna is directly transported via fibre optic cable to a Tile Processing Module (TPM) inside the MRO control building, located approximately 5 km away from the field node where it resides. The main component of a SMART box is the front-end modules, handling the copper-fibre conversion, but they also supply each antenna amplifier with 5V power.  The principal components associated with the SMART box are shown in the schematic in Figure 3.

SMART boxes have been deployed on both AAVS1.5 and EDA2.

Figure 1: Inside a SMART box, showing the power transformer, the front-end modules for coax-to-fibre conversion, and the output fibre fed through a waveguide

Figure 2: Cabling up a SMART box on EDA-2

Figure 3: A top-level diagram of the SMART box system

Figure 4: A completed SMART box on AAVS1.5