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Next: Sensitivity Up: Appendix: Considerations Specific to the VLA Previous: VLA Averaging Times

The Primary Beam


To the accuracy needed when planning observations, the primary beam of the VLA antennas can be taken to be a Gaussian with FWHM equal to tex2html_wrap_inline2947 arcsec or tex2html_wrap_inline2949 arcmin. If you must image a source, or a field of view, that is significantly larger than the FWHM of the VLA primary beam, then you should plan to make a mosaic from a number of pointings (see Lecture 14).

In standard VLA software, the primary beam correction ( tex2html_wrap_inline2951 , Lecture 2) is modeled by a power law expansion of the form tex2html_wrap_inline2953 where tex2html_wrap_inline2955 and the coefficients are tex2html_wrap_inline2957 , tex2html_wrap_inline2959 , tex2html_wrap_inline2961 , tex2html_wrap_inline2963 , and tex2html_wrap_inline2965 (Napier and Rots 1982). This correction is usually not applied at small values of X for which the Napier-Rots expansion gives tex2html_wrap_inline2969  1. It is not well determined at large values of X for which tex2html_wrap_inline2973  0.15.
Thu Jul 11 16:26:53 EDT 1996