ATNF VLBI Wiki

Technical Notes

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

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

• 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.