The SKA Bridging Phase, AAVS1.5

With the successful completion of the SKA_LOW's element-level Critical Design Review (CDR) in 2018, the project now has sufficient momentum to carry it through the all-important transition from design to delivery.

This transition is taking place with the bridging phase, an on-site roll-out of 256 SKALA-4.1 antennas in a field node placement similar to AAVS1. This new field node is denoted AAVS1.5, and incorporates technology that is more easily compared to the MWA/EDA than to AAVS1. 

These SKALA-4.1 antennas no longer use a hybrid copper/fibre cable for data transportation and power delivery, but instead a simple coaxial cable like those in the MWA. Data from a group of 16 antennas (much like an MWA tile or EDA cluster) is then combined in a SMART box ('Small Modular Aggregation & RFoF Trunk'); this box contains front-end modules that convert the coaxial cable RF signal to fibre, suitable for transport. The SMART boxes sit on the field node with the SKALA antennas and have the same physical chassis as an MWA beamformer. These SMART boxes have also been deployed for the same purpose in EDA-2.

Signal aggregation no longer happens in a central APIU either; a large shielded container now sits on the north side of the node for easy access. This container, called the Field Node Distribution Hub (FNDH), has a unit to deliver power to the node and one that combines and sends the 16 SMART box signals to the control building. One more piece of receiving equipment in the correlator room converts these signals back to copper, and then they can be passed into Tile Processing Modules (TPMs) where data computational tasks begin.