update on lba technical developments cass chris phillips 11 october 2013

Update on LBA Technical Developments

CASS

Chris Phillips11 October 2013

Linear to Circular conversion

VLBI TECHNOLOGY KOREA - Chris Phillips

Linear Polarizations•While VLBI standard is to use circular

polarizations, linear polarizations are “better”:•Easier to make wideband receivers•Better separation between polarizations•Need to convert linear to circular for

compatibility with other antennas and calibration and analysis software

• RF and IF hybrids typically narrow band

3 |


Digital Polarization Conversion• Digital polarization conversion can overcome

wideband problem• Has worked very well with ATCA for 20 years• Conceptually easy:

• Align amplitude, phase and delay between two polarizations• Rotate phase of one polarization by 90 degrees• Simply add and subtract two linear polarizations• Essentially same as hybrids• Ideally added to VLBI DAS firmware but never

implemented

4 |


L2C in DiFX• Can we do circular conversion within DIFX• Very “cheap” to do conversion after FFT in

correlator•Biggest DIFX change is to get calibration values into

correlator•Side benefit is polarization dependent delay offset

5 |

VLBI TECHNOLOGY KOREA - Chris Phillips6 |

FFT Xmult

Amplitude &Phase Correction

Add and subtract

FFT Xmult


Status•One session at ASKAP, new receiver installed with

linear rather than circular polarizations (no hybrid)• ASKAP no noisecal to aid calibration

•Also very good isolation between polarizations•Need to use VLBI cross correlations for calibration•Delays well calibrated but problem getting phase

difference• Seeking help to work out calibration problem

7 |

Xcube Wideband VLBI Backend

X-cube Data Logger• 100% COTS hardware recorder

•Proprietary software• 16 Gbps capability

•External replaceable storage modules–Up to 32 TB packs

•Management of slow or broken disks• Standard file-systems

Back View of Chassis

© 2010 XCube R&D

Ethernet(2 x 10Gb/s)

SAS Disk Cables(16 x 300MB/s)

Self Contained Disk PackCooling and Power


Xcube Internals• “Mix and Match” approach to plug in devices

•1 or 2 dual 10 Gbps Ethernet– Intel SPP+ Optical module needed

•Can support up to 4 disk modules•GPU for number crunching•Other options available

–However may run out of slots….

11 |


Xcube tests• Seems to run fine up to around 8 Gbps/diskpack (as

advertised)• Basic Ethernet recorder, similar to Mark5C

•However this is NOT a feature•Records full Ethernet frame – allows post recording

filtering• Simple easy to use control program

•Can control remotely via XML messages•Does not allow simultaneous recording and reading•Have not started using for operations yet

12 |


Data access•Data cannot be accessed directly

•Cannot directly use standard transfer software such as ftp, gridftp, tsunami-udp etc

• Supplied with easy to use library to read data from diskpack•Can copy “raw” files and decode on a different system• Easy to write code to copy off disk• Time filtering etc available not tested

13 |


Xcube sampler• 4 Channel 1 Gsample/sec

•4x512 MHz IFs• For each IF 16 channel polyphase filterbank

•32 MHz channels, complex “double sideband” sampling• Re-quantization to 2 bit• 8 Gbps VLBI

14 |


Xcube Issues•Only 8 or 4 Gbps modes

•No channel sub-selection• Clumsy quantization threshold setting

•No automatic gain adjustment•No total power monitoring•No eVLBI option• Initial firmware version had synchronization

issues…•Fixed now and “zero baseline” fringes to existing LBA

DAS

15 |

VLBI TECHNOLOGY KOREA - Chris Phillips16 |


Next Steps•Working with Xcube to transition to “production”

suitable operation•Probably combination of Firmware and software

changes• Roll out at Parkes and ASKAP

•Mopra when satisfied system is usable• ATCA Xcube recorder

•All digital system

17 |


ATCA CABB• ATCA correlator is now 2x2 GHz (dual pol)

•32 Gbps 2 bit capable• 10 Gbps (x16) Ethernet output available• Engineer assigned to implement 10 GbE output of

tied array• But wrong clock on board….

•Requires “full board” heat sink to be removed from every board

18 |


Oz eVLBI•No major changes recently

•1 Gbps between ATNF observatories•1 Gbps shared routed to elsewhere• 10 Gbps routed connection “soon”• 40 Gbps test circuit between Parkes and ATCA• 10 Gbps upgrade to observatories cheap but no

funding and VLBI only user

19 |


AARnet4• 80x100 Gbps from Adelaide to ASKAP (MRO)• 80x100 Gbps wavelengths on East coast by

middle 2014• 2x40 Gbps Sydney to USA

•Upgraded to 100 Gbps

20 |


Mopra•Mopra operational again after fires which

devastated control room• Equipment room survived with relatively little

damage

21 |

Astronomy and Space ScienceChris Phillipst +61 2 9123 4567E [email protected] www.csiro.au/atnf

ASTRONOMY AND SPACE SCIENCE

Thank you

update on lba technical developments cass chris phillips 11 october 2013

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