Table of contents
C212A Correlation Report
General information
- Session info: http://www3.mpifr-bonn.mpg.de/div/vlbi/globalmm/
- Station feedback: http://www3.mpifr-bonn.mpg.de/div/vlbi/globalmm/sessions/oct21/feedback_oct21.asc
Fringes
| Station | Code | Fringes | Plots | Comments |
|---|---|---|---|---|
| Ef | B | yes | ||
| Pv | P | yes | ||
| On | X | yes | ||
| Ys | Y | yes | ||
| Mh | Z | yes | ||
| Br | b | yes | ||
| Fd | f | yes | ||
| La | l | yes | ||
| Nl | n | yes | ||
| Ov | o | yes | ||
| Kp | k | yes | ||
| Pt | p | yes | ||
| Mk | m | yes | ||
| Sc | s | 7mm only | ||
| Hn | h | 7mm only | ||
| Gb | G | yes | Problems with vdif thread offset | |
| Nn | N | yes | ||
| Ky | y | |||
| Ku | u | yes | ||
| Kt | t | yes |
Notes
Ky: File /data/c212a/ky/c212a_KVNYS_274071501.vdif VDIF summary failed with return value -5
Kt: File /data/c212a/kt/c212a_KVNTN_274070001.vdif VDIF summary failed with return value -5
GBT issue with RCP polarization
Issue: Strong GBT fringes in LCP found but no detection in RCP (tested on scans 189 and 191).
Diagnostics: Inspection of the VDIF structure shows 8 threads as expected. However the threads with odd IDs (representing LCP channels) are offset considerably (> 150 frames). The suspicion was that RCP frames possibly get dropped by DiFX due to these gap sizes exceeding the read buffer sizes (even though this seems unlikely because of the even-threaded data yields fringes).
Test 1:
To check whether the RCP data in principle is OK the v2d setup for GBT was split into two separate datastreams; one for LCP and one for RCP:
ANTENNA GB {
datastreams=GBRCP,GBLCP
}
DATASTREAM GBRCP {
file=/mark6-06_fuse/1/C212A_GB_No0762
format=INTERLACEDVDIF/0:2:4:6/5032/2
}
DATASTREAM GBLCP {
file=/mark6-06_fuse/1/C212A_GB_No0762
format=INTERLACEDVDIF/1:3:5:7/5032/2
}
Correlation still yielded no RCP fringes (all WEIGHTS 0) with .difxlog summary:
mark6-06 INFO VDIF multiplexing statistics: nValidFrame=153 nInvalidFrame=0 nDiscardedFrame=0 nWrongThread=18421482 nSkippedByte=0 nFillByte=0 nDuplicateFrame=0 bytesProcessed=92697667320 nGoodFrame=38 nCall=8661 mark6-06 INFO VDIF multiplexing statistics: nValidFrame=9938486 nInvalidFrame=0 nDiscardedFrame=359095 nWrongThread=153 nSkippedByte=0 nFillByte=0 nDuplicateFrame=8851360 bytesProcessed=92697667320 nGoodFrame=2482554 nCall=23029 mark6-06 ERROR One or more wrong-threads were identified. This may indicate a correlator configuration error. mark6-06 ERROR One or more wrong-threads were identified. This may indicate a correlator configuration error. mark6-06 ERROR One or more duplicate data frames (same time and thread) were found. This may indicate serious problems with the digital back end configuration.
WEIGHTS for LCP are around 0.94. This might indicate also problems in LCP thread(s).
Test 2:
The VDIF file was split into two separate files using modifyVDIF:
modifyVDIF --extract=6,4,2,0 /mark6-06_fuse/1/C212A_GB_No0762 /data/c212a/gb/C212A_GB_No0762_RCP modifyVDIF --extract=7,5,3,1 /mark6-06_fuse/1/C212A_GB_No0762 /data/c212a/gb/C212A_GB_No0762_LCP
The produced files vary largely in size:
1066784 11. Mär 09:56 C212A_GB_No0766_RCP 154581691424 11. Mär 10:09 C212A_GB_No0766_LCP
Using the separated files for correlation still results in 0 WEIGHTS and no fringes in RCP.
Current conclusion: RCP data is corrupted and cannot be recovered.
