PaSD Tango devices

The Power and Signal Distribution (PaSD) system is controlled and monitored via a number of Tango devices, described in the following sections:

• Field station
• PaSD bus
• FNDH
• SMART Box
• FNCC

For more detailed information on the hardware the Tango devices are interfacing with, refer to the PaSD Monitor & Control System Firmware Description document on the SKAO ALIM system.

Overview of the PaSD system

Each of the stations in SKA-Low will consist of 256 antennae distributed in a circle 40m in diameter. Each of the 256 antennae is connected via coaxial cable to a nearby SMART Box, located on the ground screen between the antennae. The SMART Box delivers DC power over the coaxial cable to an LNA (low noise amplifier) in the antenna, and converts the incoming radio frequency (RF) from the antenna into an optical RF signal on an outgoing fibre.

Each station will typically have 24 SMART Boxes in the field, and each SMART Box has 12 antenna ports, making a total of 288 available inputs for antennae. Since there are only 256 antennae in a station, not all of the ports on each SMART Box will necessarily be in use at any given time. The remainder are available as spares in case of faults.

Each SMART Box has an internal low-speed, low-power microcontroller to monitor temperatures, currents and voltages, and to switch antennae on and off as required. Power comes from a single Field Node Distribution Hub (FNDH) for the entire station. A low-speed (9600 bps) low-RFI (radio frequency interference) communications link to the SMART Box microcontroller is carried over the 48Vdc power line.

Each station has a FNDH to provide power and communications for the SMART Boxes, and to act as a fibre aggregation point for the fibres carrying RF signals from the SMART Boxes to go back to the control building. The FNDH is powered from 240 VAC mains power, and has two 48Vdc power supplies for the SMART Boxes, and a 5V power supply for the local microcontroller.

The FNDH has 28 possible slots in which a Power and Data over Coax (PDoC) card can be installed, each providing a port to which a SMART Box can be connected. Again, not all of the slots will have PDoC cards installed at any given time, and not all PDoC cards will be connected to a SMART Box. The extra ports are provided for redundancy.

A single fibre pair from the control building to the FNDH is connected to an ethernet-serial bridge (via a media converter), allowing the monitoring control and calibration system (MCCS) in the control building to send and receive data over the network to a given FNDH (with a unique IP address). The serial data from the ethernet-serial bridge is passed to the local microcontroller in the FNDH, and shared with all of the SMART Boxes via a multi-drop serial bus. When the MCCS sends data, every device on the shared bus (the FNDH microcontroller and all of the SMART Boxes in the station) receives it.

The microcontroller in the FNDH monitors temperatures, voltages and currents in the FNDH, and allows the 28 possible output ports to be switched on and off. It does NOT communicate with the SMART Boxes at all. Instead, the SMART Boxes are controlled by the MCCS in the main building, talking to them directly via serial traffic over the shared serial bus.