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Appendix 3: EVN CAL Observations


There are a number of questions that can be addressed from routine calibrator observations:

At the correlator:

Tapes: when do the tapes and log files get there ? At playback, what is the error rate (all tracks) ? What are the clock offsets and rates ?

Post-correlation:

Phase cal signal: do the signals line up across the band? how does this compare to using a strong calibrator source to align bands ? what is its level?

Which stations suffer radio frequency interference, and at what frequencies?

Calibration:

Do TSYS values look reasonable? -- what is the multiplicative factor for each station (c.f. the FT factors in the calibration file), obtained from amp self--cal ?

Does each antenna's sensitivity (in Jy) tally with that ``advertised'' in the EVN status file (evn.sts) ? (!)

Is the gain curve correct? It should be possible to construct independent gain curves for each antenna from amplitude self-cal solutions derived from data for which the polynomial gain curves have not been applied.

[Aside - How important are opacity effects at 6cm and above ? - How can we correct for these effects (see VLBA) - How well does a polynomial function fit a typical gain curve ]

Which stations are easiest to calibrate ? Does the calibration coversheet/info easy to interpret ? ANCAL/CAL files supplied (?), gain curves in polynomial form, continous T$_{sys}$?

Data Editing (see also at correlator):

What % of data had to be deleted from each station?

vlbi@jodrell_bank.starlink