At the start of observing on 2459647, the SNAPs were in digital noise mode and all the SNAPs' digital noise sources were seeded with the same seed. This should result in perfect correlation with zero degrees of phase across the band. One SNAP, heraNode10Snap2, had a slight offset in the noise source seed sync timing (see #92) so baselines between that SNAP's antennas and other antennas have a phase slope across the band. All other SNAPs were generating synchronized identical digital noise, so they should have exactly zero phase in their cross correlations (or auto correlations). While the the should-be-zero-phase baselines did have phases very close to zero across the band, they were not exactly zero in every case. The following plot shows the percentage of baselines that have a non-zero imaginary component for each frequency channel:
Excluding the baselines involving heraNode10Snap2, the non-zero phases are noisy around zero. The following plot shows the minimum and maximum phases for each channel across all baselines (excluding heraNode10Snap2):
I suspect packet loss is causing this, but I don't have any direct proof of that so for now it's just a hypothesis.
At the start of observing on 2459647, the SNAPs were in digital noise mode and all the SNAPs' digital noise sources were seeded with the same seed. This should result in perfect correlation with zero degrees of phase across the band. One SNAP, heraNode10Snap2, had a slight offset in the noise source seed sync timing (see #92) so baselines between that SNAP's antennas and other antennas have a phase slope across the band. All other SNAPs were generating synchronized identical digital noise, so they should have exactly zero phase in their cross correlations (or auto correlations). While the the should-be-zero-phase baselines did have phases very close to zero across the band, they were not exactly zero in every case. The following plot shows the percentage of baselines that have a non-zero imaginary component for each frequency channel:
Excluding the baselines involving heraNode10Snap2, the non-zero phases are noisy around zero. The following plot shows the minimum and maximum phases for each channel across all baselines (excluding heraNode10Snap2):
I suspect packet loss is causing this, but I don't have any direct proof of that so for now it's just a hypothesis.