CORRELATOR DESIGN



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CORRELATOR DESIGN

The current VLA correlator is limited to a bandwidth of MHz. A new correlator is needed to process the 2 GHz of bandwidth and to achieve the increase in continuum sensitivity and instantaneous spectral coverage. Moreover, the current correlator limits the type of science which can be done due to its limited spectral resolution at wide bandwidths. With a 50 MHz bandwidth now, the VLA can only produce 8 (Hanning smoothed) spectral channels in total. With so few channels, wide-field imaging at low frequencies, and searches for redshifted spectral lines (e.g., H I) are extremely inefficient. Similarly, a 50 MHz bandwidth at high frequencies (e.g., 350 km/s at 43 GHz) makes observations of radio recombination lines difficult, if not impossible. It also excludes many components of those molecular lines which are split into multiple transitions.

Current specifications for the new correlator are demanding:

Careful consideration will be given to including hardware internal to the correlator for real-time detection and removal of short-time-scale interference. For example, it might be feasible (in an FX correlator) to examine each FFT for channels with excessive amplitude and delete those channels from the cross-correlation.

If possible, the development of a new VLA correlator should be combined with that of the Millimeter Array correlator. The overall similarity of the needs in terms of the antenna-bandwidth product should be exploited wherever possible. Unless the time scales on which the two correlators are required turn out to be significantly different, they should at least share the same basic architecture and the same ASIC(s).





next up previous contents
Next: Ultra-wide Bandwidth Performance Up: TECHNICAL ISSUES AND Previous: IF TRANSMISSION SYSTEM



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