Typical Observing Modes

The following are a reiteration of the standard observing modes that will usually be used. Much of this is a repeat of the previous pages.

Fringe Test

Fringe tests will be done during both a specially scheduled slot 1-2 hours before an normal experiment, and during normal tapes and disk based experiments. The VSIC should be connected to the S2 C2a output using the BG2 adapter (unless, of course, the fringe test is for a disk based recording experiment). Disk capacity is generally not enough to retain the data for an entire 12 hour experiment, and certainly not enough for saving the data from a full VLBI session. The disks should be cleaned regularly. Its is suggested that all data recorded only for fringe testing is saved into a directory specifically ear-marked for fringe testing to reduce the chance of deleting data from disk based experiments and making it easier to clean up old data. Some of the recorders have multiple RAID sets. It may be worth using one disk for all fringe tests and the other for experiments for which the data needs to be saved. It is recommenced that a file name prefix consisting of the experiment code and station code is always used (e.g. -o vt131ax_Ho). The recorder should be started at the start of the scheduled experiment by the observers at the telescope and run continuously for the entire experiment unless otherwise instructed. To preserve disk space compressed recording should always be used for parallel S2 recording (the maximum data rate coming through the S2 is 128 Mbps, half the normal data rate of the VSIB). Use compress mode -c ooxx for S2 "x" modes and mode -c oxox for "a" modes. The actual fringe testing will be run remotely. Typically usage would be:

Please to not delete all fringe test data immediately at the end of an experiment. If is often useful to run a fringe test up to a couple of hours after the end of an experiment. The perl program diskclean.pl (part of the RtFC package) is a useful way of stopping the disks filling up to much. Calculate how long fringe test data can be cached based on the available disk space (128 Mbps = 16 MB/sec, so for example if 200 GB of diskspace is available you can store 200000/16 seconds or 3.5 hours). Diskclean.pl can then be told to delete files older than this age. This is the advantage of running all fringe tests from the same directory. Be sure to never record disk based experiments into the same directory as they will be deleted! Typical usage would be:

Disk recording

Most disk recordings will require the VSIC to be connected directly to the DAS S2 output to allow 256 Mbps recording rates. If for some reason the experiment does requires lower data rates, it may be possible to record the data through the S2. Read the observers wiki for specific instructions in this case. These recording should be stored in a directory created specifically for this experiment, just using the experiment name is recommended. The file prefix should include the experiment name and telescope code (e.g. -o vt01i1_Pa). Typical useage would be: