Tied Array

A tied array capability is available for the Long Baseline Array observations (e.g., VLBI). The tied array uses 64MHz bandwidth data from the sampler and effectively adds them together. In this observation mode, the correlator is usually used only for monitoring the data but not for the processing. The output from the sampler goes to the Long Baseline Array Data Acquisition System (LBA_DAS), from where it is sent to S2 Recorder terminal and/or correlator. Output bandwidths range from 64 MHz down to 62.5kHz in factors of 2. Passbands of 16MHz and below may be tuned in 1Hz steps.

The tied array adder is controlled by the process CATIE which is now available within CAOBS. You will need to setup the system that you desire (i.e. antennas and polarisations) and adjust the reference levels to make the statistics shown on the CATIE page approximately equal to 34%.

CACAL has the option of continuously calibrating the phase to keep the tied array phased up. This mode can only be used if you are observing a calibrator (i.e., the source has calcode=C in the schedule file). You will need to run CACAL in interactive mode to be presented with this option. Another feature of CACAL is the option to put in a 90° phase shift between the X and Y channel, effectively converting the polarisations from linear to circular. This option is also accessible only by running CACAL interactively.