| CSIRO Astronomy and Space Science ATCA Users Guide |
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| 1.8.1 High Time Resolution and Pulsar Observing | ||
| 1.8.2 Solar System Objects | ||
| 1.8.3 Tied Array Mode |
CABB now offers a pulsar binning mode, and will soon offer a high time resolution mode.
In pulsar binning mode, the correlator cycle time (normally 10 seconds) is divided into an integer number of pulsar periods. Each pulsar period is further divided into N equal time intervals called bins. The integration in the correlator is done separately for each bin, such that at the end of the cycle, N quantities are produced, each of which represents the integrated value at a particular pulsar phase.
The pulsar binning mode is still in development, and the number of bins, and the pulsar period needs to be set in the correlator configuration. To do this, it is necessary to discuss your project requirements with observatory staff, particularly Warwick Wilson, before your observations.
The correlator will also record both the full 2 GHz continuum bands in addition to the pulsar binning data, analagous to how the zoom modes are recorded.
Time binning mode should be available very soon, and will likely offer 10-20 ms time resolution.
The Compact Array can track sources with non-sidereal rates, such as planets or comets. In this case delay tracking is adjusted continuously to account for source proper motion. However the pointing tracks a fixed celestial position during a scan. Thus scans must be short enough that there is not significant proper motion across the primary beam in the course of a scan. This is rarely a problem.
JPL ephemerides of the planets are built into the observing program, and a simple mechanism exists to import current JPL ephemerides of other solar system objects (e.g. new comets).
A tied array capability is available. It provides tying of the array at one or two frequencies and, for CABB, initially at a bandwidth of 64 MHz.
The tied array adder is controlled via a process called catie which
runs within CACOR. This allows the choice of which antennas are
included and whether the adder produces linear or circular
polarisation outputs. The array is phased up in the usual way, and an
option to allow the insertion of a 90^\circ phase offset
between the A and B linear polarisations at each antenna – thereby
forming circular polarisation at the tied-array output – is available.
The tied-array adder can be fed into the LBA (Long Baseline Array) DAS which provides outputs for the VLBI disk-based recorders at bandwidths between 62.5 kHz and 64 MHz. Simultaneous Compact Array and tied array operation is possible, although currently this is limited to 64 MHz in both IFs, or 64 MHz in one IF and the full 2 GHz (which is not formed into a tied array) in the other.
Users Guide last modified on 2011-04-27 15:49:06