OVSA Experience of Relevance to FASR
| Frequency-Agile Interferometry | |
| Quick Overview of OVSA | |
| Multi-frequency calibration | |
| Simplifications | |
| Complications | |
| Conclusions |
| 7 Antennas | ||
| 2 large (27 m) | ||
| 5 small (2 m) | ||
| Frequency Agile | ||
| Tune in any sequence to any of 86 frequencies in range 1-18 GHz | ||
| 10 ms sample time (takes 8 s to tune to 40 frequencies in each of RCP and LCP) | ||
| Quick Overview of OVSA | |
| Multi-frequency calibration | |
| Simplifications | |
| Complications | |
| Conclusions |
| The system phase on each individual baseline is random with frequency | |
Multi-frequency Calibration II
| However, the difference in phase for a given baseline, from one time to the next, follows a linear frequency dependence. |
| Quick Overview of OVSA | |
| Multi-frequency calibration | |
| Simplifications | |
| Complications | |
| Conclusions |
| Calibrate once | |
| every 2 hours | |
| Ref calibration |
| Quick Overview of OVSA | |
| Multi-frequency calibration | |
| Simplifications | |
| Complications | |
| Conclusions |
| Quick Overview of OVSA | |
| Multi-frequency calibration | |
| Simplifications | |
| Complications | |
| Conclusions |
| Take advantage of the smoothness of most frequency-dependent phase changes. | |
| Expect phase changes ~f for atmosphere and cables, ~f -2 for the ionosphere. Frequency-independent phase offsets are also possible. | |
| Lobe ambiguities need not be a driver for time between phase calibrations (although linearity of phase changes will be). | |
| Care must be taken to calibrate frequency-to-frequency amplitudes (self-cal is no help). | |