DFB3 for VLBI
Technical Notes
Current State
The Parkes Pulsar backend DFB3 has a baseband mode, used with APSR. This instrument fulfills the basic requirements of a broadband VLBI backend.
- 1 GHz or 256 MHz front end bandwidth
- Divide by 16 filterbank (ie 64 MHz channels with 1 GHz front end).
- 16 MHz channels with 256 MHz front end
- Bits selectable from 1-8
- UDP data transport with simple 24 byte timing header
Requirements
To convert to system suitable for VLBI the following changes are needed
- More filterbank options (divide by 32 and divide by 64 have filters already designed)
- Giving 32/16 MHz channels with 1 GHz front end or 8/4 MHz with 256 MHz front end)
- VDIF packet headers
- Packet sizes to conform to VDIF requirements, specifically an integral number of packets/sec
- Tsys monitoring
Potential extra work
- Linear->circular conversion (optionally)
- including calibration of x-y phase correction
- Single stage filter design (not the current "high resolution" filter followed by a reverse filter.
