Saving the frequency dependent SEFDs in the rxg file

[vlbi-jun-yang]

Nowadays, the observing bandwidth of the VLBI observations have been significantly boosted. A single SEFD value per polarisation may not be accurately enough to describe the broad-band VLBI observations. To really monitor the long-term system performance, it would be great to save frequency-dependent SEFDs as the third column in the rxg file. In case of the problem of dead diode, they can be used to make the more meaningful nominal antabfs file. The current gnplt is required to plot the SEFD curve and save the SEFD data (median/average) to the rxg file.

During the VLBI observations, it might be also useful to invent a command to use these SEFDs and the gain curve to predict Tsys, compare them with the observed values, and report the differences (ratio or delta Tsys). Maybe, the current Tsys monitoring window can also allow users to switch from the current absolute Tsys values to the differences.

[vlbi-jun-yang]

In FS, we have caltemp=formbbc to report Tcal values. It would be great to also have something similar for SEFDs, e.g. sefd=formbbc.