S3111b VLBI experiment. Phase jumps at GBT.


GBT in a 24 hour experiment VLBA_GBT s3111b on 2010.12.26 had a peculiar problem. Its fringe phase has a jump around -0.6 rad, or 11 ps every 1-10 sec, with each jump lasting 1 sec.

Vex file is available here.

Examples:

Observation 0194
Observation 9084
The upper green plot shows fringe phase in radians, low blue plot shows fringe amplitude.

This behavior is consistent through the entire experiment. We see these jump in almst every high scan with high enough SNR to see it. This happens only at baselines with GBT. No similar pattern was found in experiments s3111a on 2010.12.05 and s3111c in 2011.11.09 that had identical setup.

We can consider GBT to have two states: "up" and "low". I re-fringed these two scans with selecting only points in the "up" state (i.e. high phase in fringe phase plot) and in the "low" state. Fringe plots of these two states are her below: Observation 0194 up state     Observation 0194 low state
Observation 9084 up state     Observation 9084 low state

The phase difference for observations #0194 is -0.620 rad (i.e. -11.75 ps) and for observation #9084 is -0.608 rad (i.e. -11.51 ps). The difference in group delays is -8.01 ps and -8.55 ps respectively.


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Last update: 2011.01.27_16:25:39