Phased VLA Modes
HSA proposals can request the phased VLA in conjunction with the VLBA and other HSA telescopes, subject to availability of matching observing systems. Two adjuncts to the VLA Observational Status Summary, "VLBI at the VLA" and VLBI @ the VLA: Scheduling Hints, discuss the available phased-VLA capabilities, and provides instructions for their use. This sub-section of the VLBA Observational Status Summary describes only the specific compatible modes between the two instruments.
Phased-VLA observing using two independently-tunable VLA subband pairs, one polarization pair (RCP+LCP) in the A0/C0 baseband pair, and the other (RCP+LCP) in the B0/D0 baseband pair, is available as a general capability. Any matching bandwidths available on the VLA as well as the VLBA DDC data system described above can be used. Bandwidths must be uniform at each station, across the entire VLBI array, and throughout the entire duration of the observation. In particular, VLA phasing and VLBI observing must be carried out at the same bandwidth. Bandwidths of 16 MHz and wider are available as a general capability. Bandwidths narrower than 16 MHz may work if the source is strong enough, but are expected to be of limited use. Y27 modes equivalent to the VLBA PFB and 8-channel DDC modes are also available on a shared risk basis, since they are less well tested. The restrictions are fewer for the VLA than for the VLBA or other stations, so the HSA guidelines should be followed. The VLA must be set up to match the VLBA; mixed modes are not allowed.
Observing with a single VLA antenna ("Y1") in conjunction with the VLBA will only be available through the VLBA Resident Shared Risk Observing program.
Table 7 shows the available bandwidth options, their recorded data rates, and shared-risk status, for maximum VLA-VLBA sensitivity with four DDC channels on the VLBA.
Table 7: Phased-VLA / VLBA Compatibility
| Mode |
Subband Bandwidth (MHz) |
# of subbands/ channels* |
Data Rate (Mbps) |
Shared Risk? |
|---|---|---|---|---|
| DDC-4 | 128 | 4 | 2048 | No |
| DDC-4 | 64 | 4 | 1024 | No |
| DDC-4 | 32 | 4 | 512 | No |
| DDC-4 | 16 | 4 | 256 | No |
| DDC-4 | 8 | 4 | 128 | Yes |
| DDC-4 | 4 | 4 | 64 | Yes |
| DDC-4 | 2 | 4 | 32 | Yes |
| DDC-4 | 1 | 4 | 16 | Yes |
| DDC-8 | all† | 8 | all† | Yes |
| PFB | 32 | 16 | 2048 | Yes |
* This is the total number of subbands/channels and each subband/channel is a single polarization, so if you want a full polarization observation with DDC-4, 2048 Mbps, you will have two 128MHz subband pairs.
† DDC-8 is limited to 64-1MHz channels and the corresponding data rates of 2048-32 Mbps. See section on the RDBE.
