CABB for VLBI
The ATCA CABB backend currently interfaces with the existing ATNF DAS. This severely limits total bandwidth and flexibility of the system. Long term the ATNF DAS needs to be retired and CABB backend used directly for VLBI.
The current system uses a special "single channel" 64 MHz filter mode. Ideally all standard "continuum" modes could be used for VLBI with bandwidth/channel options of 1,4, 16 or 64 MHz.
To support VLBI observing the following is required
- Flexible tied array setup with 1--6 antennas
- Tied array working with all standard continuum filter band modes (ie 1--64 MHz channel widths)
- Flexible inclusion of recorded channels over at least 2 GHz of bandwidth
- Output data over 10 Gbps Ethernet as UDP packets
- VDIF packet headers
- Packet sizes to conform to VDIF requirements, specifically an integral number of packets/sec
- 10 Gbps Ethernet (or infiniband) switch to aggregate data streams to a high speed recorder or for eVLBI.
- Tsys monitoring
- Linear->circular conversion (optional, pure linear possible also)
- Appropriate phase/amplitude gain corrections before tied array to ensure telescopes are tied optimally (ie a bandpass correction)
Potential extra functionality
- Multiple simultaneous tied array beams