Subarrays

The continuum subarray option offers two 1 GHz baseband pairs with the 8-bit samplers in up to 3 subarrays or four 2 GHz baseband pairs with the 3-bit samplers, with the same spectral channel and polarization product options as are available for wideband observing. The setup for each subarray is completely independent in terms of observing frequency, polarization products, and integration times.

When using three subarrays, there are some restrictions on the number of antennas in each subarray. The Baseline Board in the correlator treats each set of 4 antennas independently, using a separate column of correlator chips. With 8 such columns, the correlator can handle up to 8×4 = 32 antennas. The correlator configuration software requires that a given column not be split across subarrays. This does not matter when using only two subarrays, but forces some subtle restrictions when using three. For instance, one cannot observe with 9 antennas in each of 3 subarrays, because 9 antennas requires three columns (two with 4 antennas each, and one with 1 antenna); three subarrays of 9 antennas each would require 3×3 = 9 columns, one more than are actually available. Splitting the array into 10, 9, and 8 antennas is allowed, since the first two subarrays use 3 columns each, while the third uses only two.

Table 3.8.1 gives four examples of how correlator resources can be split into multiple subarrays. Antennas in each subarray are color-coded: red for subarray 1, green for subarray 2 (if present), and blue for subarray 3 (if present). The last column gives the number of antennas in each subarray (e.g., in the setup shown in the first row, subarray 1 has 10 antennas, subarray 2 has 9 antennas, and subarray 3 has 8 antennas). In all cases a total of 27 antennas are used. The columns are numbered in reverse order (C7 to C0) to match the numbering scheme used on the actual Baseline Boards.

Table 3.8.1: Some Possible Subarray Options
Number of antennas correlated using each Baseline Board columnNumber
of antennas
C7 C6 C5 C4 C3 C2 C1 C0
4 4 2 4 4 1 4 4 10 + 9 + 8
4 4 4 2 4 4 4 1 14 + 13
4 4 3 4 4 3 3 2 11 + 11 + 5
4 4 4 4 4 4 3 — 27

For more information on subarrays, please see the Subarray section in the Guide to Observing with the VLA.

Connect with NRAO

The National Radio Astronomy Observatory and Green Bank Observatory are facilities of the U.S. National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Founded in 1956, the NRAO provides state-of-the-art radio telescope facilities for use by the international scientific community. NRAO telescopes are open to all astronomers regardless of institutional or national affiliation. Observing time on NRAO telescopes is available on a competitive basis to qualified scientists after evaluation of research proposals on the basis of scientific merit, the capability of the instruments to do the work, and the availability of the telescope during the requested time. NRAO also provides both formal and informal programs in education and public outreach for teachers, students, the general public, and the media.

The National Science Foundation (NSF) is an independent federal agency created by Congress in 1950 "to promote the progress of science; to advance the national health, prosperity, and welfare; to secure the national defense..."

AUI collaborates with the scientific community and research sponsors to plan, build, and operate cutting-edge facilities. We cultivate excellence, deliver value, enhance education, and engage the public.